1. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 1 Dynamic Chamber Armor Behavior in IFE and MFE A. R. Raffray 1, G. Federici 2, A. Hassanein 3, D. Haynes 4 1 University of California, San Diego, 458 EBU-II, La Jolla, CA 92093-0417, USA 2 ITER Garching Joint Work Site, Boltzmannstr. 2, 85748 Garching, Germany. 3 Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA 4 Fusion Technol. Inst., Univ. of Wisconsin, 1500 Eng. Dr., Madison, WI 53706-1687, USA ISFNT-6 San Diego April 10, 2002

2. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 2 Outline Chamber armor operating conditions –MFE and IFE –Comparison Candidate armor materials –Focus on dry walls for this presentation –Properties and characteristics Example analysis for dry walls –IFE –MFE Critical issues and required R&D –Synergy Concluding Remarks

3. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 3 IFE Operating Conditions Cyclic with repetition rate of ~1-10 Hz Target injection (direct drive or indirect drive) Driver firing (laser or heavy ion beam) Microexplosion Large fluxes of photons, neutrons, fast ions, debris ions toward the wall -possible attenuation by chamber gas Target micro- explosion Chamber wall X-rays Fast & debris ions Neutrons Energy partition for two example targets

4. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 4 Steady state conditions Load on plasma facing components dependent on location, e.g. for ITER: MFE Operating Conditions However, a number of cyclic off-normal conditions must be designed for in next step option -Vertical Displacement Events (VDE’s) -Edge Localized Mode Scenarios (ELM’s) -Disruptions Peak surface heat flux Lifetime (MW/m 2 ) (No. of cycles) First wall0.5 30000 Limiter0.5 (~8 for ~100s)30000 (5000) Baffle33000-10000 Divertor target~103000-10000

5. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 5 Comparison of IFE and MFE Operating Conditions for ITER Divertor and NRL Direct Drive Target Spectra as Example Cases Although base operating conditions of IFE and MFE are fundamentally different, there is an interesting commonality between IFE operating conditions and MFE off-normal operating conditions, in particular ELM’s - Frequency and energy density are within about one order of magnitude

6. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 6 Candidate Chamber Armor Materials Must Have High Temperature Capability and Good Thermal Properties Carbon and refractory metals (e.g. tungsten) considered for both IFE and MFE - Reasonably high thermal conductivity at high temperature (~100-200 W/m-K) -Sublimation temperature of carbon ~ 3370°C -Melting point of tungsten ~3410°C In addition, IFE considers possibility of an engineered surface to provide better accommodation of high energy deposition -e.g. ESLI carbon fiber carpet showed good performance under ion beam testing at SNL (~5 J/cm 2 with no visible damage) Beryllium considered for moderately loaded first wall of ITER - However, not compatible with commercial reactor operation because of its low melting point (1283°C) and high sputtering yield Example analysis results for IFE and MFE showed for C and W armor

7. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 7 Example IFE Threat Spectra for 154 MJ NRL Direct Drive Target Photons (1%) Debris Ions (16%) Fast Ions (12%) These photon and ion spectra used to calculate energy deposition in armor -For ions, tabulated data from SRIM used for input for ion stopping power as a function of energy -For photons, overall attenuation coefficient as a function of energy used

8. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 8 Spatial and Temporal Profiles of Volumetric Energy Deposition in C and W for Direct Drive Target Spectra Energy Deposition as a Function of Penetration Depth for 154 MJ NRL DD Target Ion Power Deposition as a Function of Time for 154 MJ NRL DD Target Chamber Radius = 6 m Penetration range in armor dependent on ion energy level -Debris ions (~20-400 kev) deposit most of their energies within 1’s  m -Fast ions (~1-14 Mev) within 10’s  m Important to consider time of flight effects -Photons in sub ns -Fast ions between ~0.2-0.8  s -Debris ions between ~ 1-3  s -Much lower maximum temperature than for instantaneous energy deposition case

9. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 9 Temperature History of C and W Armor Subject to 154MJ Direct Drive Target Spectra with No Protective Gas For a case without protective gas: -Carbon maximum temperature < 2000°C -Tungsten maximum temperature < 3000°C (MP=3410°C) - Some margin for adjustment of parameters such as target yield, chamber size, coolant temperature and gas pressure All the action takes place within < 100  m -Separate functions: high energy accommodation in thin armor, structural function in chamber wall behind Coolant at 500°C 3-mm thick Chamber Wall Energy Front h= 10 kW/m 2 -K

10. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 10 Example Analysis of Transient Energy Deposition on ITER Divertor 1.Type I ELM scenario -Initial condition based on design heat flux of 10 MW/m 2 -Energy fluence of 1 MJ/m 2 over 0.2 ms -Calculations done with the RACLETTE code neglecting any vapor shielding effect 2.Disruption scenario -Incident plasma energy of 10 MJ/m 2 over 1 ms -Calculations done with the HEIGHTS package including vapor shielding effects t q’’(W/m 2 ) 0.2 ms 10 5000

11. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 11 Example Temperature History of C and W Armor Subject to Transient ELM Scenario in ITER Maximum surface temperature is ~4200˚C for CFC and ~6000˚C for W Temperature drops to the initial value in about 10 ms ( no temperature ratcheting effect for ELM frequencies of ~ 1-2 Hz) Sublimated CFC thickness is ~5  m (this limits the number of ELMs with such energy densities that can be tolerated in ITER) Evaporated thickness in the case of W is lower (~1  m per event) However, the melt layer thickness is ~ 70  m Key lifetime issue for W would be the stability of the melt layer and the corresponding fractional loss of melted material

12. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 12 Example W Armor Behavior Under MFE Disruption Conditions Interesting comparison: MFE case under disruption and example IFE case with no protective gas for high yield (401 MJ)NRL DD target spectra to illustrate armor behavior under respective threats -IFE case is for illustration -Protective gas will be used (e.g. ~80 mtorr of Xe at RT) to spread out over time energy deposition on armor HEIGHTS calculations W T max ~ 7200°C Time to reach T max ~ 2   s Melt layer thickness at T max ~ 10  m Max. melt layer thickness ~ 100  m Evaporated thickness at T max ~ 0.5  m Max. evaporated thickness ~ 2  m Effect of vapor shielding can be observed Key lifetime issue based on number of disruptions that must be accommodated No protective gas MFEIFE ~ 7000°C ~ 2  s ~ 10  m ~ 0.1  m

13. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 13 Other Erosion Processes are of Concern in Particular for Carbon Chemical Sputtering Radiation Enhanced Sublimation - Increases with temperature Physical sputtering - Not temperature-dependent - Peaks with ion energies of ~ 1 kev ( from J. Roth, et al., “Erosion of Graphite due to Particle Impact,” Nuclear Fusion, 1991) Plots illustrating relative importance of C erosion mechanisms for example IFE case (154 MJ NRL DD target spectra) -RES and chemical sputtering lower than sublimation for this case but quite significant also -Physical sputtering is less important than other mechanisms -Increased erosion with debris ions as compared to fast ions R chamber = 6.5 m CFC-2002U

14. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 14 Tritium Inventory in Carbon is a Major Concern Operation experience in today’s tokamaks strongly indicates that both MFE and IFE devices with carbon armor will accumulate tritium by co-deposition with the eroded carbon in relatively cold areas (such as in penetration lines) (R. Causey’s talk at ISFNT-6) - H/C ratio of up to 1 -Temperature lower than ~800 K Carbon is currently chosen in ITER to clad the divertor target near the strike points because of its greater resilience to excessive heat loads during ELM’s and disruptions. Modeling predictions of tritium retention by co-deposition with C for ITER -The inventory limit (shown by double line) is predicted to be reached in approximately 100 pulses If C is to be used, techniques must be developed for removal of co-deposited T -Baking with oxygen atmosphere at >570 K -High temperature baking > 1000 K -Others, (mechnical, local discharges…)

15. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 15 Major Issues for Dry Wall Armor Include: Commonality of Key Armor Issues for IFE and MFE Allows for Substantial R&D Synergy Carbon Erosion -Microscopic erosion (RES, Chemical and Physical Sputtering) -Macroscopic Erosion (Brittle fracture) Tritium inventory -Co-deposition Refractory metal (e.g. Tungsten) Melt layer stability and splashing Material behavior at higher temperature -e.g. roughening due to local stress relief (possible ratcheting effect) -Possible relief by allowing melting? - quality of resolidified material Carbon and Tungsten He implantation leading to failure (1 to 1 ratio in ~100 days for 1  m implantation depth) -In particular for W (poor diffusion of He) -Need high temperature or very fine porous structure Fabrication/bonding (integrity of bond during operation) Search for alternate armor material and configurations In-situ repair to minimize downtime for repair Cannot guarantee lifetime MFEIFE   

16. April 10, 2002 A. R. Raffray, et al., Dynamic Chamber Armor Behavior in IFE and MFE 16 Concluding Remarks Challenging conditions for chamber wall armor in both IFE and MFE -Overlap between IFE conditions and some MFE off-normal events Different armor materials and configurations are being developed -Similarity between MFE and IFE materials Some key issues remain and are being addressed by ongoing R&D effort -Many common issues between MFE and IFE chamber armor Very beneficial to: -develop and pursue healthy interaction between IFE and MFE chamber communities -make the most of synergy between MFE and IFE Chamber Armor R&D