LARP Rotatable Collimator Status

1
LARP Rotatable Collimator Status
US LHC Accelerator Research Program
BNL - FNAL- LBNL - SLAC

• 02 April 2009
• Phase II Collimation Conceptual Review - CERN
• Jeffrey C. Smith/SLAC
• with
• John Amann, Gene Anzolone, Lew Keller, Steve
  Lundgren, Tom Markiewicz, Reggie Rogers, Liling
  Xiao /SLAC

2
Outline

• Mechanical Overview
• Current construction status
• SPS and TT60 Tests
• Installation schedule

3
Mechanical Overview
4
LHC Secondary Collimator Upgrade Requirements

• Current graphite collimators are very robust but
  low Z means poor collimation efficiency.
• Higher Z secondaries required for design beam
  intensity
• This means some type of metal
• SLAC solution is Glidcop (CU/AL alloy)
• High Z, good thermal conductivity, good
  structural rigidity
• In order to withstand without thermal
  deformation
• Transient bursts corresponding to 1.4 beam
  loss in 10 sec
• beam lifetime t 12 min or Energy loss rate
  450kW
• Up to 12 kW per jaw, abort if lasts gt 10 sec
• Note that steady state engineering loss rate is
  5x less (1 hour beam lifetime)
• Long term beam loss rate another x10-20 less
  (10-20 hour beam lifetime)
• Must be recoverable from Accident Scenario
• Beam abort system fires asynchronously with
  respect to abort gap
• 8 full intensity bunches impact collimator jaws
• 1 MJoule incident energy

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LHC Phase II Base Concept Glidcop Jaw - Cu
Mandrel wrapped with CuNi coil Hollow Glidcop
Hub / Molybdenum Shaft with 2mm gap from Mandrel
20 facets

• Beam spacing 136mm OD
• Length 1.47 m flangeflange
• 930mm overall
• 2 x 38mm 15 tapers
• 854mm long facets

Glidcop Cu Mo
Cu coolant supply tubes twist to allow jaw
rotation
Helical cooling channels 23mm below surface with
16m long 10mm square CuNi tube
Hub area
Cantilever Mo shaft _at_ both ends
2mm gap between shaft OD and mandrel ID
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RC Prototype Design (for SPS)
beam
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SLAC design details
Tank geometry allows a 60mm facet-to-facet gap
in fully retracted Jaw position
Ratchet Gear Drive
BPM assemblies at each end are fiducialized to
Collimator
LHC IR7 Style BPM Buttons 4 per end
Existing Jaw (copper)
RC-1 Jaw under const. (Glidcop)
Flex Support
Ferrite could mount to Base Plate facing Jaw facet
Drive Mechanism
Base Plate
8
Proposed Collimator/BPM Aperture Dimensions

• Odd BPM aperture may be necessary depending
  on location in SPS
• 60.5 mm round aperture in LHC

9
BPM Design Details

• BPMs are required to expedite the alignment of
  the jaws with the beam
• Right now beam loss monitors are used to align
  the jaws gt slow!
• Just need BPMs to have a resolution equal to or
  greater than the flatness of the jaws, or 25
  microns gt rather relaxed requirements for a BPM.
• BPMs planned for each end of Tank
• Standard LHC BPM buttons and processing
  electronics planned to be used.
• Already designed and ensures good compatibility
  with LHC controls
• Fiducialization with jaw surfaces should not be a
  problem
• LVDTs and possibly capacitive distance sensors
  will measure jaw position
• Expected to be within a couple microns
• Long term stability of fiducialization should be
  within 10 microns

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Jaw Rotation

• Jaw rotation after accident will be performed
  with a ratcheting mechanism with Geneva gear for
  precision rotation
• 512 ratchets per facet rotation
• Ratcheting performed by over-retracting the jaw
  so that ratchet hits actuator.
• No extra motor or linear actuators required,
  simply use motors for moving jaws in and out

11
Impedance Considerations

• Transverse impedance dominated by resistive wall
  of jaws.
• Two 1 m long copper jaws 1 mm away from beam
  dominates impedance
• Geometric component small compared to resistive
• Impedance of sliding contact also negligible with
  rhodium plated SS balls
• Only issue right now with impedance is trapped
  modes
• We have a large cavity with many nooks and
  crannies.
• Could cause heating of chamber
• High Q factor of modes may result in multibunch
  instabilities

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Trapped Modes in Omega3P
Liling Xiao
x
Engineering model
Meshed 1/2 Simulation Model

• Studies have begun with new updated and more
  accurate mesh model of collimator
• Can only use 1 plane of symmetry so simulations
  will take some time...
• Calculate the longitudinal modes heating effect
  at the worst case for jaw gap60mm
• Calculate the transverse modes kick at the worst
  case for jaws with gap2mm.

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Transverse Trapped Modes
Liling Xiao
RF Parameters for fully inserted jaws, gap2mm
Kick
Q0
When the two jaws are fully inserted with
gap2mm, the kick factors are highest due to the
strongest Ey between the two jaws.
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Ferrite-Loaded Collimator
Liling Xiao
Damping Longitudinal Trapped Modes w/ Ferrites
TT2-111R Ferrite Tile t2mm
t
e10-j0.2, µ2-j10
Jaw fully retracted gap42mm (old design)
Attaching ferrite tiles on vacuum wall above the
top and bottom of the jaws can strongly damp the
longitudinal trapped modes.
15
RF Image Current Foil Assembly

• This surface mounts to
• bearing race
• Foil only needs to shadow rotation drive from
  beam

Axial load on Rhodium coated 1mm diameter
Stainless ball bearing provides desired contact
resistance of less than 1 milliohm
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Current Construction Status
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Prototype for SPS installation

• One jaw, RC0, already built last year for use
  with thermal tests
• Used to measure deformation under heat load
• Agreement very good with ANSYS simulations
• Should work fine for SPS tests in spite of
• Made of Copper (not Glidcop)
• Has heater groove and thermocouple holes
• New jaw RC1 currently being constructed
• Glidcop surface
• Very similar design to first jaw
• Just ac couple tweaks for ease in fabrication

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First Jaw (RC0) Preparation

• First prototype jaw from thermal tests last year
  is being modified for installation in SPS
  Prototype.
• Two Moly half-shafts and half-hubs
• modifications required at ends to mount to
  current stainless jaw supports
• OFE copper jaw material, with 20 facets
• Groove cut in one facet for heater blocks
• brazed from 16 ¼-round blocks
• Facet surface finish and flatness good lt 25
  microns, but expect even better in next
  iterations

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Second Jaw (RC1) status

• RC-1 jaw in fabrication (see later slides and
  photos)
• One piece shaft assembly
• Jaws from 5 fully-round Glidcop cylinders
• Material available to make two more full length
  jaws for a total of four (two full collimators)
• Two more grooved OFE Copper mandrels identical to
  that used in RC-1
• Enough raw Glidcop material to make two more full
  length jaws

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Molybdenum Shaft Construction
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Mandrel Winding completed
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Mandrel Winding completed
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Cooling tube to Mandrel braze completed
Brazing resultslooks good
Braze prep.
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Final Mandrel Machining
Mandrel ready for jaw surfacecylinders for final
brazingwhich will happen very soon
Final Machining
First cuts
Jaw surface cylinders
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End Supports/hardware completed
A-286 SST Supports for 2 Jaws
Concept view of appropriately flexible Support
shown with Shaft mounting hardware
Ceramic bearings roll in V groove created by
the 2 45 degree chamfers on these parts
Cooling tube exits here
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More Parts are real!
Rotator parts and shaft hardware
5 Jaw Cylinders final machining
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Other Recent Progress

• Vacuum chamber and base plate drawings finished
  and parts out for fabrication and/or ordered
• First Jaw (RC-0) undergoing final machining to be
  ready for insertion in full device
• Second Jaw (RC-1) mandrel finished, Jaw cylinders
  being plated and prepared for brazing
• Documentation
• Traveler Documents to be delivered with
  collimator are being assembled, will describe in
  details all aspects of device
• Acceptance Sheet draft created
• QC and tests to be performed by SLAC and CERN
• Interface Document draft created
• Specifies what will be provided by SLAC and CERN
  for installation in SPS

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Long term durability ofRotation Mechanism

• Test Rotation Mechanism in vacuum and bake-out
• Will anything lock up after heat cycle?
• Run for long time, 20,000 cycles to confirm
  mechanism performs in vacuum

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SPS and TT60 tests
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Strategy for Prototype Tests

• Current plan
• Full mechanical prototype with BPMs tested in SPS
• After off-beamline mechanical, RF vacuum tests
  at SLAC CERN
• Goals of SPS test
• Demonstrate mechanical operation of device in an
  active machine environment.
• Demonstrate ability to align jaws with BPMs
• Measure impedance characteristics of full device,
  both broad-band and trapped modes.
• A robustness test to study damage due to direct
  beam hit
• TT60 a beam irradiation facility on an SPS
  extraction line
• of
• A simple copper block
• The RC-SPS device
• No LHC prototype test although a 3rd generation
  RC may be constructed

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Extent of molten material spray?

• Here is a miss-steered beam in the TT40 transfer
  line from the SPS to LHC.
• Comparable in energy to what we may experience
• How far will the material spray?
• Will it coat all surfaces?
• Will it drip?

SLAC beam hit test
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TT60 Beam Impact tests

• The TT60 Extraction line off the SPS is planned
  to be converted into a beam impact test facility
• up to 2.4 MJ or greater than the collimator
  accident scenario

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Installation Schedule
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SPS Installation Schedule

• Project Milestones are established to guide
  completion of Prototype Collimator for late 2010
  SPS Installation
• Confirm SPS location with aperture and stay-clear
  specifications, instrumentation/electrical/water
  available
• Collimator is planned for preliminary SLAC
  testing starting January 2010
• Test mechanicals
• Jaw motion, jaw rotation
• precision fiducialization wrt BPMs
• Vacuum checkout
• Bench-top BPM and impedance measurements
• Confirm Geometric is small
• Measure Higher Order Trapped Modes
• Shipment to CERN by August 2010
• They take over performing their own check-out
  procedure
• Interface for installation in SPS
• Tests in early 2011

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TT60 Installation Schedule and Beyond

• TT60 HiRadMat test facility installation expected
  Q3 2011
• Current intention is to use the same prototype as
  in SPS
• Plan is to begin with a simple copper block test
• Hit a copper block 1m long and see what happens
• Adjust RC prototype tests accordingly
• No LHC Prototype test planned
• It is assumed SPS and TT60 tests will fully
  demonstrate RC performance
• Technology choice for Phase II collimation some
  time after TT60 tests

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Thank You

• Special thanks to our SLAC and CERN colleagues
  for numerous discussions and recommendations