S. Hiramatsu

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.

KEKB beam instrumentation systems

For the stable high-luminosity operation and luminosity increase, the electron and positron storage rings of the KEK B-Factory (KEKB) is equipped with various beam instrumentations, which have been working well since the start of the commissioning in December, 1998. Details and performance of the beam-position monitor system based on the spectrum analysis using DSPs, the turn-by-turn BPM with four-dimensional function available for measurements of the individual bunch position, phase and intensity, the parametric beam-DCCTs designed so as to avoid the magnetic-core-selection problems for the parametric flux modulation, the bunch-by-bunch feedback system indispensable to suppress the strong multibunch instabilities in KEKB, the various optical beam diagnostic systems, such as synchrotron radiation interferometers for precise beam-size measurement, the tune meters, the bunch length monitors and the beam-loss monitors are described. Delicate machine tuning of KEKB is strongly supported by these instrumentations.

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.

Acceleration of the polarized proton beam at the KEK 12 GeV ps

Abstract Acceleration of the polarized proton beam at the KEK PS up to 3.5 GeV is described. In the booster synchrotron, 75% of the linac beam polarization was preserved without any correction for the depolarizing resonances. In the main ring, almost 100% of the booster beam polarization was preserved at 3.5 GeV by the fast passage method for the intrinsic resonances and by the closed orbit correction for the imperfection resonances. The KEK PS is the first cascaded synchrotron which has demonstrated acceleration of a polarized beam.

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. >

A Spin-Frozen Polarized Target of Proton and Deuteron

A spin-frozen polarized target of proton and deuteron was constructed for the measurement of spin dependent parameters of hadron-hadron scatterings at the 12 GeV KEK proton synchrotron. The target was also used for experiments at LAMPF-HRS. As the proton and deuteron targets, 1,2-propanediol and fully deuterated propanediol (D-8) with stable Crv complex (EHBA) were used, respectively. The characteristics and performance of the targets are described. Data on the nuclear spin lattice relaxation time (Tln) with proton beam give us information on the Kapitza resistance between the target material and liquid 3He/4He mixture.

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.