CRYSTAL COLLIMATION EXPERIMENT AT THE TEVATRON Nikolai Mokhov Fermilab

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CRYSTAL COLLIMATION EXPERIMENTAT THE TEVATRON
Nikolai MokhovFermilab
US LHC Accelerator Research Program
bnl - fnal- lbnl - slac
LARP Collaboration Meeting SLAC October 17-19,
2007
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OUTLINE

• Introduction
• Mission Statement
• Crystal Collimation
• Studies at Tevatron
• Proposal for Experiment
• Tevatron Study Plan
• Deliverables
• Collaboration, LOI and Meeting at Fermilab

See also next talks by Dean on measurements and
findings at Tevatron, and by NM on status of the
proposal and contributions
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INTRODUCTION

• The promise of bent crystal channeling technique
  for beam halo collimation at high-energy
  colliders was recognized at the SSC in 1991. A
  bent crystal, serving as a primary element,
  coherently bends halo particles onto a secondary
  collimator. First successful measurements were
  performed at IHEP in 1998 for 1 to 70 GeV
  protons. Crystal collimation was studied at RHIC
  in 2003. Experiments by IHEP, CERN, BNL and FNAL
  have shown that crystals are heat- and
  radiation-resistant. Deflection efficiency
  deteriorates at about 6/1020 p/cm2 rate.
• Based on realistic modeling (1999, 2003), it was
  proposed to implement a bent crystal into the
  Tevatron collimation system. First measurements
  (2005-2006) were quite encouraging.

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MISSION STATEMENT

We propose an experiment at Fermilabs Tevatron
to measure the predicted improvement in
collimation efficiency that could be obtained by
replacing amorphous primary collimators with bent
crystals. Considering the unique possibility
provided by the Tevatron Collider, and having
already established fruitful collaborative
efforts on crystal characterization, tests and
use for collimation, we propose to test and
confirm models of multi-turn dynamics with
crystals by exploiting channeling and newly
understood phenomena such as volume reflection as
well as to further study collimation.
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MISSION STATEMENT (contd)

In our view, this is a necessary first step to
being able to evaluate an engineering
implementation of this technique in LHC that - if
proven - promises an enhanced performance of the
LHC collimation system with a reduced impedance
and easier implementation for heavy-ion beam halo
cleaning. There is also an interest in crystal
channeling from the ILC and Muon Collider
communities.
Collimation including crystal channeling is
the first item on Oliver Brunings Accelerator
Physics wish list for LARP
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Two-Stage Collimation with Target and Crystal
Courtesy R. Assmann
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BENT CRYSTAL FOR TEVATRON COLLIMATION

• We have shown (PAC99) and later confirmed (2003)
  that implementation of a silicon bent crystal
  instead of amorphous primary collimators
  (targets), can improve the Tevatron collimation
  efficiency defined then as a reduction of beam
  loss in CDF - by a factor of
• 2 with one (horizontal) target replaced, and with
  contribution from beam-gas scattering
  unsuppressed
• 3 with one (horizontal) target replaced, and with
  contribution from beam-gas scattering suppressed
• up to a factor of 4 to 6 for the 2-plane
  collimation.

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REPLACING PRIMARY COLLIMATOR WITH CRYSTAL AT 5 s
(2005)
The primary H-collimator (D49 tungsten L-shaped
target) is before the dog-leg at bH96 m, D2.3
m. The crystal is in the dog-leg at bH73 m,
D2.5 m, about the same phase advance wrt
secondary collimators.
O-shaped 110 Si-crystal 5-mm L, 5 mm H, 1mm
V critical angle 5 mrad bending angle 439
mrad miscut angle 465 mrad
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980-GEV BEAM CHANNELING DATA vs THEORY
Oct. 6, 2005 By Dean Still
Jan. 31, 2006
With E03H out, LE033C BLM is proportional
to nuclear interact. rate in crystal
Channeled beam peak width is 224 mrad (rms)
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COMPARING EFFECTS OF PROTON HALO LOSSES FOR BENT
CRYSTAL AND TUNGSTEN TARGET
Crystal aligned at peak (118 mrad)
CDF
E03 BLM
PIN
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OUTCOME OF 2005-2006 MEASUREMENTS

• When using the crystal
• A factor of 2 is achieved in better reduction of
  CDF losses a half a ring or three kilometers
  downstream (in agreement with modeling).
• The secondary collimator could remain further (1
  mm or so) from the beam thus reducing impedance.
• Nuclear interaction rate in the crystal was 2 to
  3 times lower compared to the amorphous target,
  reducing proportionally irradiation of the
  downstream components.

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VOLUME REFLECTION
This work at RHIC/FNAL uncovered the importance
of the long neglected coherent crystal effect
predicted at Tomsk two decades ago, volume
reflection.

• Contrary to channeling, which is extremely
  sensitive to beam-crystal alignment (10-mrad
  level in Tevatron), VR is a much higher
  acceptance effect promising as a collimation
  tool for TeV beams as well as for Recycler
  (Project X) and a muon collider!
• The IHEP/PNPI/RHIC/FNAL investigation has helped
  to spark interest in the volume reflection
  process including a fast track investigation in
  the H8 400-GeV p beam at the CERN SPS in the fall
  of 2006 (W. Scandale et al.). That precision
  investigation has produced a spectacular
  confirmation of volume reflection (97
  efficiency) and also developed tools to
  characterize crystals that could potentially
  serve as LHC collimators.

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Towards Crystal Collimation Collaboration

• Encouraged by these results and recent crystal
  developments, and aiming at a high-performance
  collimation vital for the LHC, crystal
  collimation collaboration has non-formally
  started in December 2005
• Better crystals characterized mechanically,
  optically and with beams
• Beam tests at the SPS extracted beams (400 GeV)
• Crystal collimation experiment in the SPS ring
• Support crystal collimation expt at Tevatron to
  guarantee its success
• In Dec. 2005, consensus on the Tevatron
  experiment was reached
• The old crystal needs to be replaced with the
  optimal characterized one with a bending angle of
  about 0.15 mrad.
• Dedicated beam diagnostics must be implemented to
  see the deflected beam (phosphorous screen,
  crawling wire, etc.), in addition to excellent
  global beam instrumentation in Tevatron.
• The characterization and knowledge of the
  additional crystal parameters (miscut angle,
  surface perfection) are vital for success of the
  studies. The crystal preparation, etching,
  characterization and beam tests will be done with
  INFN and INTAS money.

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INSTALLING NEW CRYSTAL IN TEVATRON (1)

It turned out that the parameters of the BNLs
crystal used in the first studies were not
optimal for the Tevatron conditions. Express
simulations by V. Biryukov, have shown that the
collimation efficiency can be noticeably improved
by replacing the original 5-mm long crystal with
a shorter one which has a smaller bending angle.
Of course, the optimal parameters depend on
details of the lattice, collimation system
configuration and beam loss region layout, but
the trends shown convinced us to replace the
original crystal with a new shorter one.
Moreover, we also wanted to investigate a new
technology developed to improve crystal
performance. A custom crystal was prepared and
characterized at Protvino and Ferrara 3-mm L,
1-mm W, 150 mrad bending angle, strip, chemical
etching. It replaced the old one during the 2006
Tevatron long shutdown.
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INSTALLING NEW CRYSTAL IN TEVATRON (2)

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PROBLEMS IDENTIFIED IN 2007

1. Angular reproducibility of inchworm mechanics
2. Noise in the PIN and BLM detectors
3. Beam diagnostics is insufficient to measure
   channeled and volume reflected beams
4. Need full realistic multi-turn simulations for
   the current lattice and crystal/collimator
   configuration to confirm 1999-2003 results,
   justify a choice of a short crystal and identify
   locations for comprehensive beam diagnostics
   (single particle tracking capability?) and second
   (vertical) crystal/goniometer

In next talk, Dean will give you details on
(1)-(3) as well as on room in the Tevatron for
installation of new hardware in 2008
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PROPOSAL FOR EXPERIMENT AT TEVATRON IN 2008-2009

Aiming at the high-performance collimation vital
for the LHC, considering a unique possibility
provided by the Tevatron collider (before its
shutdown for collider physics), and having
already established fruitful collaborative
efforts on crystal characterization, tests and
use for collimation, we propose an experiment at
the Tevatron to test and confirm models of
multi-turn dynamics with crystals by exploiting
channeling and volume reflection.
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TEVATRON MEASUREMENT GOALS

• Channeled beam
• Volume-reflected beam
• Beam loss and radiation levels downstream of the
  crystal setup
• Beam loss rate in the B0 (CDF beam-halo monitors)
  for 1- and 2-plane collimation
• Possible deformation of the crystal or crystal
  holder during a vacuum baking process.
• Attempt to study crystal damage shock and
  integrated dose.
• () Add dedicated beam diagnostics
• Quantitative measure of collimation efficiency
  improvement is reduction of (3) primary LHC
  concern and (4).
• We are going to simulate the deflected beam loss
  in the Tevatron and LHC (in collaboration with
  IHEP and CERN colleagues). Consistency with the
  current secondary collimator and absorber layout
  is of a concern here need simulations and
  optimizations.

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FROM ONE-PLANE TO FULL COLLIMATION

The first system collimated only in the
horizontal plane. A comprehensive system would
also collimate in the vertical plane as well as
in dispersion for off-momentum particles. These
results are multiplicative, so the halo scraping
could be improved by up to a factor of eight, as
shown in early simulations. We aim at the full
system in Phase II of this proposal.
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TASKS End of 2007 (TeV study time 4 hrs)

1. Decide on a need to replace the goniometer and
   existing crystal with the ST4 crystal that was
   characterized in the September 2006 H8 experiment
   at CERN.
2. Perform EOS studies in early December.
3. Initiate detailed simulations of collimation
   system performance with a single strip crystal in
   the realistic Tevatron lattice for both channeled
   and volume-reflected beams.
4. Work out a plan on beam diagnostics improvement
   and specify new goniometer for 2009 beam studies.

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TASKS-2008 (three TeV study sessions)

1. Build improved beam diagnostics system and new
   Ferrara goniometer.
2. Develop new strip and multistrip crystals.
3. Complete EOS and proton-only store angular scans
   with the crystal chosen in 2007.
4. Perform detailed simulations for a complete
   two-plane crystal-based Tevatron collimation
   system.
5. Initiate tests to provide information about the
   possible deformation of the crystal or crystal
   holder during a vacuum baking process (up to 200
   degrees).
6. Investigate the possibility of a crystal damage
   experiment where crystals and instrumentation for
   assessing dose rates could be placed in the
   Fermilab beams. Once enough beam is integrated on
   one crystal, it should be moved back to CERN for
   H8 beam line characterization.

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GOAL-2009

• Demonstrate efficiency of a well-prepared bent
  crystal collimation system for 2 planes with
  channeled and volume-reflected 1-TeV beams at
  least for two crystal types (single and
  multi-layer) in comparison with tungsten target
  results.
• This plan will be adjusted based on 2007-2008
  measurements.

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TASKS-2009 (TeV study time 6 shifts 48 hrs)

• Install New Hardware
• Remove E01 collimator to replace with vertical
  crystal assembly
• Crystal, goniometer, instrumentation tunnel
  installation
• 2. 150-GeV Beam Tests (1.25 shifts)
• Test BLM response, inchworm and channel the beam
• Debug all motion control and instrumentation
• 3. 980-GeV End-of-Store Beam Studies (4.75
  shifts)
• Find and characterize channeling (V-plane)
• Collimate channeled beam (V, H)
• Collimate volume-reflected beam (V, H)
• Attempt full channeled collimation (VH)
• Attempt full volume-reflected collimation (VH)
• Repeat with another crystal type

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DELIVERABLES

• Realistic simulations of multi-turn dynamics with
  crystals by exploiting channeling and volume
  reflection, benchmarked in measurements at the
  Tevatron.
• Conclusive data and directly relevant input for
  decisions on a possible upgrade path for LHC
  collimation improved collimation efficiency,
  reduced impedance and irradiation of downstream
  components in a quantitative agreement with
  corresponding calculations, and quantitative
  answers to the questions on damage limits and
  sensitivity analyses.
• 3. Crystal technology, process, hardware
  (goniometer etc.) instrumentation most suitable
  for 2-plane collimation of LHC beams, transferred
  to CERN.

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COLLABORATION, LOI AND MEETING ON DEC. 6-7
We received a very encouraging support from the
LARP, Fermilab, CERN and INFN management, and
also from the August Accelerator Advisory
Committee at Fermilab (see my next talk). It was
proposed that we prepare a Letter-of-Intent
(LOI), Crystal Collimation Experiment at the
Tevatron and form an official collaboration. A
zero-order draft Discussion Document can be
downloaded. 15 Institutions expressed an interest
to join with quite substantial contributions in
some cases. We are planning a first organizing
meeting at Fermilab on December 6-7, 2007, with a
complete LOI draft and organizational proposals
distributed before that.