Current and Future High Power Operation of Fermilab Main Injector

Abstract

Fermilab's Main Injector on acceleration cycles to 120 GeV has been running a mixed mode operation delivering beam to both the antiproton source for pbar production and to the NuMI[1] target for neutrino production since 2005. On January 2008 the slip stacking process used to increase the beam to the pbar target was expanded to include the beam to the NuMI target increasing the MI beam power at 120 GeV to 400KW. The current high power MI operation will be described along with the plans to increase the power to 700KW for NOvA and to 2.1 MW for project X.

Full text

CURRENT AND FUTURE HIGH POWER OPERATION OF FERMILAB
MAIN INJECTOR*
I. Kourbanis# ,P. Adamson, B. Brown, D. Capista, W. Chou, D. Morris, K. Seyia, G. Wu, M.J. Yang,
Fermilab, Batavia, IL 60510, U.S.A.
Abstract
Fermilab’s Main Injector on acceleration cycles to 120
GeV has been running a mixed mode operation delivering
beam to both the antiproton source for pbar production
and to the NuMI[1] target for neutrino production since
2005. On January 2008 the slip stacking process used to
increase the beam to the pbar target was expanded to
include the beam to the NuMI target increasing the MI
beam power at 120 GeV to 400KW. The current high
power MI operation will be described along with the plans
to increase the power to 700KW for NOvA and to 2.1
MW for project X.
FERMILAB ACCELERATOR COMPLEX
The Fermilab accelerator complex consists of an 400
MeV Linac, an 8 GeV Booster, the Main Injector (MI)
and the Tevatron. The accelerator complex also includes a
Pbar source and a Pbar storage Ring (Recycler) located in
the MI tunnel. The Main Injector is used to accelerate
protons and pbars to 150 GeV for injection in the TeV and
protons to 120 GeV for pbar production and for the
neutrino beam-line (NuMI).
MI MULTI-BATCH SLIP STACKING[2]
Since the ratio of the harmonic numbers between MI
and Booster is 7 up to 7 Booster batches can be injected in
MI at a time. Since we would like to maintain some
spacing for kicker gaps the total number of Booster
batches is limited to 6.
At the beginning of the MI mixed mode operation two
Booster batches were slipped stacked into a double
intensity batch and recaptured. After recapture 5
additional Booster batches were injected filling up the MI.
Following acceleration to 120 GeV a bunch rotation was
performed in order to reduce the bunch length and the
double intensity batch was extracted to the pbar target.
The rest of the beam was extracted ¼ of synchrotron
period later to the NuMI target.
Since January 2008 we have extended slip stacking to
include the beam to NuMI. A total of 10 Booster batches
are now slipped stacked together in MI resulting in 5
double intensity batches. After recapture an additional
Booster batch in injected. This way the total Booster
batches to NuMI is increased from 5 to 9. A mountain
range picture of the multi-batch slip stacking is shown in
Figure 1. The beam power to the NuMI target is expected
to increase to 320 KW from 190 KW while the total beam
power at 120 GeV will be increased to 400 KW.
Following the end of the collider run we plan to use the
Recycler storage ring for slip stacking while the MI is
accelerating, increasing the final 120 GeV beam power to
700KW.
Figure 1: Mountain Range Picture of multi-batch slip
stacking. The horizontal axis is time across the MI
azimuth in nsec and the vertical axis time in machine
turns.
UNDERSTANDING AND CONTROLLING
LOSSES
Most of the losses are coming from slip stacking. With
95% efficiency if all of the losses were distributed
uniformly around MI they correspond to about 0.5W/m
average loss. Unfortunately the losses are localized and
need to be controlled. Three types of losses were
indentified and are currently being addressed.
1) Un-captured beam loss. The beam that is not
captured after the slip stacking process is not accelerated
and is getting lost when it hits the momentum aperture at
9.1 GeV. This loss is the largest in percent; 3-3.5% out of
total loss of 5%. In order to address this loss a two stage
collimation system was installed in MI [3]. This system is
now operational and we have achieved collimator
efficiencies 97% or better [4].
2) Injection kicker gap loss. During slip stacking some
beam is spilling out in the gap left open for injecting new
batches. This loss is localized at the injection kicker area
___________________________________________
*Operated by Fermi Research Alliance, LLC under Contract No. DE-
AC02-07CH11359 with the United States Department of Energy.
# ioanis@fnal.gov
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MI-100. In order to address this loss we are building
gap clearing kickers that will be fired just before the
injection kickers and send the beam left in the gap in the
MI abort. The construction of the kickers is under way
and we currently planning to install them in the Summer
of 2009.The kickers are expected to be operational in
early 2010 when the new kicker building required to
house the power supplies and cooling systems is ready.
3) Beam in the extraction kicker gap. After the slip
stacking process there is some beam captured between the
batch for pbar production and the train of NuMI batches.
This beam is accelerated to 120 GeV and is getting lost
when the batch to the pbar target is extracted. Even if this
loss in percentage is very small (0.2%-0.3%) since it
happens at 120 GeV it represents an important fraction of
our power loss. It is concentrated at the extraction area for
pbar production MI-520.
The bunch by bunch transverse damper [5] is used to
reduce the beam in the gap between the batch used for
pbar production and the batches used for NuMI. The
beam in the gap is anti-damped by driving the damper at
the tune value. Since the damper is limited in voltage the
anti-damping is most effective at low energies. Recently
we were able to reduce this loss an order of magnitude by
adding another kicker.
Figure 2: MI loss plot. The vertical axis is the integrated
loss at each MI beam loss monitor at the end of each cycle
(in log scale). Most of the losses are concentrated at the
collimator region 229-309. The injection kicker gap loss
(104-106) is also evident.
CURRENT STATUS
Since January 2008 when we switched to the multi-
batch slip stacking we have made great progress in
increasing the MI intensity and beam power. A typical
plot of the MI intensity with the percentages of the
various losses is shown in Figure 3. The beam intensity to
the NuMI target has been increased by 30% and the MI
beam power at 120 GeV has reached 340KW; 85% of the
design goal of 400KW. We are now running routinely
with beam power greater than 320 KW (Figure 4).
Currently the Injection kicker gap loss is preventing us
from further increasing the beam intensity.
Figure 3:Typical plot of the MI beam intensity (green).
The blue line shows the sum of the injected beam, the red
trace indicates the injection kicker gap loss and the purple
trace shows the lost beam.
Figure 4: MI beam power at 120 GeV since August 10
2008. The gap in the middle represent a period where the
NuMI horn was changed.
The MI high power operation has also been very
reliable. From January1, 2008 to April 3, 2009 the total
MI downtime was 325 Hrs, i.e. 3.8% of the total running
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time. A pie chart with the sources of the downtime is
shown in Figure 5.
Figure 5: Sources of MI downtime.
700 KW OPERATION (NOVA)
When the collider programs concludes we plan to use
Recycler as proton Injector, accepting beam directly from
the Booster. The Recycler momentum aperture is large
enough to allow slip stacking operation for up to 12
Booster batches injected. Six Booster batches are slipped
with respect to the other six and, at the time they line up,
they are extracted to MI in a single turn, are captured and
accelerated. The MI cycle time can now be reduced to
1.33 sec from 2.2 sec increasing the 120 GeV beam power
to 700KW. Since the power increase comes mainly
because of the cycle time reduction and not the increase in
MI intensity no new problems with beam instabilities and
transition crossing in MI are expected. The MI collimators
are designed to handle the additional power.
The main elements of this upgrade are outlined below:
• New Injection line from Booster into Recycler
• New Extraction line from Recycler to MI.
• New Injection, Extraction and Abort kickers for
Recycler.
• New 53 MHz rf system for slip stacking.
• New Low Level rf system for Recycler.
• Two extra rf cavities in MI (from spares).
• MI quad power supply upgrade.
• Cooling and power supply upgrades in the NuMI
beam line.
• New NuMI targets and horns.
All these modifications are scheduled to be in place in
2012 and the NOvA detector will be ready for beam in
2014.
2.1 MW OPERATION (PROJECT X)[6]
As part of the Project X upgrade, the Fermilab’s Proton
Source will be replaced with an 8 GeV superconducting
Linac operating at 5 Hz and delivering 1.6E14 H- ions per
pulse. The H- ions are stripped at injection into the
Recycler in a manner that “paints” the beam both
transversely and longitudinally to reduce space charge
forces. Following the 1.25 ms injection, the proton beam
is moved off the stripping foil and is transferred in a
single turn into the Main Injector where are accelerated to
120 GeV and fast extracted to a neutrino target. The 120
GeV MI cycle takes 1.4 sec, producing 2.1 MW of beam
power. MI will be able to provide the same beam power
throughout the energy range 60-120 GeV by adjusting the
cycle time. Accelerating 3 times the intensity required for
NOvA represents a major challenge for MI. We have
developed an R&D program to address the major
issues[7]. Work has already started in designing a new MI
rf system, simulating and measuring electron cloud effects
[8],[9] and designing a transition jump system In addition
we plan to install a 3ft long piece of pipe coated with TiN
during this summer shutdown for electron cloud studies.
REFERENCES
[1] Sam Childress, “The NuMI Beam at Fermilab:
Successes and challenges” proceedings of HB2008.
[2] K. Seiya et al. “Multi-batch Slip Stacking in the Main
Injector at Fermilab” PAC’07, Albuquerque, New
Mexico, June 2007, p. 742-744
[3] Bruce Brown, “Collimation System for Beam Loss
Localization with Slip Stacking Injection in the
Fermilab Main Injector” proceedings of HB2008.
[4] Bruce Brown et al. “Fermilab Main Injector
Collimation Systems: Design, Commissioning and
Operation ” these proceedings.
[5] P. Adamson et al. “Operational Performance of a
bunch by bunch Digital Damper in the Fermilab Main
Injector” PAC’05, Knoxville, Tennessee, June 2005,
p. 1440-1442.
[6] http://projectx.fnal.gov/
[7] http://projectx.fnal.gov/RnDplan/index.html
[8] Nathan Eddy et al. “Measurement of Electron Cloud
Development in the Fermilab Main Injector Using
Microwave Transmission” These proceedings.
[9] Miguel Furman et al. “Status of Electron-Cloud
Build-Up simulations for the Main Injector ” These
proceedings.
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