Experimental study of a simple method to chop Penning SPS H(sup (minus)) beams

摘要

Accumulator rings proposed for use in high-intensity spallation-neutron sources require a chopped beam with particle-free gaps (approx)100 ns wide at 1--2 MHz rates with rise and fall times (le) 20 ns. Chopping the beam directly in the ion source may be an attractive way to provide the desired beam structure. A grounded collar placed in the drift region next to the emission aperture lowers the e(sup (minus))/H(sup (minus)) ratio in the 8X source H(sup (minus)) beam. We electrically isolated the collar and biased it to modulate the extracted H(sup (minus)) current. Positive collar bias decreases the H(sup (minus)) beam by up to 90%. The fastest H(sup (minus)) current fall and rise times achieved to date are 400 ns and 2 (mu)s, respectively. The fall time is close to the pulser rise time ((approx)300 ns). The rise time is considerably longer than the pulser fall time ((approx)500 ns). Negative collar bias lowers the H(sup (minus)) beam by up to 50%.