Development of a seven-cell S-band standing-wave RF-deflecting cavity for Tsinghua Thomson scattering X-ray source

A 2856-MHz,π-mode,seven-cell standingwave deflecting cavity was designed and fabricated for bunch length measurement in Tsinghua Thomson scattering X-ray source(TTX)facility.This cavity was installed in the TTX and provided a deflecting voltage of 4.2 MV with an input power of 2.5 MW.Bunch length diagnoses of electron beams with energies up to 39 MeV have been performed.In this article,the RF design of the cavity using HFSS,fabrication,and RF test processes are reviewed.High-power operation with accelerated beams and calibration of the deflecting voltage are also presented.

Numerical simulation for all-optical Thomson scattering X-ray source

Energy spectra, angular distributions, and temporal profiles of the photons produced by an all-optical Thomson scat- tering X-ray source are explored through numerical simulations based on the parameters of the SILEX-I laser system （800 nm, 30 fs, 300 TW） and the previous wakefield acceleration experimental results. The simulation results show that X-ray pulses with a duration of 30 fs and an emission angle of 50 mrad can be produced from such a source. Using the optimized electron parameters, X-ray pulses with better directivity and narrower energy spectra can be obtained. Besides the electron parameters, the laser parameters such as the wavelength, pulse duration, and spot size also affect the X-ray yield, the angular distribution, and the maximum photon energy, except the X-ray pulse duration which is slightly changed for the case of ultrafast laser-electron interaction.

Simultaneous fluorescence and Compton scattering computed tomography based on linear polarization X-ray

Purpose To propose a method for simultaneous fluorescence and Compton scattering computed tomography by using linearly polarized X-rays.Methods Monte Carlo simulations were adopted to demonstrate the feasibility of the proposed method.In the simulations,the phantom is a polytetrafluoroethylene cylinder inside which are cylindrical columns containing aluminum,water,and gold(Au)-loaded water solutions with Au concentrations ranging between 0.5 and 4.0 wt%,and a parallel-hole collimator imaging geometry was adopted.The light source was modeled based on a Thomson scattering X-ray source.The phantom images for both imaging modalities were reconstructed using a maximumlikelihood expectation maximization algorithm.Results Both the X-ray fluorescence computed tomography(XFCT)and Compton scattering computed tomography(CSCT)images of the phantom were accurately reconstructed.A similar attenuation contrast problem for the different cylindrical columns in the phantom can be resolved in the XFCT and CSCT images.The interplay between XFCT and CSCT was analyzed,and the contrast-to-noise ratio(CNR)of the reconstruction was improved by correcting for the mutual influence between the two imaging modalities.Compared with K-edge subtraction imaging,XFCT exhibits a CNR advantage for the phantom.Conclusion Simultaneous XFCT and CSCT can be realized by using linearly polarized X-rays.The synergy between the two imaging modalities would have an important application in cancer radiation therapy.

Simulation study of a photo-injector for brightness improvement in Thomson scattering X-ray source via ballistic bunching

Increasing the peak brightness is beneficial to various applications of the Thomson scattering X-ray source. A higher peak brightness of the scattered X-ray pulse demands a shorter scattering electron beam realized by beam compression in the electron beam-line. In this article, we study the possibility of compressing the electron beam in a typical S-band normal conducting photo-injector via ballistic bunching, through just adding a short RF linac section right behind the RF gun, so as to improve the peak brightness of the scattered x-ray pulse. Numerical optimization by ASTRA demonstrates that the peak current can increase from 50 A to 300 A for a 500 pC, 10 ps FWHM electron pulse, while normalized transverse RMS emittance and RMS energy spread increases very little. Correspondingly, the peak brightness of the Thomson scattering X-ray source is estimated to increase about three times.

Preliminary experiment of the Thomson scattering X-ray source at Tsinghua University

The X-ray source based on Thomson scattering of ultrashort laser pulse with a relativistic electron beam is a means of generating a tunable, narrow bandwidth and ultrashort pulse of hard X-rays. Such a sub-picosecond hard X-ray source is proposed at Tsinghua University, and a preliminary experiment with a 16 MeV Backward Traveling electron linac and a 1.5 J, 6 ns Q-switched Nd：YAG laser is carried out first. A 6 ns pulse X-ray with a peak energy of 4.6 keV and an intensity of 1.Tx 104 per pulse is generated successfully in the experiment. The experimental setup, result and discussion are reported in this paper.

A simulation study of Tsinghua Thomson scattering X-ray source

Thomson scattering X-ray sources are compact and a?ordable facilities that produce short duration, high brightness X-ray pulses enabling new experimental capacities in ultra-fast science studies, and also medical and industrial applications. Such a facility has been built at the Accelerator Laboratory of Tsinghua University, and upgrade is in progress. In this paper, we present a proposed layout of the upgrade with design parameters by simulation, aiming at high X-ray pulses flux and brightness, and also enabling advanced dynamics studies and applications of the electron beam. Design and construction status of main subsystems are also presented.

Attosecond x-Ray Pulse Generation by Linear Thomson Scattering of Intense Laser Beam with Relativistic Electron

Abstract Linear Thomson scattering of a short pulse laser by relativistic electron has been investigated using computer simulations. It is shown that scattering of an intense laser pulse of -33 fs full width at half maximum, with an electron of γ0 = 10 initial energy, generates an ultrashort, pulsed radiation of 76 attoseconds with a photon wavelength of 2.5 nm in the backward direction. The scattered radiation generated by a highly relativistic electron has superior quality in terms of its pulse width and angular distribution in comparison to the one generated by lower relativistic energy electron.

Demonstration of X-ray Thomson Scattering on Shenguang-Ⅱ Laser Facility

X-ray Thomson scattering technique for diagnosing dense plasma was demonstrated on Shenguang-Ⅱ laser facility. Laser plasma x-ray source of titanium He-a lines （-4.75 keV）, generated by laser beam （1.5 kJ/527 nm/2 ns） heated titanium thin foil, was used as x-ray probe beam. The x-ray probe was then scattered by cold CH foam column of 1 g/cm^3 density. The scattered radiation at 90° was diffracted by polyethylene terephthalate （PET） crystal and recorded on x-ray charge-coupled device. Well-defined scattering spectra were obtained with good signal to noise ratio.

High-brightness photo-injector with standing-wave buncher-based ballistic bunching scheme for inverse Compton scattering light source

We report our recent progress in the design and simulation of a high-brightness S-band photo-injector with a ballistic bunching scheme aimed at driving an inverse Compton scattering(ICS)X-ray source.By adding a short standing-wave buncher between the RF gun and first booster in a conventional S-band photo-injector,electron bunches with a 500 pC charge can be compressed to the sub-picosecond level with very limited input RF power and an unchanged basic layout of the photo-injector.Beam dynamics analysis indicates that fine tuning of the focusing strength of the gun and linac solenoid can well balance additional focusing provided by the standing wave buncher and generate a well-compensated transverse emittance.Thorough bunching dynamics simulations with different operating conditions of the buncher show that a buncher with more cells and a moderate gradient is suitable for simultaneously obtaining a short bunch duration and low emittance.In a typical case of a 9-cell buncher with a 38 MV/m gradient,an ultrashort bunch duration of 0.5 ps(corresponding to a compression ratio of>5)and a low emittance of<1 mm mrad can be readily obtained for a 500 pC electron pulse.This feasible ballistic bunching scheme will facilitate the implementation of an ultrashort pulse mode inverse Compton scattering X-ray source on most existing S-band photo-injectors.

A High-Efficiency X-Ray Crystal Spectrometer for X-Ray Thomson Scattering

Highly oriented pyrolitic graphite （HOPG） has high X-ray diffraction efficiency due to its unique mosaic crystal structure, and thus is very suitable for its application to X-ray Thomson scattering measurement of solid-density plasmas. In this article, by using the K-shell X-ray source from laser-produced Ti plasma, the properties of the HOPG spectrometer are characterized and compared with those of the flat Pentaerythritol （PET） spectrometer. The results show that the diffraction efficiency of the HOPG spectrometer under focusing condition is an order higher than that of the PET spectrometer, while the spectral resolution of the HOPG is about 320, high enough to be used in the measurement of X-ray Thomson scattering spectra.

Optics for the lattice of the compact storage ring for a Compton X-ray source

We present two types of optics for the lattice of a compact storage ring for a Compton X-ray source. The optics design for different operation modes of the storage ring are discussed in detail. For the pulse mode optics, an IBS-suppression scheme is applied to optimize the optics for lower IBS emittance growth rate; as for the steady mode, the method to control momentum compact factor is adopted [Gladkikh P, Phys. Rev. ST Accel. Beams 8, 050702] to obtain stability of the electron beam.

清华大学汤姆逊散射超短脉冲X射线源研究

介绍了清华大学加速器实验室近年来关于汤姆逊散射超短X射线源的研究工作;研究了在任意散射角度下电子束参数和激光束参数对散射光子参数的影响,给出了散射光子的参数如光子产额、脉冲长度、时间抖动等与电子束参数、激光束参数和散射角度的关系;利用实验室已有的16 MeV反波行波加速器与中国工程物理研究院激光聚变研究中心提供的ns调Q激光搭建了汤姆逊散射初步实验平台并开展了实验研究;加工了1.6-cell光阴极微波电子枪,搭建了高功率实验平台,对产生的电子束参数进行了初步测量;对汤姆逊散射超短X射线源进行了设计并开展了相关的平台建设工作,对产生的X射线脉冲参数进行了模拟。

激光同步辐射源原理性实验的理论计算

利用强激光和相对论性电子束在任意相互作用方向发生的非线性Ｔｈｏｍｓｏｎ散射理论，计算了平面偏振激光在相互作用角为１８０°、１７８．５°和９０°三种条件下发生Ｔｈｏｍｓｏｎ散射所产生的Ｘ射线波长、相互作用时间等结果，并作出了１７８．５°散射时Ｘ射线强度的空间和频域分布图。利用ＹＡＧ倍频激光器和２５ＭｅＶ电子束对正向散射部分进行了实验验证。

全光汤姆逊散射X光源数值模拟

使用蒙特卡罗数值模拟程序研究了不同电子束和激光强度下,尾场电子束与超短脉冲激光发生汤姆逊散射获得的X光子能谱、角分布等,初步探索了180°散射下高质量X射线光源所需要的电子束与激光强度。数值模拟结果显示,为了尽量提高光子产额并抑制非线性效应,激光归一化强度应为1的量级。为了获得方向性和单色性好、亮度高的X射线脉冲,需要较高的电子能量和较小的电子能散,电子束脉冲尽量短,且发散角尽量小。

Analytic RF design of a linear accelerator with a SLED-Ⅰ type RF pulse compressor

This study presents the RF design of a linear accelerator(linac)operated in single-bunch mode.The accelerator is powered by a compressed RF pulse produced from a SLED-I type RF pulse compressor.The compressed RF pulse has an unflattened shape with a gradient distribution which varies over the structure cells.An analytical study to optimize the accelerating structure together with the RF pulse compressor is performed.The optimization aims to maximize the efficiency by minimizing the required RF power from the generator for a given average accelerating gradient.The study shows that,owing to the compressed RF pulse shape,the constant-impedance structure has a similar efficiency to the optimal structure using varying iris apertures.The constant-impedance structure is easily fabricated and is favorable for the design of a linac with a pulse compressor.We utilize these findings to optimize the RF design of a X-band linac using the constant-impedance accelerating structure for the Tsinghua Thomson X-ray source facility.

Design of the beam transport line and injection system of the compact storage ring for TTX

In this article, we present the design of the beam transport line and injection system of the compact storage ring for the Tsinghua Thomson scattering X-ray (TTX) source. The layout of the beam transport line fits in with the limited available space. The injection system is simplified, consisting of only one single kicker; the stray field on the reference orbit is also reduced without the septum magnet. We choose a travelling wave kicker and present both 2D and 3D simulations for the structure design.