SHINTAKE, Tsumoru XFEL 2. 1 L
Advanced Electron Beam Physics Laboratory is study- ing electron beam dynamics in the X-ray FEL machine, which will be built at RIKEN SPring-8 as a future SR The SASE-FEL (Self Amplified Spontaneous source. Emission mode Free Electron Laser) is the only one realis- tic scheme to realize X-ray laser in Angstrom wavelength. It requires a long undulator section and a low emittance electron beam with high peak current. In order to satu- rate the FEL within 20m long undulator at 3 nm wave- length, the emittance should be lower than 2π-mm-mrad with peak current higher than 2 kA. To obtain this high quality beam, we start from HV pulse electron gun to generate 3 A beam and compressing bunch length in two stages: the buncher injector system, and the bunch compressor using magnetic chicane.  We are studying beam dynamics in this process. We are also 500 MHz 476 MHz 1 nC 2π-mm-mrad 10 psec participating hardware R&D on the low-emittance electron gun, and C-band main accelerator in the X-ray FEL. 1. Development of low emittance electron gun In the X-ray FEL, we need to generate low emittance electron beam. The normalized emittance should be lower than 2π-mm-mrad, which is much lower value than that Therefore, we started our re- in any existing machine. search from primitive effect on emittance dilution such as the surface roughness of cathode material, space charge ef- fect between cathode and anode, geometric aberration in magnetic focusing lens.  After this study, we found that it is necessary to use a single-crystal cathode made by CeB6 with 3mm in diameter, and applying high voltage of 500kV in 50mm gap. The estimated emittance is 0.5π- mm-mrad at the exit of anode electrode of the gun.
2. Optimization of electron buncher injector sys-
tem
In the buncher injector, the electron beam from the gun is velocity modulated. We analyzed emittance growth due to RF field and chose the RF frequency at 476 MHz in sub-harmonic buncher and L-band (1428 MHz) in buncher accelerator. In order to estimate emittance dilution due to space charge we simulated beam trajectory using Parmella code and optimized the operation parameter. It was found that the beam emittance of 2π-mm-mrad could be obtained for 1 nC bunch charge, 10 psec bunch length, 20 MeV beam energy at the exit of injector system. 3. Optimization of Chicane Bunch Compressor At the beam energy of 500 MeV, the bunch length will be shortened four times in the magnetic chicane bunch- compressor. On big problem here is the emittance dilution due to the coherent synchrotron radiation (CSR). We stud- ied analytically and numerically this effect using Elegant particle tracking code.  By optimizing the chicane mag- net configuration, we found the emittance dilution will be small enough if we limit the compression factor at four. Research Subject and Members of Advanced Electron Beam Physics Laboratory 1. Development of low emittance electron injector 2. Study of very short electron bunch generation 3. Theoretical investigation of beam dynamics in elec- tron injector Head Dr. Tsumoru SHINTAKE Members Dr. Takahiro INAGAKI in collaboration with Dr. Kazuaki TOGAWA (Coherent Synchrotron Light Source Physics Lab.) Dr. Yujong KIM (Coherent Synchrotron Light Source Physics Lab.) Visiting Members Prof. Hiroshi MATSUMOTO (KEK) Prof. Shigeru TAKEDA (KEK) Dr. Anahid Dian YEREMIAN (SLAC, USA)
Publications
Tanaka T., Kitamura H., and Shintake T.: "Misalignment effects of segmented undulator in self-amplified sponta- neous emission", Phys. Rev. Spec. Top.: Accel. Beams 5 , 40701-1–40701-7 (2002).
Oral Presentations
Kamiya N. and Shen J.:  "Crystal structure analysis of pho- tosystem II from Synechococcus bulcanus at BL41XU of SPring-8", 19th Congr. and General Assembly of the Int. Union of Crystallography (IUCr XIX), Geneva, Switzer- land, Aug. (2002).