Recent progress in beam-fusion studies of the ETIGO Project at Nagaoka

Systematic studies have been carried out of R & D on ion-beam fusion at Tech. Univ. of Nagaoka, called ETIGO Project. It consists of several sub programs associated with generation, focusing, transport, post-acceleration, bunching, target irradiation of the LIB, and so on. Their progresses will be reviewed here. I) Focusing: Using a spherically-shaped, magnetically insulated diode (MID), we have studied the detailed focusing properties of proton beam. An annular distribution of ion-current density observed experimentally has been found to be due to space-charge effect by ion-tranjectory calculations. The space-charge neutralization factor is evaluated to be more than 99.9%, Besides the proton beam, we have also produced boron, nitrogen, carbon, and deuteron beams, the dynamics of which have been studied in detail. Basic physics of MID and Br diodes as well as a pinched reflex diode are examined by use of an image converter camera. II) Transport: Proton-beam (800-keV of energy) transport has been studied in a wall-confined, z-discharged plasma channel (1-m long). Good transport efficiency (∼80 %) has been obtained. Under certain conditions, however, the beam ceases to be transported due to some plasma instabilities. Using an image converter camera, we have obtained clear evidences of a sausage instability, being reasonable agreement between the experiment and the theory. Preliminary experiments have also been carried out to study beam transport through multi-channels with return paths. III) Post-Acceleration: An induction accelerator (420-kV, 6-kA, 50-ns) has been constructed to study post-acceleration of a medium-mass ion beam (MIB). The transport of the MIB is also studied without using a conventional z-discharged plasma channel. An estimate is presented to use a 166-MeV, 60-kA, B
⁺
beam for an inertial-confinement fusion by the MIB.