# Presentation: 143316

## Irradiation Damage in LHC Beam Collimating Materials

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

- Proposal - LHC Material Studies

## 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 (> 0.2 10^21 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

- Proposal - LHC Material Studies

## 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.

- Proposal - LHC Material Studies

## LHC Collimator Material Identified NeedsReaching 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.

- Proposal - LHC Material Studies

## Collimator and Absorber Materials Workshop

- Proposal - LHC Material Studies

## LHC Collimator Material Identified NeedsWorkshop 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?)

- Proposal - LHC Material Studies

## Slide 7

- Proposal - LHC Material Studies

## LHC Collimator Material Identified NeedsWorkshop 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

- Proposal - LHC Material Studies

## 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

- Proposal - LHC Material Studies

## 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

- Proposal - LHC Material Studies

## Neutron/Gamma Irradiation at BNL

- 112-MeV protons

- At 1012 p/s

- Proposal - LHC Material Studies

## Neutron/Gamma Irradiation at BNL

- At 1012 p/s

- Proposal - LHC Material Studies

## Protons, neutrons, photons and electrons in Invar

- <E> (MeV)   Flux (cm-2 s-1)
- p:   23           8.6e5
- n:    9            1.9e9
- :     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!

- At 1012 p/s

- Proposal - LHC Material Studies

## Summary of Results of Interest (to-date)

- Proposal - LHC Material Studies

## 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

- Proposal - LHC Material Studies

## Annealing behavior also exhibited by 2D Carbon ! (fluence ~ 10^20 protons/cm2)

- Fiber (strong) direction

**Weak direction (orientation normal to fibers)**

- Proposal - LHC Material Studies

## A threshold exists on carbon composites and graphite (fluence ~10^21 p/cm2)P-bar Target Experience (when enclosed in CC composite damage was seen with similar fluences)

- 3-D carbon

- 2-D carbon

- graphite

- Proposal - LHC Material Studies

## Irradiation Effects on Copper (fluence ~ 10^21 protons/cm2)

- Proposal - LHC Material Studies

## Irradiation Effects on Glidcop (fluence ~ 10^21 protons/cm2)

- Proposal - LHC Material Studies

## 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

- Proposal - LHC Material Studies

## “annealing” of super-Invar

**Following 1****st**** irradiation**

**Following annealing and 2nd irradiation**

**ONGOING 3rd irradiation phase: neutron exposure**

- Proposal - LHC Material Studies

## Radiation Damage Studies – Other Candidates

- Proposal - LHC Material Studies

## Radiation Effects on Conductivity

- Proposal - LHC Material Studies

## Electrical resistivity  Thermal conductivity

- Proposal - LHC Material Studies

## 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

- Proposal - LHC Material Studies