Thomson Scattering X-ray Source Research Articles

Tsinghua Thomson scattering X-ray source

We proposed the Tsinghua Thomson scattering X-ray (TTX) source as an ultra-fast, high flux source for advanced X-ray imaging studies and applications. A linac system, which consists of an S-band photocathode RF gun, a SLAC type 3 m traveling wave tube and two X-band structures, generates ultra-short, high brightness electron pulses to scatter with tera-watt femto-second laser pulses. A compact low energy electron storage ring is also designed to dramatically enhance the average X-ray flux. In this paper, we present the simulation studies and optimized parameters of the electron and X-ray pulses. The construction and commissioning status of TTX is also reported.

Temporal resolution of MeV ultrafast electron diffraction based on a photocathode RF gun

Photocathode RF guns serve as electron sources in various ultrafast pump–probe experiments, such as in X-ray free-electron lasers, Thomson scattering X-ray sources, and MeV ultrafast electron diffractions (UED), for studying structural dynamics on the fundamental scales of atomic motions. The temporal resolutions of these experiments are of great concern. In this paper, we study each contributing term to the temporal resolution, including the RF compression effect, the dependence of time-of-flight of the electron pulses on the RF-to-laser timing jitter, and the effect of fluctuation of the RF field amplitude. We employ a simple single-particle model, and demonstrate inherent connections of all these effects to the single-particle dynamics. Particularly, the correlation between the RF compression effect and the fluctuation of time-of-flight induced by the RF-to-laser timing jitter, makes the temporal resolution considerably smaller than simply adding each term quadratically. We apply these results to a MeV UED and evaluate its temporal resolution, showing that a ∼ 100 fs resolution is already achievable with state-of-the-art hardware performances. Since these results are inherent properties of photocathode RF guns, they are also applicable to other facilities.

Preliminary experiment of the Thomson scattering X-ray source at Tsinghua University**Supported by National Natural Science Foundation of China (10645002) and Program for New Century Excellent Talents in University (NCET)

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 1.7×104 per pulse is generated successfully in the experiment. The experimental setup, result and discussion are reported in this paper.

First Beam Measurements of the S-Band photocathodeRadio-Frequency Gun at Tsinghua University

During the last decades, photocathode rf gun has been proven to besuccessful in generating the high brightness electron beam(~1nC,~1πmmmrad,~1 ps) which is required by the ILC,XFEL, Thomson scattering x-ray source, etc. A photocathode rf gun systemis built to develop electron source for the Thomson scattering x-raysource at Accelerator Laboratory of Tsinghua University. The systemconsists of a BNL/ATF-type 1.6 cell S-band rf cavity, a solenoid foremittance compensation, a laser system and some simple equipments forbeam diagnosis. The first beam measurements of the photocathode rf gun,including the dark current, transverse beam profile, charge and quantumefficiency, are reported.

Review of various approaches to address high currents in SRF electron linacs

The combination of high-brightness electron sources and high-current SRF Energy Recovery Linacs (ERL) leads to a new emerging technology: high-power, high-brightness electron beams. This technology enables extremely high average power free-electron lasers, a new generation of extreme brightness light sources, electron coolers of high-energy hadron storage rings, polarized electron–hadron colliders of very high luminosity, compact Thomson scattering X-ray sources, terahertz radiation generators and much more. What is typical for many of these applications is the need for very high current, defined here as over 100 mA average current, and high brightness, which is charge dependent, but needs to be in the emittance range of between submicron up to perhaps 50 μm, usually the lower – the better. Suffice it to say that while there are a number of projects aiming at this level of performance, none is anywhere near it. This work will review the problems associated with the achievement of such performance and the various approaches taken in a number of laboratories around the world to address the issues.

Femtosecond Thomson scattering X-ray source based on laser wakefield accelerator for ultrafast X-ray absorption spectroscopy

A novel source of femtosecond keV X-ray pulses based on Thomson scattering from a terawatt laser wakefield accelerator is being developed for chemical studies. The characteristics of the source, based on recent calculations and experiments, are discussed. Due to its short pulse duration, high flux and collimation this X-ray source is very well suited for ultrafast time-resolved X-ray absorption experiments to study short-living transient structures in gasses, liquids and solids. As an example of such an experiment, we propose to study the solvent-solute dynamics in charge-transfer-to-solvent processes.

Evaluation and simulations of a Thomson scattering X-ray source based on ray tracing methods

We propose to build up a facility of sub-picosecond hard X-ray pulses based on Thomson scattering between femtosecond laser pulses and relativistic electrons which is a useful tool for the purpose of material investigation, plasma diagnostics, and shock wave measurement. This article reviews the principles and the development of X-ray sources based on Thomson scattering. ThenNew Light Source®, the Thomson scattering X-ray facility we will develop is introduced. The characteristics of a Thomson scattering X-ray source are analyzed. A computer model of the Thomson source to be developed is described in order to provide a source of the rays used in a ray tracing method, which has proved to be an essential computer tool for designing and optimizing the optical system of high brightness X-ray facilities. A code for the ray tracing source model is created based on the Monte Carlo approach. It is able to evaluate the properties and performances of the light source under development using this model. According to the simulation results, we discuss the dependence of imaging quality and source properties including spectral distribution, emittance, flux which depends on the laser and electron beam parameters, in order to check if operation performances are as expected. We also estimate the possibility of measuring the energy spectrum of a Thomson scattering source by using a crystal diffraction method. Ray tracing calculations are performed using SHADOW program package, and a new model of Thomson scattering X-ray source which can be processed in that program is established with additional code.

Experimental characterization of an ultrafast Thomson scattering x-ray source with three-dimensional time and frequency-domain analysis

We present a detailed comparison of the measured characteristics of Thomson backscattered x rays produced at the Picosecond Laser-Electron Interaction for the Dynamic Evaluation of Structures facility at Lawrence Livermore National Laboratory to predicted results from a newly developed, fully three-dimensional time and frequency-domain code. Based on the relativistic differential cross section, this code has the capability to calculate time and space dependent spectra of the x-ray photons produced from linear Thomson scattering for both bandwidth-limited and chirped incident laser pulses. Spectral broadening of the scattered x-ray pulse resulting from the incident laser bandwidth, perpendicular wave vector components in the laser focus, and the transverse and longitudinal phase spaces of the electron beam are included. Electron beam energy, energy spread, and transverse phase space measurements of the electron beam at the interaction point are presented, and the corresponding predicted x-ray characteristics are determined. In addition, time-integrated measurements of the x rays produced from the interaction are presented and shown to agree well with the simulations.

Short-pulse, high-brightness X-ray production with the PLEIADES Thomson-scattering source

PLEIADES is a compact, tunable, high-brightness, ultra-short-pulse, Thomson-scattering X-ray source. Picosecond pulses of hard X-rays (10–200 keV) are created by colliding an ultra-relativistic (20–100 MeV), picosecond-duration electron beam with a high-intensity, sub-picosecond, 800-nm laser pulse. Initial operation of this source has produced 78-keV X-rays with 106 photons per pulse using a 57-MeV, 0.3-nC, 50-μm rms width electron beam and a 180-mJ, 15-μm rms width laser pulse. The angular distribution, energy, and energy spectrum of the source are found to agree well with theory and simulations. Source optimization is expected to increase X-ray output to between 107 and 108 photons per pulse with a peak brightness approaching 1020 photons/s/0.1% bandwidth/mm2/mrad2.