Time Structure of the Test Beam

The test beam originates from the resonant extraction of at least one
Booster batch inside the Main Injector (MI).  This batch usually 
consists of 60-80 RF 'buckets', with each bucket 19 nsec long.  Thus 
the batch is about 1.5 microseconds long.  The full circumference 
of the MI is about 10 microseconds.  It is possible to run with up
to 5 Booster batches in the MI.  The batch or batches are accelerated to 
120 GeV, circulate around the MI and are slowly extracted over a 
macroscopic slow spill.  This extraction takes place through an
area known as the 'SwitchYard'.  The program of 120 GeV extraction
through the SwitchYard is known as SY120 operations.

For most usage of the test beam, there will be less than 100 kHz of 
beam.  If beam were smoothly extracted, this would imply that at most 
1 particle per rotation of the MI batch will occur.  The beam is not 
that smooth and we see up to 35% double occupancy per MI rotation. 
(see the beamline description section of this web site for a plot of 
this.)  

The length and duty cycle of the spill is determined by the Accelerator
Division (AD), with guidance from Program Planning.  For much of 2004
it was a single 0.6 second long spill per minute.  At the end of the 
summer of 2004, the AD implemented a mixed mode extraction, in 
conjuction with fast extraction of protons to the pbar complex.  In 
that mode we can run up to 650 spills/hour.  

Currently (May, 2007), with NUMI and the Tevatron fully operational, then
mixed mode extraction does not work.  Thus we operate with a dedicated
spill to SY120.  That spill is limited to have a 5% impact on NUMI and
the Tevatron.  Thus we typically operate with a single 4 second spill
every minute, for 12 hours out of the day.  The Accelerator Division is
investigating an implementation where this can be switched over quickly
to two 1 second spills every minute, for 12 hours per day.