Post-Irradiation Results of the LHC Collimator Carbon-Carbon Nick Simos BNL Report to the Collaboration March 28, 2006

There is good news & bad news In the end the good news win !!!

The Bad News First These good news follow the not-so-good observation that the material suffers damage when it is exposed to very high proton fluence The material damage, HOWEVER, is associated with material that has seen protons in excess of 3x10^21 protons/cm^2. I do not believe that that will ever be anticipated at LHC. Therefore, that issue is put to rest.

Fiber (strong) direction The Bad News First Fiber (strong) direction Weak direction

Good News Regarding PHASE-I LHC Collimator Material While the analysis of the 2D carbon-carbon material of the LHC PHASE I collimator is continuing, it is evident that there is good news regarding the ability of the material to maintain the 25 micron constrain These good news follow the not-so-good observation that the material suffers damage when it is exposed to very high proton fluence. The material damage, HOWEVER, is associated with material that has seen protons in excess of 3x10^21 protons/cm^2. I do not believe that that will ever be anticipated at LHC. Therefore, that issue is put to rest.

Non-Irradiated State of 2D carbon-carbon

Shown below are some important and very relevant findings regarding the self-healing of the 2D carbon-carbon. While irradiation alters the thermal expansion characteristics of the material (key property in maintaining 25 micron movement of the jaws), thermal cycling even of 200C corrects the damage or change induced. The damage is corrected even on the heavily irradiated material (which is shown below). On the left is the annealing at 300C. On the right is the search for the temperature threshold. The experiment revealed that most of the damage is annealed even at 200C. It is likely that the damage is continuously corrected for as long as the operating temperature exceeds say 200 C. 2D CC “annealing” behavior along the fiber planes

2D CC “annealing” behavior along the fiber planes

2D CC “annealing” behavior along the fiber planes

2D CC “annealing” behavior along the fiber planes

The striking (and very positive thing for the collimator jaws) is that self-healing also takes place along the weak direction (direction with no fiber reinforcement) 2D CC “annealing” behavior NORMAL to fiber planes

The 2D carbon-carbon apparently has company! Similar self-healing behavior is observed in the 3D carbon-carbon (that has fibers normal to the x-y planes) and the super-Invar that has very low thermal expansion coefficient.

“annealing” behavior of super-Invar “annealing” behavior of 3D CC AlBeMet “apparent reduction in CTE

Phase-II LHC Collimator Material Irradiation Primary Materials: Copper, Glidcop (85% Cu – 15% Al) Other Potential Candidates: Super Invar, Gum Metal, Test under same conditions: 2D CC and 3D CC

SUMMARY 2D carbon-carbon selected is expected to meet the 25 micron requirement For as long as the collimator jaws intercepting the beam do not see more that 1.0 x 10^20 p/cm^2 then there should not be any concern of material damage (even along the weak direction) It is in the plan to irradiate the 2D carbon again together with the 3D carbon this May and along with materials considered for Phase II. This way there will be direct correlation between 2D and 3D carbon-carbon on the basis that they will both be exposed to the same conditions Further experimental scrutiny of the irradiated 2D carbon for effects of irradiation on thermal conductivity is planned for this summer