IFE Ion Threat Spectra Effects Upon Chamber Wall Materials G E. Lucas, N. Walker UC Santa Barbara

Threat Spectra Projected number of ions and ion energy levels Depends on the type of target drive system Lasers –NRL Direct Drive Target –High Yield Direct Drive Target Heavy Ions –HI Indirect Drive Target Threat spectra consists of both Debris and Burn Product Ions

Threat Spectra

Analytical Procedure SRIM Software –Stopping and Range of Ions in Matter –Uses statistical algorithms to simulate ion and target material collisions and interactions –Inputs Ion Type Ion Energy Target Material (C or W) # of Ions Desired output tables –Outputs Displacements per Ion Ion range in target material Ion Statistics

Analytical Procedure Data Interpolation –Data for threat spectra is only known at a specific set of data points –Interpolation must be used in order to find data points in- between known data points –Distribution is divided into small finite number of “bins” –Each data point falling within each bin is assumed to have the “mid-bin energy” –Reasonable approximation since bin size is small compared to range of distribution

Analytical Procedure Initial Damage Profiles –Utilizing interpolated ion range data, ion concentration distribution can be found –Ion concentration distribution and displacement distribution along with physical properties of the chamber wall material allow DPA (displacements per atom) to be determined –Initial assessment of damage due to displacement can be determined

Analytical Procedure Blistering/Exfoliation –Ion concentration distribution can be used to determine the number of ions per chamber wall atom –The thickness of the blister is determined by the location of maximum concentration (region of maximum gas concentration) –Once critical ion/atom concentration is achieved blister will exfoliate 15 at. % for He ions 50 at. % for H ions –All material before the blister is exfoliated from the chamber wall –Knowing the critical ion/atom concentration, maximum ion concentration as well as the operating conditions of the reactor, the time needed for a blister to exfoliate can be determined

Analytical Procedure Steady-State Exfoliation –After blister layer exfoliates the penetrating ion concentration distribution is the same as before –However, the previous ion concentration distribution is still present in the material –The two concentration distributions add to give the final ion concentration distribution –The final ion concentration distribution dictates a new maximum ion concentration and a new location of maximum ion concentration

Analytical Procedure Steady-State Exfoliation –The ion concentration distribution continues to change after each exfoliation until it reaches a steady-state distribution –At steady-state The exfoliation thickness is constant (controlled by location of maximum concentration) The time to exfoliate is constant (controlled by value of maximum concentration) –The exfoliation thickness and the time required to exfoliate essentially control the decay rate of the surface material

Results Initial Damage Profiles –After the initial fusion reaction the initial ion concentration distribution and DPA distribution are determined –As more reactions occur these distributions build up on top of one another –Blisters form and exfoliation eventually occurs –Representative distributions are shown in the two figures for Low Yield Direct Drive Debris Ions into C

Results Exfoliation Rates –After the first exfoliation occurs a new concentration distribution evolves –The new concentration distribution will have a Higher maximum concentration value –Makes time to exfoliate smaller –Increases exfoliation rate Shallower region of maximum concentration –Makes exfoliation thickness smaller –Decreases exfoliation rate –Exfoliation rate and exfoliation thickness vs. time plotted in figure, Low Yield Direct Drive Debris T into C –After certain amount of time exfoliation rate and exfoliation thickness become constant

Results Steady State Exfoliation Rates

Diffusion Check to determine longevity of concentration profile H diffusivity from literature Run finite element diffusion simulation

Diffusion Profiles at Temperature H profile rapidly decays in W at temperatures above 150 C H profile does not decay In graphite below 1750 C

Conclusions Burn Product Ion damage may be survivable Debris Ion damage is unacceptably high –Diffusion may help –Still need better diffusivities to complete analysis