Masao Kuriki

High-voltage testing of a 500-kV dc photocathode electron gun

A high-voltage dc photocathode electron gun was successfully conditioned up to a voltage of 550 kV and a long-time holding test for 8 h was demonstrated at an acceleration voltage of 500 kV. The dc photocathode electron gun is designed for future light sources based on energy-recovery linac and consists of a Cockcroft-Walton generator, a segmented cylindrical ceramic insulator, guard-ring electrodes, a support-rod electrode, a vacuum chamber, and a pressurized insulating gas tank. The segmented cylindrical ceramic insulator and the guard-ring electrodes were utilized to prevent any damage to the insulator from electrons emitted by the support-rod electrode.

Generation of a 500-keV electron beam from a high voltage photoemission gun

High-brightness, high-current electron guns for energy recovery linac light sources and high repetition rate X-ray free-electron lasers require an exit beam energy of ≥500 keV to reduce space-charge induced emittance growth in the drift space from the gun exit to the following superconducting accelerator entrance. At the Japan Atomic Energy Agency, we have developed a DC photoemission gun employing a segmented insulator to mitigate the field emission problem, which is a major obstacle for operation of DC guns at ≥500 kV. The first demonstration of generating a 500-keV electron beam with currents up to 1.8 mA is presented.

1 ms Pulse Beam Generation and Acceleration by Photocathode Radio Frequency Gun and Superconducting Accelerator

We report the successful generation and acceleration of a 1-ms-long pulse and multibunch electron beam by a normal conducting photocathode RF gun and a super conducting accelerator at the KEK Superconducting Test Facility (STF). A 1.3 GHz normal conducting RF gun generates a 1 ms and 10 mA macropulse that fully satisfies the designed parameters. This is the longest macropulse generated by a normal conducting RF gun with a frequency of more than 1 GHz. A beam acceleration of up to 40 MeV was demonstrated with more than 60% of the designed average current. The accelerated beam properties were evaluated: the intensity and energy fluctuations were 3.8% and less than 0.08%, respectively. These beam properties are sufficient for the requirement of the STF operation including that in the quantum beam project, which is high-brightness-X-ray generation by inverse laser Compton scattering. The intensity fluctuation should be improved toward the International Linear Collider (ILC) for uniform acceleration.

Development of a 500-kV Photocathode DC Gun for ERLS

We have developed a 500-kV, 10-mA photocathode DC gun for energy recovery linac (ERL) light sources. A segmented ceramic insulator with guard rings is employed to improve robustness at high voltage operation, because this structure can prevent field emission electrons from directly striking the ceramic surface. We have recently succeeded in applying 500 kV on the ceramics for eight hours without any discharge. This high voltage testing was performed with a simple configuration without NEG pumps, cathode and anode electrodes to mainly study the field emission from a tube supporting the cathode electrode. The same high voltage testing with a full configuration necessary for beam generation was carried out up to 380 kV where some increase of radiation was observed. Up-to-date status of our gun development is presented in detail.

Development of an S-band Cs2Te-cathode RF gun with new RF Tuners

The photo-cathode RF gun is one of the good alternatives for the electron injector, because of its high gradient on the electron emitter causing small beam emittance, and better operationality especially for electron bunch length. Therefore, several institutes which study FEL, early response of a radiochemical processes [2, 3], and/or advanced accelerator technologies specially for International Linear Collider (ILC) adopted the photo-cathode RF gun as their injector. In this paper, we present a modified RF gun with new compact tuners and show results of a conditioning study using high power RF field. A starting point of this study is an design of the S-band Cs2Te-cathode RF gun used in the Accelerator Test Facility of KEK (KEK-ATF).

Initial Emittance Measurements for Polarized Electron Gun with NEA‐GaAs Type Photocathode

Extremely low emittance electron beams are necesarry for new generation accelerators. The value of the required emittances is as low as 0.1 π.mm.mrad. NEA‐type photocathodes have an intrinsic advantage for generating such a low emittance beam. In this paper, emittance measuremets of photelectrons extracted from two different NEA phtocahtodes are described. The measurements were carried out using Nagoya University 200kV polarized electron source. The normalized RMS emittances of bulk‐GaAs and GaAs‐GaAsP superlattice strained photocathodes are as low as 0.12–0.17 ± 0.02 π.mm.mrad and 0.09 ± 0.01 π.mm.mrad with very low charge density, respectively.

The CLIC electron and positron polarized sources

The CLIC polarized electron source is based on a DC gun where the photocathode is illuminated by a laser beam. Each micro-bunch has a charge of 6x10 9 e

Status of R&D efforts toward the ERL-based future light source in Japan

The energy recovery linac is a very promising synchrotron light source in future. We are contemplating to realize a ERL_based next generation light source in Japan, under a collaboration between KEK, JAEA, ISSP, and other SR institutes. To this end, we started R&D efforts on its key technologies, including a low-emittance photocathode gun and superconducting cavities. We also plan to assemble these technologies into a small test ERL, and to demonstrate their operations. We report our R&D status.

L-band Photocathode RF gun at KEK-STF

The superconducting RF test facility (STF) in KEK is a facility to promote R&D of the International Linear Collider (ILC) cavities and cryomodule. L-band photocathode RF gun has been developed at KEK-STF as an electron beam source for cryomodule test scheduled in autumn of 2011. The RF cavity of the gun will be operated with a 1.3 GHz RF frequency, 1 msec RF pulse width, 5 Hz repetition rate at normal conductivity. The cavity was prepared by collaborative work with DESY and FNAL, and fabricated by FNAL. The RF conditioning of the cavity has been started since April 2010. A cesium telluride thin film as a photocathode material has been adopted, and the preparation equipment for cesium telluride has been newly designed and constructed. By using this new system, a fabrication and a performance estimation of the cesium telluride thin film as a photocathode are the next step of the research.

HIGH FIELD GRADIENT POLARIZED ELECTRON GUN FOR ILC

A 200-keV gun has been developed for generation of bunch charge of 2 3.2 nC, bunch length of 5 2 ns multi-bunch polarized electron beam that is required for International Linear Collider. In this paper, the beam simulations using General Particle Tracer (GPT) code for such space-charge dominated regions, and a fabrication method of electrode for higher electric field (2 3 MV/m) at the photocathode surface by using a titanium anode and a molybdenum cathode are described.