The Pohang Accelerator Laboratory operates an electron linac for a pulsed neutron source as one of the long-term nuclear R&D programs at the Korea Atomic Energy Research Institute. The designed beam parameters are as follows; The nominal beam energy is 100 MeV, the maximum beam power is 10 kW, and the beam current is varied from 300 mA to 5A depends on the pulse repetition rate. The linac has two operating modes: one for the short pulse mode with the repetition rates of 2 -100 ns and the other for the long pulse mode with the 1 µs repetition rate. We tested an electron linac based on the existing equipment such as a SLAC-5045 klystron, two constant gradient accelerating sections, and a thermionic RF-gun. We investige the characteristics of the linac, and we report the status of the pulsed neutron source facility including a target system and the time-offlight paths.

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This paper briefly surveys the three compact, high-current accelerators that are presently under development in the United States in support of a national program. In addition, it reports recent experimental results from the Naval Research Laboratory (NRL) modified betatron [Phys. Rev. Lett. 64, 2374 (1990)] with emphasis on the electron-cyclotron resonance that presently limits the energy of the beam to approximately 18 MeV. Finally, it briefly addresses selective existing and prospective applications of accelerators.

The lifetime of the circulating electron beam in the NRL modified betatron has been substantially increased from a few sec to over 700 sec by the addition of strong focusing windings to the device. The injected beam consistently spirals from the injector to the minor axis and is trapped. The s0.5 kA trapped electron ring has been accelerated to 12 MeV from the injection energy of MeV. The beam acceleration has been confirmed not only by the x-ray attenuation technique but also with the detection. of photoneutrons from the reaction D('y, n)H.The experimental observations show that during acceleration the electrons cross initially higher order cyclotron resonances. Eventually, when the ratio of the vertical B to toroidal magnetic field B0 is 1/9, i.e., at I = 9, a substantial fraction of the ring electrons is lost. The remaining electrons are lost at higher B, that is, at lower £ values. Experiments are in progress to locate and eliminate the field error(s) that excite the resonances and thus to accelerate the electron ring to even higher energy.

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