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Abstract A high efficiency simulation method for propagation-based phase-contrast imaging, called directional macro-wavefront (DMWF), is developed with the aim of simulating high-energy phase-contrast imaging. This method takes both Monte Carlo and wave optical propagation into consideration. Traditional wave-optics-based simulation methods for phase-contrast imaging encounter unacceptable computational complexity when high-energy radiation is used. In contrast, this method effectively addresses this issue by using macro-wavefront integration. Several simulation examples using typical parameters of inverse Compton scattering sources are presented to illustrate the excellent energy adaptability and efficiency of the DMWF method. This method provides a more efficient approach for phase-contrast imaging simulations, which will drive the advancement of high-energy phase-contrast imaging.

A light source project named very compact inverse Compton scattering gamma-ray source (VIGAS) is under development at Tsinghua University. VIGAS aims to generate monochromatic high-energy gamma rays by colliding 350-MeV electron beams with 400-nm laser photons within a 12-m beamline. To produce a high-energy electron beam in such a compact space, the system consists of an S-band high-brightness injector and six X-band high-gradient accelerating structures. The goal of the X-band structure is to operate at a high gradient of 80 MV/m. Therefore, we adopts the constant gradient traveling wave approach, where the iris from the first cell to the end cell is tapered. The structure has 72 cells, including 70 cells and 2 couplers, so we named it XT72. The frequency of XT72 is selected to 11.424 GHz, and the 2π/3 mode is adopted. In this paper, we present a comprehensive study covering the detailed design, fabrication, rf tuning, and high-power test results of the first XT72. Additionally, we compare the performance of this structure to that of the previous constant impedance structure. Our results demonstrate that the XT72 is capable of operating at an 80-MV/m gradient with a lower breakdown rate. This advancement paves the way for the development of VIGAS project and contributes to the wider application of X-band room-temperature high-gradient structures in compact accelerator facilities.

In this study, we propose a physical design of a compact all-optical terahertz (THz)-driven electron source. The 300-mm accelerator beamline, powered by a Joule-level laser system, can be easily integrated into the tabletop scale. A THz-driven electron gun, a tapered dielectric-loaded cylindrical waveguide, THz-driven bunch compressors, and permanent magnetic solenoids (PMSs) have been designed and optimized. Dynamic simulations show that the electron source can deliver 19 fC electron beams at 3 MeV, with a normalized transverse emittance of 0.079 π.mm.mrad. A minimum relative energy spread of 0.04% or a minimum root-mean-square (RMS) bunch length of 6.1 fs can be achieved. Sensitivity analysis shows that the THz-driven electron source can effectively work with a laser power jitter within 1.5%. Simulation studies also reveal the potential of the designed THz-driven electron source for achieving high-quality ultrafast electron diffraction (UED). Prototype THz-driven electron guns have been fabricated and are currently under testing, and more comprehensive results will be reported in future works.

Steady-state microbunching (SSMB) storage rings are an appealing option for high-power extreme ultraviolet (EUV) light sources. In this paper, we propose a generalized longitudinal strong focusing (GLSF) scheme to boost the average power of short-wavelength radiation from an SSMB source with a technical demand within the present reach. This scheme employs transverse-longitudinal coupling dynamics to produce steady-state ultrashort bunches and reduces the required modulation laser power significantly by exploiting the low vertical beam emittance in a planar ring. Linear beam dynamics are studied in detail, including bunch compression, modulation cancellation, and vertical-longitudinal decoupling. An instance of a linear lattice layout is given, and kW-level quasicontinuous-wave 13.5-nm EUV radiation can be achieved in a GLSF SSMB storage ring with 1-MW modulation laser power. We believe that the GLSF scheme can also be used in conventional storage rings for various purposes concerning beam manipulation.

Tsinghua University is currently developing a very-high-frequency electron gun that operates in continuous-wave (cw) mode at 216.667 MHz. This gun will serve as the beam source for the Shanghai high repetition rate XFEL and extreme light facility. The cavity profile has been optimized to minimize input power, peak surface electric field, and peak wall power density. The profile optimization also takes into account the suppression of multipacting effect. Additionally, thermal analysis has been performed to guide the design of water cooling channels in coordination with gun mechanical design. The fabrication of the gun has been completed, and the frequency and quality factor measured in cold test are in good agreement with simulation expectations. During high power conditioning, 75 kW cw radio frequency power was successfully fed into the gun, corresponding to a cathode gradient of 27 MV/m and a gun voltage of 780 keV. This operating gradient is currently the highest in the world for room-temperature VHF guns. Under this condition, the maximum dark current collected by the Faraday cup at the gun exit was 376 nA when the strength of the gun solenoid was scanned. To measure and optimize the beam quality, a test beamline was constructed. After preliminary optimization, the 95% projected transverse emittance was 0.161 mm mrad for 10 pC bunches with a bunch length of 0.49 mm rms, 0.429 mm mrad for 50 pC bunches with a bunch length of 1.15 mm rms, and 0.853 mm mrad for 100 pC bunches with a bunch length of 1.44 mm rms.

The next generation of accelerator based scientific facilities, such as the megahertz repetition rate free electron laser and electron-ion collider, relies on photoelectron sources of high peak and high average brightness. Therefore, photocathodes with both low transverse momentum spread (TMS) and high quantum efficiency (QE) are required. The conventional positive correlation between QE and TMS leads to a tradeoff between peak and average brightness. In this study, a negative correlation between QE and TMS is experimentally observed for the first time on a semiconductor photocathode (Cs_{2}Te). Two models are proposed to explain such an anomalous correlation. One model considers the junction between the semiconductor cathode and the metal substrate in the case of slightly excessive cesium deposition, and the other model considers different Cs-Te composites. Our studies inspire a new way to break the conventional correlation between QE and TMS, and open a new perspective to advance the beam brightness frontiers.

High-energy electron radiography (HEER) is a promising diagnostic tool for high-energy-density physics, as an alternative to tools such as X/γ-ray shadowgraphy and high-energy proton radiography. Impressive progress has been made in the development and application of HEER in the past few years, and its potential for high-resolution imaging of static opaque objects has been proved. In this study, by taking advantage of the short pulse duration and tunable time structure of high-energy electron probes, time-resolved imaging measurements of high-energy-density gold irradiated by ultrashort intense laser pulses are performed. Phenomena at different time scales from picoseconds to microseconds are observed, thus proving the feasibility of this technique for imaging of static and dynamic objects.

Abstract Background Cattle are commonly infected with the microsporidian parasite Enterocytozoon bieneusi. Sequence characterization of E. bieneusi in these animals at the ribosomal internal transcribed spacer (ITS) locus had identified I, J and BEB4 as the dominant genotypes. However, current studies on E. bieneusi in dairy cattle are mostly on infection rates and genotype distribution. This study aims to examine the intragenotypic diversity within dominant E. bieneusi genotypes in pre-weaned dairy calves in Shanghai, China. Methods Enterocytozoon bieneusi genotypes and subtypes were identified by PCR sequence analysis of ITS and multilocus sequence typing (MLST), based on material from farms. Chi-square test was used to examine differences in E. bieneusi infection rates between farms or age groups. Results The overall infection rate of E. bieneusi was 26.5% (214/809), ranging from 12.6% (Farm 5) to 38.5% (Farm 4). Infection rates increased with age during early life, with the peak infection rate (43.0%; 43/100) occurring at six weeks. Four genotypes were present, including J (n = 145, 67.8%), BEB4 (n = 59, 27.6%), CHN4 (n = 4, 1.9%) and CHN15 (n = 1, 0.5%), with the former two belonging to Group 2 and the latter two belonging to Group 1. Differences were detected in the distribution of the dominant genotypes J and BEB4 among five study farms. Altogether, 10 multilocus genotypes (MLGs) were identified in the two dominant ITS genotypes, including MLG-J1 to MLG-J8 of genotype J and MLG-B1 to MLG-B2 of genotype BEB4. MLG-B1 and MLG-B2 were recovered in Farms 1, 2 and 5, whereas MLG-J1 to MLG-J5 and MLG-J6 to MLG-J8 were found in Farms 3 and 4, respectively. Conclusions There is extensive genetic heterogeneity within the dominant E. bieneusi genotypes J and BEB4 in dairy calves in Shanghai, China, and MLST should be used in molecular epidemiological studies of E. bieneusi in cattle.

Emittance is a key figure-of-merit for high brightness electron beams that enable the success of a broad range of modern accelerator-based instruments. With the successful implementation of the emittance compensation scheme and beam-shaping techniques to align each temporal beam slice in phase space, slice emittance starts to play a more dominating role in determining the beam quality. In this paper, we develop an approach, combining simulations and analytical calculations, to systematically study the evolution of the slice emittance in a very high frequency gun photoinjector, which is under intense R&D worldwide for driving the next generation continuous-wave accelerators. Our approach is capable of tracing various sources that introduce curvature in the transverse phase space, corresponding to the growth of the slice emittance. It is shown that nonlinear transverse space charge forces in the vicinity of cathodes and the spherical aberration of the focusing solenoid are the main sources of nonlinear forces, while in a long drift section space charge forces can actually compensate for nonlinear transverse position-momentum correlations and hence recover the emittance. We further demonstrate that the sources of nonlinearities can be controlled by tailoring the transverse beam density profile and the design of solenoid lenses.

Coherent transition radiation (CTR) is a widely used approach to characterize the electron beam in accelerator science and technology. Characterization of the CTR with an efficient, versatile and compact setup is in considerable demand for a wide range of applications such as free electron lasers, electron storage rings and other related scientific researches. In this article, we report on spatial-temporal electric field measurements of CTR using the single-shot electro-optic spatial decoding method. A quasi-half-cycle temporal waveform of the THz pulse with peak electric field strength of ∼42 MV/m has been measured. A symmetrical field profile across the transverse center and the distorted wave front of CTR THz pulses near the focal plane were demonstrated. Moreover, timing jitters of the ultrashort electron beams are also monitored via this method with tens of femtosecond accuracy. This comprehensive method provides the temporal waveform and the one-dimensional spatial imaging of THz fields simultaneously, showing it has the potential for single-shot diagnostics of ultrashort electron beams.

Thermal emittance and quantum efficiency (QE) are key figures of merit of photocathodes, and their uniformity is critical to high-performance photoinjectors. Several QE mapping technologies have been successfully developed; however, there is still a dearth of information on thermal emittance maps. This is because of the extremely time-consuming procedure to gather measurements by scanning a small beam across the cathode with fine steps. To simplify the mapping procedure and to reduce the time required to take measurements, we propose a new method that requires only a single scan of the solenoid current to simultaneously obtain thermal emittance and QE distribution by using a pattern beam with multiple beamlets. In this paper, its feasibility has been confirmed by both beam dynamics simulation and theoretical analysis. The method has been successfully demonstrated in a proof-of-principle experiment using an L-band radio-frequency photoinjector with a cesium telluride cathode. In the experiment, seven beamlets were generated from a microlens array system and their corresponding thermal emittance and QE varied from 0.93 to 1.14 μm/mm and from 4.6% to 8.7%, respectively. We also discuss the limitations and future improvements of the method in this paper.

In state of the art photoinjector electron sources, thermal emittance from photoemission dominates the final injector emittance. Therefore, low thermal emittance cathode developments and diagnostics are very important. Conventional thermal emittance measurements for the high gradient gun are time-consuming and thus thermal emittance is not measured as frequently as quantum efficiency during the lifetime of photocathodes, although both are important properties for the photoinjector optimizations. In this paper, a single shot measurement of photoemission transverse momentum, i.e., thermal emittance per rms laser spot size, is proposed for photocathode rf guns. By tuning the gun solenoid focusing, the electrons’ transverse momenta at the cathode are imaged to a downstream screen, which enables a single shot measurement of both the rms value and the detailed spectra of the photoelectrons’ transverse momenta. Both simulations and proof of principle experiments are reported.

In state of the art photoemission electron sources, the transverse emittance of the electron beam is approaching its intrinsic value from the cathode. To reduce the intrinsic emittance, it is straightforward to tune the photon energy of the drive laser toward the photocathode emission threshold. This paper aims at constructing an improved model which takes into account an intermediate energy level to better explain the near threshold photoemission for semiconductors. A dynamic model is also proposed to evaluate the cathode degradation process due to surface oxidation. The models agree well with published results for different materials under various conditions, including electric field, temperature and vacuum condition. The dynamic model predicts that near threshold emission of an oxidized Cs_{3}Sb cathode outperforms UV photoemission of typical metal cathodes in terms of both quantum efficiency and intrinsic emittance. With the oxidization layer, the robustness of semiconductor cathodes to gun vacuum condition may be comparable to a metal cathode. This, however, needs further testing.

The production of electron bunches with low transverse emittance approaches the thermal emittance of the photocathode as various aberrations are corrected. Recently, the coupled-transverse-dynamics aberration was theoretically identified as a significant source of emittance growth, and a corrector magnet was proposed for its elimination [Phys. Rev. Accel. Beams 21, 010101 (2018)PRABCJ2469-988810.1103/PhysRevAccelBeams.21.010101]. This aberration arises when the beam acquires an asymmetric distribution that is then rotated with respect to the transverse reference axis, thus introducing a correlation in the vertical and horizontal planes. The asymmetry is introduced by a weak quadrupole field in the rf gun or emittance compensation solenoid and the rotation is caused by the solenoid. This manuscript presents an experimental study of the coupled-transverse-dynamics aberration in an rf photoinjector and demonstrates its elimination by a quadrupole corrector consisting of a normal and a skew quadrupole. The experimental results agree well with theoretical predictions and numerical simulations, showing that the corrected emittance could reach the thermal value for an electron bunch with a low charge and a short length.

The Xian gamma-ray light source (XGLS) is a proposed novel high brightness gamma-ray source based on inverse Compton scattering (ICS) between the high brightness electron and laser beams. The photoinjector of the accelerator is one of the main components that determines the electron beam quality and related gamma-ray parameters [Phys. Rev. Accel. Beams 21, 030701 (2018)PRABCJ2469-988810.1103/PhysRevAccelBeams.21.030701; 20, 080701 (2017)PRABCJ2469-988810.1103/PhysRevAccelBeams.20.080701; 8, 100702 (2005)PRABFM1098-440210.1103/PhysRevSTAB.8.100702]. In order to reduce the risk of this project, a photoinjector including a laser-driven photocathode rf gun, two S-band tubes, and a diagnostic section was constructed and installed from 2016, serving as a pilot plant for the development of the key technologies for the projects. The injector is designed to deliver high quality electron bunches of typically 500 pC charge and ∼120 MeV energy with low emittance and jitter at 10 Hz repetition. Initial system commissioning with an electron beam was finished in the end of 2017, with a goal of a stable 0.6–0.7 mm mrad emittance in a 500-pC bunch clearly demonstrated. In this paper, we report the experimental results and experience obtained in the commissioning, including rf gun, drive laser system, timing and synchronization system, and beam diagnostics.

The solenoid scan is a widely used method for the in-situ measurement of the thermal emittance in a photocathode gun. The popularity of this method is due to its simplicity and convenience since all rf photocathode guns are equipped with an emittance compensation solenoid. This paper shows that the solenoid scan measurement overestimates the thermal emittance in the ordinary measurement configuration due to a weak quadrupole field (present in either the rf gun or gun solenoid) followed by a rotation in the solenoid. This coupled transverse dynamics aberration introduces a correlation between the beam’s horizontal and vertical motion leading to an increase in the measured 2D transverse emittance, thus the overestimation of the thermal emittance. This effect was systematically studied using both analytic expressions and numerical simulations. These studies were experimentally verified using an L-band 1.6-cell rf photocathode gun with a cesium telluride cathode, which shows a thermal emittance overestimation of 35% with a rms laser spot size of 2.7 mm. The paper concludes by showing that the accuracy of the solenoid scan can be improved by using a quadrupole magnet corrector, consisting of a pair of normal and skew quadrupole magnets.

The twin-bunch technique has been a subject of intense investigation due to its application in diverse fields, such as two-color free-electron lasers and beam-driven wakefield acceleration. In this paper, we investigate the generation of twin bunches (tunable in both time and energy space) via a velocity bunching (VB) scheme in a traveling wave accelerator (TWA) by varying the TWA phase across a very large range for the first time. The results of both simulations and experiments are presented. The results show that when the phase injected into the TWA tube is set to ≪-100 degrees, VB occurs in a deep overcompression mode, where the twin bunches are continuously and widely tunable under a large TWA phase acceptance. The energy and time spaces can be adjusted in the ranges [0–3] MeV and [0–6] ps, respectively, by varying the phase of the injected bunch train from -170 degrees to -120 degrees. The deep overcompression mode is a newly explored working mode for the VB scheme. Moreover, the emittance of each sub-bunch can be preserved when the strength of the long solenoid surrounding the TWA is optimized for emittance compensation, thus maintaining the high-quality beams from photoinjectors.

High-energy charged particle radiography has been used for diagnostics of high-energy density matter, and electrons can serve as a promising radiographic probe that acts as a complement to commonly used proton probes. Here we report on an electron radiography experiment using 45 MeV electrons from an S-band photoinjector, where scattered electrons, after interacting with a sample, are collected and imaged by a quadrupole imaging system. We achieve a spatial resolution of a few microns (∼4 μm) and a thickness resolution of a few percent for a silicon target of 300–600 μm in thickness. With additional dark-field images captured by selecting electrons with large scattering angles, we show that complementary information for determining external details such as outlines, boundaries and defects can be obtained.

Premodulated comblike electron bunch trains are used in a wide range of research fields, such as for wakefield-based particle acceleration and tunable radiation sources. We propose an optimized compression scheme for bunch trains in which a traveling wave accelerator tube and a downstream drift segment are together used as a compressor. When the phase injected into the accelerator tube for the bunch train is set to ≪-100°, velocity bunching occurs in a deep overcompression mode, which reverses the phase space and maintains a velocity difference within the injected beam, thereby giving rise to a compressed comblike electron bunch train after a few-meter-long drift segment; we call this the deep overcompression scheme. The main benefits of this scheme are the relatively large phase acceptance and the uniformity of compression for the bunch train. The comblike bunch train generated via this scheme is widely tunable: For the two-bunch case, the energy and time spacings can be continuously adjusted from +1 to -1 MeV and from 13 to 3 ps, respectively, by varying the injected phase of the bunch train from -220° to -140°. Both theoretical analysis and beam dynamics simulations are presented to study the properties of the deep overcompression scheme.

The measurement of electron bunch temporal profile is one of the key diagnostics in accelerators, especially for ultrashort bunches. The electro-optic (EO) technique enables the precise longitudinal characterization of bunch electric field in a single-shot and nondestructive way, which can simultaneously obtain and analyze the time jitter between the electron bunch and the synchronized laser. An EO monitor based on spatial decoding for temporal profile measurement and timing jitter recoding has recently been demonstrated and analyzed in depth for low-energy bunches at the Tsinghua Thomson scattering X-ray source. A detailed description of the experimental setup and measurement results are presented in this paper. An EO signal as short as 82 fs (rms) is observed with 100 μm gallium phosphide for a 40 MeV electron bunch, and the corresponding length is 106 fs (rms) with 300 μm zinc telluride. Owing to the field-opening angle, we propose a method to eliminate the influence of energy factor for bunches with low energy, resulting in a bunch length of ∼60 fs (rms). The monitor is also successfully applied to measure time jitter with approximately 10 fs accuracy. The experiment environment is proved to be the main source of the slow drift, which is removed using feedback control. Consequently, the rms time jitter decreases from 430 fs to 320 fs.

A novel method using high-power laser as a circular deflector is proposed for the measurement of femtosecond (fs) and sub-fs electron beam. In the scheme, the electron beam interacts with a laser pulse operating in a radially polarized doughnut mode (TEM_{01^{*}}) in a helical undulator, generating angular kicks along the beam in two directions at the same time. The phase difference between the two angular kicks makes the beam form a ring after a propagation section with appropriate phase advance, which can reveal the current profile of the electron beam. Detailed theoretical analysis of the method and numerical results with reasonable parameters are both presented. It is shown that the temporal resolution can reach up to ∼100 attosecond, which is a significant improvement for the diagnostics of ultrashort electron beam.

We propose a method based on the slice energy spread modulation to generate strong subpicosecond density bunching in high-intensity relativistic electron beams. A laser pulse with periodic intensity envelope is used to modulate the slice energy spread of the electron beam, which can then be converted into density modulation after a dispersive section. It is found that the double-horn slice energy distribution of the electron beam induced by the laser modulation is very effective to increase the density bunching. Since the modulation is performed on a relativistic electron beam, the process does not suffer from strong space charge force or coupling between phase spaces, so that it is straightforward to preserve the beam quality for terahertz (THz) radiation and other applications. We show in both theory and simulations that the tunable radiation from the beam can cover the frequency range of 1–10 THz with high power and narrow-band spectra.

Two closely spaced electron bunches have attracted strong interest due to their applications in two color X-ray free-electron lasers as well as witness bunch acceleration in plasmas and dielectric structures. In this paper, we propose a new scheme of delay system to vary the time delay up to several picoseconds while not affecting the bunch compression. Numerical simulations based on the Linac Coherent Light Source are performed to demonstrate the feasibility of this method.

The roughness of a photocathode could lead to an additional uncorrelated divergence of the emitted electrons and therefore to an increased thermal emittance. To calculate the emittance growth due to the cathode roughness, people usually choose a simple 2D sinusoidal surface model to avoid mathematical complexity. In this paper, we demonstrate an analytical method, which is inspired by the point spread function that has been widely used in radiation imaging field, to accurately evaluate the emittance growth due to the random roughness of a real-life cathode. Both analytical and numerical studies are performed. Our analytical formulas clearly reveal the relationship between the surface roughness and the emittance growth. Both analytical and numerical results surprisingly show that in the typical 3D random surface case, the influence of the surface roughness on the emittance growth is much smaller than the 2D sinusoidal case with typical roughness properties, however with roughness properties which are matched to the 3D case, the emittance growth conditions in these two cases are very similar. Even with applied electric field strength up to 120 MV/m, the total emittance growth is still below 10%. It implies that the large emittance growth (50%–100%) observed on metallic cathodes in some experiments, which is generally believed to be the result of the electric field on the rough surface, might be due to some other reasons.

Radio frequency breakdown is one of the fundamental phenomena that limits the operational performance of most of high power and high gradient vacuum rf devices. We report on experimental results of rf breakdown in an S-band photocathode gun triggered by an intensity controlled laser. Through measurement and analysis of the time dependence of the collected current at the gun exit and the stored rf energy in the cavity, one can gain insight into the time evolution of the rf breakdown process. Multiple breakdowns were observed within one rf pulse due to power flow between cells after the initial emission. Similarities of the laser-triggered breakdowns to those occurring in the course of cavity conditioning and normal operation are found by comparing the postbreakdown signals in both cases. It is shown that an intense laser can offer a more controllable and flexible method for rf breakdown studies.

Characterizing the rf-to-laser jitter in the photocathode rf gun and its possible origins is important for improving the synchronization and beam quality of the linac based on the photocathode rf gun. A new method based on the rf compression effect in the photocathode rf gun is proposed to measure the rf-to-laser jitter in the gun. By taking advantage of the correlation between the rf compression and the laser injection phase, the error caused by the jitter of the accelerating field in the gun is minimized and thus 10 fs time resolution is expected. Experimental demonstration at the Tsinghua Thomson scattering x-ray source with a time resolution better than 35 fs is reported in this paper. The experimental results are successfully used to obtain information on the possible cause of the jitter and the accompanying drifts.

Recently cold cathodes based on field emission have drawn attention and been considered to drive accelerators and free electron lasers, due to the progress in field emitter arrays and planar emitters like diamond films. In this paper, we reviewed the characteristics of field emission in rf fields. Simulations of S-band rf guns consisting of a cathode cell and a full cell were done. We showed that a shorter cathode cell with a length of 0.25–0.3 of λ/2 is in favor of obtaining both low emittance and low energy spread bunches when the amplitude of electric field on the cathode surface ranges from 60 to 80 MV/m. A single cell test cavity has been installed to study field emission of diamond films and the measured beam current showed a good agreement with theoretical calculations.

C-band low-energy electron linear accelerators are preferable for applications which require compact structure and accurate positioning. During the past two years, the accelerator laboratory of Tsinghua University has developed a C-band 6 MeV standing-wave biperiodic on-axis coupled linear accelerator. The weight of the accelerator is 7.4 kg and the length is about 39 cm, which includes the thermal-cathode gun and the flange for tests. High capture ratio, narrow energy spectrum, and small spot size have been achieved in the high power rf test, which shows good performance of this accelerator and its great potential for industrial and medical applications.

Choke-mode damped structures are being studied as an alternative design to waveguide damped structures for the main linac of the Compact Linear Collider (CLIC). Choke-mode structures have the potential for lower pulsed temperature rise and simpler and less expensive fabrication. An equivalent circuit model based on transmission line theory for higher-order-mode damping is presented. Using this model, a new choke geometry is proposed and the wakefield performance is verified using Gdfidl. This structure has a comparable wakefield damping effect to the baseline design which uses waveguide damping. A prototype structure with the same iris dimensions and accelerating gradient as the nominal CLIC design, but with the new choke geometry, has been designed for high-power tests.

Coherent pulse stacking (CPS) is a new time-domain coherent addition technique that stacks several optical pulses into a single output pulse, enabling high pulse energy and high average power. A Z-domain model targeting the pulsed laser is assembled to describe the optical interference process. An algorithm, extracting the cavity phase and pulse phases from limited data, where only the pulse intensity is available, is developed to diagnose optical cavity resonators. We also implement the algorithm on the cascaded system of multiple optical cavities, achieving phase errors less than 1.0°(root mean square), which could ensure the stability of CPS.