FEL2011 - List of Keywords (acceleration)

Paper	Title	Other Keywords	Page
MOPC09	Use of Re-Acceleration and Tapering in High Gain Free Electron Lasers to Enhance Power and Energy Extraction	FEL, undulator, electron, extraction	115
	R. Dusad, G. Travish UCLA, Los Angeles, USA
	In high gain Free Electron Lasers (FELs), it is possible to use undulator tapering to increase power and energy extraction beyond saturation. For some applications, however, tapering is not sufficient or results in excessively long structures. Here we the study use of tapered undulators interrupted by short accelerator sections to increase the power extracted per unit length. Re-acceleration restores nominal energy to the beam with minimal disruption to bunching, and allows repeated use of a single taper profile. We show that for suitable parameter sets this approach can perform better than ideal tapering alone, and may serve to greatly improve and simplify high peak and average power FELs. Based on these findings, we propose a first experiment to test the re-acceleration with tapering concept.

TUPA01	Tunable THz-pulse-train Photoinjector	laser, electron, bunching, beat-wave	187
	Y.-C. Huang, F.H. Chao, C.H. Chen, H.H. Chen, K.Y. Huang NTHU, Hsinchu, Taiwan
	Funding: This work is jointly supported by the National Science Council, under Contract NSC97-2112-M-007-018-MY2; the National Synchrotron Radiation Research Center,under Project 955LRF01N. A THz-pulse-train photoinjector is under construction at the High-energy OPtics and Electronics (HOPE) Laboratory at National Tsinghua University, Taiwan. This photoinjector is believed to be useful for generating high-power THz radiation, as well as for driving or loading a plasma-wave accelerator. A THz laser beat wave with full tunability in its beat frequency is employed to induce the emission of the THz electron pulses from the photoinjector. We show in our study that such a photoinjector is capable of generating periodically bunched MeV electrons with a bunching factor larger than 0.1 at THz frequencies for a total amount of 1 nC charges in a 10-ps time duration. We will also present a driver laser technology that can tune the electron bunch frequency with ease and help the growth of the high harmonics in the bunching spectrum of accelerated electrons. Experimental progress on this photoinjector will be reported in the conference.

WEPA11	Longitudinal Stability of ERL with Two Accelerating RF Structures	linac, electron, RF-structure, cavity	345
	Ya.V. Getmanov, O.A. Shevchenko BINP SB RAS, Novosibirsk, Russia N. Vinokurov NSU, Novosibirsk, Russia
	Modern ERL projects use superconductive accelerating RF structures. Their RF quality is typically very high. Therefore, the RF voltage induced by electron beam is also high. In ERL the RF voltage induced by the accelerating beam is almost cancelled by the RF voltage induced by the decelerating beam. But, a small variation of the RF voltage may cause the deviations of the accelerating phases. These deviations then may cause further voltage variation. Thus the system may be unstable. The stability conditions for ERL with one accelerating structure are well known [1, 2]. The ERL with split RF structure was discussed recently [3, 4]. The stability conditions for such ERLs are discussed in this paper. [1] L. Merminga et al., Annu. Rev. Nucl. Part. Sci. 53(2003) 387. [2] N.A. Vinokurov et al., Proc. SPIE 2988 (1997) 221. [3] D. Douglas, ICFA BD-Nl 26 (2001)40. [4] N.A. Vinokurov et al., Proc. IPAC’10.

WEPA15	S-band High Gradient Linac for a Compact XFEL	linac, klystron, FEL, LLRF	356
	F. Wang SLAC, Menlo Park, California, USA
	With the successful operation of the first hard X-ray FEl, LCLS, other XFEL facilities are being developed worldwide. Due to the limited site size, many proposed XFELs are based on C-band technology. Switching from S-band to C-band enables a higher acceleration gradient (>35 MV/m) that is nearly double that of the SLAC S-band Linac. Based on the high gradient research, it found that the actually operational gradient is scaled as 1/6 power of the required rf pulse length at constant rf breakdown rate. Therefore, it is possible to have a S-band linac at higher gradient (>35MV/m) operated at very short rf pulse length, such like the single/two bunch operating XFEL.

THPA28	Lasing of Near Infrared FEL with the Burst-mode Beam at LEBRA	FEL, electron, linac, gun	535
	K. Nakao, K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nogami, T. Tanaka LEBRA, Funabashi, Japan
	Improvement of the electron beam injector system in the linac at the Laboratory for Electron Beam Research and Application (LEBRA) of Nihon University made possible to accelerate the burst-mode beam extracted from the conventional DC triode electron gun. The electron beam with the pulse width less than 1ns and the period of 44.8ns, which corresponds to the round-trip time in the FEL optical resonator, has been extracted by using a high-speed grid pulser (Kentec Inc.). Taking into account of the electron beam pulse width, sequence of two or three FEL pulses with the accelerating RF period was possible. In the lasing experiment a single FEL pulse or a row of two FEL pulses was observed using a streak camera. By the adjustment of the timing of the high-speed grid pulse generated in synchronous with the accelerating RF, lasing of a single FEL pulse in the single short beam pulse has been observed at an FEL wavelength of approximately 1800nm. The result suggests that a single FEL pulse with 44.8ns period is available in the wavelength range from 1600 to 6000nm at the LEBRA FEL system.

Paper

Title

Other Keywords

Page

MOPC09

Use of Re-Acceleration and Tapering in High Gain Free Electron Lasers to Enhance Power and Energy Extraction

FEL, undulator, electron, extraction

115

R. Dusad, G. Travish
UCLA, Los Angeles, USA

In high gain Free Electron Lasers (FELs), it is possible to use undulator tapering to increase power and energy extraction beyond saturation. For some applications, however, tapering is not sufficient or results in excessively long structures. Here we the study use of tapered undulators interrupted by short accelerator sections to increase the power extracted per unit length. Re-acceleration restores nominal energy to the beam with minimal disruption to bunching, and allows repeated use of a single taper profile. We show that for suitable parameter sets this approach can perform better than ideal tapering alone, and may serve to greatly improve and simplify high peak and average power FELs. Based on these findings, we propose a first experiment to test the re-acceleration with tapering concept.

TUPA01

Tunable THz-pulse-train Photoinjector

laser, electron, bunching, beat-wave

187

Y.-C. Huang, F.H. Chao, C.H. Chen, H.H. Chen, K.Y. Huang
NTHU, Hsinchu, Taiwan

Funding: This work is jointly supported by the National Science Council, under Contract NSC97-2112-M-007-018-MY2; the National Synchrotron Radiation Research Center,under Project 955LRF01N.
A THz-pulse-train photoinjector is under construction at the High-energy OPtics and Electronics (HOPE) Laboratory at National Tsinghua University, Taiwan. This photoinjector is believed to be useful for generating high-power THz radiation, as well as for driving or loading a plasma-wave accelerator. A THz laser beat wave with full tunability in its beat frequency is employed to induce the emission of the THz electron pulses from the photoinjector. We show in our study that such a photoinjector is capable of generating periodically bunched MeV electrons with a bunching factor larger than 0.1 at THz frequencies for a total amount of 1 nC charges in a 10-ps time duration. We will also present a driver laser technology that can tune the electron bunch frequency with ease and help the growth of the high harmonics in the bunching spectrum of accelerated electrons. Experimental progress on this photoinjector will be reported in the conference.

WEPA11

Longitudinal Stability of ERL with Two Accelerating RF Structures

linac, electron, RF-structure, cavity

345

Ya.V. Getmanov, O.A. Shevchenko
BINP SB RAS, Novosibirsk, Russia
N. Vinokurov
NSU, Novosibirsk, Russia

Modern ERL projects use superconductive accelerating RF structures. Their RF quality is typically very high. Therefore, the RF voltage induced by electron beam is also high. In ERL the RF voltage induced by the accelerating beam is almost cancelled by the RF voltage induced by the decelerating beam. But, a small variation of the RF voltage may cause the deviations of the accelerating phases. These deviations then may cause further voltage variation. Thus the system may be unstable. The stability conditions for ERL with one accelerating structure are well known [1, 2]. The ERL with split RF structure was discussed recently [3, 4]. The stability conditions for such ERLs are discussed in this paper.
[1] L. Merminga et al., Annu. Rev. Nucl. Part. Sci. 53(2003) 387.
[2] N.A. Vinokurov et al., Proc. SPIE 2988 (1997) 221.
[3] D. Douglas, ICFA BD-Nl 26 (2001)40.
[4] N.A. Vinokurov et al., Proc. IPAC’10.

WEPA15

S-band High Gradient Linac for a Compact XFEL

linac, klystron, FEL, LLRF

356

F. Wang
SLAC, Menlo Park, California, USA

With the successful operation of the first hard X-ray FEl, LCLS, other XFEL facilities are being developed worldwide. Due to the limited site size, many proposed XFELs are based on C-band technology. Switching from S-band to C-band enables a higher acceleration gradient (>35 MV/m) that is nearly double that of the SLAC S-band Linac. Based on the high gradient research, it found that the actually operational gradient is scaled as 1/6 power of the required rf pulse length at constant rf breakdown rate. Therefore, it is possible to have a S-band linac at higher gradient (>35MV/m) operated at very short rf pulse length, such like the single/two bunch operating XFEL.

THPA28

Lasing of Near Infrared FEL with the Burst-mode Beam at LEBRA

FEL, electron, linac, gun

535

K. Nakao, K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nogami, T. Tanaka
LEBRA, Funabashi, Japan

Improvement of the electron beam injector system in the linac at the Laboratory for Electron Beam Research and Application (LEBRA) of Nihon University made possible to accelerate the burst-mode beam extracted from the conventional DC triode electron gun. The electron beam with the pulse width less than 1ns and the period of 44.8ns, which corresponds to the round-trip time in the FEL optical resonator, has been extracted by using a high-speed grid pulser (Kentec Inc.). Taking into account of the electron beam pulse width, sequence of two or three FEL pulses with the accelerating RF period was possible. In the lasing experiment a single FEL pulse or a row of two FEL pulses was observed using a streak camera. By the adjustment of the timing of the high-speed grid pulse generated in synchronous with the accelerating RF, lasing of a single FEL pulse in the single short beam pulse has been observed at an FEL wavelength of approximately 1800nm. The result suggests that a single FEL pulse with 44.8ns period is available in the wavelength range from 1600 to 6000nm at the LEBRA FEL system.