LINAC2012 - List of Authors (Dewa, H.)

Paper	Title	Page
THPB068	First Observation of Photoemission Enhancement from Copper Cathode Illuminated by Z-Polarized Laser Pulse	996
	H. Tomizawa, H. Dewa, A. Mizuno, T. Taniuchi JASRI/SPring-8, Hyogo-ken, Japan
	Since 2006, we have developed a novel photocathode gun gated by laser-induced Schottky-effect. This new type of gun utilizes a laser’s coherency to aim at a compact femtosecond laser oscillator as an IR laser source using Z-polarization on the photocathode. This Z-polarization scheme reduces the laser photon energy (making it possible to excite the cathode with a longer wavelength) by reducing the work function of cathode due to Schottky effect. A hollow laser incidence is applied with a hollow convex lens in a vacuum that is focused after passing the laser beam through a radial polarizer. According to our calculations (convex lens: NA=0.15), a Z-field of 1 GV/m needs 1.26 MW at peak power for the fundamental wavelength (792 nm). In the first demonstration of Z-field emission, enhancement was done with a copper cathode at THG (264 nm). Consequently, we observed 1.4 times enhancement of photoemission at 1.6 GV/m of an averaged laser Z-field on the cathode surface. We report the first observation and analysis of the emission enhancements with this laser-induced Schottky-effect on metal copper photocathodes by comparing radial and azimuthal polarizations of the incident laser pulses.

THPB092	Recent Improvements in SPring-8 Linac for Early Recovery from Beam Interruption	1035
	S. Suzuki, T. Asaka, H. Dewa, H. Hanaki, T. Kobayashi, T. Magome, A. Mizuno, T. Taniuchi, H. Tomizawa, K. Yanagida JASRI/SPring-8, Hyogo-ken, Japan
	The 1GeV SPring-8 linac is an injector for the SPring-8 synchrotron radiation storage ring with 8GeV booster synchrotron. In recent years, backup systems were installed to eliminate long-time interruption of the beam injections: The main gun system is usually operated, and the second gun is always pre-heated and can inject electron beams into a buncher section with an interval of several minutes in case the main gun failed. The first klystron, that feeds RF powers to the buncher system and the downstream klystrons, can be relieved by the next klystron with an interval of about 20 minutes by switching the waveguide circuit. When one of the eleven working klystrons faults, one of standby klystrons, which are kept for hot spares on line, is automatically activated to accelerate beams instead of the failed one without beam interruption. The total downtime in FY2012 was 0.12% in top-up operation user time. The averaged fault frequency was 0.2 times per day.

Paper

Title

Page

First Observation of Photoemission Enhancement from Copper Cathode Illuminated by Z-Polarized Laser Pulse

996

H. Tomizawa, H. Dewa, A. Mizuno, T. Taniuchi
JASRI/SPring-8, Hyogo-ken, Japan

Since 2006, we have developed a novel photocathode gun gated by laser-induced Schottky-effect. This new type of gun utilizes a laser’s coherency to aim at a compact femtosecond laser oscillator as an IR laser source using Z-polarization on the photocathode. This Z-polarization scheme reduces the laser photon energy (making it possible to excite the cathode with a longer wavelength) by reducing the work function of cathode due to Schottky effect. A hollow laser incidence is applied with a hollow convex lens in a vacuum that is focused after passing the laser beam through a radial polarizer. According to our calculations (convex lens: NA=0.15), a Z-field of 1 GV/m needs 1.26 MW at peak power for the fundamental wavelength (792 nm). In the first demonstration of Z-field emission, enhancement was done with a copper cathode at THG (264 nm). Consequently, we observed 1.4 times enhancement of photoemission at 1.6 GV/m of an averaged laser Z-field on the cathode surface. We report the first observation and analysis of the emission enhancements with this laser-induced Schottky-effect on metal copper photocathodes by comparing radial and azimuthal polarizations of the incident laser pulses.

THPB092

Recent Improvements in SPring-8 Linac for Early Recovery from Beam Interruption

1035

S. Suzuki, T. Asaka, H. Dewa, H. Hanaki, T. Kobayashi, T. Magome, A. Mizuno, T. Taniuchi, H. Tomizawa, K. Yanagida
JASRI/SPring-8, Hyogo-ken, Japan

The 1GeV SPring-8 linac is an injector for the SPring-8 synchrotron radiation storage ring with 8GeV booster synchrotron. In recent years, backup systems were installed to eliminate long-time interruption of the beam injections: The main gun system is usually operated, and the second gun is always pre-heated and can inject electron beams into a buncher section with an interval of several minutes in case the main gun failed. The first klystron, that feeds RF powers to the buncher system and the downstream klystrons, can be relieved by the next klystron with an interval of about 20 minutes by switching the waveguide circuit. When one of the eleven working klystrons faults, one of standby klystrons, which are kept for hot spares on line, is automatically activated to accelerate beams instead of the failed one without beam interruption. The total downtime in FY2012 was 0.12% in top-up operation user time. The averaged fault frequency was 0.2 times per day.