A new scheme of direct beam chopping in a negative hydrogen ion source

Direct fast H- beam chopping in a surface-plasma-type negative hydrogen ion source has been studied at KEK. The H- beam is chopped at several MHz by m odulating the converter bias voltage of the ion source. However, in this ca se, a slow rise time of the chopped H- beam is one of the most serious prob lems for synchrotron injection. In order to make the rise time faster, a ne gative voltage was applied to the anode electrode. In the new scheme, mesh inserts were installed inside the ion extraction hole of the anode. Applyin g a retarding voltage on the meshes, the fast beam chopping was tested and the results are reported and discussed in the article. (C) 2000 American In stitute of Physics. [S0034-6748(00)61502-2].