Transverse Phase Space Time Dependence of LAMPF's High Intensity H+ Beam

The LAMPF H+ injector is pulsed 120 times a second with pulse lengths from 500 to 750 μsec long. Large transients in transverse phase space, lasting 100 to 200 μsec after turn-on, are regularly observed. The magnitude of these transients appears to increase with increasing currents and source brightness. Because high-current accelerators require great precision in phase-space tailoring to avoid excessive emittance growth during acceleration, these transients cause severe operational problems and can no longer be neglected in the beam tuning procedure. Measurements of transverse phase space as a function of time for the 750-keV, 30-mA peak current H+ beam are presented.