  The peak current limit for the Fermilab Linac was recently studied. The
purpose was to learn what components of the present Linac can be used for the
first stage of a proposed proton driver[1]. For this application the Linac must
provide a H- beam in excess of 5000 mA-msec per pulse. The original Fermilab
Linac was designed for protons with a peak current of 75 mA and a pulse length
of four Booster turns (~10 msec). The high energy replacement was designed for
a peak current of 35 mA and a beam pulse length of 50 msec. The present H-
source cannot deliver more than ~80 mA which produces 55 mA in the Linac. Using
a proton source allows the system to be tested to currents of ~100 mA and pulse
lengths long enough to observe the effects of long pulses. This test has shown
that the present Linac can accelerate beam having a peak current up to ~85 mA
with beam loss comparable to the present Linac operation (~45 mA). The results
of the test will be presented.
