Abstract:
Systems, methods, and apparatuses for triggering electrical arcs are disclosed. Such arcs are useful for testing combustible fluids and equipment operating near ignition hazards. In some embodiments, arcs are produced with a defined energy at a defined time with little variation in arc energy. Consistent production of arcs is facilitated by one or more of conditioned electrodes, control and/or reduction of parasitic capacitance, avoidance of corona sources, and non-interfering arc triggers. In some embodiments, electrodes are conditioned by repeated application of conditioning arcs. Conditioned electrodes have relatively physically consistent and chemically consistent tips. In some embodiments, arc triggers are charged particle sources such as light sources operating in cooperation with a target to produce free electrons proximate the electrodes.

Description:
FIELD 
     The present disclosure relates to systems, methods, and apparatuses for triggering electrical arcs. 
     BACKGROUND 
     In many situations, devices must operate in potentially hazardous conditions, such as where a fuel mixture may be ignited by uncontrolled operating or environmental conditions. For example, vehicles, including aerospace vehicles, typically operate with a fuel that must be maintained in a safe condition during storage and use. The ignition hazard should be minimized even when the vehicle is subject to uncontrolled events such as an accident, electrical malfunction, a lightning strike, or static electrical discharge. Other applications requiring ignition hazard consideration include fuel transport, fuel storage, mining operations, and operations which involve combustible particulate such as sawdust, flour, and grain. 
     In the aerospace industry, lightning strikes of aircraft are a concern because they could result in electrical arcs and/or heating sufficient to ignite vaporous fuel mixtures. Though lightning passes through metallic aircraft virtually always without resulting harm, manufacturers and regulators are vigilant to the potential for harm. The Federal Aviation Authority (FAA) recognizes that arc energies as low as 200 μJ (microjoules) may be sufficient to cause unwanted ignition of vaporous fuels. 
     Design of apparatuses exposed to ignition hazards typically involves reducing the likelihood of ignition, containing the ignition hazard, and/or withstanding the ignition hazard. Test systems may facilitate the design by simulating ignition of a combustible fluid in a controlled environment. To initiate ignition of a combustible fluid, test systems may include an arc source, i.e., a source of electric discharge, sometimes referred to as a spark. This discharge may be used to ignite a combustible and/or explosive material (typically gaseous or vaporous), in particular to test a test sample, such as combustible and/or explosive materials (including fuel mixtures), and structures, devices, and/or apparatuses intended to operate near ignition hazards. The arc source may be used to simulate unwanted electrical discharge, to verify that test conditions are proper for ignition, and/or to calibrate the ignition point for a combustible and/or explosive material. 
     SUMMARY 
     Controlled electrical arcs may be produced in test systems and/or apparatuses by applying a voltage across an electrode gap and triggering an arc across the electrode gap. The applied voltage may be approximately the same as a breakdown voltage of a medium spanning the electrode gap and/or may be about 0-300 V less than the breakdown voltage. The triggering may include supplying charged particles into the electrode gap while not otherwise interfering with the triggered arc. Supplying may be accomplished with a trigger source, such as a light source in cooperation with a target. Illuminating a target with the appropriate optical power and/or photon energy may cause the target to emit electrons, ions, and/or other charged particles. 
     Systems and/or apparatuses for producing controlled electrical arcs include at least two electrodes with electrode tips. The electrode tips are spaced apart to delimit an electrode gap. When a sufficiently high voltage is applied across the electrode gap, a medium spanning the electrode gap will break down, causing an electrical arc. The systems and/or apparatuses include a trigger source, such as a light source in cooperation with a target. The trigger source may further include a delivery conduit, such as a fiber optic, which delivers energy to the target. The target may include a portion of one of the electrodes delimiting the electrode gap. 
     Test systems may include a test chamber, an electrical arc source at least partially enclosed by the test chamber, and a test sample at least partially enclosed by the test chamber. The test chamber may further enclose a combustible fluid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of systems and apparatuses according to the present disclosure. 
         FIG. 2  is a schematic perspective drawing of a non-exclusive, illustrative example of an apparatus according to the present disclosure. 
         FIG. 3  is a diagram of methods according to the present disclosure. 
     
    
    
     DESCRIPTION 
     The present disclosure relates to systems, methods, and apparatuses for controlled-energy electrical arcs.  FIG. 1  schematically presents systems  10  and apparatuses  20  for controlled-energy electrical arcs. Systems  10  incorporate one or more apparatuses  20 , and may be used to test the effect of electrical arcs, or electrical energy discharge, on a test sample  11  potentially exposed to ignition hazards within a test chamber  12 . 
     Systems  10  may be used to test, to calibrate, and/or to verify test samples  11  with respect to controlled ignition hazards. Test samples  11  may include, and may be, one or more of a solid, liquid, and gas. For example, a test sample  11  may be a solid structural member of an aircraft, a liquid fuel, or a fuel vapor-air mixture. Test samples  11  may include, and optionally be, a fuel mixture, an aerospace component, a fuel handling component, a ventilator component, and/or equipment. Illustrative, non-exhaustive examples include an aircraft skin, an aircraft frame, a fuel pump, a fuel tank, mining equipment, ventilator equipment, dust handling equipment, monitoring equipment, and a camera. 
     The test chamber  12  of a system  10  may enclose all or part of the test sample  11 . The test chamber  12  may be a pressure bomb, a sealed chamber, an enclosed space, and/or a partitioned space. Within the test chamber  12 , and in contact with at least part of the test sample  11 , may be a combustible fluid  13 . The combustible fluid  13  may be combustible, flammable, and/or explosive. The presence of the combustible fluid  13  near the test sample  11  allows the test sample  11  to be tested for the ability to ignite the combustible fluid  13  and/or to survive the combustion, explosive or otherwise, of the combustible fluid  13 . Typically, the combustible fluid  13  is liquid or gaseous, potentially including a suspension of solid particles and/or liquid droplets. Illustrative, non-exclusive examples of combustible fluids  13  include one or more of air, oxygen, hydrogen, a hydrocarbon, a fuel, a fuel vapor, an oxidant, dust, powder, and particulate. 
     Systems  10  may include a test energy source  15  to apply energy to the test sample  11  and/or the combustible fluid  13 . The energy imparted may simulate use of the test sample  11 , and/or may simulate environmental conditions. Illustrative, non-exclusive examples of test energy sources  15  include a lightning simulator, a heater, and an exposed electrical arc. 
     Systems  10  may include monitoring equipment  16  to observe and/or record conditions during the test. Monitoring equipment  16  may measure one or more of temperature, pressure, electrical power, electrical charge, electrical voltage, electrical properties, light, sound, and chemical properties. Illustrative, non-exclusive examples of monitoring equipment include pressure transducers, pressure indicators, microphones, heat transducers, heat indicators, photodetectors, cameras, electrical power meters, electrostatic voltmeters, oscilloscopes, and current sensors (e.g. Rogowski coils). 
     Systems  10  incorporate at least one apparatus  20  to create an electrical arc. The system  10  and/or the test conducted using the system  10  may depend upon the actual arc energy and/or the timing of the arc. The arc may be used to ignite the combustible fluid  13  when present, may be used to detect the presence of a combustible fluid  13 , may be used to verify the absence of a combustible fluid  13 , and/or may be used to detect the composition of a combustible fluid  13 . 
     Apparatuses  20  comprise at least two electrodes  21 , a first electrode  24  and a second electrode  26 , that are spaced apart to delimit an electrode gap  28  between the tips  22  of the electrodes  21 . Electrical arcs may be created across the electrode gap  28  when a sufficient source of electrical energy is connected across the electrodes and when a sufficient voltage is applied across the electrode gap  28 . Electrical arcs typically are created by causing any material spanning the electrode gap  28  to dielectrically break down. Arcs may be created in a medium such as a combustible fluid  13  and may be created in conditions other than standard temperature and pressure. The breakdown voltage, or discharge voltage, is dependent upon many factors, including material properties and geometries. For example, the breakdown voltage may be affected by the length of the electrode gap  28 , the shape of the electrode tips  22 , the material properties of the electrode tips  22 , and/or the composition of any material spanning the electrode gap  28 . 
     The breakdown voltage of a material may be characterized by the dielectric strength of the material. In an insulating material, dielectric strength is a measure of the resistance to breakdown. It is the minimum voltage required to cause dielectric breakdown and/or ionization of the material. Dielectric strength is measured in volts per unit thickness. Generally, a higher dielectric strength indicates a better insulator. Many common insulating materials have a dielectric strength between 1 MV/m (megavolt per meter) and 100 MV/m. For example, air and nitrogen have a dielectric strength of about 3 MV/m, while insulating fluids, like mineral oil, have a dielectric strength of about 10-20 MV/m. When operating with an air mixture in an electrode gap  28  of several millimeters, the breakdown voltage that will generate an arc is several thousand volts. Typical electrode gaps  28  are less than 10 mm, less than 8 mm, less than 6 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2.5 mm, less than 2 mm, less than 1.5 mm, less than 1 mm, less than 0.5 mm, 0.5-10 mm, or 0.5-3 mm. 
     To create an arc, electrodes  21  are generally conductive and capable of enduring high voltages. Electrodes  21  may include, or be composed of, a metal or similar conductor such as tungsten, aluminium, stainless steel, copper, brass, nickel, silver, gold, platinum, and/or palladium. Electrodes  21  may be metallic and/or plated with a metal or similar conductor. Electrodes  21  may have a generally wire-like form with a diameter of less than 8 mm, less than 6 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2 mm, less than 1.5 mm, less than 1 mm, greater than 1 mm, greater than 1.5 mm, greater than 2 mm, greater than 3 mm, about 1-6 mm, and/or about 1-3 mm. The electrode tips  22  may be substantially planar, beveled, conical, rounded, convex, and/or substantially hemispherical. 
     Apparatuses  20  to create a controlled-energy electrical arc comprise at least one capacitor  30  with a first terminal  32  electrically connected, optionally via a first lead  33 , to the first electrode  24  and a second terminal  34  electrically connected, optionally via a second lead  35 , to the second electrode  26 . The capacitor  30  may store energy that may be readily discharged across the electrode gap  28  to create an arc. The stored energy of a capacitor is related to the capacitance and the voltage across the capacitor: E=½CV 2 , where E is the energy, C is the capacitance, and V is the voltage. The capacitor  30  is configured to store a defined discharge energy at a defined discharge voltage that may be substantially discharged across the electrode gap  28  in an arc between the electrode tips  22  when electric breakdown occurs across the electrode gap  28 . 
     To store energy sufficient to create an ignition-producing arc, the capacitor  30  may be configured to operate with a high voltage between the first terminal  32  and the second terminal  34 . Typical operating voltages, and hence typical defined discharge voltages, are at least 3 kV (kilovolts), at least 4 kV, at least 5 kV, at least 6 kV, at least 7 kV, at least 8 kV, at least 9 kV, at least 10 kV, at least 11 kV, at least 12 kV, 0-10 kV, 0-8 kV, 6-8 kV, less than 15 kV, less than 12 kV, and/or less than 10 kV. The energy stored as a defined discharge energy may be a low energy and may be about 10 μJ, about 20 μJ, about 50 μJ, about 80 μJ, about 100 μJ, about 150 μJ, about 200 μJ, about 250 μJ, about 300 μJ, about 400 μJ, about 500 μJ, about 1,000 μJ, 50-500 μJ, 100-250 μJ, and/or less than 1,000 μJ. The capacitor  30  may have a capacitance of about 1 pF (picofarads), about 2 pF, about 4 pF, about 6 pF, about 8 pF, about 10 pF, about 12 pF, about 15 pF, about 20 pF, about 25 pF, about 30 pF, about 50 pF, about 2-10 pF, about 2-15 pF, about 4-20 pF, less than 50 pF, less than 20 pF, or less than 10 pF. The capacitor  30  may be a variable capacitor which may be adjusted between arcs and which may be manually and/or automatically adjusted. 
     The arc energy may be substantially the same as, greater than, or less than, the defined discharge energy, the energy stored in the capacitor  30 . For example, the defined discharge energy may be greater than 50%, greater than 70%, greater than 80%, greater than 90%, greater than 95%, greater than 99%, greater than 100%, or greater than 110% of the arc energy. Where the arc energy is greater than the defined discharge energy, the excess energy may be contributed by outside energy sources e.g., from energy stored in parasitic capacitance and/or from energy contributed by an arc trigger. Where system  10  and/or the apparatus  20  is configured with few to no outside energy sources, the arc energy is dominated by, and may be essentially the same as, the defined discharge energy. 
     In other electrical arc generating systems and apparatuses, the arc energy may include significant contributions from external sources and/or may not completely discharge the capacitor. For example, all electrical components have parasitic capacitance, i.e., capacitance between the component and another in the system or environment. Parasitic capacitance typically is a few picofarads to a few hundred picofarads. At high voltages, such levels of parasitic capacitance may store several millijoules of energy. Systems  10  and/or apparatuses  20  of the present disclosure may be configured to have low parasitic capacitance and/or non-interfering energy storage from parasitic capacitance. For example, systems  10  and/or apparatuses  20  may have a parasitic capacitance of less than 2 pF, less than 1 pF, less than 0.5 pF, less than 0.2 pF, or less than 0.1 pF. Additionally or alternatively, systems  10  and/or apparatuses  20  may be configured to have a controlled parasitic capacitance, a parasitic capacitance that does not significantly change during utilization of the system  10  and/or apparatus  20 . If the net capacitance, the capacitance of the capacitor  30  and the parasitic capacitance, is predictable, the energy stored in capacitance, and hence the energy available for discharge, may be consistent and predictable. The net capacitance of systems  10  and/or apparatuses  20  may be about 1 pF, about 2 pF, about 4 pF, about 6 pF, about 8 pF, about 10 pF, about 12 pF, about 15 pF, about 20 pF, about 25 pF, about 30 pF, about 50 pF, about 2-10 pF, about 2-15 pF, about 4-20 pF, less than 50 pF, less than 20 pF, or less than 10 pF. 
     Systems  10  and/or apparatuses  20  may comprise an isolation resistor  42  in series with the capacitor  30 . The isolation resistor  42  may be in series with a power supply  50 , in which case voltage would be applied across the isolation resistor  42  and the capacitor  30 . Generally, the isolation resistor  42  has a sufficiently high resistance to electrically isolate the capacitor  30  and the electrodes  21  from any other electrical components, such as power supply  50 . Further, the isolation resistor  42  and the capacitor  30  may act as a low pass filter, isolating high frequency arc energy from any other electrical components. Electrical isolation allows for the discharge of the defined discharge energy from the capacitor  30  into the electrode gap  28  with little interference from outside energy sources. The isolation resistor  42  may have a resistance greater than 1 GΩ (gigaohms), greater than 10 GΩ, greater than 50 GΩ, greater than 100 GΩ, greater than 150 GΩ, greater than 200 GΩ, greater than 300 GΩ, or greater than 500 GΩ. 
     Because a simple electrical system may provide low parasitic capacitance and high isolation from outside influences, apparatuses  20  may comprise a discharge circuit that consists essentially of, and optionally consists of, the capacitor  30 , and, when present, the isolation resistor  42 . The discharge circuit may include other electrical components but, in its simplest form, does not include additional electrical components. The discharge circuit is electrically coupled to the electrodes  21  and may be electrically coupled to other electrical components, such as a power source  50 . 
     For isolation from outside influences, simplified handling and/or compact packaging, the capacitor  30  may be enclosed in a housing  40 . The housing  40  may seal, protect, and/or isolate the capacitor  30 , the optional first lead  33 , the optional second lead  35 , the optional isolation resistor  42 , and a portion of each electrode  21 , not including the electrode tips  22 . The electrodes  21  may be detachable from the housing  40  and if so may be connected to the housing  40  through at least a first electrode connector  47  and a second electrode connector  48 . The housing  40  may be fabricated with dimensionally stable materials that are electrically insulating and that generally would not interfere with or be damaged by test conditions in system  10 . 
     To seal, to protect, and/or to isolate the components within the housing, the housing may be composed of a housing material  41 . For example, to protect from electrical breakdown, the housing material  41  may have a high dielectric strength of greater than 3 MV/m, greater than 4 MV/m, greater than 5 MV/m, greater than 7 MV/m, greater than 10 MV/m, greater than 15 MV/m, greater than 20 MV/m, about 10 MV/m, about 15 MV/m, or about 20 MV/m. To reduce parasitic capacitance, the housing material  41  may have a low dielectric constant, also called the relative permittivity (a measure of a material&#39;s ability to store energy under an applied voltage). The dielectric constant of the housing material  41  may be less than about 10, less than about 5, less than about 3, or less than about 2. For example, the housing may be substantially composed of, and/or may include, PTFE (polytetrafluoroethylene), fluoropolymer, PEEK (polyether ether ketone), polyoxymethylene (Delrin plastic), hard rubber, phenolic resin, polyamide, ceramic, and/or glass. 
     Additionally or alternatively, to seal, to protect, and/or to isolate the components within the housing  40 , the housing  40  may be filled with a fill material  44  and/or may contain a vacuum. The fill material  44  may have a high dielectric strength of greater than 3 MV/m, greater than 4 MV/m, greater than 5 MV/m, greater than 7 MV/m, greater than 10 MV/m, greater than 15 MV/m, greater than 20 MV/m, about 10 MV/m, about 15 MV/m, or about 20 MV/m. The fill material  44  may have a low dielectric constant of less than about 10, less than about 5, less than about 3, or less than about 2. For example, the fill material  44  may include insulating oil, mineral oil, silicone oil, perfluorinated fluid (Fluorinert fluid), silicone resin, polyurethane, epoxy, and/or potting compound. 
     Use of high dielectric strength materials and/or arc suppression materials may facilitate a compact size for the housing  40 . Under high voltage, electrical components may arc between terminals or between components. Arc failures may be reduced by spacing components apart and/or by use of high dielectric strength materials. Hence, with appropriate materials choice and design, the housing  40  may be a compact package. The housing may have a volume of less than 1,000 cm 3 , less than 500 cm 3 , less than 200 cm 3 , or less than 100 cm 3 . For example, the housing may be about 12 cm×8 cm×10 cm, or about 10 cm×6 cm×4 cm, but other dimensions are within the scope of the present disclosure. 
     The housing  40  may be configured not to interfere and/or not to interact with systems  10 , apparatuses  20 , test conditions, and/or arcs in the electrode gap  28 . To protect the components within the housing  40  and/or to make the housing  40  durable under test conditions, the housing  40  may be configured to not readily absorb and/or to not readily react with components within systems  10 , e.g., moisture, fuels, liquids, gases and/or chemicals. Further, the housing  40  may be poorly electrically conductive and/or not readily combustible. The housing  40  may be one or more of electrically insulating, non-absorbent, non-hygroscopic, inert, non-reactive, non-reactive with hydrocarbon fuels, and non-flammable. 
     Systems  10  and/or apparatuses  20  may be configured to produce repeatable arcs, with a consistent arc energy. The consistency in arc energy, the reproducibility of an arc by the system  10  and/or apparatus  20 , may be due in part to the simple, highly isolated, electrical configurations described above, to optional conditioning of the electrodes  21 , and to an optional trigger source  60 . Generally systems  10  and/or apparatuses  20  are sufficiently repeatable when arcs may be reproduced under essentially the same conditions with essentially the same energy. For example, systems  10  and/or apparatuses  20  may produce a series of arcs with substantially the same arc energies. The relative standard deviation (the standard deviation divided by the mean) in arc energy may be less than 30%, less than 20%, less than 10%, less than 5%, less than 2%, or less than 1%. Determining the relative standard deviation in arc energy may include determining the arc energy for at least 10 arcs, at least 30 arcs, at least 100 arcs, at least 300 arcs, or at least 1,000 arcs. 
     The electrode tips  22  may be conditioned to facilitate repeatable arcs within a system  10  and/or an apparatus  20 . Conditioning generally results in electrodes  21  with a relatively consistent surface at the electrode tips  22 , both in terms of surface features and chemical composition. The conditioned electrodes  21  generally have no dominant microscopic feature that would lead to variability in arc energy and/or breakdown voltage. Microscopic protrusions and/or domains of dielectric material on the electrode tips  22  may influence the local electric field and hence lead to variability of the breakdown voltage and/or arc energy. Conditioned electrode tips  22  may include inhomogeneous surface properties, e.g., protrusions and/or dielectric domains, provided that the surface properties remain stable from arc to arc. 
     The relatively consistent surfaces of the electrode tips  22  are generally consistent spatially and temporally. The electrode tips  22  may be conditioned by repeatedly electrically arcing the system  10  and/or apparatus  20  until the arc is relatively consistent. Conditioning may involve repeatedly electrically arcing for more than 100, more than 200, more than 300, more than 400, more than 500, more than 1,000, more than 2,000, more than 3,000, more than 4,000, more than 5,000, more than 6,000, more than 7,000, more than 10,000, 100-500, 200-1,000, 1,000-10,000, 2,000-5,000, about 200, about 400, about 2,000, about 3,000, about 4,000, or about 5,000 arcs. 
     The arc is relatively consistent when an arc parameter and/or a surface parameter is sufficiently reproducible. An arc parameter may include one or more of arc energy, arc voltage, arc duration, and arc power. Sufficiently reproducible arc parameters may have a relative standard deviation of less than 30%, less than 20%, less than 10%, less than 5%, less than 2%, less than 1%, less than 0.5%, less than 0.2%, or less than 0.1%. A surface parameter may include surface roughness and/or chemical composition. 
     Generally, when the arc energy is repeatable to a desired consistency, the electrode tips  22  are conditioned. The act of electrically arcing imparts some arc energy to the electrode tips  22 , potentially causing the electrode tips  22  to be microscopically shaped and reformed. For example, protrusions, which may concentrate the electric field, are preferentially heated by the arc, leading to flow of the protrusion into the local surface plane or ‘burning’ of the protrusion (e.g., evaporation, sputtering, etc.). Also, contaminants and dielectric surface domains are subjected to at least resistive heating during an arc. Upon repeated electrical arcing, the contaminants and/or domains may be ‘burned’ off the surface and/or the surface may come to a chemical equilibrium wherein a certain fraction of the surface maintains contaminants and/or dielectric domains. 
     Ultimately, conditioning of the electrode tips  22  results in properties that do not significantly change when subjected to the energy of a typical arc, i.e., where the arc has an energy of about 10 μJ, about 20 μJ, about 50 μJ, about 80 μJ, about 100 μJ, about 150 μJ, about 200 μJ, about 250 μJ, about 300 μJ, about 400 μJ, about 500 μJ, about 1,000 μJ, 50-500 μJ, 100-250 μJ, and/or less than 1,000 μJ. For example, the surface features and chemical composition of the electrode tips  22  are not significantly altered by a typical arc. 
     The surface features may be characterized by the surface roughness, a measure of the deviation from a smooth surface. One measure of roughness is the average roughness, the average deviation of the actual surface from the local surface plane. Electrode tips  22 , when conditioned, may have an average roughness of less than 1 μm, less than 0.5 μm, less than 0.2 μm, less than 0.1 μm, less than 0.05 μm, or less than 0.01 μm. Additionally or alternatively, the surface features, such as roughness, may vary across an electrode tip  22 . For example, the roughness may be less towards the axial center of the electrode tip  22  and higher away from the axial center to the electrode tip  22 . 
     Electrode tips  22  are not generally conditioned simply by mechanical abrasion, such as sanding, buffing, and/or polishing. Fine polishing may lead to a microscopically smooth surface but the abrasion typically results in a surface that rapidly reacts with the environment, often forming dielectric coatings and/or surface domains that interfere with consistent arc generation. 
     Proximate to each electrode  21  may be a flange  54 . Flanges  54  may be configured to interact with a flame kernel that forms near the arc. A flame kernel is a nascent flame formed, for example, as a result of an arc in a combustible fluid. The flanges  54  may be configured to encourage a flame kernel to grow. The flanges  54  may delimit a flange gap, optionally a substantially planar parallel gap, that includes the electrode gap  28 . Appropriate flange gap spacings to interact with a flame kernel include greater than 1 mm, greater than 2 mm, greater than 3 mm, greater than 4 mm, greater than 5 mm, greater than 6 mm, greater than 7 mm, greater than 8 mm, greater than 10 mm, greater than 12 mm, 2-10 mm, 3-10 mm, 6-12 mm, less than 15 mm, less than 12 mm, less than 10 mm, less than 8 mm, and/or less than 6 mm. In directions transverse to the flange gap spacing, the flanges  54  may be less than 50 mm, less than 25 mm, less than 20 mm, less than 15 mm, less than 12 mm, less than 10 mm, less than 8 mm, less than 6 mm, less than 5 mm, 5-50 mm, 6-25 mm, 6-20 mm, 6-12 mm, greater than 5 mm, greater than 6 mm, greater than 8 mm, greater than 10 mm, greater than 12 mm, and/or greater than 20 mm. 
     The flanges  54  may be configured not to interfere and/or not to interact with systems  10 , apparatuses  20 , test conditions, and/or arcs in the electrode gap  28 . The flanges  54  may be configured to not readily absorb and/or to not readily react with components within systems  10 , e.g., moisture, fuels, liquids, gases and/or chemicals. Further, the flanges  54  may be poorly electrically conductive and/or not readily combustible. The flanges  54  may be one or more of electrically insulating, non-absorbent, non-hygroscopic, inert, non-reactive, non-reactive with hydrocarbon fuels, and non-flammable. The flanges  54  may include, and optionally be composed of, a material with a low dielectric constant, optionally wherein the dielectric constant is less than about 10, less than about 5, or less than about 3. Suitable materials for flanges  54  include PTFE, fluoropolymer, PEEK, polyoxymethylene, hard rubber, phenolic resin, polyamide, ceramic, and/or glass. 
     Consistency of the system  10  and/or apparatus  20  may be affected by the stochastic nature of the breakdown and arc formation process. When a breakdown voltage is placed across a dielectric, generally the dielectric does not immediately break down. Instead, the dielectric may resist the breakdown until a seed event occurs. Typically, the seed event is the introduction of a charged particle. The charged particle may drift from another location in the dielectric, may be generated by processes in the dielectric, such as cosmic ray interactions, and/or may be supplied by a charged particle source outside the dielectric. One source of charged particles is a corona source, an electrode operated at a sufficiently high voltage to ionize the surrounding medium and create electrons and/or ions. As the processes to create a corona and to create a breakdown are similar, the energy from a corona may be significant relative to a breakdown event. Hence, the use of a corona source may impart significant energy to an arc discharge initiated by the presence of the corona. 
     Systems  10  and/or apparatuses  20  may include a trigger source  60 , or an arc trigger, to initiate, or trigger, an arc across the electrode gap  28  at a defined time and/or a defined voltage. The trigger source  60  may be configured to provide charged particles, e.g., eject electrons via the photoelectric effect, proximate the electrode gap  28  when the electrode gap  28  is held at a voltage near the breakdown voltage in the electrode gap  28 . The trigger source  60  may include, be, or consist essentially of, at least one of an ion source, a plasma source, a radioactive source, an electron source, an ionizing energy source, and a light source. The charged particles may be emitted by the trigger source  60  and/or may be created due to energy emitted from the trigger source  60 . The charged particles may include electrons, positrons, protons, alpha particles, and/or ions. Energy emissions may include ionizing radiation. 
     Because any energy near the electrode gap  28  may influence the reproducibility of the arc energy, the trigger source  60  may be configured substantially to not interfere with the arc after arc initiation. Typically, the trigger source  60  contributes little energy to the arc, and alteration of the arc characteristics generally is negligible. For example, a trigger source  60  that provides electrons to the electrode gap  28  by inducing the photoelectric effect in a metal proximate to the electrode gap  28 , may inject an insignificant amount of energy into the electrode gap  28  and may not significantly affect the arc characteristics. The trigger source  60  may be configured to contribute less than 10%, less than 5%, less than 2%, less than 1%, less than 0.5%, less than 0.2%, or less than 0.1% to the arc energy. The trigger source  60  may be configured to contribute less than 50 μJ, less than 20 μJ, less than 10 μJ, less than 5 μJ, less than 2 μJ, less than 1 μJ, less than 0.5 μJ, less than 0.2 μJ, or less than 0.1 μJ to the arc energy. 
     Since coronas may inject significant energy into the electrode gap  28 , the trigger source  60  may be essentially corona-free, include no corona sources, and/or be free of corona sources. Coronas may be generated at high voltages, hence the trigger source  60  may operate at lower voltages such as less than 1,000 V, less than 100 V, or less than 10 V. 
     To facilitate control of the arc initiation process, the trigger source  60  may be configured to be selectively enabled, selectively disabled, and/or regulated. Where the trigger source  60  is electronic, the control may be electronic. Additionally or alternatively, the trigger source  60  may be controlled by mechanical devices such as a shutter and/or a diverter. The trigger source  60  may include a delivery conduit  66  to deliver energy and/or charged particles proximate the electrode gap  28 . The delivery conduit  66  may include one or more of an optical system, a fiber optic, a light guide, an electron multiplier, an electron accelerator, an ion accelerator, and an ion optic. 
     The trigger source  60  may include, or may be essentially composed of, an energy emitter  62  and a target  64  that emits charged particles (e.g., electrons, ions, and/or nuclear particles) upon absorbing energy from the energy emitter  62 . The energy emitter  62  and the target  64  are configured to cooperate to produce charged particles. For example, the energy emitter  62  may be configured to emit sufficient energy to ionize the target  64  and/or to photoionize the target  64 . Ionization occurs when sufficient energy is applied to a material to generate and/or release a charged particle from the material. The material may be solid, liquid, and/or gaseous. Typically, ionization liberates an electron from a material, resulting in a free electron and/or ion. Photoionization is a type of ionization in which the energy applied is in the form of electromagnetic radiation (radiant energy). For example, one type of photoionization, the photoelectric effect, may cause electrons to be ejected from a metal surface when radiant energy is absorbed by the surface. 
     Generally, ionization requires energy above a critical threshold of the material, typically the ionization energy (the energy required to generate a free electron and/or create an ion from the material). Photoionization typically requires the photon energy (related to the wavelength) to be greater than the ionization energy. However, in the photoelectric effect, the critical threshold for photoionization of a metallic material may be lower than the ionization energy of an isolated atom from the material. The critical energy threshold for the photoelectric effect of a metallic material is called the work function of the material. The target  64  may have an ionization energy of less than about 14 eV (electron volt), less than about 12 eV, less than about 10 eV, less than about 6 eV, less than about 5 eV, less than about 4.5 eV, less than about 4 eV, less than about 3.5 eV, greater than about 3 eV, greater than about 3.5 eV, greater than about 4 eV, greater than about 4.5 eV, 3.5-10 eV, and/or 3.5-6 eV. Additionally or alternatively, the target  64  may have a work function of less than about 10 eV, less than about 6 eV, less than about 5 eV, less than about 4.5 eV, less than about 4 eV, less than about 3.5 eV, greater than about 3 eV, greater than about 3.5 eV, greater than about 4 eV, greater than about 4.5 eV, 3.5-10 eV, 4-6 eV, and/or 4-5 eV. 
     The target  64  may include a metal, such as tungsten, aluminium, stainless steel, copper, brass, nickel, silver, gold, platinum, and/or palladium. The target  64  may be located proximate to the electrode gap  28  and may be a portion of one or more of the electrode tips  22  and/or electrodes  21 . 
     The energy emitter  62  of a trigger source  60  may include, and optionally may be, a light source (a radiant energy source) with sufficient photon energy to produce charged particles from the target. The energy of a photon is related to its wavelength: E=hc/λ, where E is the energy, h is Planck&#39;s constant, c is the speed of light, and λ is the wavelength. Planck&#39;s constant times the speed of light is about 1,240 eV·nm (electron volt-nanometers). Therefore, photon energies of several electron volts, which may ionize materials or otherwise create charged particles, correspond to wavelengths in the ultraviolet (UV) range, generally about 10-400 nm. Hence, the light source may be a UV light source and/or provide light primarily in the UV range. The light source may emit light with wavelengths of about 10-400 nm, about 80-400 nm, about 80-350 nm, about 80-280 nm, about 80-180 nm, about 200-350 nm, about 200-280 nm, or about 260-280 nm. Wavelengths of about 400-700 nm are considered visible light. An energy emitter  62  which emits significant visible light and/or light of longer wavelengths may interfere with monitoring of the arc, monitoring for combustion, and/or monitoring the system  10  generally. The energy emitter may be configured to emit shorter wavelength light while not substantially emitting longer wavelength light. The energy emitter  62  may be configured to not substantially emit visible light, light of wavelength greater than about 440 nm, greater than about 400 nm, greater than about 350 nm, greater than about 320 nm, or greater than about 280 nm. Additionally or alternatively, the energy emitter  62  may emit photons with an energy greater than or equal to a work function of the target and/or an ionization energy of the target. 
     Where the trigger source  60  includes a light source as an energy emitter  62 , the light source may deliver light to the target  64  and/or the electrode gap  28  via a delivery conduit  66 . Thus, the light source may be located distant from the target  64  and/or the electrode gap  28 . 
     The trigger source  60  may be operatively coupled to other components of system  10  and/or apparatus  20 . For example, the trigger source  60  may be operatively coupled to test chamber  12 , electrode  21 , housing  40 , and/or flange  54 . Where the trigger source  60  includes a delivery conduit  66 , the delivery conduit  66  may be operatively coupled to other components of system  10  and/or apparatus  20 . 
     Systems  10  and/or apparatuses  20  may include a power supply  50  to supply energy to the capacitor  30 , an energy meter  52  to measure the electrical energy discharged through the electrode gap  28 , and/or a controller  58  programmed to control one or more components of the system  10  and/or apparatus  20 . The power supply  50  may be configured to apply the defined discharge voltage across the capacitor  30 , may be connected to the optional housing  40  through one or more power supply connectors  45 , may be adjustable, and may be controlled automatically and/or manually. The energy meter  52  may be, or may include, an electrostatic voltmeter, a current sensor, and/or a Rogowski coil. The energy meter  52  may be connected to the optional housing  40  through one or more energy meter connectors  46 . The controller  58  may be programmed to control one or more of the storage of the defined discharge energy in the capacitor  30 , the discharge of the defined discharge energy in an arc across the electrode gap  28 , the setting of the defined discharge voltage, and the operation of the trigger source  60 . The controller  58  may be configured to set the defined discharge voltage to a voltage near a breakdown voltage of a medium within the electrode gap  28  and the set voltage may optionally be about equal to, about 100 V less than, about 200 V less than, about 300 V less than, about 400 V less than, about 0-100 V less than, or about 0-300 V less than the breakdown voltage. 
       FIG. 2  is a perspective drawing of an illustrative non-exclusive example of apparatus  20 . In the example, the capacitor  30  is located within the housing  40  while the electrodes  21  are located above the housing  40 . The electrodes  21  include flanges  54  and one flange  54  is operatively coupled to a delivery conduit  66 . The apparatus has external connectors, a power supply connector  45  and an energy meter connector  46 , to accommodate connection of a power supply  50  and/or an energy meter  52 . The housing  40  also includes an adjustment knob  38  that may be used to manually adjust the capacitor  30 . 
       FIG. 3  is a schematic diagram of methods  100  that may be employed to produce a controlled arc. Methods  100  comprise emitting  104  an arc with an arc energy across an electrode gap delimited by a first electrode tip and a second electrode tip. The systems  10  and apparatuses  20  described above may be useful to perform the methods  100 , but other electrical arc systems and apparatuses may be used. The arc energy may be predefined, may be low, and/or may be about 10 μJ, about 20 μJ, about 50 μJ, about 80 μJ, about 100 μJ, about 150 μJ, about 200 μJ, about 250 μJ, about 300 μJ, about 400 μJ, about 500 μJ, about 1,000 μJ, 50-500 μJ, 100-250 μJ, and/or less than 1,000 μJ. The emitting  104  may include electrical arcing, discharging the arc and/or triggering the arc. For example, the emitting  104  may include discharging the arc into a combustible fluid spanning the electrode gap. The combustible fluid may be a liquid, a gas, a suspension of solid particles, and/or a suspension of liquid droplets. For example, the combustible fluid may include, or may be, air, oxygen, hydrogen, a hydrocarbon, a fuel, a fuel vapor, an oxidant, dust, powder, and/or particulate. 
     The emitting  104  may include triggering the arc, optionally at a defined time and/or a defined voltage, for example, by using an arc trigger such as the trigger source  60 . Additionally or alternatively, the triggering may include supplying charged particles into the electrode gap and/or regulating a supply of charged particles, for example, using the trigger source  60 . The triggering may cause the arc to occur less than 2,000 ms, less than 1,000 ms, less than 500 ms, less than 100 ms, less than 10 ms, less than 1 ms, less than 0.1 ms, less than 0.01 ms, or less than 0.01 ms after the triggering begins. The triggering may be substantially non-interfering with the arc energy. For example, the triggering may contribute less than 10%, less than 5%, less than 2%, less than 1%, less than 0.5%, less than 0.2%, or less than 0.1% to the arc energy. Additionally or alternatively, the triggering may contribute less than 50 μJ, less than 20 μJ, less than 10 μJ, less than 5 μJ, less than 2 μJ less than 1 μJ, less than 0.5 μJ, less than 0.2 μJ, or less than 0.1 μJ to the arc energy. The triggering may be corona-free and/or may not include using a corona source. Generally, emitting  104  may be corona-free and/or may be in the absence of corona sources. Discharging may include stabilizing the arc voltage and/or the arc energy, e.g. by use of conditioned electrodes. Such stabilizing may be in the absence of corona sources. 
     The supplying charged particles and/or regulating a supply of charged particles may include illuminating a target proximate to the electrode gap. The target may include, or may be composed of, metal such as tungsten, aluminium, stainless steel, copper, brass, nickel, silver, gold, platinum, and/or palladium. The target may be the first electrode tip, the second electrode tip, and/or a portion of one or both of the electrodes. The illuminating may include transmitting light to the target and/or the electrode gap, optionally using a delivery conduit such as an optical system, a fiber optic, and/or a light guide. The light may be essentially UV light and/or may include little to no visible light. For example, the light may consist essentially of wavelengths of about 10-400 nm, about 80-400 nm, about 80-350 nm, about 80-280 nm, about 80-180 nm, about 200-350 nm, about 200-280 nm, or about 260-280 nm. Illuminating may include transmitting light of shorter wavelengths while not substantially transmitting light of longer wavelengths. For example, the light may consist essentially of wavelengths less than about 440 nm, less than about 400 nm, less than about 350 nm, less than about 320 nm, or less than about 280 nm. Transmitting visible and/or longer wavelength light to the electrode gap may interfere with monitoring of the arc, monitoring for combustion in the gap, and/or monitoring the system generally. 
     The illuminating may include transmitting photons with an energy greater than or equal to a work function of the target and/or a photoionization energy of the target. The target may have a work function less than about 10 eV, less than about 6 eV, less than about 5 eV, less than about 4.5 eV, less than about 4 eV, less than about 3.5 eV, greater than about 3 eV, greater than about 3.5 eV, greater than about 4 eV, greater than about 4.5 eV, 3.5-10 eV, 4-6 eV, and/or 4-5 eV. The target may have a photoionization energy of less than about 14 eV, less than about 12 eV, less than about 10 eV, less than about 6 eV, less than about 5 eV, less than about 4.5 eV, less than about 4 eV, less than about 3.5 eV, greater than about 3 eV, greater than about 3.5 eV, greater than about 4 eV, greater than about 4.5 eV, 3.5-10 eV, and/or 3.5-6 eV. 
     Methods  100  may comprise emitting  104  after one or more of positioning  106  the electrodes to delimit the electrode gap, storing  108  stored energy in a capacitor, and applying  110  an electrode voltage across the electrode gap. 
     Positioning  106  may include delimiting the electrode gap at less than 10 mm, less than 8 mm, less than 6 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2.5 mm, less than 2 mm, less than 1.5 mm, less than 1 mm, less than 0.5 mm, 0.5-10 mm, or 0.5-3 mm. Additionally or alternatively, emitting  104  may include emitting an arc across an electrode gap of this distance. 
     Storing  108  may include storing the arc energy in a capacitor, and/or storing energy to be discharged across the electrode gap. The stored energy may be substantially the same as the arc energy and/or may be greater than 50%, greater than 70%, greater than 80%, greater than 90%, greater than 95%, greater than 99%, greater than 100%, or greater than 110% of the arc energy. 
     Applying  110  may include applying an electrode voltage which is a high voltage. The electrode voltage may be sufficient to cause dielectric breakdown of any medium spanning the electrode gap. For example, the voltage may be at least 3 kV, at least 4 kV, at least 5 kV, at least 6 kV, at least 7 kV, at least 8 kV, at least 9 kV, at least 10 kV, at least 11 kV, at least 12 kV, less than 15 kV, less than 12 kV, and/or less than 10 kV. Additionally or alternatively, the applying  110  may include setting the electrode voltage near a breakdown voltage of a medium spanning the electrode gap. The electrode voltage may be set to about equal to, about 100 V less than, about 200 V less than, about 300 V less than, about 400 V less than, about 0-100 V less than, or about 0-300 V less than the breakdown voltage. 
     Methods  100  may comprise determining  116  whether combustion occurred in response to the emitting  104 . Determining  116  may include observing, monitoring, measuring, and/or recording one or more system parameters such as electrical power, electrical energy, pressure, temperature, sound level, light level, gas density, gas concentration, and chemical composition. Combustion typically creates at least a flame kernel that consumes at least part of the combustible material. The combustion may generate light, heat, pressure differences and chemical products (such as water and carbon oxides). Determining may include using monitoring equipment, such as monitoring equipment  16 . 
     Methods  100  may comprise repeating  114  the emitting  104 . The repeating  114  may include repeating the optional storing  108 , the optional applying  110 , and/or the optional determining  116 . The repeating  114  may produce arcs with a consistent arc energy. For example, the arc energies from the repeated arcs may be substantially the same and/or may have a relative standard deviation that is less than 30%, less than 20%, less than 10%, less than 5%, less than 2%, or less than 1%. 
     Methods  100  may comprise conditioning  102  the first electrode tip and the second electrode tip before the emitting  104 . The conditioning  102  prepares the electrode tips to produce a consistent arc energy upon each emitting  104 . The conditioning  102  may include producing a consistent roughness and a consistent surface chemical composition on each of the first electrode tip and the second electrode tip. 
     Conditioning  102  may include repeatedly applying a conditioning arc between the first electrode tip and the second electrode tip until at least one of an arc parameter and a surface parameter is relatively consistent (as discussed above). Conditioning  102  may include repeatedly electrically arcing for more than 100, more than 200, more than 300, more than 400, more than 500, more than 1,000, more than 2,000, more than 3,000, more than 4,000, more than 5,000, more than 6,000, more than 7,000, more than 10,000, 100-500, 200-1,000, 1,000-10,000, 2,000-5,000, about 200, about 400, about 2,000, about 3,000, about 4,000, or about 5,000 arcs. 
     Conditioning  102  may include spacing apart  112  the electrode tips prior to applying a conditioning arc. The electrode tip spacing may delimit an electrode gap for conditioning  102 , at a conditioning distance, that may be the same as, or different from, the electrode gap for emitting  104 . For example, the conditioning distance may be less than 10 mm, less than 8 mm, less than 6 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2.5 mm, less than 2 mm, less than 1.5 mm, less than 1 mm, and/or less than 0.5 mm. The electrode tips may be spaced apart  112  in a conditioning surrounding which may be a vacuum or a gaseous medium. Generally, the conditioning surrounding is generally non-combustible and/or inert, e.g., air and/or an inert gas. 
     The conditioning arcs may have energies about the same as, or different from, an arc from emitting  104 . For example, the conditioning arcs may have low energies and/or energies of about 10 μJ, about 20 μJ, about 50 μJ, about 80 μJ, about 100 μJ, about 150 μJ, about 200 μJ, about 250 μJ, about 300 μJ, about 400 μJ, about 500 μJ, about 1,000 μJ, 50-500 μJ, 100-250 μJ, and/or less than 1,000 μJ. 
     The methods  100  may be used to operate a test system and/or test apparatus, optionally one of the systems  10  and the apparatuses  20 . The methods may be used to test a test sample, to calibrate a test system, and/or to validate a test condition. The testing, calibrating, and/or validating may include one or more of simulating a lightning strike, initiating combustion of a fuel, applying an electrical arc, qualifying an aerospace component, qualifying an aircraft structural member, qualifying a fuel handling component, qualifying a ventilator component, and qualifying monitoring equipment. 
     Illustrative, non-exclusive examples of inventive subject matter according to the present disclosure are described in the following enumerated paragraphs: 
     A1. A controlled-energy electrical arc source comprising: 
     a first electrode with a tip having a consistent roughness and a consistent surface chemical composition; 
     a second electrode with a tip having a consistent roughness and a consistent surface chemical composition, wherein the tip of the first electrode and the tip of the second electrode are spaced apart to delimit an electrode gap; and 
     a capacitor to store a defined discharge energy at a defined discharge voltage, wherein the capacitor has a first terminal electrically connected to the first electrode and a second terminal electrically connected to the second electrode. 
     A2. The controlled-energy electrical arc source of paragraph A1, wherein the tip of the first electrode and the tip of the second electrode each independently have an average roughness of less than 1 μm, less than 0.5 μm, less than 0.2 μm, less than 0.1 μm, less than 0.05 μm, or less than 0.01 μm. 
     A3. The controlled-energy electrical arc source of any of paragraphs A1-A2, wherein the tip of the first electrode and the tip of the second electrode are configured such that an arc across the electrode gap does not significantly alter the roughness of the tip of the first electrode and the roughness of the tip of the second electrode, optionally wherein the arc has an energy of about 10 μJ, about 20 μJ, about 50 μJ, about 80 μJ, about 100 μJ, about 150 μJ, about 200 μJ, about 250 μJ, about 300 μJ, about 400 μJ, about 500 μJ, about 1,000 μJ, 50-500 μJ, 100-250 μJ, and/or less than 1,000 μJ. 
     A4. The controlled-energy electrical arc source of any of paragraphs A1-A3, wherein the tip of the first electrode and the tip of the second electrode are configured such that an arc across the electrode gap does not significantly alter the surface chemical composition of the tip of the first electrode and the surface chemical composition of the tip of the second electrode, optionally wherein the arc has an energy of about 10 μJ, about 20 μJ, about 50 μJ, about 80 μJ, about 100 μJ, about 150 μJ, about 200 μJ, about 250 μJ, about 300 μJ, about 400 μJ, about 500 μJ, about 1,000 μJ, 50-500 μJ, 100-250 μJ, and/or less than 1,000 μJ. 
     A5. The controlled-energy electrical arc source of any of paragraphs A1-A4, wherein the first electrode and/or the second electrode includes one or more of metal, tungsten, aluminium, stainless steel, copper, brass, nickel, silver, gold, platinum, and palladium. 
     A6. The controlled-energy electrical arc source of any of paragraphs A1-A5, wherein the first electrode and/or the second electrode has a diameter less than 8 mm, less than 6 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2 mm, less than 1.5 mm, less than 1 mm, greater than 1 mm, greater than 1.5 mm, greater than 2 mm, greater than 3 mm, about 1-6 mm, and/or about 1-3 mm. 
     A7. The controlled-energy electrical arc source of any of paragraphs A1-A6, wherein the tip of the first electrode and/or the tip of the second electrode is rounded, convex, or substantially hemispherical. 
     A8. The controlled-energy electrical arc source of any of paragraphs A1-A7, wherein the electrode gap is less than 10 mm, less than 8 mm, less than 6 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2.5 mm, less than 2 mm, less than 1.5 mm, less than 1 mm, less than 0.5 mm, 0.5-10 mm, or 0.5-3 mm. 
     A9. The controlled-energy electrical arc source of any of paragraphs A1-A8, wherein the first electrode and the second electrode are configured to produce an arc in a combustible fluid spanning the electrode gap, optionally wherein the combustible fluid includes at least one of a liquid, a gas, a suspension of solid particles, and a suspension of liquid droplets, and optionally wherein the combustible fluid is air, and/or includes one or more of air, oxygen, hydrogen, a hydrocarbon, a fuel, a fuel vapor, an oxidant, dust, powder, and particulate. 
     A9.1. The controlled-energy electrical arc source of paragraph A9, wherein the arc has an arc energy substantially the same as the defined discharge energy, optionally wherein the defined discharge energy is greater than 50%, greater than 70%, greater than 80%, greater than 90%, greater than 95%, greater than 99%, greater than 100%, or greater than 110% of the arc energy. 
     A10. The controlled-energy electrical arc source of any of paragraphs A1-A9.1, wherein the tip of the first electrode and the tip of the second electrode are configured to produce a series of arcs with substantially the same arc energies, optionally wherein a relative standard deviation in arc energy is less than 30%, less than 20%, less than 10%, less than 5%, less than 2%, or less than 1%. 
     A11. The controlled-energy electrical arc source of any of paragraphs A1-A10, wherein the capacitor is a variable capacitor, optionally wherein the capacitor is an automatically controlled variable capacitor or is a manually controlled variable capacitor. 
     A12. The controlled-energy electrical arc source of any of paragraphs A1-A11, wherein the capacitor is about 1 pF, about 2 pF, about 4 pF, about 6 pF, about 8 pF, about 10 pF, about 12 pF, about 15 pF, about 20 pF, about 25 pF, about 30 pF, about 50 pF, about 2-10 pF, about 2-15 pF, about 4-20 pF, less than 50 pF, less than 20 pF, or less than 10 pF. 
     A13. The controlled-energy electrical arc source of any of paragraphs A1-A12, wherein the controlled-energy electrical arc source has a parasitic capacitance of less than 2 pF, less than 1 pF, less than 0.5 pF, less than 0.2 pF, or less than 0.1 pF. 
     A14. The controlled-energy electrical arc source of any of paragraphs A1-A13, wherein the controlled-energy electrical arc source has a net capacitance of about 1 pF, about 2 pF, about 4 pF, about 6 pF, about 8 pF, about 10 pF, about 12 pF, about 15 pF, about 20 pF, about 25 pF, about 30 pF, about 50 pF, about 2-10 pF, about 2-15 pF, about 4-20 pF, less than 50 pF, less than 20 pF, or less than 10 pF. 
     A15. The controlled-energy electrical arc source of any of paragraphs A1-A14, wherein the defined discharge energy is about 10 μJ, about 20 μJ, about 50 μJ, about 80 μJ, about 100 μJ, about 150 μJ, about 200 μJ, about 250 μJ, about 300 μJ, about 400 μJ, about 500 μJ, about 1,000 μJ, 50-500 μJ, 100-250 μJ, and/or less than 1,000 μJ. 
     A16. The controlled-energy electrical arc source of any of paragraphs A1-A15, wherein the defined discharge voltage is at least 3 kV, at least 4 kV, at least 5 kV, at least 6 kV, at least 7 kV, at least 8 kV, at least 9 kV, at least 10 kV, at least 11 kV, at least 12 kV, 6-8 kV, less than 15 kV, less than 12 kV, and/or less than 10 kV. 
     A17. The controlled-energy electrical arc source of any of paragraphs A1-A16, further comprising: 
     a housing enclosing the capacitor and a first lead to the first electrode and a second lead to the second electrode, optionally wherein the housing is filled with a fill material with a high dielectric strength, optionally wherein the high dielectric strength is greater than 3 MV/m, greater than 4 MV/m, greater than 5 MV/m, greater than 7 MV/m, greater than 10 MV/m, greater than 15 MV/m, greater than 20 MV/m, about 10 MV/m, about 15 MV/m, or about 20 MV/m. 
     A17.1. The controlled-energy electrical arc source of paragraph A17, wherein the housing is one or more of electrically insulating, non-absorbent, non-hygroscopic, inert, non-reactive, non-reactive with hydrocarbon fuels, and non-flammable. 
     A17.2. The controlled-energy electrical arc source of any of paragraphs A17-A17.1, wherein the housing includes, or is composed of, a housing material with a low dielectric constant, optionally wherein the dielectric constant is less than about 10, less than about 5, less than about 3, or less than about 2. 
     A17.3. The controlled-energy electrical arc source of any of paragraphs A17-A17.2, wherein the housing includes one or more of PTFE, fluoropolymer, PEEK, polyoxymethylene, hard rubber, phenolic resin, polyamide, ceramic, and glass. 
     A17.4. The controlled-energy electrical arc source of any of paragraphs A17-A17.3, wherein the housing has a volume less than 1,000 cm 3 , less than 500 cm 3 , less than 200 cm 3 , or less than 100 cm 3 . 
     A17.5. The controlled-energy electrical arc source of any of paragraphs A17-A17.4, wherein the fill material includes one or more of insulating oil, mineral oil, silicone oil, perfluorinated fluid, silicone resin, polyurethane, epoxy, and potting compound. 
     A18. The controlled-energy electrical arc source of any of paragraphs A1-A17.5, further comprising: 
     an isolation resistor in series with the capacitor, optionally wherein the isolation resistor is greater than 1 GΩ, greater than 10 GΩ, greater than 50 GΩ, greater than 100 GΩ, greater than 150 GΩ, greater than 200 GΩ, greater than 300 GΩ, or greater than 500 GΩ. 
     A19. The controlled-energy electrical arc source of any of paragraphs A1-A18, further comprising: 
     a power supply to supply energy to the capacitor, optionally wherein the power supply is configured to apply the defined discharge voltage across the capacitor. 
     A19.1. The controlled-energy electrical arc source of paragraph A19, wherein the power supply is configured to apply an adjustable voltage across the capacitor, optionally wherein the adjustable voltage is between 0-10 kV, 0-8 kV, or 6-8 kV. 
     A20. The controlled-energy electrical arc source of any of paragraphs A1-A19.1, further comprising: 
     an energy meter to measure the electrical energy discharged through the electrode gap, optionally wherein the energy meter is, or includes, an electrostatic voltmeter, a current sensor, and/or a Rogowski coil. 
     A21. The controlled-energy electrical arc source of any of paragraphs A1-A20, further comprising: 
     at least two flanges to allow a flame kernel to grow, wherein a flange is proximate the first electrode and another flange is proximate the second electrode, optionally wherein the at least two flanges delimit a flange gap that includes the electrode gap. 
     A21.1. The controlled-energy electrical arc source of paragraph A21, wherein the at least two flanges are one or more of electrically insulating, non-absorbent, non-hygroscopic, inert, non-reactive, non-reactive with hydrocarbon fuels, and non-flammable. 
     A21.2. The controlled-energy electrical arc source of any of paragraphs A21-A21.1, wherein the at least two flanges include, or are composed of, a flange material with a low dielectric constant, optionally wherein the dielectric constant is less than about 10, less than about 5, or less than about 3. 
     A21.3. The controlled-energy electrical arc source of any of paragraphs A21-A21.2, wherein each flange independently includes one or more of PTFE, fluoropolymer, PEEK, polyoxymethylene, hard rubber, phenolic resin, polyamide, ceramic, and glass. 
     A21.4. The controlled-energy electrical arc source of any of paragraphs A21-A21.3, wherein a maximum lateral dimension of one or more of the at least two flanges is less than 50 mm, less than 25 mm, less than 20 mm, less than 15 mm, less than 12 mm, less than 10 mm, less than 8 mm, less than 6 mm, less than 5 mm, 5-50 mm, 6-25 mm, 6-20 mm, 6-12 mm, greater than 5 mm, greater than 6 mm, greater than 8 mm, greater than 10 mm, greater than 12 mm, and/or greater than 20 mm. 
     A21.5. The controlled-energy electrical arc source of any of paragraphs A21-A21.4, wherein flange gap is a substantially planar parallel gap, and optionally is greater than 1 mm, greater than 2 mm, greater than 3 mm, greater than 4 mm, greater than 5 mm, greater than 6 mm, greater than 7 mm, greater than 8 mm, greater than 10 mm, greater than 12 mm, 2-10 mm, 3-10 mm, 6-12 mm, less than 15 mm, less than 12 mm, less than 10 mm, less than 8 mm, and/or less than 6 mm. 
     A22. The controlled-energy electrical arc source of any of paragraphs A1-A21.5, further comprising: 
     an arc trigger to initiate an arc with an arc energy across the electrode gap, optionally wherein the arc trigger is configured to provide charged particles proximate to the electrode gap. 
     A22.1. The controlled-energy electrical arc source of paragraph A22, wherein the arc trigger includes, is, or consists essentially of, at least one of an ion source, a plasma source, a radioactive source, an electron source, an ionizing energy source, and a light source. 
     A22.2. The controlled-energy electrical arc source of any of paragraphs A22-A22.1, wherein the arc trigger is configured to operate at less than 1,000 V, less than 100 V, or less than 10 V. 
     A22.3. The controlled-energy electrical arc source of any of paragraphs A22-A22.2, wherein the arc trigger does not include a corona generator and/or is free of a corona source. 
     A22.4. The controlled-energy electrical arc source of any of paragraphs A22-A22.3, wherein the arc trigger is configured to emit one or more of electrons, positrons, protons, alpha particles, ions, and ionizing radiation. 
     A22.5. The controlled-energy electrical arc source of any of paragraphs A22-A22.4, wherein the arc trigger is configured to be selectively enabled, selectively disabled, and/or regulated. 
     A22.6. The controlled-energy electrical arc source of any of paragraphs A22-A22.5, wherein the arc trigger is configured to initiate the arc at a defined time and/or a defined voltage. 
     A22.7. The controlled-energy electrical arc source of any of paragraphs A22-A22.6, wherein the arc trigger is configured to contribute less than 10%, less than 5%, less than 2%, less than 1%, less than 0.5%, less than 0.2%, or less than 0.1% to the arc energy, and optionally wherein the arc trigger is configured to contribute less than 50 μJ, less than 20 μJ, less than 10 μJ, less than 5 μJ, less than 2 μJ, less than 1 μJ, less than 0.5 μJ, less than 0.2 μJ, or less than 0.1 μJ to the arc energy. 
     A22.8. The controlled-energy electrical arc source of any of paragraphs A22-A22.7, wherein the arc trigger includes a delivery conduit to deliver energy and/or charged particles proximate the electrode gap, optionally wherein the delivery conduit includes one or more of an optical system, a fiber optic, a light guide, an electron multiplier, an electron accelerator, an ion accelerator, and an ion optic, and optionally, when dependent from paragraph A20, wherein the delivery conduit is operatively coupled to at least one of the at least two flanges. 
     A22.9. The controlled-energy electrical arc source of any of paragraphs A22-A22.8, wherein the arc trigger includes an energy emitter and a target that emits charged particles upon absorbing energy from the energy emitter. 
     A22.9.1. The controlled-energy electrical arc source of paragraph A22.9, wherein the energy emitter is configured to emit sufficient energy to ionize the target, optionally to photoionize the target. 
     A22.9.2. The controlled-energy electrical arc source of any of paragraphs A22.9-A22.9.1, wherein the energy emitter is configured to emit sufficient energy to eject electrons from the target. 
     A22.9.3. The controlled-energy electrical arc source of any of paragraphs A22.9-A22.9.2, wherein the target has a work function less than about 10 eV, less than about 6 eV, less than about 5 eV, less than about 4.5 eV, less than about 4 eV, less than about 3.5 eV, greater than about 3 eV, greater than about 3.5 eV, greater than about 4 eV, greater than about 4.5 eV, 3.5-10 eV, 4-6 eV, or 4-5 eV. 
     A22.9.4. The controlled-energy electrical arc source of any of paragraphs A22.9-A22.9.3, wherein the target has an ionization energy of less than about 14 eV, less than about 12 eV, less than about 10 eV, less than about 6 eV, less than about 5 eV, less than about 4.5 eV, less than about 4 eV, less than about 3.5 eV, greater than about 3 eV, greater than about 3.5 eV, greater than about 4 eV, greater than about 4.5 eV, 3.5-10 eV, or 3.5-6 eV. 
     A22.9.5. The controlled-energy electrical arc source of any of paragraphs A22.9-A22.9.4, wherein the energy emitter includes, optionally is, a light source or a UV light source; optionally wherein light emitted includes wavelengths of about 10-400 nm, about 80-400 nm, about 80-350 nm, about 80-280 nm, about 80-180 nm, about 200-350 nm, about 200-280 nm, or about 260-280 nm; and optionally wherein the source does not substantially emit visible light, light of wavelength greater than about 440 nm, greater than about 400 nm, greater than about 350 nm, greater than about 320 nm, or greater than about 280 nm. 
     A22.9.5.1. The controlled-energy electrical arc source of paragraph A22.9.5, wherein the energy emitter emits photons with a photon energy greater than or equal to a work function of the target. 
     A22.9.5.2. The controlled-energy electrical arc source of any of paragraphs A22.9.5-A22.9.5.1, wherein the energy emitter emits photons with a photon energy greater than or equal to a photoionization energy of the target. 
     A22.9.6. The controlled-energy electrical arc source of any of paragraphs A22.9-A22.9.5.2, wherein the target includes one or more of a metal, tungsten, aluminium, stainless steel, copper, brass, nickel, silver, gold, platinum, and palladium. 
     A22.9.7. The controlled-energy electrical arc source of any of paragraphs A22.9-A22.9.6, wherein the target is proximate to the electrode gap. 
     A22.9.8. The controlled-energy electrical arc source of any of paragraphs A22.9-A22.9.7, wherein the target includes, optionally is, one or more of a portion of the first electrode, a portion of the second electrode, the tip of the first electrode, and the tip of the second electrode. 
     A23. The controlled-energy electrical arc source of any of paragraphs A1-A22.9.8, further comprising: 
     a controller programmed to control one or more of the storage of the defined discharge energy in the capacitor, the discharge of the defined discharge energy in an arc across the electrode gap, the setting of the defined discharge voltage, and, when dependent from paragraph A22, the operation of the arc trigger. 
     A24. The controlled-energy electrical arc source of any of paragraphs A1-A23, further comprising: 
     a discharge circuit consisting essentially of, optionally consisting of, the capacitor, and, when dependent from paragraph A18, the isolation resistor. 
     A25. A test system, optionally an aerospace component test system, comprising: 
     a test chamber; 
     the controlled-energy electrical arc source of any of paragraphs A1-A24, at least partially enclosed by the test chamber; and 
     a test sample at least partially enclosed by the test chamber. 
     A25.1. The test system of paragraph A25, further comprising: 
     an energy source to apply energy to the test sample, optionally wherein the energy source includes, optionally is, one or more of a lightning simulator, a heater, and an exposed electrical arc. 
     A25.2. The test system of any of paragraphs A25-A25.1, further comprising: 
     a combustible fluid enclosed by the test chamber, optionally wherein the combustible fluid includes at least one of a liquid, a gas, a suspension of solid particles, and a suspension of liquid droplets, and optionally wherein the combustible fluid is air, and/or includes one or more of air, oxygen, hydrogen, a hydrocarbon, a fuel, a fuel vapor, an oxidant, dust, powder, and particulate. 
     A25.3. The test system of any of paragraphs A25-A25.2, further comprising: 
     monitoring equipment, optionally wherein the monitoring equipment includes, optionally is, one or more of a pressure transducer, a pressure indicator, a microphone, a heat transducer, a heat indicator, a photodetector, a camera, an electrical power meter, an electrostatic voltmeter, an oscilloscope, a current sensor, and a Rogowski coil. 
     A25.4. The test system of any of paragraphs A25-A25.3, wherein the test sample is at least partially solid, liquid and/or gaseous. 
     A25.5. The test system of any of paragraphs A25-A25.4, wherein the test sample includes, optionally is, a fuel mixture, an aerospace component, an aircraft structural member, a fuel handling component, a ventilator component, and/or equipment. 
     A26. A fuel mixture calibrated using the controlled-energy electrical arc source of any of paragraphs A1-A24 and/or the test system of any of paragraphs A25-A25.5. 
     B1. A method of generating a controlled electrical arc, comprising: 
     conditioning a first electrode tip and a second electrode tip to produce a consistent roughness and a consistent surface chemical composition on each of the first electrode tip and the second electrode tip; and 
     discharging, after the conditioning, an arc with an arc energy across an electrode gap delimited by the first electrode tip and the second electrode tip, optionally wherein the discharging includes using the controlled-energy electrical arc source of any of paragraphs A1-A24. 
     B2. The method of paragraph B1, wherein the conditioning includes repeatedly applying a conditioning arc between the first electrode tip and the second electrode tip until at least one of an arc parameter and a surface parameter is relatively consistent. 
     B2.1. The method of paragraph B2, wherein the arc parameter includes one or more of an arc energy, an arc voltage, an arc duration, and an arc power, optionally wherein a relative standard deviation in the arc parameter is less than 30%, less than 20%, less than 10%, less than 5%, less than 2%, less than 1%, less than 0.5%, less than 0.2%, or less than 0.1%. 
     B2.2. The method of any of paragraphs B2-B2.1, wherein the surface parameter includes the roughness of the first electrode tip and the roughness of the second electrode tip, and optionally wherein the first electrode tip and the second electrode tip each independently have an average roughness of less than 1 μm, less than 0.5 μm, less than 0.2 μm, less than 0.1 μm, less than 0.05 μm, or less than 0.01 μm. 
     B2.3. The method of any of paragraphs B2-B2.2, wherein the surface parameter includes the roughness of the first electrode tip and the roughness of the second electrode tip, and the surface parameter is relatively consistent when a conditioning arc does not significantly alter the roughness of the first electrode tip and the roughness of the second electrode tip. 
     B2.4. The method of any of paragraphs B2-B2.3, wherein the surface parameter includes the surface chemical composition of the first electrode tip and the surface chemical composition of the second electrode tip, and wherein the surface parameter is relatively consistent when a conditioning arc does not significantly alter the surface chemical composition of the first electrode tip and the surface chemical composition of the second electrode tip 
     B2.5. The method of any of paragraphs B2-B2.4, wherein the repeatedly applying includes applying more than 100, more than 200, more than 300, more than 400, more than 500, more than 1,000, more than 2,000, more than 3,000, more than 4,000, more than 5,000, more than 6,000, more than 7,000, more than 10,000, 100-500, 200-1,000, 1,000-10,000, 2,000-5,000, about 200, about 400, about 2,000, about 3,000, about 4,000, or about 5,000 conditioning arcs. 
     B2.6. The method of any of paragraphs B2-B2.5, further comprising: 
     prior to the repeatedly applying the conditioning arc, spacing apart the first electrode tip and the second electrode tip a conditioning distance in a conditioning surrounding, wherein the conditioning surrounding is a vacuum or a gaseous medium, optionally wherein the gaseous medium includes air and/or an inert gas, and optionally wherein the conditioning distance is less than 10 mm, less than 8 mm, less than 6 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2.5 mm, less than 2 mm, less than 1.5 mm, less than 1 mm, or less than 0.5 mm. 
     B2.7. The method of any of paragraphs B2-B2.6, wherein the conditioning arc has an energy of about 10 μJ, about 20 μJ, about 50 μJ, about 80 μJ, about 100 μJ, about 150 μJ, about 200 μJ, about 250 μJ, about 300 μJ, about 400 μJ, about 500 μJ, about 1,000 μJ, 50-500 μJ, 100-250 μJ, and/or less than 1,000 μJ. 
     B3. The method of any of paragraphs B1-B2.7, wherein the arc energy is predefined. 
     B4. The method of any of paragraphs B1-B3, wherein the arc energy is about 10 μJ, about 20 μJ, about 50 μJ, about 80 μJ, about 100 μJ, about 150 μJ, about 200 μJ, about 250 μJ, about 300 μJ, about 400 μJ, about 500 μJ, about 1,000 μJ, 50-500 μJ, 100-250 μJ, and/or less than 1,000 μJ. 
     B5. The method of any of paragraphs B1-B4, further comprising: 
     positioning the first electrode tip and the second electrode tip to delimit the electrode gap. 
     B6. The method of any of paragraphs B1-B5, wherein the electrode gap is delimited at less than 10 mm, less than 8 mm, less than 6 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2.5 mm, less than 2 mm, less than 1.5 mm, less than 1 mm, less than 0.5 mm, 0.5-10 mm, or 0.5-3 mm. 
     B7. The method of any of paragraphs B1-B6, wherein the discharging includes discharging the arc into a combustible fluid spanning the electrode gap, optionally wherein the combustible fluid includes at least one of a liquid, a gas, a suspension of solid particles, and a suspension of liquid droplets, and optionally wherein the combustible fluid is air, and/or includes one or more of air, oxygen, hydrogen, a hydrocarbon, a fuel, a fuel vapor, an oxidant, dust, powder, and particulate. 
     B8. The method of any of paragraphs B1-B7, further comprising: 
     repeating the discharging. 
     B8.1. The method of paragraph B8, wherein the arcs from the repeating have an arc energy which is substantially the same, optionally wherein a relative standard deviation in arc energy is less than 30%, less than 20%, less than 10%, less than 5%, less than 2%, or less than 1%. 
     B9. The method of any of paragraphs B1-B8.1, further comprising: 
     storing, optionally after the conditioning and/or before the discharging, stored energy in a capacitor to be discharged across the electrode gap, optionally wherein the stored energy is substantially the same as the arc energy, and optionally wherein the stored energy is greater than 50%, greater than 70%, greater than 80%, greater than 90%, greater than 95%, greater than 99%, greater than 100%, or greater than 110% of the arc energy. 
     B10. The method of any of paragraphs B1-B9, further comprising: 
     applying an electrode voltage which is a high voltage across the electrode gap before the discharging, optionally wherein the electrode voltage is at least 3 kV, at least 4 kV, at least 5 kV, at least 6 kV, at least 7 kV, at least 8 kV, at least 9 kV, at least 10 kV, at least 11 kV, at least 12 kV, less than 15 kV, less than 12 kV, and/or less than 10 kV. 
     B10.1. The method of paragraph B10, wherein the applying includes setting the electrode voltage near a breakdown voltage of a medium spanning the electrode gap, optionally wherein the electrode voltage is about equal to, about 100 V less than, about 200 V less than, about 300 V less than, about 400 V less than, about 0-100 V less than, or about 0-300 V less than the breakdown voltage. 
     B11. The method of any of paragraphs B1-B10.1, further comprising: 
     determining whether combustion occurred in response to the discharging. 
     B12. The method of any of paragraphs B1-B11, wherein the discharging includes triggering the arc, optionally at a defined time and/or a defined voltage. 
     B12.1. The method of paragraph B12, wherein the triggering includes using an arc trigger. 
     B12.2. The method of any of paragraphs B12-B12.1, wherein the triggering causes the arc to occur less than 2,000 ms, less than 1,000 ms, less than 500 ms, less than 100 ms, less than 10 ms, less than 1 ms, less than 0.1 ms, less than 0.01 ms, or less than 0.01 ms after the triggering begins. 
     B12.3. The method of any of paragraphs B12-B12.2, wherein the triggering contributes less than 10%, less than 5%, less than 2%, less than 1%, less than 0.5%, less than 0.2%, or less than 0.1% to the arc energy. 
     B12.4. The method of any of paragraphs B12-B12.3, wherein the triggering contributes less than 50 μJ, less than 20 μJ, less than 10 μJ, less than 5 μJ, less than 2 μJ, less than 1 μJ, less than 0.5 μJ, less than 0.2 μJ, or less than 0.1 μJ to the arc energy. 
     B12.5. The method of any of paragraphs B12-B12.4, wherein the triggering includes supplying charged particles into the electrode gap and/or regulating a supply of charged particles, and optionally wherein the supplying charged particles and/or the regulating a supply of charged particles includes illuminating a target proximate to the electrode gap. 
     B12.5.1. The method of paragraph B12.5, wherein the target includes one or more of metal, tungsten, aluminium, stainless steel, copper, brass, nickel, silver, gold, platinum, and/or palladium. 
     B12.5.2. The method of any of paragraphs B12.5-B12.5.1, wherein the target is the first electrode tip and/or the second electrode tip. 
     B12.5.3. The method of any of paragraphs B12.5-B12.5.2, wherein the illuminating includes illuminating with a photon energy greater than or equal to a work function of the target. 
     B12.5.4. The method of any of paragraphs B12.5-B12.5.3, wherein the target has a work function less than about 10 eV, less than about 6 eV, less than about 5 eV, less than about 4.5 eV, less than about 4 eV, less than about 3.5 eV, greater than about 3 eV, greater than about 3.5 eV, greater than about 4 eV, greater than about 4.5 eV, 3.5-10 eV, 4-6 eV, or 4-5 eV. 
     B12.5.5. The method of any of paragraphs B12.5-B12.5.4, wherein the illuminating includes illuminating with a photon energy greater than or equal to a photoionization energy of the target. 
     B12.5.6. The method of any of paragraphs B12.5-B12.5.5, wherein the target has a photoionization energy of less than about 14 eV, less than about 12 eV, less than about 10 eV, less than about 6 eV, less than about 5 eV, less than about 4.5 eV, less than about 4 eV, less than about 3.5 eV, greater than about 3 eV, greater than about 3.5 eV, greater than about 4 eV, greater than about 4.5 eV, 3.5-10 eV, or 3.5-6 eV. 
     B12.6. The method of any of paragraphs B12-B12.5.6, wherein the illuminating includes transmitting light to the target and/or the electrode gap, wherein the light consists essentially of wavelengths of about 10-400 nm, about 80-400 nm, about 80-350 nm, about 80-280 nm, about 80-180 nm, about 200-350 nm, about 200-280 nm, or about 260-280 nm; and optionally does not include transmitting to the electrode gap light of wavelength greater than about 440 nm, greater than about 400 nm, greater than about 350 nm, greater than about 320 nm, or greater than about 280 nm. 
     B13. The method of any of paragraphs B1-B12.6, wherein the discharging includes discharging in the absence of corona sources. 
     B14. The method of any of paragraphs B1-B13, wherein the discharging includes triggering the arc in the absence of corona sources. 
     B15. The method of any of paragraphs B1-B14, wherein the discharging includes stabilizing an arc voltage and/or the arc energy in the absence of corona sources. 
     B16. The method of any of paragraphs B1-B15, wherein the discharging is used in a test system, optionally in a test system of any of paragraphs A25-A25.5, for one or more of testing a test sample, calibrating a test system, and validating a test condition. 
     B16.1. The method of paragraph B16, wherein the testing, the calibrating, and/or the validating includes one or more of simulating a lightning strike, initiating combustion of a fuel, applying an electrical arc, qualifying an aerospace component, qualifying an aircraft structural member, qualifying a fuel handling component, qualifying a ventilator component, and qualifying monitoring equipment. 
     C1. A triggered electrical arc source comprising: 
     a first electrode with a tip; 
     a second electrode with a tip, wherein the tip of the first electrode and the tip of the second electrode are spaced apart to delimit an electrode gap; 
     a capacitor to store a defined discharge energy at a defined discharge voltage, wherein the capacitor has a first terminal electrically connected to the first electrode and a second terminal electrically connected to the second electrode; and 
     a trigger source that is configured to provide charged particles proximate to the electrode gap. 
     C2. The triggered electrical arc source of paragraph C1, wherein the trigger source includes, is, or consists essentially of, at least one of an ion source, a plasma source, a radioactive source, an electron source, an ionizing energy source, and a light source. 
     C3. The triggered electrical arc source of any of paragraphs C1-C2, wherein the trigger source is configured to operate at less than 1,000 V, less than 100 V, or less than 10 V. 
     C4. The triggered electrical arc source of any of paragraphs C1-C3, wherein the trigger source does not include a corona generator and/or is free of a corona source. 
     C5. The triggered electrical arc source of any of paragraphs C1-C4, wherein the trigger source is configured to emit one or more of electrons, positrons, protons, alpha particles, ions, and ionizing radiation. 
     C6. The triggered electrical arc source of any of paragraphs C1-C5, wherein the trigger source is configured to be selectively enabled, selectively disabled, and/or regulated. 
     C7. The triggered electrical arc source of any of paragraphs C1-C6, wherein the trigger source is configured to initiate an arc with an arc energy across the electrode gap at a defined time and/or a defined voltage. 
     C7.1. The triggered electrical arc source of paragraph C7, wherein the trigger source is configured to contribute less than 10%, less than 5%, less than 2%, less than 1%, less than 0.5%, less than 0.2%, or less than 0.1% to the arc energy, and optionally wherein the trigger source is configured to contribute less than 50 μJ, less than 20 μJ, less than 10 μJ, less than 5 μJ, less than 2 μJ, less than 1 μJ, less than 0.5 μJ, less than 0.2 μJ, or less than 0.1 μJ to the arc energy. 
     C8. The triggered electrical arc source of any of paragraphs C1-C7.1, wherein the trigger source includes a delivery conduit to deliver energy and/or charged particles proximate the electrode gap, optionally wherein the delivery conduit includes one or more of an optical system, a fiber optic, a light guide, an electron multiplier, an electron accelerator, an ion accelerator, and an ion optic. 
     C9. The triggered electrical arc source of any of paragraphs C1-C8, wherein the trigger source includes an energy emitter and a target that emits charged particles upon absorbing energy from the energy emitter. 
     C9.1. The triggered electrical arc source of paragraph C9, wherein the energy emitter is configured to emit sufficient energy to ionize the target, optionally to photoionize the target. 
     C9.2. The triggered electrical arc source of any of paragraphs C9-C9.1, wherein the energy emitter is configured to emit sufficient energy to eject electrons from the target. 
     C9.3. The triggered electrical arc source of any of paragraphs C9-C9.2, wherein the target has a work function less than about 10 eV, less than about 6 eV, less than about 5 eV, less than about 4.5 eV, less than about 4 eV, less than about 3.5 eV, greater than about 3 eV, greater than about 3.5 eV, greater than about 4 eV, greater than about 4.5 eV, 3.5-10 eV, 4-6 eV, or 4-5 eV. 
     C9.4. The triggered electrical arc source of any of paragraphs C9-C9.3, wherein the target has an ionization energy of less than about 14 eV, less than about 12 eV, less than about 10 eV, less than about 6 eV, less than about 5 eV, less than about 4.5 eV, less than about 4 eV, less than about 3.5 eV, greater than about 3 eV, greater than about 3.5 eV, greater than about 4 eV, greater than about 4.5 eV, 3.5-10 eV, or 3.5-6 eV. 
     C9.5. The triggered electrical arc source of any of paragraphs C9-C9.4, wherein the energy emitter includes, optionally is, a light source or a UV light source; optionally wherein light emitted includes wavelengths of about 10-400 nm, about 80-400 nm, about 80-350 nm, about 80-280 nm, about 80-180 nm, about 200-350 nm, about 200-280 nm, or about 260-280 nm; and optionally wherein the source is configured to not substantially emit visible light, light of wavelength greater than about 440 nm, greater than about 400 nm, greater than about 350 nm, greater than about 320 nm, or greater than about 280 nm. 
     C9.5.1. The triggered electrical arc source of paragraph C9.5, wherein the energy emitter is configured to emit photons with a photon energy greater than or equal to a work function of the target. 
     C9.5.2. The triggered electrical arc source of any of paragraphs C9.5-C9.5.1, wherein the energy emitter is configured to emit photons with a photon energy greater than or equal to a photoionization energy of the target. 
     C9.6. The triggered electrical arc source of any of paragraphs C9-C9.5.2, wherein the target includes one or more of a metal, tungsten, aluminium, stainless steel, copper, brass, nickel, silver, gold, platinum, and palladium. 
     C9.7. The triggered electrical arc source of any of paragraphs C9-C9.6, wherein the target is proximate to the electrode gap. 
     C9.8. The triggered electrical arc source of any of paragraphs C9-C9.7, wherein the target includes, optionally is, one or more of a portion of the first electrode, a portion of the second electrode, the tip of the first electrode, and the tip of the second electrode. 
     C10. The triggered electrical arc source of any of paragraphs C1-C9.8, wherein the first electrode and/or the second electrode includes one or more of metal, tungsten, aluminium, stainless steel, copper, brass, nickel, silver, gold, platinum, and palladium. 
     C11. The triggered electrical arc source of any of paragraphs C1-C10, wherein the first electrode and/or the second electrode has a diameter less than 8 mm, less than 6 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2 mm, less than 1.5 mm, less than 1 mm, greater than 1 mm, greater than 1.5 mm, greater than 2 mm, greater than 3 mm, about 1-6 mm, and/or about 1-3 mm. 
     C12. The triggered electrical arc source of any of paragraphs C1-C11, wherein the tip of the first electrode and/or the tip of the second electrode is rounded, convex, or substantially hemispherical. 
     C13. The triggered electrical arc source of any of paragraphs C1-C12, wherein the electrode gap is less than 10 mm, less than 8 mm, less than 6 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2.5 mm, less than 2 mm, less than 1.5 mm, less than 1 mm, less than 0.5 mm, 0.5-10 mm, or 0.5-3 mm. 
     C14. The triggered electrical arc source of any of paragraphs C1-C13, wherein the tip of the first electrode and the tip of the second electrode are configured to produce an arc in a combustible fluid spanning the electrode gap, optionally wherein the combustible fluid includes at least one of a liquid, a gas, a suspension of solid particles, and a suspension of liquid droplets, and optionally wherein the combustible fluid is air, and/or includes one or more of air, oxygen, hydrogen, a hydrocarbon, a fuel, a fuel vapor, an oxidant, dust, powder, and particulate. 
     C14.1. The triggered electrical arc source of paragraph C14, wherein the arc has an arc energy substantially the same as the defined discharge energy, optionally wherein the defined discharge energy is greater than 50%, greater than 70%, greater than 80%, greater than 90%, greater than 95%, greater than 99%, greater than 100%, or greater than 110% of the arc energy. 
     C15. The triggered electrical arc source of any of paragraphs C1-C14.1, wherein the tip of the first electrode and the tip of the second electrode are configured to produce a series of arcs with substantially the same arc energies, optionally wherein a relative standard deviation in arc energy is less than 30%, less than 20%, less than 10%, less than 5%, less than 2%, or less than 1%. 
     C16. The triggered electrical arc source of any of paragraphs C1-C15, wherein the capacitor is a variable capacitor, optionally wherein the capacitor is an automatically controlled variable capacitor or is a manually controlled variable capacitor. 
     C17. The triggered electrical arc source of any of paragraphs C1-C16, wherein the capacitor is about 1 pF, about 2 pF, about 4 pF, about 6 pF, about 8 pF, about 10 pF, about 12 pF, about 15 pF, about 20 pF, about 25 pF, about 30 pF, about 50 pF, about 2-10 pF, about 2-15 pF, about 4-20 pF, less than 50 pF, less than 20 pF, or less than 10 pF. 
     C18. The triggered electrical arc source of any of paragraphs C1-C17, wherein the triggered electrical arc source has a parasitic capacitance of less than 2 pF, less than 1 pF, less than 0.5 pF, less than 0.2 pF, or less than 0.1 pF. 
     C19. The triggered electrical arc source of any of paragraphs C1-C18, wherein the triggered electrical arc source has a net capacitance of about 1 pF, about 2 pF, about 4 pF, about 6 pF, about 8 pF, about 10 pF, about 12 pF, about 15 pF, about 20 pF, about 25 pF, about 30 pF, about 50 pF, about 2-10 pF, about 2-15 pF, about 4-20 pF, less than 50 pF, less than 20 pF, or less than 10 pF. 
     C20. The triggered electrical arc source of any of paragraphs C1-C19, wherein the defined discharge energy is about 10 μJ, about 20 μJ, about 50 μJ, about 80 μJ, about 100 μJ, about 150 μJ, about 200 μJ, about 250 μJ, about 300 μJ, about 400 μJ, about 500 μJ, about 1,000 μJ, 50-500 μJ 100-250 μJ, and/or less than 1,000 μJ. 
     C21. The triggered electrical arc source of any of paragraphs C1-C20, wherein the defined discharge voltage is at least 3 kV, at least 4 kV, at least 5 kV, at least 6 kV, at least 7 kV, at least 8 kV, at least 9 kV, at least 10 kV, at least 11 kV, at least 12 kV, 6-8 kV, less than 15 kV, less than 12 kV, and/or less than 10 kV. 
     C22. The triggered electrical arc source of any of paragraphs C1-C21, further comprising: 
     a housing enclosing the capacitor and a first lead to the first electrode and a second lead to the second electrode, optionally wherein the housing is filled with a fill material with a high dielectric strength, optionally wherein the high dielectric strength is greater than 3 MV/m, greater than 4 MV/m, greater than 5 MV/m, greater than 7 MV/m, greater than 10 MV/m, greater than 15 MV/m, greater than 20 MV/m, about 10 MV/m, about 15 MV/m, or about 20 MV/m. 
     C22.1. The triggered electrical arc source of paragraph C22, wherein the housing is one or more of electrically insulating, non-absorbent, non-hygroscopic, inert, non-reactive, non-reactive with hydrocarbon fuels, and non-flammable. 
     C22.2. The triggered electrical arc source of any of paragraphs C22-C22.1, wherein the housing includes, or is composed of, a housing material with a low dielectric constant, optionally wherein the dielectric constant is less than about 10, less than about 5, less than about 3, or less than about 2. 
     C22.3. The triggered electrical arc source of any of paragraphs C22-C22.2, wherein the housing includes one or more of PTFE, fluoropolymer, PEEK, polyoxymethylene, hard rubber, phenolic resin, polyamide, ceramic, and glass. 
     C22.4. The triggered electrical arc source of any of paragraphs C22-C22.3, wherein the housing has a volume less than 1,000 cm 3 , less than 500 cm 3 , less than 200 cm 3 , or less than 100 cm 3 . 
     C22.5. The triggered electrical arc source of any of paragraphs C22-C22.4, wherein the fill material includes one or more of insulating oil, mineral oil, silicone oil, perfluorinated fluid, silicone resin, polyurethane, epoxy, and potting compound. 
     C22.6. The triggered electrical arc source of any of paragraphs C22-C22.5, wherein the trigger source is operatively coupled to the housing, and optionally, when dependent from paragraph C8, wherein the delivery conduit is operatively coupled to the housing. 
     C23. The triggered electrical arc source of any of paragraphs C1-C22.6, further comprising: 
     an isolation resistor in series with the capacitor, optionally wherein the isolation resistor is greater than 1 GΩ, greater than 10 GΩ, greater than 50 GΩ, greater than 100 GΩ, greater than 150 GΩ, greater than 200 GΩ, greater than 300 GΩ, or greater than 500 GΩ. 
     C24. The triggered electrical arc source of any of paragraphs C1-C23, further comprising: 
     a power supply to supply energy to the capacitor, optionally wherein the power supply is configured to apply the defined discharge voltage across the capacitor. 
     C24.1. The triggered electrical arc source of paragraph C24, wherein the power supply is configured to apply an adjustable voltage across the capacitor, optionally wherein the adjustable voltage is between 0-10 kV, 0-8 kV, or 6-8 kV. 
     C25. The triggered electrical arc source of any of paragraphs C1-C24.1, further comprising: 
     an energy meter to measure the electrical energy discharged through the electrode gap, optionally wherein the energy meter is, or includes, an electrostatic voltmeter, a current sensor, and/or a Rogowski coil. 
     C26. The triggered electrical arc source of any of paragraphs C1-C25, further comprising: 
     at least two flanges to allow a flame kernel to grow, wherein a flange is proximate the first electrode and another flange is proximate the second electrode, optionally wherein the at least two flanges delimit a flange gap that includes the electrode gap. 
     C26.1. The triggered electrical arc source of paragraph C26, wherein the at least two flanges are one or more of electrically insulating, non-absorbent, non-hygroscopic, inert, non-reactive, non-reactive with hydrocarbon fuels, and non-flammable. 
     C26.2. The triggered electrical arc source of any of paragraphs C26-C26.1, wherein the at least two flanges include, or are composed of, a flange material with a low dielectric constant, optionally wherein the dielectric constant is less than about 10, less than about 5, or less than about 3. 
     C26.3. The triggered electrical arc source of any of paragraphs C26-C26.2, wherein each flange independently includes one or more of PTFE, fluoropolymer, PEEK, polyoxymethylene, hard rubber, phenolic resin, polyamide, ceramic, and glass. 
     C26.4. The triggered electrical arc source of any of paragraphs C26-C26.3, wherein a maximum lateral dimension of one or more of the at least two flanges is less than 50 mm, less than 25 mm, less than 20 mm, less than 15 mm, less than 12 mm, less than 10 mm, less than 8 mm, less than 6 mm, less than 5 mm, 5-50 mm, 6-25 mm, 6-20 mm, 6-12 mm, greater than 5 mm, greater than 6 mm, greater than 8 mm, greater than 10 mm, greater than 12 mm, and/or greater than 20 mm. 
     C26.5. The triggered electrical arc source of any of paragraphs C26-C26.4, wherein the flange gap is a substantially planar parallel gap, and optionally is greater than 1 mm, greater than 2 mm, greater than 3 mm, greater than 4 mm, greater than 5 mm, greater than 6 mm, greater than 7 mm, greater than 8 mm, greater than 10 mm, greater than 12 mm, 2-10 mm, 3-10 mm, 6-12 mm, less than 15 mm, less than 12 mm, less than 10 mm, less than 8 mm, and/or less than 6 mm. 
     C26.6. The triggered electrical arc source of any of paragraphs C26-C26.5, when dependent from paragraph C8, wherein the delivery conduit is operatively coupled to at least one of the at least two flanges. 
     C27. The triggered electrical arc source of any of paragraphs C1-C26.6, further comprising: 
     a controller programmed to control one or more of the storage of the defined discharge energy in the capacitor, the discharge of the defined discharge energy in an arc across the electrode gap, the setting of the defined discharge voltage, and the provision of charged particles from the trigger source. 
     C27.1. The triggered electrical arc source of paragraph C27, wherein the controller is configured to set the defined discharge voltage to a set voltage near a breakdown voltage of a medium within the electrode gap, optionally wherein the set voltage is about equal to, about 100 V less than, about 200 V less than, about 300 V less than, about 400 V less than, about 0-100 V less than, or about 0-300 V less than the breakdown voltage. 
     C27.2. The triggered electrical arc source of any of paragraphs C27-C27.1, wherein the controller is configured to control the provision of charged particles, and optionally configured to enable the provision of charged particles, after setting of the defined discharge voltage. 
     C28. A test system, optionally an aerospace component test system, comprising: 
     a test chamber; 
     the triggered electrical arc source of any of paragraphs C1-C27.2, at least partially enclosed by the test chamber; and 
     a test sample at least partially enclosed by the test chamber. 
     C28.1. The test system of paragraph C28, further comprising: 
     an energy source to apply energy to the test sample, optionally wherein the energy source includes, optionally is, one or more of a lightning simulator, a heater, and an exposed electrical arc. 
     C28.2. The test system of any of paragraphs C28-C28.1, further comprising: 
     a combustible fluid enclosed by the test chamber, optionally wherein the combustible fluid includes at least one of a liquid, a gas, a suspension of solid particles, and a suspension of liquid droplets, and optionally wherein the combustible fluid is air, and/or includes one or more of air, oxygen, hydrogen, a hydrocarbon, a fuel, a fuel vapor, an oxidant, dust, powder, and particulate. 
     C28.3. The test system of any of paragraphs C28-C28.2, further comprising: 
     monitoring equipment, optionally wherein the monitoring equipment includes, optionally is, one or more of a pressure transducer, a pressure indicator, a microphone, a heat transducer, a heat indicator, a photodetector, a camera, an electrical power meter, an electrostatic voltmeter, an oscilloscope, a current sensor, and a Rogowski coil. 
     C28.4. The test system of any of paragraphs C28-C28.3, wherein the test sample is at least partially solid, liquid, and/or gaseous. 
     C28.5. The test system of any of paragraphs C28-C28.4, wherein the test sample includes, optionally is, a fuel mixture, an aerospace component, an aircraft structural member, a fuel handling component, a ventilator component, and/or equipment. 
     C29. A fuel mixture calibrated using the triggered electrical arc source of any of paragraphs C1-C27.2 and/or the test system of any of paragraphs C28-C28.5. 
     D1. A method of generating a controlled electrical arc, comprising: 
     applying an electrode voltage across an electrode gap delimited by a first electrode tip and a second electrode tip; and 
     triggering an arc with an arc energy across the electrode gap by supplying charged particles into the electrode gap, optionally wherein the triggering includes using the controlled-energy electrical arc source of any of paragraphs A1-A24 and/or the triggered electrical arc source of any of paragraphs C1-C27.2. 
     D2. The method of paragraph D1, wherein the applying includes setting the electrode voltage to a high voltage, optionally wherein the high voltage is at least 3 kV, at least 4 kV, at least 5 kV, at least 6 kV, at least 7 kV, at least 8 kV, at least 9 kV, at least 10 kV, at least 11 kV, at least 12 kV, less than 15 kV, less than 12 kV, and/or less than 10 kV. 
     D3. The method of any of paragraphs D1-D2, wherein the applying includes setting the electrode voltage near a breakdown voltage of a medium spanning the electrode gap, optionally wherein the electrode voltage is about equal to, about 100 V less than, about 200 V less than, about 300 V less than, about 400 V less than, about 0-100 V less than, or about 0-300 V less than the breakdown voltage. 
     D4. The method of any of paragraphs D1-D3, wherein the triggering includes triggering the arc at a defined time and/or a defined voltage, optionally wherein the triggering includes regulating a supply of charged particles. 
     D5. The method of any of paragraphs D1-D4, wherein the triggering causes the arc to occur less than 2,000 ms, less than 1,000 ms, less than 500 ms, less than 100 ms, less than 10 ms, less than 1 ms, less than 0.1 ms, less than 0.01 ms, or less than 0.01 ms after the triggering begins. 
     D6. The method of any of paragraphs D1-D5, wherein the triggering contributes less than 10%, less than 5%, less than 2%, less than 1%, less than 0.5%, less than 0.2%, or less than 0.1% to the arc energy. 
     D7. The method of any of paragraphs D1-D6, wherein the triggering contributes less than 50 μJ, less than 20 μJ, less than 10 μJ, less than 5 μJ, less than 2 μJ, less than 1 μJ, less than 0.5 μJ, less than 0.2 μJ, or less than 0.1 μJ to the arc energy. 
     D8. The method of any of paragraphs D1-D7, wherein the supplying charged particles includes illuminating a target proximate to the electrode gap. 
     D8.1. The method of paragraph D8, wherein the target includes one or more of metal, tungsten, aluminium, stainless steel, copper, brass, nickel, silver, gold, platinum, and/or palladium. 
     D8.2. The method of any of paragraphs D8-D8.1, wherein the target is the first electrode tip and/or the second electrode tip. 
     D8.3. The method of any of paragraphs D8-D8.2, wherein the illuminating includes illuminating with a photon energy greater than or equal to a work function of the target. 
     D8.4. The method of any of paragraphs D8-D8.3, wherein the target has a work function less than about 10 eV, less than about 6 eV, less than about 5 eV, less than about 4.5 eV, less than about 4 eV, less than about 3.5 eV, greater than about 3 eV, greater than about 3.5 eV, greater than about 4 eV, greater than about 4.5 eV, 3.5-10 eV, 4-6 eV, or 4-5 eV. 
     D8.5. The method of any of paragraphs D8-D8.4, wherein the illuminating includes illuminating with a photon energy greater than or equal to a photoionization energy of the target. 
     D8.6. The method of any of paragraphs D8-D8.5, wherein the target has an photoionization energy of less than about 14 eV, less than about 12 eV, less than about 10 eV, less than about 6 eV, less than about 5 eV, less than about 4.5 eV, less than about 4 eV, less than about 3.5 eV, greater than about 3 eV, greater than about 3.5 eV, greater than about 4 eV, greater than about 4.5 eV, 3.5-10 eV, or 3.5-6 eV. 
     D8.7. The method of any of paragraphs D8-D8.6, wherein the illuminating includes transmitting light to the target and/or the electrode gap, wherein the light consists essentially of wavelengths of about 10-400 nm, about 80-400 nm, about 80-350 nm, about 80-280 nm, about 80-180 nm, about 200-350 nm, about 200-280 nm, or about 260-280 nm; and optionally does not include transmitting to the electrode gap light of wavelength greater than about 440 nm, greater than about 400 nm, greater than about 350 nm, greater than about 320 nm, or greater than about 280 nm. 
     D9. The method of any of paragraphs D1-D8.7, wherein the triggering includes triggering the arc in the absence of corona sources. 
     D10. The method of any of paragraphs D1-D9, wherein the triggering includes discharging in the absence of corona sources, optionally wherein the discharging includes stabilizing an arc voltage and/or the arc energy in the absence of corona sources. 
     D11. The method of any of paragraphs D1-D10, wherein the arc energy is predefined. 
     D12. The method of any of paragraphs D1-D11, wherein the arc energy is about 10 μJ, about 20 μJ, about 50 μJ, about 80 μJ, about 100 μJ, about 150 μJ, about 200 μJ, about 250 μJ, about 300 μJ, about 400 μJ, about 500 μJ, about 1,000 μJ, 50-500 μJ, 100-250 μJ, and/or less than 1,000 μJ. 
     D13. The method of any of paragraphs D1-D12, further comprising: 
     positioning the first electrode tip and the second electrode tip to delimit the electrode gap. 
     D14. The method of any of paragraphs D1-D13, wherein the electrode gap is delimited at less than 10 mm, less than 8 mm, less than 6 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2.5 mm, less than 2 mm, less than 1.5 mm, less than 1 mm, less than 0.5 mm, 0.5-10 mm, or 0.5-3 mm. 
     D15. The method of any of paragraphs D1-D14, wherein the triggering includes discharging the arc into a combustible fluid spanning the electrode gap, optionally wherein the combustible fluid includes at least one of a liquid, a gas, a suspension of solid particles, and a suspension of liquid droplets, and optionally wherein the combustible fluid is air, and/or includes one or more of air, oxygen, hydrogen, a hydrocarbon, a fuel, a fuel vapor, an oxidant, dust, powder, and particulate. 
     D16. The method of any of paragraphs D1-D15, further comprising: 
     repeating the triggering. 
     D16.1. The method of paragraph D16, wherein the arc energy of the arcs from the repeating is substantially the same, optionally wherein a relative standard deviation in arc energy is less than 30%, less than 20%, less than 10%, less than 5%, less than 2%, or less than 1%. 
     D17. The method of any of paragraphs D1-D16.1, further comprising: 
     storing, optionally before the triggering, stored energy in a capacitor to be discharged across the electrode gap, optionally wherein the stored energy is substantially the same as the arc energy, and optionally wherein the stored energy is greater than 50%, greater than 70%, greater than 80%, greater than 90%, greater than 95%, greater than 99%, greater than 100%, or greater than 110% of the arc energy. 
     D18. The method of any of paragraphs D1-D17, further comprising: 
     determining whether combustion occurred in response to the triggering. 
     D19. The method of any of paragraphs D1-D18, wherein the triggering includes using a test system, optionally a test system of any of paragraphs A25-A25.5 and/or a test system of any of paragraphs C28-C28.5, for one or more of testing a test sample, calibrating a test system, and validating a test condition. 
     D19.1. The method of paragraph D19, wherein the testing, the calibrating, and/or the validating includes one or more of simulating a lightning strike, initiating combustion of a fuel, applying an electrical arc, qualifying an aerospace component, qualifying an aircraft structural member, qualifying a fuel handling component, qualifying a ventilator component, and qualifying monitoring equipment. 
     As used herein, the terms “selective” and “selectively,” when modifying an action, movement, configuration, or other activity of one or more components or characteristics of an apparatus, mean that the specific action, movement, configuration, or other activity is a direct or indirect result of user manipulation of an aspect of, or one or more components of, the apparatus. 
     As used herein, the terms “adapted” and “configured” mean that the element, component, or other subject matter is designed and/or intended to perform a given function. Thus, the use of the terms “adapted” and “configured” should not be construed to mean that a given element, component, or other subject matter is simply “capable of” performing a given function but that the element, component, and/or other subject matter is specifically selected, created, implemented, utilized, programmed, and/or designed for the purpose of performing the function. It is also within the scope of the present disclosure that elements, components, and/or other recited subject matter that is recited as being adapted to perform a particular function may additionally or alternatively be described as being configured to perform that function, and vice versa. Similarly, subject matter that is recited as being configured to perform a particular function may additionally or alternatively be described as being operative to perform that function. 
     The various disclosed elements of apparatuses and steps of methods disclosed herein are not required to all apparatuses and methods according to the present disclosure, and the present disclosure includes all novel and non-obvious combinations and subcombinations of the various elements and steps disclosed herein. Moreover, one or more of the various elements and steps disclosed herein may define independent inventive subject matter that is separate and apart from the whole of a disclosed apparatus or method. Accordingly, such inventive subject matter is not required to be associated with the specific apparatuses and methods that are expressly disclosed herein, and such inventive subject matter may find utility in apparatuses and/or methods that are not expressly disclosed herein.