## 1 Introduction  
A spark discharge (SD) [1, 2] is a good method for producing nanoparticles (NPs) of small size (less than 20 nm) by the electrical erosion [1] of the electrode material [3] with a fast response due to instantaneous changes in the parameters of the electrical discharge circuit [4]. In the SD processes, high-energy spark discharges are created between two electrodes in a controlled gasflow, eroding the electrode material and forming NPs in the form of aerosol [5]. A large set of SD parameters makes it possible to fine-tune the shape, size, and concentration of the synthesized NPs. For instance, this method can be applied for NP synthesis for the purpose of formation and doping of multicomponent structures: metal alloys [6, 7], semiconductor quantum dots [8, 9, 10, 11], optical and magnetic materials [12], and high-temperature superconductors [13, 14]. Additionally, the method is convenient for manufacturing devices for microelectronics and photonics [15], gas [16, 17] and biological sensors [18] based on NPs, microconductors, resistors [19, 20] and capacitive elements [2]. However, incorrect selection of method parameters leads to non-optimal use of the discharge energy [21] and the production of large parasitic particles (more than 40 nm). SD parameters, determining the diversity of NPs and the stability of their synthesis, have been studied by different methods, but there are still questions that require detailed consideration. Thus, the authors of [4, 22] studied the size and shape dependence of the synthesized particles from the discharge pulse energy, frequency of discharge repetition, and parameters of the carrier gas, such as the composition, flow rate, pressure, and temperature of the gas medium [23, 24, 25]. For example, the energy released in the discharge and the pulse repetition rate are both key parameters that strongly influence the size, shape, and concentration of the synthesized NPs [8]. However, determining the exact value of the energy in the discharge is a complex experimental task, solved by measuring the current and voltage in the interelectrode gap in SD processes for NP synthesis [4] and for micro-electro discharge machining (EDM) [26; 27]. The authors of [4] were measuring pulsed voltage across the interelectrode gap and proposed an algorithm for determining the energy transferred into the discharge gap. In the paper [26] [PERSON] et al. received the spark discharge waveforms in the gap and presented a model for the micro-EDM parameters' prediction. [PERSON] et al. [27] performed a method for the evaluation of discharge parameters and investigated their influence and the influence of electrode size on stainless steel drilling by micro-EDM. A simpler approach is to estimate the energy released in the spark gap by approximating the active impedance of the gap with an equivalent constant electrical resistance [1; 5]. Additionally to the energy parameters, the influence of the electrodes' relative position and the gas flow blowing past them on the synthesis of particles is of great interest. There are many configurations of the electrode arrangement for spark discharge generators (SDG): rod-to-rod, rod-to-tube, pin-to-plate, wire-in-hole, and wire-to-hole [28; 29]. Each of them requires precise adjustment and control of the electrodes' positions. For instance, in wire-in-hole and wire-to-hole configurations with a wire thickness of about 0.5 mm, it is quite difficult to stabilize the position of the wire electrode in the gas flow. Thus, in the work [30], electrodes were constantly adjusted to prevent the electrical circuit break. Currently, the rod-to-rod configuration is the most common. It involves a pair of cylindrical electrodes fixed in crimping holders and separated by a gap [31]. At the same time, this configuration is the least demanding for the electrodes' setup accuracy for the purpose of particle synthesis repeatability.