K. Ebihara

First result of the KEK X-band free electron laser in the ion channel guiding regime

Abstract Recent experimental results are reported for an induction-driven X-band FEL, with ion channel guiding inside the wiggler. Power in excess of 10 MW at 9.4 GHz, has been observed with a beam energy of 750 keV and a current of 520 A. Maximum gain is 22 dB/m, with no saturation after 15 wiggler periods. A self-amplified spontaneous power of 4 kW was also measured. Data for the detuning curve, field evolution and current transmission are presented and discussed.

X-band prebunched FEL amplifier

Abstract We have designed and constructed a prebunched FEL amplifier consisting of a prebuncher and a standard FEL. Microwave power saturation with a short wiggler length has been realized by a prebunched beam. We have also examined microwave phase evolutions. It has been demonstrated the adjustable range of the output microwave phase by changing the input microwave phase is restricted within a narrow band due to spontaneous emission radiated by the prebunched beam.

RF systems for the KEK B-Factory

This paper describes the design features and operational status of the RF systems for the KEK B-Factory (KEKB). Two types of new RF cavities have been developed to store very high-intensity beams with many short bunches. The design and performance of the cavities and other critical components, such as the input couplers and HOM dampers, are reported. The configuration of the RF systems is given and descriptions of various control loops are made, including a direct RF feedback loop and a 0-mode damping loop. The effects of transient beam loading due to a bunch gap on bunch phase modulations were simulated and measured. The development of a superconducting crab cavity, which is a component of luminosity upgrade strategy, is also presented.

Experimental results on the 1.5 MeV ion-channel guided X-band free-electron laser

Abstract Experiments on the ion-channel guided X-band free-electron laser amplifier (IXFEL) generated peak microwave power exceeding 100 MW at 9.4 GHz with a gain of 21 dB/m. Saturation in the evolution curve has been achieved and a frequency spread of 0.9% was observed. The amplified microwaves were separated from the driving beam line and extracted without breakdown.

Experimental studies of microwave amplification in the ion-focused regime

Studies of microwave amplification with an in-focused electron beam drawn from an induction injector are reported. A free-electron laser (FEL) operating at 9.4 GHz and employing ion-focusing within the interaction region has achieved power in excess of 30 MW at 9.4 GHz, with a beam energy of 0.8 MeV and current of 0.7 kA. Peak gain is 20 dB/m, with no saturation after 15 wiggler periods. Also reported are the first evolution and detuning data for an ion-channel laser/maser (ICL). Two shortcomings of the prematurely halted ICL studies are poor frequency discrimination and a large axial plasma gradient. Prospects for operation with an upgraded 1.6 MeV accelerator are discussed. >

Proposal for an X-band single-stage FEL

Abstract A single-stage X-band FEL with a high repetition rate (∼ kHz) has been designed and is now under construction at the KEK FEL facility. The microwave FEL will be driven with a 1 MeV, 1 kA electron beam which is generated in the induction gun energized by magnetic switches. A 9.4 GHz microwave signal introduced from the 50 kW magnetron is expected to be amplified to ∼ 300 MW as a result of the interaction with the electron beam in the undulating tapered planar wiggler field. Details of the design including the induction gun, a post-accelerator, a wiggler magnet and an rf measuring system are described. The status and the preliminary operation of the pulsed power system is presented.

1.5 MeV ion‐channel guided x‐band free‐electron laser amplifier

Experiments on the ion‐channel guided x‐band free‐electron laser amplifier generated peak microwave power exceeding 100 MW at 9.4 GHz with a gain of 21 dB/m. Saturation in the evolution curve has been achieved and a frequency spread of 0.9% was observed. The amplified microwave was separated from the driving beam line and extracted without breakdown.

X-band ion-focused free-electron laser

Abstract To assess the feasibility of a free-electron laser two-beam accelerator (TBA/FEL), an induction driven FEL test stand in the X-band microwave regime has been constructed and the energy of the driving beam is being increased year by year. The FEL operating at 9.4 GHz and employing ion focusing even in the interaction region has achieved a power in excess of 30 MW and a gain of 20 dB/m for a 0.6 kA, 0.8 MeV beam. We have found that FEL performance is strongly limited by longitudinal space charge. To mitigate space charge effects, the injector of the test stand has been upgraded to 1.6 MeV and the FEL is under test operation. The outline of the test stand is described and its preliminary experimental results and expected performance are discussed.

Non-destructive emittance measurement of a beam transport line

Abstract In order to measure the transverse beam emittance non-destructively, we have developed a new method using profile monitors. The usual assumption of Gaussian distribution is not necessary for it to measure the percent emittance. So, even if the profile is far from Gaussian, the percent emittance can be measured accurately. This method was applied to the 20 MeV KEK beam transport line and resulted in horizontal and vertical emittances of ϵh = 85 mm mrad and ϵv = 25 mm mrad containing 85% of the particles.

RF Acceleration in KEK Booster

The KEK booster synchrotron is a rapid-cycling machine with a repetition rate of 20 Hz. The rf system was designed for accelerating the proton beam injected at 20 MeV up to its final energy of 500 MeV. The booster succeeded in accelerating 8 x 10/sup 10/ protons/pulse to the designed energy on Dec. 12, 1974. Since then the beam intensity was steadily increased to 5.7 x 10/sup 11/ protons/pulse with adjustments and improvements of the machine components, especially of the rf system. An outline of the rf system and the present status of its operation are presented. Main parameters characterizing the rf system are listed, and accelerating parameters and the estimated beam characteristics are shown.