Beam extraction at the Prototype Injector Unit for JT-60

The Prototype Injector Unit has been constructed to test and demonstrate single beam line performances prior to fabrication of the 14 injector units for JT-60. Operation of the system was started in December 1981, and ion beams of 75 keV, 70 A, which is the standard design conditions for JT-60, were extracted for 10 sec in February, 1982. This beam produced a total neutral beam power of 1.43 MW with a proton ratio of 80%. Reionization loss was 5% of the total neutral beam power and the blocking effect of the drift tube was not observed. An attempt to increase beam energy up to 100 keV, resulted in successful operation at 100 keV, 70 A, 10 sec in March 1983. Through these tests, design performance of the ion sources, beam line components, and cryopumping system was confirmed. In parallel with these tests, a new advanced source plasma generator was developed to provide a higher proton ratio. Performance tests on this new source were initiated at the prototype injector unit in August 1983. Ion beams of 90 keV, 30 A, 10 sec and 100 keV, 39 A, 6.8 sec were extracted so far using one advanced source. The neutral beam power of 0.73 MW, which corresponds to 20 MW neutral beam injection, was produced with a beam energy of 75-90 keV and a reionization loss of 4-5%. The advanced source has been adopted as the production ion source for the JT-60 Neutral Beam Injection system