Patent Description:
The disclosed embodiments relate generally to x-ray and charged particle pulses, and more specifically to synchronizing charged particle pulses with light pulses (e.g., to determine a time of arrival of a charged particle pulse relative to a light pulse).

State-of-the-art x-ray light sources are useful for time-resolved scientific studies, where the desired time resolution is at the femtosecond (fs) level. In such studies, multiple beams including laser, x-ray, and electron beams are synchronized at the same (e.g., femtosecond) level to accomplish new science. Achieving this level of synchronization is a pressing challenge in the field.

<CIT> discloses an extreme UV radiation source having an electron radiation source for generating electronic radiation, and a pre-stage light source for producing pre-stage light rays with a wavelength that is long compared to wavelength of extreme UV-radiation. A polarization-presetting device is arranged in an optical path of the rays to preset defined polarization condition of the produced extreme UV-radiation. An overlapping device is arranged in the optical path of the rays after the presetting device and overlaps the electronic radiation with the rays in an overlapping volume. There are means for observing the overlapping volume.

In one aspect, a method includes directing a first light beam to intersect with a charged particle beam at a first location in a first region to produce a first x-ray beam. The method includes detecting a position on a detector where at least a portion of the first x-ray beam impinges; and determining a timing synchronization of the charged particle beam relative to the first light beam based on the position.

In some embodiments, the first light beam includes a plurality of pulses of the first light beam, the charged particle beam includes a plurality of pulses of the charged particle beam. When a respective pulse of the plurality of pulses of the first light beam impinges a respective pulse of the plurality of pulses of the charged particle beam, a pulse of the first x-ray beam is produced. The timing synchronization is between the respective pulse of the first light beam and the respective pulse of the charged particle beam.

In some embodiments, the method further includes directing a second light beam to intersect the charged particle beam, before the first light beam intersects the charged particle beam, to produce a second x-ray beam; and directing the second x-ray beam to an experimental end station. In some embodiments, the first light beam and the second light beam are derived from a common light source.

In some embodiments, the method further includes directing a third light beam from the common light source to the experimental end station. In some embodiments, the charged particle beam travels along a curved trajectory caused by a magnetic field in the first region. In some embodiments, the timing synchronization is a function of a position along the curved trajectory at which the first light beam intersects the charged particle beam. In some embodiments, the position on the detector is determined by the position along the curved trajectory at which the first light beam intersects the charged particle beam.

In some embodiments, the method includes selecting a magnitude of the magnetic field so that charged particles having a central energy in the charged particle beam travel along a selected path. In some embodiments, a larger portion of energy from the common light source is in the second light beam than in the first light beam.

In some embodiments, the method includes recording a first position on the detector where a first x-ray pulse impinges, the first x-ray pulse generated using a first pulse of the charged particle beam and a first pulse of the first light beam, The method further includes recording a second position on the detector where a second x-ray pulse impinges, the second x-ray pulse generated using a second pulse of the charged particle beam and a second pulse of the first light beam. The method includes converting a distance between the first position and the second position to time delays between respective times of arrival of respective pulses of the charged particle beam relative to respective pulses of the first light beam.

In some embodiments, converting the distance to the time delay is based on a distance between the first location and the detector. In some embodiments, the first x-ray pulse is produced through inverse Compton scattering (ICS). In some embodiments, the pulsed charged particle beam is a relativistic beam. In some embodiments, the first light beam is a pulsed laser beam. In some embodiments, the charged particle beam includes an electron beam. In some embodiments, the electron beam comprises pulses of electrons.

In some embodiments, the first light beam comprises pulses of light and a repetition rate of the pulses of light is equal to a repetition rate of the pulses of electrons. In some embodiments, the repetition rate is <NUM>.

In one aspect, a time synchronization device includes a detector configured to measure a position where an x-ray pulse produced by a charged particle beam impinges on the detector, a camera configured to produce an image of the position on the detector where the x-ray pulse impinges; and a computer system including one or more processors and memory storing instructions for converting the position on the detector to a measurement of a timing synchronization between the charged particle beam and a light beam.

In some embodiments, the x-ray pulse is produced by colliding the charged particle beam with the light beam from a light source. In some embodiments, the charged particle beam collides with the light beam in a region having a magnetic field. In some embodiments, the magnetic field is configured to cause the charged particle beam to travel on a curved trajectory. In some embodiments, the detector is configured to be placed within a housing that is held under vacuum. In some embodiments, the camera is configured to be placed outside the housing. In some embodiments, the detector includes a scintillator, and the scintillator is configured to emit luminescence when excited by the x-ray pulse. In some embodiments, the scintillator includes a yttrium aluminum garnet (YAG) screen. In some embodiments, the charged particle beam is produced by an accelerator. In some embodiments, the charged particle beam is a relativistic beam. In some embodiments, the light beam includes a pulsed laser beam. In some embodiments, the charged particle beam includes an electron beam. In some embodiments, the electron beam includes pulses of electrons. In some embodiments, the light beam includes pulses of light and a repetition rate of the pulses of light is equal to a repetition rate of the pulses of electrons. In some embodiments, the repetition rate is <NUM>.

In one aspect, a method includes determining a timing synchronization between an electron pulse and a light pulse, generating an x-ray pulse by colliding the light pulse with the electron pulse at a first location, measuring a position on a detector where the x-ray pulse impinges, and calculating the timing synchronization based on the position and a distance between the detector and the first location.

In some embodiments, the first location is within a magnetic field and the electron pulse travels along a circular trajectory. In some embodiments, calculating the timing synchronization further includes using a value of a radius of curvature of the circular trajectory of the electron pulse. In some embodiments, the electron pulse travels at greater than <NUM>% of the speed of light.

For a better understanding of the various described embodiments, reference should be made to the Description of Embodiments below, in conjunction with the following drawings in which like reference numerals refer to corresponding parts throughout the figures.

Some embodiments of the present disclosure provide a method that includes colliding (e.g., intersecting, interacting) a laser with an electron beam to produce backscattered x-rays while the electron beam is traversing a circular arc. Hereinafter, the terms "colliding", "intersecting", and "interacting" as used in this description denote the same types of interaction between an electron pulse and a light pulse, unless otherwise stated. This backscattering process is inverse Compton scattering (ICS). ICS x-rays are emitted in the same direction as the electrons (e.g., tangential to the direction of travel of the electrons). A direction of x-rays emitted via ICS changes as a function of time due to movement of the electron pulse along a circular trajectory. This causes a position of the x-ray beam on a detector to change depending on a timing (and thus the position or location) of the electron laser collision (and the resulting x-ray generation). This position change is readily detected and converted to a timing measurement sensitive at the femtosecond scale, converting a very difficult timing measurement of laser pulse, electron pulse, and x-ray pulse synchronization into a simple and robust position measurement.

<FIG> are schematic diagrams illustrating a light source <NUM> (e.g., a free-electron laser) in accordance with some embodiments. For brevity, only some of the most pertinent aspects of the light source <NUM> are discussed in detail below.

In some embodiments, light source <NUM> produces x-rays. In some embodiments, light source <NUM> produces hard x-rays (e.g., x-rays having energies above <NUM> keV). In some embodiments, light source <NUM> produces soft x-rays or extreme ultraviolet light. In some embodiments, as described below, the light (e.g., x-rays) produced by light source <NUM> is fully spatially- and temporally-coherent (e.g., light source <NUM> produces light with coherence properties similar to those of conventional lasers emitting light at optical, ultraviolet, infrared, or other wavelengths). In some embodiments, light source <NUM> generates light by interacting a relativistic electron beam with an electromagnetic field (e.g., either from a UV laser, in the case of inverse Compton scattering, as described below, or from an undulator, as in an embodiment not being part of the claimed invention ). For some embodiments in which an undulator is used and which are not part of the claimed invention, light source <NUM> generates light using a much shorter undulator than conventional FELs (e.g., ~<NUM> meters as opposed to ~<NUM> meters). Thus, light source <NUM> is sometimes referred to as a compact x-ray free-electron laser (CXFEL).

<FIG> shows an electron photoinjector <NUM> generating and initially accelerating an electron bunch. For example, in some embodiments, a <NUM> MeV electron beam is generated by a <NUM> cell x-band photoinjector, which comprises a solenoid and an RF gun. The photoinjector is followed (e.g., downstream) by one or more linear accelerator (LINAC) sections (LINAC sections 104a-104c, respectively), powered by one or more klystrons (klystrons 106a-106b). For example, in some embodiments, three <NUM> long LINAC sections 104a-106c accelerate the electron beam to <NUM> MeV.

In some embodiments, RF power from a single klystron <NUM> is applied to several different components (e.g., klystron 106b powers both LINAC section 104b and LINAC section 104c as well as RF deflector cavity and accelerator cavity <NUM>, whereas klystron 106a powers both the initial acceleration of the electron bunch and LINAC 105c). Further, in some embodiments, phase shifters <NUM> (e.g., phase shifters 108a-108d) apply a phase shift to the power supplied by the various klystrons <NUM> to the various components. In some embodiments, RF loads <NUM> (e.g., RF loads 128a-128b) are introduced for load balancing and control.

The diffraction grating <NUM> is arranged in a transmission geometry with respect to the path of the electron bunch (e.g., the direction of propagation of the electron bunch). In some embodiments, the diffraction grating <NUM> diffracts the electron beam having a tunable energy with a maximum of <NUM> MeV.

<FIG> and <FIG> show a variety of electron optics for patterning and shaping the electron bunch downstream of the LINAC sections <NUM>. The electron optics of light source <NUM> includes three main sections: a nano-pattern imaging section <NUM>, an emittance exchange (EEX) section <NUM>, and an inverse Compton scattering (ICS) interaction section <NUM>. In some embodiments , not being part of the claimed invention, the ICS interaction section <NUM> is replaced with an undulator (e.g., an undulator less than <NUM> in length).

The nano-patterning imaging section <NUM> is downstream of LINAC section 104c and, in some embodiments, includes two quadrupole triplets <NUM> (e.g., quadrupole triplet 118a and quadrupole triplet 118b) forming a telescope system. Quadrupole magnets create a magnetic field whose magnitude grows rapidly with the radial distance from its longitudinal axis. This property is useful in particle beam focusing.

The EEX section <NUM> includes four bend magnets 120a-120d, an RF deflector cavity and an accelerator cavity (collectively <NUM>) that are independently phased and powered, along with sextupoles magnets 122a-<NUM>-c and octopole magnets <NUM> for aberration correction.

After the EEX section <NUM>, the ICS interaction section <NUM> starts with a focusing triplet <NUM> that reduces the electron beam size at the ICS interaction point <NUM> (e.g., to approximately a micron) before colliding the electron beam with ICS laser field from an inverse Compton scattering laser <NUM> (e.g., light from the inverse Compton scattering laser <NUM> is piped in and redirected to be nearly parallel with the electron beam at the ICS interaction point <NUM>). The collision of the electron beam with the ICS laser field produces x-rays (or other light) <NUM>. Downstream the ICS interaction point <NUM>, two dipoles 134a-134b respectively bend the beam into a beam dump (e.g., by <NUM> degrees horizontally and <NUM> degrees, respectively, into a vertical beam dump). In some embodiments, as shown in <FIG>, the beam dump is below the magnetic 134b, along the x-direction (into the plane of the drawing).

In some embodiments, the collision of the electron beam with the ICS laser field is within a magnet field of dipole magnet 134a. ICS interaction section <NUM> is an example of a light-generating apparatus. An undulator (not shown and not being part of the claimed invention ) is another example of a light-generating apparatus.

<FIG> is a schematic diagram illustrating an apparatus <NUM> for synchronizing a timing of a pulsed charged particle beam <NUM> with a pulsed light beam <NUM>, according to some embodiments. In some embodiments, synchronizing a pulsed charged particle beam with a pulsed light beam includes determining a time of arrival of the pulsed charged particle beam relative to the pulsed light beam. Hereinafter, the pulsed charged particle beam will be referred to as an electron beam. In general, however, the methods and systems disclosed herein can be used for charged particle beams such as ions or other charged particles. The terms "charged particle pulses" and "pulsed charged particle beam" are synonymous, as used in this description, unless otherwise indicated.

The apparatus <NUM> includes an x-ray detector. In some embodiments, the x-ray detector includes a scintillator <NUM> and a camera <NUM> that measures light emitted by the scintillator <NUM>. The scintillator <NUM> includes a material that exhibits scintillation, in which a small flash of visible or ultraviolet light is emitted by fluorescence or phosphorescence (e.g., luminescence), when the material is struck by a charged particle or high-energy photon (or otherwise excited by ionizing radiation).

The scintillator <NUM> glows when impinged by an x-ray pulse, and the camera <NUM> images the scintillator, allowing for the capture and measurement of the position of the glow. In some embodiments, the scintillator is a yttrium aluminum garnet (YAG) screen. In some circumstances, a beam diameter of the x-ray pulse <NUM> produced via ICS in the collision of the light pulse <NUM> and the electron beam <NUM> at a location <NUM> is on the order of tens of microns. In some embodiments, the scintillator <NUM> provides a spatial resolution of at least <NUM> (e.g., two points <NUM> or more apart on the scintillator can be distinguished). In some embodiments, the scintillator provides spatial resolution up to <NUM>.

In some embodiments, the electron beam is a relativistic beam produced by an accelerator <NUM> (not drawn to scale). In some embodiments, the accelerator <NUM> includes the components <NUM> through <NUM> shown in <FIG>, such as one or more of an RF gun, klystrons, chicanes, and the like. The accelerator <NUM> denotes all the components used to deliver an electron beam to the interaction region at the final focus of the light source <NUM>. In some embodiments, the relativistic beam is an electron beam traveling close to the speed of light (e.g., <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>% the speed of light).

In some embodiments, the pulsed light beam is a pulsed laser beam. In some embodiments, the pulsed laser beam has a wavelength λ<NUM> in the infrared, optical, or ultraviolet spectra.

The apparatus <NUM> operates in a first region <NUM> having a magnetic field <NUM>. The magnetic field <NUM> is produced by a magnet. In some embodiments, the magnet is an electromagnet. In some embodiments, the magnet is a permanent magnet. In some embodiments, the magnet is a dipole magnet. In accelerators, a dipole magnet creates a homogeneous magnetic field over some distance (region). Charged particle motion in that field will be circular in a plane perpendicular to the field. In some circumstances, a charged particle injected into a region having a magnetic field created by a dipole magnet travels along a circular (e.g., when the magnetic field is perpendicular to the velocity of the charged particle). By adding several dipole sections on the same plane, the bending radial effect of the charged particle beam increases.

In some embodiments, the first region <NUM> corresponds to the region within the magnetic field produced by the dipole magnet 134a in <FIG> (the magnetic field <NUM> is generated by the dipole magnet 134a). In some embodiments, the apparatus <NUM> does not include the magnet, and the apparatus <NUM> is simply placed in a region already subjected to the magnetic field <NUM>. For example, the magnetic field <NUM> is already present to direct the charged particle beam <NUM> toward a beam dump to safely dispose of charged particles used to produce x-ray pulses <NUM>, independently of the timing synchronization. In some embodiments, the apparatus <NUM> includes the magnet used to produce the magnetic field <NUM>.

In some embodiments, a radius of curvature, R, (as shown in <FIG>) of the circular trajectory is about <NUM>. A magnetic field needed used to produce such a radius of curvature is can be estimated by assuming that the electrons are moving at nearly the speed of light. A stronger magnetic field produces a smaller R, which improves time resolution. However, the spent electron beam <NUM> leaving the interaction region <NUM> should be disposed of at the beam dump, which restricts possible trajectories of the electron beam <NUM> and also the size of R.

The energy of the electron beam <NUM> also influences the size of R. Under a constant magnetic field, R increases as the energy of the electron beam increases. <FIG> shows an energy distribution <NUM> of an electron beam. The energy distribution <NUM> has a central energy <NUM>, and a spread <NUM> of electron energies. In some embodiments, a magnetic field strength is adjusted (e.g., by adjusting a size of a current through an electromagnet) to keep electrons having the central energy <NUM> on the same trajectory (i.e., same R), regardless of the value of the central energy <NUM>.

Varying the magnetic field strength to keep the electrons on the same trajectory helps to ensure that a majority of the spent electron beam leaving the interaction region <NUM> reaches the beam dump. In some embodiments, a typical energy (e.g., a central energy <NUM>) is about <NUM> MeV. In some embodiments, the range of electron energy is between <NUM>-<NUM> MeV for a compact x-ray light source (CXLS). In contrast to CXFEL, x-ray pulses generated from CXLS are not coherent.

In some embodiments, the pulsed light beam is a pulsed laser beam from a laser source that has a first repetition rate. In other words, pulses of laser light are emitted from the laser source at the first repetition rate. In some embodiments, the laser source that produces the light <NUM> is a Trumpf Dira <NUM>-<NUM> Yb:YAG amplifier. In some embodiments, the Trumpf Dira generates pulses that are <NUM> ps long with a pulse energy of <NUM> mJ at <NUM> repetition rate. Optics (e.g., mirrors, beamsplitter, etc.) direct light <NUM> from the laser source to intersect or collide (e.g., interact) with the electron beam <NUM>, as shown in <FIG>.

In some embodiments, the electron beam is a sequence of electron pulses at a second repetition rate. In some embodiments, the first repetition rate is equal to the second repetition rate. In some embodiments, the first repetition rate and the second repetition rates are both <NUM>.

<FIG> shows a timing sequence <NUM> in which a laser source produces light pulses (e.g., 402a, 402b, 402c, 402d) at a repetition rate (e.g., <NUM>) that is identical to the repetition rate of the pulses of electrons (e.g., 404a, 404b, 404c, 404d) emitted from the accelerator <NUM>. There is shot-to-shot jitter between pulses of electrons. There is also shot-to-shot jitter between light pulses. To improve clarity, <FIG> shows optical pulses without shot-to-shot jitter. In general, there is jitter in both the optical pulses and the electron pulses. In some embodiments, the laser light pulses 402a - 402d have a smaller shot-to-shot timing jitter compared to the electron pulses. The timing synchronization described herein is able to measure a time of arrival of each electron pulse relative to a corresponding light pulse.

For example, a first delay 406a between the light pulse 402a and the electron pulse 404a is larger than a delay 406b between the light pulse 402b and the electron pulse 404b. Magnitudes of changes in time delays are exaggerated for illustration purposes in <FIG>. Due to differences in the delays 406a - 406d, x-ray pulses generated by the electron pulses 404a - 404d would appear on different spatial locations on a scintillator <NUM> (shown in <FIG>), depending on a time of arrival of the electron pulse relative to its corresponding light pulse (e.g., between a respective electron-light pair: 404a and 402a; 404b and 402b, etc.).

When the repetition rate of the laser pulses is the same to the repetition rate of the electron pulses (except for jitter), the methods and apparatus disclosed herein provide a way to provide shot-to-shot timing synchronization for every electron pulse that is produced by the accelerator <NUM>. For example, in an experiment involving optical pump pulses (e.g., first portion 106a) and x-ray probe pulses (e.g., x-ray pulse 320a), a precise timing for every x-ray probe pulse is determined relative to the optical pump pulses, even when there is shot-to-shot jitter in both the optical light pulses (e.g., 402a) and the electron pulses (e.g., 404a). In other words, because the light (<NUM>) sent directly to the experiment, (<NUM>) the light used to generate the x-ray pulse for probing, and (<NUM>) the light used to generate the x-ray pulse for timing synchronization, come from a common laser source, the jitters in the light pulses are the same, and the timing of the x-ray pulse can be synchronized to the timing of the light used for the experiment.

In some embodiments, a distance L (shown in <FIG>) between the location <NUM> and the scintillator <NUM> is about <NUM> (e.g., less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, more than <NUM>). The scintillator <NUM> is placed inside a vacuum housing <NUM> (shown in <FIG>) within which the electron beam is enclosed, and the distance L can be adjusted within the housing <NUM>. In some embodiments, the camera ++<NUM> is a CCD camera In some embodiments, the camera is outside the vacuum housing. In some embodiments, additional optics are used to image the scintillator <NUM> onto an image sensor on the CCD camera.

Using ICS, the x-rays are emitted in a direction tangential to the path of the electron beam <NUM>. <FIG> shows a trajectory of the electron beam <NUM> curved by the magnetic field <NUM>. The methods and systems disclosed herein are not limited to embodiments in which the light beam <NUM> has low shot-to-shot timing jitter, and every pulse of the light beam <NUM> arrives at substantially the same location at the same time instance after leaving the light source. Rather, the methods and systems detect a time of arrival of the electron pulse relative to its corresponding light pulse (e.g., electron pulse 404a against light pulse 402a).

For example, when the electron beam <NUM> arrives slightly earlier than its corresponding light pulse, the direction that the x-rays are emitted will be different than if the electron beam <NUM> arrives slightly later. For example, when the electron beam <NUM> arrives slightly earlier (relative to light beam <NUM>), at relative time = T1, it would have travelled a longer distance to a position <NUM>, before intersecting with the light beam <NUM>. Conversely, when the electron beam <NUM> arrives slightly later (relative to light beam <NUM>), at relative time = T2, electron beam <NUM> would have travelled a shorter distance to a position <NUM> before intersecting light beam <NUM>. Thus, the position of scintillation on the scintillator <NUM> is convertible to a measurement of a timing synchronization between the pulsed electron beam <NUM> and the pulsed light beam <NUM>. T1 and T2 are marked on <FIG>, and T1 is earlier (e.g., the electron beam <NUM> arrives earlier in time relative to the light beam <NUM>) than T2.

In some embodiments, the methods and systems provide a time resolution of about <NUM> fs. For example, the timing synchronization apparatus <NUM> is able to distinguish between a first electron pulse that arrives <NUM> fs or more earlier or later relative to its corresponding light pulse than a second electron pulse.

In some embodiments, the apparatus <NUM> is calibrated for synchronizing timing between the electron beam <NUM> and the light beam <NUM>. For example, a calibration determines how a distance between luminescence emitted from two spatial points on the scintillator <NUM> corresponds to a particular time delay (between the electron beam <NUM> and the light beam <NUM>).

In some embodiments, a known delay is applied to the electron beam <NUM> to introduce additional (known) delay (e.g., <NUM> fs) to the electron beam. In general, the known delay can be added electronically to the electron beam or it can be added optically to delay the optical pulse from the laser (e.g., by sending the optical pulse through a variable delay stage).

A first position of the luminescence produced by a x-ray pulse generated from the ICS interaction of the delayed electron beam and the light beam <NUM> is recorded on the scintillator <NUM>, and imaged by camera <NUM>. In some embodiments, it is the light beam <NUM> that is delayed relative to the electron beam. After the known delay is removed from the electron beam, a second position of the luminescence produced by another x-ray pulse generated from the ICS interaction of the electron beam and the light beam <NUM> is recorded on the scintillator <NUM>. The second (i.e., delayed) electron pulse is subject to the same shot-to-shot jitter that the timing synchronization accounts for. For example, the electron beam shot-to-shot jitter averages <NUM> fs (given a time resolution of <NUM> fs). By applying a delay of <NUM> fs, the measured pulse could be anywhere from an actual delay of <NUM> fs to <NUM> fs.

<FIG> shows a distribution of electron pulses as observed on the detector (e.g., scintillator <NUM>). In some embodiments, a first number of electron pulses (e.g., <NUM>) are measured without the time delay to determine an average <NUM> of a distribution <NUM> of the times of arrival of the electron pulses. A known time delay is added to either the electron beam or the light beam, and a second number of electron pulses (e.g., <NUM>) are measured with the time delay to determine an average <NUM> of a distribution <NUM> of the times of arrival of the electron pulses. Image processing techniques, for example, are used to measure a distance between the first position in the first image and the second position in the second image. A spatial distance <NUM> between the average <NUM> and the average <NUM> provides a calibration. The calibration is obtained by taking a ratio between the distance between distributions <NUM> and the known time delay. For example, a distance of <NUM> on the scintillator corresponds to a time difference (e.g., the known time delay) of <NUM> fs.

<FIG> illustrates how system parameters are used to obtain timing synchronization between a pulse of an electron beam and a pulsed light beam. For ease of illustration, dimensions are greatly exaggerated along the y-direction.

A first pulse of electron beam <NUM>, having an earlier time of arrival, travels further along its circular trajectory before intersecting the light beam <NUM> at a position 222a, at time t1. The first pulse of electron beam <NUM> undergoes ICS with the light beam <NUM>, producing a first x-ray pulse 220a that impinges on the scintillator <NUM>. A second pulse of electron beam <NUM>, having a later time of arrival, travels a shorter distance along its circular trajectory before intersecting the light beam <NUM> at a position 222b, at time t2, which is later than t1. The second pulse of electron beam <NUM> undergoes ICS with the light beam <NUM>, producing a second x-ray pulse 220b that impinges on the scintillator <NUM>.

A time shift Δt between arrival times of the two electron pulses relative to their respectively light pulses equals the difference between the time of arrival t1 of the first electron pulse, and the time of arrival t2 of the second electron pulse. The time difference Δt is equivalent to the time taken by an electron beam to travel a distance ds on the arc, between the position 222a and the position 222b. Note that ds = R * θ where R is the radius of curvature of the electron beam's trajectory, and θ is the angle subtended by the arc between the positions 222a and 222b. The electron beam travels nearly the speed of light c.

Similarly, the distance D between the locations were the x-ray pulses 220a and 220b impinge on the scintillator is related to (for small angles) a distance L, the distance between the electron beam (e.g., at positions 222a and 222b) and the scintillator <NUM> according to the equation D = L * θ. Equating θ: <MAT>.

Gives a direct measure of the time difference Δt: <MAT>.

As c, R, L are all known, measuring D provides Δt. Note that, because the locations of intersection between the electron beam and the light beam are close together, L is nearly constant (and can be assumed to be constant for the purposes of approximation).

<FIG> shows an x-ray source <NUM>, in accordance with embodiments in which a laser <NUM> produces light that is split for multiple uses. A first portion 156a of the light <NUM> is directed towards an experimental end station <NUM> for use in an experiment. In some embodiments, the first portion 156c of light is used to excite (e.g., "pump") an experimental sample placed in the experimental end station <NUM>. A second portion 156b of the light <NUM> is directed by a first beamsplitter 304a towards the electron beam <NUM> emitted by the accelerator <NUM>.

The second portion 156b of the light <NUM> is further divided by a second beamsplitter 304b into two separate arms: a third portion 106c, and a fourth portion 106d. The third portion 106c of the light <NUM> in the first arm is directed to an interaction point <NUM>, where the electron beam <NUM> and the light beam <NUM> interact through ICS to produce a pulsed x-ray beam 320a that is directed towards the experimental setup <NUM>. In some embodiments, at the interaction point <NUM>, a size of the electron beam <NUM> is on the micron level. In some embodiments, the optical light beam has a beam diameter on the order of tens of microns, and is able to easily intersect the narrower electron beam.

The fourth portion 156d of the light <NUM> in the second arm is directed by additional optics (e.g., a mirror 304c) to interact with the electron beam <NUM> in a first region <NUM> that is under the influence of a magnetic field <NUM>. For example, the fourth portion 156d of light interacts with the electron beam <NUM> in a second region <NUM> to produce second x-ray pulse 320b. Because of the presence of the magnetic field <NUM>, the second region <NUM> is along the circular or helical trajectory of the electron beam <NUM>. Because the optical light beam has a beam diameter on the order of tens of microns, it is able to easily intersect the narrower electron beam at multiple positions along the circular trajectory. In addition, a temporal profile of the relativistic beam <NUM> is not significantly changed after the first ICS interaction at the interaction point <NUM>. As a result, measuring a time of arrival of the electron beam in the second region <NUM> is equivalent to measuring a time of arrival of the electron beam at the interaction point <NUM>. In some embodiments, a spatial profile of the relativistic beam <NUM> changes after further propagation.

In some embodiments, more energy is sent to the third portion 156c than the fourth portion 156d. In some embodiments, <NUM>% of the energy from the second portion 156b is sent to the third portion 156c and <NUM>% of the energy is sent to the fourth portion 156d.

The actual location of the second region <NUM> depends on a time of arrival of the electron beam <NUM>. An electron beam that arrives later, with respect to the fourth portion 106d of the light, would intersect the fourth portion 106d of the light at a location closer to the interaction point <NUM> illustrated in <FIG>.

When the time of arrival of the electron beam is later than the fourth portion 106d of the light, the interaction point <NUM> also moves further down along the -z direction than is illustrated in <FIG>. In such a case, the x-ray pulse produced from the second region <NUM> would strike a different portion of the scintillator <NUM> (e.g., in a region along the +y direction on the scintillator <NUM>).

Similarly, an electron beam that arrives earlier, with respect to the fourth portion 106d of the light, would intersect the fourth portion 106d of the light at a location further from the interaction point <NUM> illustrated in <FIG>. In such a case, the interaction point <NUM> moves further up along the +z direction than is illustrated in <FIG>. The x-ray pulse produced from the second region <NUM> would then strike a different portion of the scintillator <NUM> (e.g., in a region along the -y direction on the scintillator <NUM>).

Since the third portion 106c and the fourth portion 106d are produced by the same light source (e.g., laser source <NUM>), their timing synchronization is relatively fixed (e.g., based on optical path lengths of the two portions) and easy to determine. For example, an absolute distance between the interaction point <NUM> and the second region <NUM> is determined by the difference between optical path lengths of the third portion 106c of the light and the fourth portion 106d of the light <NUM> to their respective locations where ICS occurs (i.e., the difference in the lengths of the paths travelled by the third portion 106c and the fourth portion 106d after the second beamsplitter 304b). The absolute distance is not affected by a time of arrival of the electron beam relative to the light beam <NUM> from the laser source <NUM>. Thus, the timing relationship between the x-ray pulse 320b (used for timing synchronization), and the x-ray pulse 320a (used for experiments), is fixed. Any change in the position of the scintillation caused by the the x-ray pulse 320b on the scintillator <NUM> indicates a shot-to-shot change in a time of arrival of the electron pulse <NUM>, relative to the light pulse <NUM>.

In some embodiments, the x-ray pulse 320a can be delayed or advanced relative to the first portion 106a by changing an optical path length of the second portion 106b, between the first beamsplitter 304a and the second beamsplitter 304b. Fine-tuning of the actual timing between the first portion 106a and the x-ray pulse 320a is provided by the measurement recorded on the scintillator <NUM>.

Having the interaction point <NUM> be just outside of the magnetic field <NUM> better allows the x-ray pulse 320a to reach the experimental end station <NUM> without significant (e.g., any) adjustment of x-ray optics regardless of the arrival time of the electron beam <NUM>. In such cases, the electron beam used to produce the x-ray pulses 320a does not yet move along a circular or helical trajectory. Because ICS produces x-ray pulses that emits tangentially from a direction of travel of the electron beam, when the electron beam <NUM> travels along a straight line (e.g., along the +z direction), the emitted x-ray pulse 320a would also travel along the +z direction no matter the actual location along the z-direction where the third portion 156c of the light <NUM> intersects with the electron beam <NUM> and produces x-ray pulses via ICS.

X-ray source <NUM> further includes a computer system <NUM> including one or more processors and memory storing instructions for converting the measured position to a measurement of a timing synchronization between the pulsed charged particle beam and the pulsed light beam. In some embodiments, the computer system <NUM> receives images from the camera <NUM>.

It will be understood that although the terms "first," "second," etc. may be used herein to describe various elements, these elements should not be limited by these terms. For example, a first widget could be termed a second widget, and, similarly, a second widget could be termed a first widget, without changing the meaning of the description, so long as all occurrences of the "first widget" are renamed consistently and all occurrences of the "second widget" are renamed consistently. The first widget and the second widget are both widgets, but they are not the same widget.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the claims. As used in the description of the embodiments and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

As used herein, the term "if' may be construed to mean "when" or "upon" or "in response to determining" or "in accordance with a determination" or "in response to detecting," that a stated condition precedent is true, depending on the context. Similarly, the phrase "if it is determined [that a stated condition precedent is true]" or "if [a stated condition precedent is true]" or "when [a stated condition precedent is true]" may be construed to mean "upon determining" or "in response to determining" or "in accordance with a determination" or "upon detecting" or "in response to detecting" that the stated condition precedent is true, depending on the context.

Claim 1:
A method, comprising:
directing a first light beam to intersect with a charged particle beam at a first location in a first region to produce a first x-ray beam;
detecting a position on a detector where at least a portion of the first x-ray beam impinges; and
determining a timing synchronization of the charged particle beam relative to the first light beam based on the position.