GRID POWER LOADING IN A MULTIAPERTURE, MULTIGRID NEGATIVE-ION ACCELERATOR

Grid power loading in a multistage, multigrid accelerator was calorime trically measured using the Japan Atomic Energy Institute 400 keV acce lerator. This is the first result on the grid power loading in the mul tistage accelerator. It is turned out that the extracted electrons are effectively suppressed in an extractor. The leakage of the electrons extracted from the source plasma to the first acceleration grid, the s econd grid and the grounded grid were no more than 0.8%, 0.2%, and nea rly zero of the extracted electron current, respectively. Under the op timum beam optics that gives the lowest beam divergence, the power loa dings of the acceleration grids were dominated by acceleration of the stripped electrons. At a typical source operating pressure of 0.3 Pa, the power loadings of a first acceleration grid, a second acceleration grid, and a grounder grid were 3.4%, 5.0%, and 2.8% of the total beam power, respectively. From the comparison with the calculated grid pow er loading, it is found that the stripped electrons can be intercepted by intermediate acceleration grids before fully accelerated. (C) 1998 American Institute of Physics.