Introduction
There are typically four situations that lead to
operator intervention in the SY120 beam line (in increasing order of
complexity):
1)
Recovery
from a pbar transfer, or a Tevatron reload,
2)
A
request to change Energy of the MTest secondary beam line,
3)
A
cold start of the SY120 complex after a shutdown of the SY120 area,
4)
Indications
that the beam is being lost somewhere in the Switchyard or complaints about the
beam quality.
These 4
situations are covered in the four sections below.
Section I - Recovery from a Pbar
Transfer or a Tevatron Reload
First
request a $20 (1 second spill length) or $21 (4 second spill length) be
reinserted in the timeline. Enable the
Switchyard F:MCDC and reset SY BEAM PERMIT on ACNET
page S68. Run the sequencer script
‘Establish Slow Extraction‘ found on ACNET page S48
MESON. Check positions and intensities
on the SWIC and FTP displays (remembering that it may take a few pulses for the
SY120 supplies to thermally settle down).
Section II - A Request to Change
Secondary Energy of MTest or MCenter
Go to
ACNET page S18 <30> MESON, change the energy parameter S:SYNRG and run the energy script @’SY_ENERGY_MODE’.
Check
the MT4/MT5 power supplies on page S18<7> MESON and the MT6 pion intensity on the
scintillation counter, MT6SC2.
Section III - Cold Start of the
SY120 Complex after a Shutdown
Restore
save/restore file 400 – this should set all the power supplies etc. in the
whole SY120 complex to transmit 120 GeV protons to MT6. Then go to Section I above and then check the
positions and intensities at S:F1SEM in the
F1-enclosure using FTP(Switchyard) plot 2 and the SWICs on page S45 (SY MESON
subpage). Next go to Section II above
and set in an MTest secondary pion energy, if
requested by the experimenters. Warn the
experimenters before enabling F:MTPCDC and
F:MTSCDC. Check the intensity of the
secondary yield F:MT6SC2 as in Section II above.
Section IV - Indications that Beam
is being Lost or Complaints about Beam Quality
Before
calling the on-call SY120 expert, there are some things that can be
checked. In general, there are 7 almost
completely independent sections of the SY120 beam line. This property helps isolate the origin of
problems that might arise. The 7 sections
are:
P1
beamline (K520A
to T:ILAM)
P2
beamline (T:ILAM to I:F17B3)
P3
beamline (F17-4
to QF49D)
Transfer
Hall and Encl-B beamline (S:Q80 to S:VT103)
ACNET page S18<1> MESON
Encl-C -> F1/F2/F3 manholes ->
M01 (SWICs S200 to MW1 [Meson
Target Train]) ACNET
S18<2> MESON
Meson
Target Train -> MT6 (F:MT2Q1
to F:MT5Q2) ACNET S18<4> MESON
Meson
Secondary Pion Beam Line (F:MT3W to F:MT5Q2) in pion mode – ACNET S18<7> MESON
Note
that the parameter pages from S18 <1> Meson to S18 <7> Meson are organized approximately in a sequential fashion for
the magnetic elements starting at P3 and proceeding to the downstream end of
the Meson Lab beam lines (the elements in P1, P2 and P3 are found on ACNET page
I68).
A link
to a schematic of the complete SY120 beam line can be found at: http://home.fnal.gov/~koizumi/SY120/Extracted%20Beam%2011Jan07.pdf
Multiwire/SWIC displays
A quick
glance at the multiwire and SWIC displays can usually narrow the search for the
origin of some problem with the beam.
Note that after a period when the $20 or $21 event has been disabled
(for Tevatron shots or antiproton maneuvers) the SY120 beam often takes a few
pulses to reach equilibrium. One should
not tune until it is clear that something has changed; and that one is not
observing just an initial thermal drift.
If the value of S:F1SEM/I:BEAM21, displayed on
plot FTP Switchyard #2 is greater than 0.25, the problem is most likely downstream
of the F1 enclosure (and vice versa).
A recent nominal set of beam profiles is shown
here:
A quick
look at the following parameter pages, S18<1>Meson through
S18<9>Meson, possibly with a comparison with a recent good running
condition or file 400, is an important tool in tracing down problems with the
beam. Some parameter pages are shown
here for a recent nominal tune:
1. MCenter or MTest alone:
If
there is only one user for the beam on a $20 or $21 event, the straightforward
way to adjust the intensity is to adjust the beam intensity in the Main
Injector. The product of three variables
gives the $20 or $21 event intensity in the MI: the number of filled RF bunches
per booster batch, the number of booster turns per booster batch, and the
number of booster batches loaded into the MI. ACNET page B4 controls the number of RF
bunches and the number of Booster turns while D69, the time line generator,
determines the number of batches that are requested.
Remember when changing the intensity of
the SY120 beam to check the administrative limits on the allowed
intensity. The Switchyard is only
approved for intensities of 2.4e15 protons/hour, or below on I:BEAM21. The MTest
primary beam line is only approved for intensities of 1.2e14 protons/hour, or
below on F:MW1SEM.
There are also administrative limits on the amount of beam that reaches
the experimental areas. The intensity in
MTest, as measured by MT6SC1, must be less than 1e9 particles/hr.
Note: ALARA reminds us that less radiation is
created if the Linac chopper is set to 84 bunches, thus a typical event $20 or
$21 intensity of 8e11/pulse can be obtained with 84 bunches, 1 turn, and 1
batch.
Intensities higher than 8e11 per $20 or
$21 event should be tuned by an expert to minimize losses in the Switchyard.
If the
lone user in MTest or MCenter wants an intensity below about 1e11, or 1 turn,
10 bunches, 1 batch, it is necessary to create a double split with the
FSEP7/FSEP8 septa (note FSEP7 and FSEP8 should always be set to the same
vertical position) in order to direct some of the unwanted beam to the other
beam line or to the Meson Target Train absorber (if the other beam line is
OFF). This situation occurs because the
low level RF in the MI wants at least 10 bunches in order for the feedback loops
to work correctly.
2. MCenter and MTest simultaneously:
The
relative intensities of the MTest and MCenter beamlines
are determined by the setting of the double split created by the FSEP7/FSEP8
septa. Consider the case where FSEP7U
and FSEP7D are both set to +200 mils and FSEP8U and FSEP8D are also both set to
+200 mils (remember that the horizontal stretched wires of the FSEPs are
charged up to about -20 kV):
The
fraction of the beam with y>+200 mils gets kicked upward by both FSEP7 and
FSEP8 to become the MWest/MTest beam, and the fraction of the beam below +200
mils gets kicked downward by both FSEP7 and FSEP8 to become the MCenter
beam. By adjusting the heights of FSEP7
and FSEP8 as well as the intensity of the MI beam as above, one should be able
to satisfy the requests of both MCenter and MTest.
Note: the FSEP7 and FSEP8 have mechanical limits at about +/- 500 mils, so
it is wise to not exceed a limit of +/- 450 mils on either septa
unless an expert is present. Always
check that the electrostatic septa are level and equal, i.e.:
FSEP7U=FSEP7D= FSEP8U=FSEP8D.
Momentum changes in Secondary beamlines
MCenter:
The momentum setting of the primary beam in MCenter, as far as the MC6IC
ion chamber (just upstream of the primary production target in MC6) is always
set for 120 GeV protons. A recent
typical tune for this part of the MCenter beam line is:
The momentum of the secondary beam line in MCenter in MC6
and MC7 can be +120 GeV when the MCenter interlocks are set for proton mode or
anywhere from –80 GeV to +66 GeV secondary hadrons (pions, kaons and
(anti)protons) when the interlocks are in pion mode. A typical tune in proton mode is:
The power supplies for the secondary beam line in MC6,
from F:MC6D to MC6Q6, have reversing switches and
hence they can be set to transport either positive or negative secondary
hadrons down to the experimental area in MC7.
A typical recent tune for +42.5 GeV hadrons in MCenter/MC6 is:
The SWICs and Multiwire chambers in MCenter may have to
have their voltages adjusted in order to respond without saturation to the
large range of intensities produced at the different secondary energy settings.
The most recent MTest settings
for the many different energy settings for the MTest beam line are found in
Save/Restore files:
120 GeV protons: file 400
+1 GeV secondary beam: file 401
+2 GeV secondary beam: file 402
+4 GeV secondary beam: file 403
+8 GeV secondary beam: file 404
+16 GeV secondary beam: file 405
+32 GeV secondary beam: file 406
By using Wally Kissel’s script on ACNET page S18 <26> MESON one can
change the MTest energy setting from one energy to another in a minimum time
(this script has the advantage that it only sets the MTest line components and
leaves the primary Switchyard upstream of the MTest secondary production target
untouched).
When the MTest interlocks are set to 120 GeV proton mode, the primary protons are attenuated by a pinhole collimator in M03. The remaining low-intensity 120 GeV proton beam is then transported to the Meson Test Facility in MT6. A recent typical 120 GeV tune is:
When the Mtest interlocks are set to pion mode, the beam
energy can be set to anything from –66 GeV to +66 GeV. Note that changing the polarity of the MTest
beam line requires physically changing the leads on the top of some of the
Transrex power supplies in MS2 and MS4 and hence should only be attempted after
consultation with experts. A typical
recent MTest tune at +16 GeV is:
A new Low Energy Pion Mode has been implementd
in the interlock system for MTest. In
the Low Energy mode, the pinhole collimator is OUT, the MT2Q1/2Q2 and
MT3Q1/MT3Q2 quads are energized, and the primary 120 GeV beam interacts on
MT4TGT. The elements downstream of
MT4TGT are interlocked to provide excitations up to 30 GeV/C. Thus, in this mode, the second half of the
MTest beam line can be tuned to transmit secondary particles from 1 GeV to 30
GeV to the Meson Test Facility in MT6.
A recent low energy PION tune for 16 GeV is shown below.
Any small changes in the tune of the MI, Booster or Linac
can potentially alter the slow-resonant extraction process from the MI. The QXR circuitry can adjust for many of the
small drifts in the operating point and tune of these accelerators; this does
not happen instantly, it may take of order 10 pulses. Often the change is large enough that the QXR
circuitry fails to converge to a new stable operating point. In this case the spill can get very uneven
and it may signal real problems within the MI/Booster/Linac complex. Rebooting the QXR is a last-chance attempt to
straighten out the feedback loops of the QXR.
If this fails, call the expert, Peter Prieto,
for QXR. The display below shows a nice
linear extraction from the MI over about 4 seconds with the corresponding
linear increase in the total beam seen in the S:F1SEM
and the F:MT6SC1 scintillation counter.
If the efficiency of transport to the F1 enclosure – as
measured by S:F1SEM/I:BEAM21 (see picture above) – falls below 25% there is
probably some missteering and scraping of the beam upstream of this point. It is also possible that the orbit in the MI
has moved with respect to the electrostatic septa. Check the multiwire and SWIC
positions and the BLM displays against nominals first to get an indication of
the location of the loss point. Tweaking
the trims, starting at VTF18, upstream of the approximate location of the loss
point by +/- 1 A, while watching the yield as measured by S:F1SEM/I:BEAM21,
can usually fix the problem; if not, consult an expert. The ACNET picture above shows a measurement
of S:F1SEM/I:BEAM21 greater than 50%
4. Intensity ratios to MTest and MCenter changing:
A change in the ratio of intensities to MTest and MCenter
is usually the direct result of a vertical movement of the beam at the septa
location in the F1-Enclosure. Vertical
motion at this point in the beam line lattice can be caused by a change in the
fringe field of the Tevatron (i.e. the Tevatron ramping up to 980 GeV or down
to 150 GeV). This can be compensated by
changing the excitation of the vertical bend dipole, S:V204,
or the vertical trims, S:VT201 and S:VT202.
There are other sources of motion in the vertical plane generated in the
MI/Booster/Linac. Adjustment of vertical
trims is needed to compensate for these motions. If the apparent vertical change is larger
than can be zeroed with a few amps change in the trim magnet excitations, Chuck
Brown or Rick Coleman should be consulted.