Makio Ohkubo

Status of the JAERI FEL - beam test for injection system

Abstract The injection system of the JAERI superconducting linac for far infrared FEL oscillation was installed and commissioned. The characteristics of the electron beam measured, so far, are as follows: an electron beam of 100 mA with 4 ns bunch length was extracted from the gun at the accelerating voltage of 180–220 kV. The beam was compressed tentatively to less than 70 ps at the end of the transport line by preliminary operation of both the sub-harmonic buncher and the buncher.

Nonrandom Distributions of Neutron Resonance Levels

Analysis of correlations between spacings of arbitrary pairs of neutron resonance levels for intermediate and heavy nuclei is described. It is found that pairs of levels separated at particular spacings appear very frequently and the observed levels are also preferentially distributed at periodical positions with particular periods. These correlations are found in the observed resonances of 75 As, 121 Sb, 123 Sb, 146 Nd, 166 Er, 174 Yb, 177 Hf, 234 U, 240 Pu, etc.. It is shown that these regular level distributions are rarely expected for statistically distributed levels.

Performance of the undulator for JAERI FEL project

Abstract A newly designed hybrid undulator (DFTH-1), whose field termination parts are a novel implementation of the displacement-free termination scheme, has been constructed for the JAERI FEL project. The field termination part of the undulator was designed to minimize the electron trajectory walkoff by using the 3D magnetic field computational code named ELF/Magic. The DFTH-1 undulator could reduce the walkoff by one third of that of the conventional hybrid undulator with non-steering termination.

Status of the JAERI FEL system

Abstract An overview of the JAERI (Japan Atomic Energy Research Institute) FEL program and its status are described. Design and construction of the JAERI FEL system based on a superconducting linac are in progress, aiming at FEL oscillation in the 10–20 μm infrared wavelength region. A part of the vacuum system, a subharmonic buncher have been fabricated.

JAERI quasi-cw, and high-average power free electron laser driven by a superconducting rf linac

Abstract We have developed and constructed a prototype for a quasi-cw, and high-average power free electron laser driven by a superconducting rf linac at the Japan Atomic Energy Research Institute (JAERI), Tokai. We have successfully demonstrated expected performances of the JAERI 250 keV electron gun and bunching system, and completed an extension to an old 5.5 MV electrostatic accelerator building as an FEL accelerator vault in the 1991 Japanese fiscal year. All solid state rf amplifiers, liquid He refrigerators, a hybrid undulator and vacuum pumping stations are ready for use now. The first superconducting accelerator module is now under preparation for a cold rf test, and the other three modules are now under assembly. A description and the latest results of the JAERI superconducting rf linac FEL will be discussed, and reported in detail.

Design concept for the second phase project of the JAERI free electron laser facility

Abstract We present a conceptual design of the second phase project of the JAERI FEL facility. The FEL project is planned with the electron beam accelerated by low-frequency superconducting cavities to accomplish high average output laser power. While in the first phase the project the FEL wavelength is in far infrared region, in the second phase it is planned to ge in the near-infrared or shorter range.

Neutron resonances in 133Cs

Neutron capture and neutron transmission measurements on 133Cs were made to obtain neutron resonance parameters. Neutron capture areas up to 2 keV and neutron widths up to 5.9 keV for each resonance were derived. Below 100 eV five neutron radiative capture widths were obtained from the shape analysis of the transmission data. The following average s-wave resonance parameters were obtained: S0 = (0.77 ± 0.09) × 10−4, D = 22.4 ± 1.5 eV, \qGγ = 119 ± 3 meV. The distribution of the level spacings is consistent with the two-population Wigner distribution predicted theoretically. The statistic Δ3 is in good agreement with the value which Dyson and Mehta derived by using the orthogonal ensemble.

An rf system using all-solid-state amplifiers for the JAERI FEL

Abstract The JAERI FEL linac is energized with four kinds of all-solid-state amplifiers having 5, 1.5, 4, and 50 kW of peak power with a 1–2 ms pulse length. Amplitude and phase stabilities of the 50 kW amplifiers are ∼ 1% and ∼1°, respectively. A feed-forward loop circuit is effective when a feedback loop circuit is not able to stabilize the output of rf power.

A linac for a free electron laser oscillator

Abstract Design parameters of the linac for a free electron laser (FEL) oscillator are finally fixed in the phase-I R&D (aiming at an infrared (10.6 μm) oscillation) schedule. Two units of the five-cell superconducting cavity (508 MHz) contained in one cryostat, which is the same as used in TRISTANs Main Ring at KEK, will be a main part of the linac. The injector to this linac consists of a grid-pulsed thermoionic cathode gun with an applied voltage of higher than 200 kV, a subharmonic ( 1 6 of a main frequency) buncher, a buncher and two single-cell superconducting cavity preaccelerators. The temporal format of the beam pulse at the exit of the gun is expressed by a timing sequence 4 ns wide and with a 80 ns separation of the pulses, and the macropulses has a 1 ms duration and a 1% duty (10 Hz). The FEL scheme is presented with an R&D schedule. The design study is now in progresses, however, some preliminary results are reported.

Neutron capture cross section measurements of 155Gd and 157Gd from 1.1 to 235 keV

Abstract Neutron capture cross section measurements of 155 Gd and 157 Gd were made at the Japan Atomic Energy Research Institute linac in the energy range from 1.1 to 235 keV. The results were compared to other measurements and to the JENDL-2 evaluation. The analysis of the capture cross sections by the least squares method gives the following average resonance parameters: 10 4 S 0 = 3.00 ± 0.28, 10 4 S 1 = 3.7 ± 1.1, 〈 Γ s γ 〉 = 119 ± 29 eV, 〈 Γ p γ 〉 = 140 ± 60 eV for 155 Gd; and 10 4 S 0 = 2.23 ± 0.57, 10 4 S 1 = 2.2 ± 0.7, 〈 Γ s γ 〉 = 115 ± 28 eV, 〈 Γ p γ 〉 = 129 ± 25 eV for 157 Gd.