• S.J. Park, C. Kim, I.S. Ko, J.-S. Oh, Y.W. Parc, P.C.D. Park, J.H. Park
  PAL, Pohang, Kyungbuk
• X.J. Wang
  BNL, Upton, Long Island, New York

A X-Ray Free Electron Laser (XFEL) project based on the Self-Amplified Spontaneous Emission (SASE) is under progress at the Pohang Accelerator Laboratory (PAL). One of the critical R&D for the PAL XFEL* is to develop the Pohang Photo-Injector (PPI) which is required to deliver electron beams with normalized emittance < 1.5 mm-mrad. In order to achieve the required beam quality with high stability and reliability, we will use photocathode with quantum efficiency > 0.1 % and long lifetime. This will greatly lessen the laser energy requirement for producing flat-top UV pulses, and open the possibility of using only regenerative amplifiers (RGAs) to drive the photocathode RF gun. The RGAs can produce mJs output with much better stability than multi-pass amplifiers. Both the Cs2Te and Mg are under consideration for the possible photo-cathode. To demonstrate the suitability of the Mg and Cs2Te for the future 4th generation light source application, an improved BNL-type S-band RF gun with a high-performance load-lock system will be developed for the PPI. In this article, we present the design concept of the PPI, the expected performance, and report on its development status.

*J.S. Oh, S.J. Park et al., "0.3-nm SASE-FEL at PAL," NIM A528, 582 (2004); S.J. Park, J.S. Oh et al., "Design Study of Low-Emittance Injector for SASE XFEL at Pohang Accelerator Laboratory," FEL2004, Italy, 2004.

• J.H. Park, I.S. Ko, J.-S. Oh, Y.W. Parc, S.J. Park
  PAL, Pohang, Kyungbuk
• X.J. Wang
  BNL, Upton, Long Island, New York
• D. Xiang
  TUB, Beijing

A BNL GUN-IV type RF photo-cathode gun is under fabrication for use in the FIR (Far Infra-Red) facility being built at the Pohang Accelerator Laboratory (PAL). Performance test of the gun will include the measurement of transverse emittance profile along the longitudinal direction. Successful measurement of the emittance profile will provide powerful tool for the commissioning of the 4GLS (4th generation light source) injectors based on the emittance compensation principle. We are going to achieve this withthe use of pepper-pot based emittance meters that can be moved along the longitudinal direction. In this article, we present design considerations on the emittance meter with the resolution of 1 mm mrad.

• J.-S. Oh, Y.J. Han, I.S. Ko, W. Namkung, S.S. Park
  PAL, Pohang, Kyungbuk

The PAL linac is planed to be converted to a SASE-XFEL facility (PAL XFEL) that supplies coherent X-rays down to 0.3-nm wavelength. PAL XEL requires a 3-GeV driver linac and a 60-m long in-vacuum undulator to realize an X-ray SASE-FEL. The linac should supply highly bright beams with emittance of 1.2 mm-mrad, a peak current of 3.5 kA, and a low energy spread of 0.03%. The RF stability of 0.06% rms is required for both RF phase and amplitude for reasonably stable SASE output. This stability is mainly determined by a klystron-modulator. Therefore present stability level of the modulator has to be improved 10 times better to get the pulse stability of 0.05%. The regulation methods such as traditional de-Q’ing and precision inverter charging technology are reviewed. Design considerations for the stability improvement of klystron-modulator for PAL XFEL are presented.

• J.-S. Oh, I.S. Ko, T.-Y. Lee, W. Namkung
  PAL, Pohang, Kyungbuk

The PAL XFEL will supply coherent radiations from VUV to X-rays. X-ray FEL for 0.3 nm lasing requires a 3-GeV driver linac and a 60-m long in-vacuum undulator with a narrow variable gap. The linac should supply highly bright beams with emittance of 1.2 mm-mrad, a peak current of 3.5 kA, and a low energy spread of 0.03%. The beam quality is degraded along the undulator trajectory due to the energy loss, the wake field, and the magnetic field errors, etc. Especially the wake field effect is most sensitive parameter due to the narrow gap of the undulator. The preliminary design details of undulators for PAL-XFEL are presented with parametric analysis. The temporal SASE performance is analyzed using simulation tools such as GENESIS and SIMPLEX.