Irradiation Damage in LHC Beam Collimating Materials

1
Irradiation Damage in LHC Beam Collimating
Materials

• N. Simos (BNL) N. Mokhov (FNAL)
• LARP Collaboration Meeting
• SLAC
• October 17-19, 2007

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LHC Collimator Material Irradiation Damage
Studies to date

• Carbon composites (including the 2-D carbon used
  in Phase I) exhibit stability in their thermal
  expansion coefficient in the temperature range
  they are expected to operate normally during
  PHASE I.
• Carbon composites experience dramatic change in
  their CTE with increased radiation BUT are able
  to fully reverse the damage with thermal
  annealing
• Carbon composites also showed that with increased
  proton fluence (gt 0.2 1021 p/cm2) they
  experience serious structural degradation. This
  finding was confirmed for the family of such
  composites and not only for the 2-D composite
  used in the LHC (recent data on P-bar target at
  FNAL confirm the findings of this study)
• Thermal conductivity loss measured after
  irradiation is a serious problem for these
  composites
• Also experimentally shown, and under similar
  conditions, graphite also suffers structurally
  the same way as the carbon composites (also
  experiences serious thermal conductivity loss)
• Proton radiation was shown to not effect the
  thermal expansion of Copper and Glidcop that are
  considered for Phase II. Reduction in thermal
  conductivity is observed but not anywhere near
  what carbon and graphite sees. Still an issue for
  Glidcop (this is primarily the effect of alloying
  copper with aluminum)
• Encouraging results were obtained for
  super-Invar, Ti-6Al-4V alloy and AlBeMe

3
LHC Collimator Material Irradiation Damage
Studies to date

• Study results have provided key information on
  the choices made thus far in collimating the LHC
  beam and on where should one looks (or avoid
  looking altogether as power is increased).
• The proceedings of the recent Materials Workshop
  and the needs identified, form the basis (along
  with the findings of the study thus far) of what
  to do next.

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LHC Collimator Material Identified NeedsReaching
nominal power and planned upgrades

• Pool of common materials (including Phase I and
  II choices) unable to get the machine to the next
  level
• While design schemes can get more clever, still
  the limitations are dictated by materials
• Identified new materials and composites
  (diamond-metal composites, carbides, etc.) have
  no track record and therefore irradiation studies
  are needed
• As power of the machine increases, gamma and
  neutron fluxes downstream of the collimation
  space becomes more of an issue. Studies attending
  to the effects on materials induced by the
  gamma/neutron cocktail are a wise step forward
• As power increases, shock-induced damage to
  collimator from a full beam is an issue. For
  current matrix of materials and for new pool
  under consideration, response under such
  high-strain rate is unknown
• High-strain rate (shock) on collimator materials
  in un-irradiated state is one thing, BUT shock on
  irradiated materials is a different ball game.

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Collimator and Absorber Materials Workshop
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LHC Collimator Material Identified NeedsWorkshop
Summary (1)

• Interesting new materials include Diamond-Metal
  Composites, CarbonNanoFiber/Cu, etc.
• Not a single solution for all applications and
  problems can be found
• A material matrix to be prepared to point out
  strengths and weaknesses of each material and
  availability in time
• A similar matrix should be prepared for different
  protection devices  and requirement in time
• Collaboration to be launched for mechanical tests
  to be followed by irradiation studies
• Reconsider surface coating to improve RF behavior
• Carefully consider material vs. vacuum behavior
• Qualify materials at high strain rates (change of
  physical properties with strain rate)
• Better qualify anisotropic material
• Should we go beyond the continuum material
  assumption?
• Material optimization must go with design
  optimization (an idea for next workshop?)

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7
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LHC Collimator Material Identified NeedsWorkshop
Summary (2)

• Experimental results and future tests
•         Techniques to detect beam accidents that
  might have damaged collimators / beam absorbers
  the efficiency of the detection methods need
  still to be demonstrated.
•         Material characterization, static and
  dynamic (parameters might change during shock
  impact)
• Radiation issues and irradiation tests
•         great interest of several labs, possibly
  also for ITER
•         further tests at BNL and at Kurchatov
  Institute are planned
•         there are other accelerators where tests
  could be done (Fermilab, Los Alamos, CERN, )
•         there are several factors to radiation
  damage such as particle spectra, time scale of
  irradiation and dose rate
•         concrete plans with time schedules are
  required, who does what?
•         observations of past accidents should be
  simulated with codes

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REQUEST TO LARP

• To further investigate materials already
  identified as promising as well as new exotic
  composites for LHC-like irradiation conditions -
  particles, energy spectra and temporal - initiate
  a task LHC Materials Studies.
• This would be a continuation of the previous
  LARP task, utilizing the unique BNL set-up and
  expertise. Deliverables would also include an
  integrated software package for reliable
  prediction of radiation effects, benchmarked in
  dedicated measurements. The list can be extended
  to materials used in superconducting magnets and
  a crystal collimation setup.
• Estimated load is 0.2FTE 200k/yr for 3 years.
• Interested parties BNL, FNAL, SLAC, CERN, PSI
  GSI

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Plan for LHC Materials Studies

• Damage assessment of materials that thus far
  exhibited good behavior (AlBeMet, Ti-alloy and
  super-Invar) under higher fluences than those
  achieved to-date
• Irradiation damage of new and exotic composites
  (under discussion at CERN) that may get LHC to
  both nominal and upgraded power (diamond-metal
  composites, nano-structured materials, etc.)
• Neutron/gamma irradiation studies (see next 3
  slides)
• Shock (high-strain rate) effects on irradiated
  materials. High-power laser based studies
  utilizing the BNL set-up in the hot area where
  irradiated materials are studied
• Numerical simulation study of damage under normal
  and shock operations by interfacing MARS code
  with non-linear structural analysis codes
  exploring shock-induced behavior. Use laser
  induced shock to benchmark such a numerical
  approach

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Neutron/Gamma Irradiation at BNL
112-MeV protons
At 1012 p/s
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Neutron/Gamma Irradiation at BNL
At 1012 p/s
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Protons, neutrons, photons and electrons in Invar

At 1012 p/s
ltEgt (MeV) Flux (cm-2 s-1) p 23
8.6e5 n 9 1.9e9 g 1
3.2e9 e 1 7.1e6 Here protons
include those from neutron-induced reactions
(recoils etc) Contributions to absorbed dose are
not very different!
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Summary of Results of Interest (to-date)
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Collimation Irradiation Damage Studies

• PRIMARY
• Carbon Composites (2-D and 3-D structure)
• Copper (annealed)
• Glidcop_15AL Cu alloyed with .15 Al (axial
  cut and transverse cut)
• SECONDARY
• Super-Invar
• Toyota Gum Metal
• Graphite (IG-430 isotropic)
• ALSO candidates under consideration
• Ti Alloy (6Al-4V)
• Tungsten
• Tantalum
• Low-Z alloy - AlBeMet

LHC-relevant Materials
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Annealing behavior also exhibited by 2D Carbon !
(fluence 1020 protons/cm2)
Weak direction (orientation normal to fibers)
Fiber (strong) direction
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A threshold exists on carbon composites and
graphite (fluence 1021 p/cm2)P-bar Target
Experience (when enclosed in CC composite damage
was seen with similar fluences)
2-D carbon
graphite
3-D carbon
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Irradiation Effects on Copper (fluence 1021
protons/cm2)
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Irradiation Effects on Glidcop (fluence 1021
protons/cm2)
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Irradiation studies on super-Invar

• invar effect found in Fe-Ni alloys ? low CTE
• inflection point at around 150 C

Effect of modest irradiation
Annealing or defect mobility at elevated
temperature
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annealing of super-Invar
Following 1st irradiation
Following annealing and 2nd irradiation
ONGOING 3rd irradiation phase neutron exposure
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Radiation Damage Studies Other Candidates
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Radiation Effects on Conductivity
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Electrical resistivity ? Thermal conductivity
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Some VERY preliminary results
Glidcop in both axial and transverse directions
( 1 dpa) sees 40 reduction3-D CC ( 0.2 dpa)
conductivity reduces by a factor of 3.22-D CC
(0.2 dpa) measured under irradiated conditions
(to be compared with company data)Graphite
(0.2 dpa) conductivity reduces by a factor of 6