Design Choices for the cold LHC-BPMs

1
Design Choices for the cold LHC-BPMs
CARE-N3 networking for High energy, High
intensity Hadron beams Lueneburg - 30th
November -1st December 2006 3rd half day Cold
BPM technology Christian Boccard, (CERN AB/BI)
2
Outline

• Design parameters and Choices
• BPM Types in the LHC
• BPM Integration
• Components
• Design , Specification, Integration, Construction
  Installation
• Bodies
• Buttons
• Striplines
• Cold Cables
• Cryostat feedthroughs
• BPM Installation Tests
• Summary

3
Design Parameters

• BEAM STRUCTURE AND INTENSITY
• LIFETIME OF THE LHC
• INSTALLATION SCHEDULE
• OPERATION COSTS
• NUMBER OF THERMAL CYCLES
• NUMBER OF QUENCHES
• OPERATIONAL SCENARIO
• ACCESS TO EQUIPMENT
• INTERVENTION ON THE COLLIDER
• COOLDOWN TIME
• INTERFACE AND ENVIRONMENTAL CONDITIONS
• VACUUM
• PRESSURE
• RADIATION DOSE
• ACTIVATION
• ELECTRICAL WITHSTAND

LHC Project Document No. LHC-PM-ES-0002.00
rev.1.1 EDMS Document No. 100513.00
4
Early choice

• Buttons . or Striplines ?

Simple robust More expensive to
build Removable from outside of chamber More
parts less reliable ? Less cumbersome Require
precise machining Well adapted to LHC short
pulses More sensitive but more heat load No
effect on longitudinal impedance
Final choice (1996) was Buttons for the arcs (and
Directional Couplers around experimental areas)
5
How many BPM Types in the LHC ?
Cold BPMs Arc Beam Position Monitor (Arc type
DS) 864 Special BPM for end of arcs
12 BPM with Rotated Beam Screen
20 Enlarged Aperture BPM
36 Directional Stripline Coupler
8 Combined pick-ups for RF 16 Warm BPMs Warm
LHC BPM adapted for Elliptic shape
16 Enlarged Warm BPM 28 Enlarged
Warm BPM with Quick flanges 16 Diam 80
Warm BPM for Roman Pots 12 Warm
Directional Stripline Coupler
16 Beam Dumping System BPM Aperture 80mm for
Interlock System 8 BPM Aperture 130mm for
Interlock System 8 Other Special BPMs Trigger
for Experiments 8 Long Striplines
for Transverse Damper, Tune Chromaticity
Measurements 14 RF Wideband Transverse pick-up
2 Total 30 Equipment Codes
1092
RF BI
Dump
Cleaning
Cleaning
6
BPM Integration
7
BPM Integration
BPM are housed in the Technical Service
Module Must share the crowded area. BPM used
for Interconnect and VAC responsibility change
with function. BPM became a Vacuum component
when welded to the beam screen.(BPMs are used to
feed beam Screen capillaries with super fluid
helium at 1.9 K ) Then became an Interconnect
component when welded to the SSS Exceptions
require same amount of work !
8
Integrationexperience from arc

• Tooling development of the monolithic first BPM
  for Arcs was lengthly and costly.
• Later the design of Enlarged BPM and Coupler
  evolved to a modular design basis.
• To standardize components and tooling.
• Re-use of VAC
• Plug-In module from dipoles

Stripline Coupler
9
Components
10
Beam Position Monitor Body

• Tight mechanical tolerances nice but
• should be maintained during production
• Machining cost is proportional
• 3 axis Dimensional checks are also expensive
• Help to design ANSYS 3D analysis of temperature
  or mechanical constraints.
• Material Specify forged austenitic stainless
  steel of type AISI 316LN
• Up to now, 50 leaks found in LHC (not yet on
  BPMs) due to macro-inclusion in material. Can
  affect thickness up to some milimeters.
• (A new CERN specification will replace 1001-Ed.
  3-02.08.1999)
• Electroplated inner copper layer of the BPM body
  is 100 um ? 20 um (for longitudinal impedance)
• witness samples are required to assure clean
  material and Copper plating quality, e.g.
  adherence, blisters.
• nickel not allowed, use gold strike.
• Welds should be re-qualified regularly during
  production.

Deformation contours due to Helicoflex washers
surface pressure
11
Button Feedthoughs

• The only VAC chamber non welded component !
  (Helicoflex gaskets)
• Glass-metal preferred to Brazed Ceramic
• Choice was done after Invitation to Tender and
  test of prototypes
• Systematic tests done by contractor
• Tests and pairing at CERN
• vacuum tests mechanical data on samples
• AB/BI measures final capacitance on all buttons
• Pairing is done on amplitude response

12
Striplines

• Insulator Spec UHV, cryo temp, radiations,
  losses -gt ultem
• Coupler Feedthroughs same technology as buttons
• Gold - Rhodium Sliding contact do not stick at
  cryo temp
• Electron Beam welding of a 2mm pin on washer
• Electrode gap not easy to trim
• achieved directivity 28dB at 70MHz
• Risk to have 50um error from cross-talk for 25ns
  spaced beam

• Cryo tests were funny

13
Cryogenic Coaxial Cables

• Strong specification
• The cables must be cryogenically compatible,
  radiation resistant, mechanically preformed ,
  have low heat leak and VSWR, and most important,
  have good electrical stability.
• electrical length difference less than 10ps for
  the 4 cables of each BPM
• In addition the cable must be electrically stable
  when subjected to the above mentioned radiation,
  flexing, and temperature gradients.
• Dielectric materials under consideration include
  silicon dioxide, magnesium oxide, ultem
  (polyimide)
• Contract awarded to KAMAN for 4250 units in 2001
• Leading to the choice of silicon dioxide foam
  (SIO2) dielectric
• MEGGITT takeover of KAMAN
• Gold reference used to ease production and
  logistic
• Integration is a challenge
• First prototype was not mountable in SSS
• gt new design produced
• Forming not as accurate as specified
• Additional Configurations
• Design of 5 different configurations required for
  other SSS types
• cabling of BPMS in Q2 is done in the tunnel
  during interconnection
• Connector nuts are locked by twisted wires

BPMS in FNAL Q2
14
Warm Cable Cryostat Feedthroughs

• Spec insulation vacuum, warm temperature, low
  VSWR
• Use of NBR (Nitrile Rubber) gaskets in place of
  ceramic welded connectors. (Factor 10 in price)
• Measure of relative phase and detection of
  crossed wires
• Simple test of wiring included in assembly work
  package

15
BPM Installation
16
BPM Installation

• Forms part of a Work Package
• Sub-contracted for the 480 SSS magnets
• Procedure
• Weld beam screen to BPM body (contract)
• Select button feedthroughs for mounting (BI)
• Mount button feedthroughs (contract)
• Perform leak test (VAC)
• Insert BPM/beam screen assembly (contract)
• Spot weld BPM to support (contract)
• Measure and adjust position and tilt of BPM
  (Survey)
• Weld BPM to support (contract)
• Measure position and tilt of BPM (Survey)
• Install and connect BPM cables (contract)
• Mount warm feedthrough on cryostat (contract)
• Perform electrical test of BPM system (BI)
• Worries
• ICS contract started slowly in December 2003
• Technology transfer repeated many times

17
Summary

• Schedule
• All hardware received (just) in time
• Installation nearing completion
• (840 BPMs assembled in SSS)
• Budget
• currently within budget
• Cables budget was under estimated
• Design
• Experience (from a previous machine) is very
  important
• Specification
• material issues to be treated at the project
  level
• Integration
• We learned during the project.
• What I would change if I would do it once again
• Construction Installation
• Always slower then planned

18
Thank you !
And Seasons Greetings