TUB, Beijing
Recent years have witnessed rapid advances of MeV ultrafast electron diffraction (UED), in which high quality, ultrashort, MeV electron pulses from a photocathode RF gun are employed as probes for ultrafast structural dynamics. We've built a prototype MeV UED system at the Accelerator Laboratory of Tsinghua University, optimized the the electron pulse parameters as well as hardware performances, and achieved high quality single-shot diffraction patterns. Moreover, MeV UED can be operated in a so-called 'continuously time-resolved (CTR)' mode, in which an RF deflecting cavity streaks the electron pulse thus each diffraction pattern constitutes an 'atomic movie'. We report our experimental progress on MeV UED in this paper.
TUB, Beijing
For the miniaturization of low energy linear accelerators, X-band pulsed magnetron with stable performance of 1.5 MW peak power is needed to be developed. This paper presents the 3D particle-in-cell (PIC) of an X-band coaxial magnetron. A time evolved electron flow exhibits N/2 spokes in the simulations, which confirms the generation of pi-mode. Computer modeling indicates the mode competition in the startup process according to the spectra. By changing the DC voltage, we got the voltage-current characteristics of this magnetron, and comparison with the experiment was also been presented.
TUB, Beijing
The coherent Smith-Purcell radiation (CSPR) has been demonstrated as an efficient technique for measuring the longitudinal profile of beam bunches. To measure the ultrashort beam bunches, the simulations for the measurements using CSPR are anlyzed with tools of three dimensional particle-in-cell simulations and Kramer-Kronig reconstruction. Different parameters such as rms length of beam bunch and profiles of grating are studied. Furthermore, the measurement device based on a Martin-Puplett Interferometer is introduced, in which noises and attenuation can be reduced.
TUB, Beijing
The Tsinghua Thomson scattering X-ray source (TTX) has a strict laser-electron synchronization requirement and a comprehensive system structure including dual high-power laser system, RF system and beam diagnostic instruments, etc. Recently, a synchronization and control system is developed to meet these requirements, which includes a laser-RF synchronizer with 100fs time jitter, a FPGA based event generator for laser and RF systems with 250ps time resolution, and an EPICS based control system for system integration and remote monitor and control. The electron bunch arrival time jitter is carefully measured and analyzed with the help of a RF deflecting cavity. This paper reports the development status, technical implementation, and measurement results of the synchronization and control system.
TUB, Beijing
In this paper, we present the preliminary structure design and optimization of a C-band photocathode RF gun for a compact electron diffraction facility. It will work at 5.712GHz. A dual coupler and elliptical iris between half-cell and full-cell are adopt in this gun for lower emittance and larger mode separation. A detailed 3D simulation of the C-band RF gun with coupler is performed. This paper likewise presents the beam dynamics parameters and analysis of this gun.
TUB, Beijing
Smith-Purcell radiation (SPR) is emitted when an electron passes near the surface of a periodic metallic grating. The radiation wavelength λ observed at the angle θ measured from a direction of surface grating is determined by λ=D/|n|(1/β cosθ), Where D is the grating period, βc is the electron velocity, c is the speed of light, and the integer n is the spectral order. This radiation mechanism is widely applicated to THz radiation source, for which can be developed into tunable and compact one. In this paper, the radiation characteristics of terahertz (THz) SPR generated from the ultrashort electron beam are analyzed with the three-dimensional particle-in-cell simulation. For obtaining the intense THz radiation, the grating parameters and that of ultrashort electron beam are optimum. The radiation power and energy are obtained by the PIC simulation. The band width of train bunches is compared with that of single bunch. The formation factors including the longitudinal and transverse are calculated. Through this study, we observe that the radiation power is enhanced and the band width can be adjusted.
TUB, Beijing
Tsinghua University Thomson X-ray source ( TTX ) has been proposed at Tsinghua University. With the nominal electron beam parameters ( beam energy of 50MeV, slice energy spread of 5keV, peak current of 600A, rms normalized emittance of 2 mm mrad ) of the TTX linac , the design of Free Electron Laser ( FEL ) by the Echo-Enabled Harmonic Generation ( EEHG ) scheme is presented in this paper. High harmonics of the seeding laser is generated by the EEHG scheme. Parameters of the undulators and seeding lasers are optimized. Simulation results using the GENESIS code are also presented in this paper.
TUB, Beijing
Different kinds of accelerators, such as electron linacs, cyclotrons, microtrons, HV DC accelerators, synchrotrons and betatrons, can be used in radiotherapy, Non-Destructive Test, and irradiations. The accelerator industry in Asia almost covers all of the accelerators and application areas above. In this paper, the status and the trend of the accelerator industry in Asia will be introduced. Typical examples, in the areas of medial and industrial applications, will be described about their technology, achievement and relationship with universities or institutes. For the accelerator technology is strongly relied on the development of components, we will also briefly introduce the industry in Asia of some components, such as rf power sources, HV power sources (modulator), magnets and so on.
TUB, Beijing
LANL, Los Alamos, New Mexico
IHEP Beijing, Beijing
NUCTECH, Beijing
CIAE, Beijing
Institute of Physics, Chinese Academy of Sciences, Beijing
IMP, Lanzhou
Tsinghua University, Beijing
CERN, Geneva
This paper reports the design and construction status, technical challenges, and future perspectives of the proton-linac based Compact Pulsed Hadron Source (CPHS) at the Tsinghua University, Beijing, China.
TUB, Beijing
Ultrashort relativistic electron beam can be applied to produce high power coherent THz radiation by mechanisms such as FEL, CSR, CTR et al. The THz modulated electron beams, or THz-repetition-rate ultrashort electron bunch trains exhibit further enhancement of coherent THz radiation. This article will report the experimental results on the ultrashort electron bunch train production by copper based photocathode RF gun via direct UV laser pulse stacking using birefringent α-BBO crystal serials at our laboratory. The temporal profile of the electron beam was measured by deflecting cavity. Space charge effect downstream the photocathode is simulated. This shaping method of laser pulse by α-BBO crystals can also be applied to form quasi flattop UV laser pulse for reducing the initial emittance of the electron beam from the photocathode RF gun.
Euclid TechLabs, LLC, Solon, Ohio
ANL, Argonne
TUB, Beijing
Tsinghua University, Beijing
Wakefield excitation has been experimentally studied in a 3-cell X-band standing wave Photonic Band Gap (PBG) accelerating structure. Major monopole (TM01- and TM02-like) and dipole (TM11- and TM12-like) modes were indentified and characterized by precisely controlling the position of beam injection. The quality factor Q of the dipole modes was measured to be ~10 times smaller than that of the accelerating mode. A charge sweep, up to 80 nC, has been performed, equivalent to ~30 MV/m accelerating field on axis. A variable delay low charge witness bunch following a high charge drive bunch was used to calibrate the gradient in the PBG structure by measuring its maximum energy gain and loss. Experimental results agree well with numerical simulations.