Testing of an advanced ‘‘volume’’ H− source and preaccelerator

In testing a cesiated volume-production negative ion source, we have obtained 75 mA of H− beam current in a 270 ms pulse length delivered downstream of the 87 keV preaccelerator. Optimum pressure in the source was less than 8 mT and the electron-to-ion ratio in the beam was less than 4. With future improvements in the electron trap, it is anticipated that higher H− current can be obtained by operating with a higher discharge power and a lower plasma electrode bias.