Operating Procedure Changes to Improve Antiproton Production at the Fermilab Tevatron Collider Page: 2 of 4
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Beam Line Tuner
There are over 600 m of 120GeV beam line between
the Main Injector and target, and approximately 275 m of
8GeV beam line between the target and the Debuncher.
As a result, small changes in the upstream P1 line orbit
can translate into changes in the downstream AP2 line
orbit significant enough to reduced stacking rates. Prior to
the implementation of new software, any beam line orbit
drift was manually corrected by changing a pair of trim
magnets in the API line to maximize the beam intensity to
the end of the AP2 line. This process, called "target
tuning", was performed a number of times each day.
The target tuning procedure has been replaced by a C
application called the Oscillation Overthruster. This
application corrects the 120 GeV orbit for protons in the
P1, P2 and API lines, as well as the 8 GeV secondaries in
the AP2 line.
" During stacking, the Oscillation Overthruster reads
in beam line Beam Position Monitor (BPM) data
and alternates making corrections between the 120
GeV and 8 GeV beam lines.
" Trim magnets are used to correct both the 120 GeV
proton and 8 GeV pbar orbits.
" If the 120 GeV BPM data is out of range, the 8
GeV correction reverts back to only using the two
"target tune" trims until the 120 GeV BPM data is
back in range.
" If the BPM data cannot be read, the BPM crates are
reset to recover BPM functionality.
" During beam interruptions, corrections are
temporarily delayed to allow the beam line
elements to stabilize.
The implementation of the Oscillation Overthruster was
made possible by improvements in instrumentation and
controls. The P1, P2, API and AP3 lines all share the
Echotek style Beam Position Monitor (BPM) electronics
that were built as part of the "Rapid Transfers" Run II
Upgrade. These BPMs are designed to detect seven to 84
consecutive 53MHz proton bunches in stacking mode and
communicate to the control system over Ethernet via
VME crates located in five different service buildings .
The AP2 line BPMs also have been upgraded to allow
beam orbit information during stacking cycles .
Secondary particles in the AP2 line have the same 53
MHz bunch structure as the targeted proton beam,
providing the RF structure needed for the BPMs to
function. One of the challenges faced when designing
this system is the small beam intensities in the line. When
stacking, the number of antiprotons and other negative
secondaries (mostly pions and electrons) in the AP2 line
is on the order of 1 x 1011 at the beginning of the line and
1 x 1010 at the end of the line. AP2 BPM electronics
communicate to the controls system over Ethernet via
NIM downconverter modules in three service buildings.
Stochastic Cooling Power Management
Transverse and longitudinal beam cooling is provided
by stochastic cooling systems in both the Debuncher and
Accumulator. In the Debuncher, the cooling systems are
run near maximum power to cool the beam as much as
possible before transfer to the Accumulator. Accumulator
stochastic cooling power levels are set based on both
stack size and stacking conditions. Prior to the
introduction of automation, the process of setting
stochastic cooling power levels was manual and required
constant attention. Three tools were developed to assist in
stochastic cooling power management: the Debuncher
babysitter, the Core Momentum babysitter and the
The Debuncher babysitter is a C application developed
to monitor traveling wave tube (TWT) power supplies and
turn them back on if they trip. These supplies run near
maximum output and will sometimes trip off with
changing beam conditions. If there are six consecutive
trips, the babysitter turns itself off to avoid damaging
equipment. When this happens, power levels are manually
adjusted and the babysitter turned back on.
The Core Momentum babysitter is an application that
regulates power levels on the Core 2-4 GHz and 4-8 GHz
momentum systems. Power levels have been determined
empirically over time.
The Stacktail Monitor is an Accelerator Command
Language (ACL) script that controls the Accumulator
Stacktail Momentum system as shown in Figure 2. The
" regulates stacktail power based on stack size based
on operational experience,
" reduces stacktail power, if necessary, to control
core transverse emittances,
" provides the core momentum target power levels
used by the Core Momentum babysitter,
" turns off the Core 4-8 GHz momentum system
when stacking beam is not being introduced to the
" sequentially turns off stacktail amplifiers to reduce
heating if transverse emittances become excessive.
The Stacktail Monitor -
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Figure 2: Stacktail Monitor Operation
The creation of the Stacktail Monitor was made possible
by the creation of ACL scripts , which is an easy to use
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Drendel, B.; Morgan, J.P.; Vander Meulen, D. & /Fermilab. Operating Procedure Changes to Improve Antiproton Production at the Fermilab Tevatron Collider, article, April 1, 2009; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc931528/m1/2/: accessed November 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.