HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 1 Progress Towards Realization of a Laser IFE Solid Wall Chamber A.R. Raffray 1, J. Blanchard 2, J. Latkowski 3, F. Najmabadi 1, T. Renk 4, J. Sethian 5, S. Sharafat 6, L. Snead 7, and the HAPL Team 1 University of California, San Diego, 460 EBU-II, La Jolla, CA , USA 2 University of Wisconsin, Fusion Technology Institute, Madison, WI 53706, USA 3 Lawrence Livermore National Laboratory, Livermore, CA 94550, USA 4 Sandia National Laboratories, Albuquerque, NM 87185, USA 5 Naval Research Laboratory, Washington, DC, USA 6 University of California Los Angeles, Los Angeles, CA, USA 7 Oak Ridge National Laboratory, PO Box 2008, MS-6169, Oak Ridge, TN, USA ISFNT-7 Tokyo, Japan May 22-27, 2005

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 2 Outline HAPL Program Overview Dry Wall Chamber Configuration Key Issue: Wall Survival R&D Effort -Experiments -Modeling Conclusions

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 3 IFE Chamber Studies in US ARIES-IFE study concluded a couple of years ago -focused on evolving parameter design space -laser and heavy ion drivers -direct and indirect-drive targets -dry wall, wetted wall and thick liquid wall chambers - results reported at several conferences and most recently in special issue of Fusion Science & Technology (November 2004) Termination of effort on heavy ion, indirect-drive target, thick liquid wall chamber studies (HYLIFE) Currently IFE technology is funded through the following two programs: -HAPL study (multi-year, multi-institution effort led by NRL) -Z-pinch study (starting last year, led by SNL)

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 4 Electricity Generator Target factory Modular Laser Array Modular, separable parts: lowers cost of development AND improvements Conceptually simple: spherical targets, passive chambers Builds on significant progress in US Inertial Confinement Fusion Program The HAPL Program Aims at Developing a New Energy Source: IFE Based on Lasers, Direct Drive Targets and Solid Wall Chambers Target injection, (survival and tracking) Chamber conditions (physics) Final optics (+ mirror steering) Blanket (make the most of MFE design and R&D info) System (including power cycle) Dry wall chamber (armor must accommodate ion+photon threat and provide required lifetime)

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 5 Chamber Wall Must Accommodate Threat Spectra from Direct Drive Target Ion Threat Spectra Photon Threat Spectra Example 154 MJ direct drive target (350 MJ target also considered)

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 6 Power Deposition Occurs in a Very Thin Armor Region Example power deposition profile in W armor for 154 MJ direct drive target and 6.5 m chamber radius Only thin armor region sees huge temperature transients This led to the configuration choice of a thin armor layer (~ 1 mm) on a FS substrate Blanket at the back sees quasi steady state (can make use of MFE effort) W chosen as preferred armor material (high- temperature capability, no tritium concern) However, lifetime is a key issue and is the focus of the R&D in this area Example temperature history at different spatial location in W armor

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 7 W Armor Lifetime Several possible mechanisms could lead to premature armor failure: -ablation -melting (is it allowable?) -surface roughening & fatigue (due to cyclic thermal stresses) -accumulation of implanted helium -fatigue failure of the armor/substrate bond R&D effort includes modeling and experimental testing of the armor thermo-mechanical behavior. Ablation Depth T or  T Net Ablation No net ablation, but surface roughening Threshold for ablation Threshold for roughening Because the exact IFE ion and X-ray threat spectra on the armor cannot be duplicated at present, experiments are performed in simulation facilities: -Ions (RHEPP) -X-ray(XAPPER and Z) -Laser (Dragonfire) -Fatigue testing of the W/FS bond in ORNL infrared facility (initial results show good adhesion of 0.1 mm W diffusion bonded or plasma-sprayed on FS after 1000’s of thermal cycle pulses). -He management is addressed by conducting implantation experiments (ORNL) along with modeling of He behavior in tungsten (UCLA). The possibility of utilizing an engineered porous armor is also considered to help in enhancing the transport of implanted helium and in accommodating thermal stresses.

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 8 RHEPP Ion Beam Facility (SNL) Ion beam with energy of up to 800 keV for singly- charged He ions, and up to 1.6 MeV for doubly- charged N ions with a pulse-width of ns. Energy within the range expected for IFE but pulse- width shorter than few  s expected for IFE. Uncertainty includes variation in cycle to cycle energy deposition of up to about ±50% and lack of real-time diagnosis (e.g. temp. measurement). Result interpretation must consider RHEPP energy deposition characteristics as compared to IFE (i.e melting of a W sample requires ~ 2 J/cm 2 in RHEPP but more than 4 times this fluence in IFE) Surface roughening measured by 1-D profilometry (DekTak). Studies have focused on determining the roughening thresholds for different armor sample materials at different base temperatures.

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 9 Observations from RHEPP Experimental Results Roughening threshold for powder metallurgy W (PM W) ~ 1 J/cm 2 at RT -Heating the PM W reduces the roughening and possibly increases the threshold but with additional pulses (up to 1000), the roughness reaches the level of the RT sample. Single crystal W shows less roughening than PM W, and possibly higher threshold. Rhenium (Re) and Re/W alloy show much better resistance to roughening than W. Roughening seems to increase linearly with the number of pulses at a given ion fluence. It also increases with the fluence per pulse. Roughening trends seem independent of the predicted W surface T melt (~3410°C at a fluence of ~ J/cm 2 ) perhaps because of very short melt duration (<150 ns). Does roughening saturate? -Needs to verified by testing over more prototypic number of pulses and less variation in energy deposition (e.g. testing in a rapid cyclic heat load facility such as with a laser).

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 10 XAPPER X-Ray Facility (LLNL) XAPPER is based upon an extreme ultraviolet (EUV) X-ray source designed and built by PLEX LLC using a plasma pinch as source. An ellipsoidal focusing optic is used to increase the per-shot X-ray fluence to ~1 J/cm 2 over a spot size of ~ 1 mm. The X-ray spectra show energy around 100 eV, ~ one order of magnitude lower than the typical IFE X-ray energy, but the attainable fluence for the given spectra is sufficient to reproduce the peak temperature of the W armor under the IFE spectra (with melt occurring at a fluence of about J/cm 2 ). However, the time deposition of the energy is short, of the order ~0.01  s compared to the ~1  s in the IFE case (governed by the time of flight of ions). Samples can be irradiated with up to pulses (the latter requiring about 28 hrs of continuous testing).

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 11 Observations from Initial XAPPER Results Initial results suggest that there may be a roughening threshold (somewhat higher for single crystal W than for PM W). Further experiments are needed to understand better whether the roughening increases linearly with number of pulses and also whether it saturates after a number of cycles. One major improvement is the future installation of an optical thermometer (from UCSD) to measure the surface temperature.

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 12 Single Shot Testing in Z Machine (SNL) Z can provide up to 10 keV X-rays. W samples (single crystal, powder metallurgy and chemical vapor deposition) exposed to various fluences. The results showed no melting below a fluence of 1.3 J/cm 2. Heated samples (600°C) were exposed to fluences of 0.27 and 0.9 J/cm 2, and surfaces examined with 2-dimensional VEECO profilometry: - The surface appearance of the polycrystalline samples, i.e. the PM W and CVD W, is different from the SC W, with an indicated roughening threshold between 0.3 and 0.9 J/cm 2. -The SC sample showed no evidence of roughening at 0.9 J/cm 2, indicating a higher roughening threshold for SC W than for the other polycrystalline W samples Fluence (J/cm 2 ) SC W PM W CVD W

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 13 Dragonfire Laser Facility (UCSD) The samples are heated using a YAG laser with a rep rate of 10 Hz. The high rep-rate of the laser allows testing to cycles. Modeling has shown the possibility to simulate the IFE W armor surface temperature temporal and spatial to some extent) temperature profiles by adjusting the laser pulse. A high-speed optical thermometer was developed to measure the real-time temperature of sample surface with ns resolution. Additional diagnostics, such as QMS & RGA to measure and characterize per-shot ejecta and constituents are to be installed. A high-temperature sample holder is included to allow testing at prototypical “equilibrium” temperature.

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 14 Initial Dragonfire Results It seems that the samples evolve at two different time scales: -Defect planes appear at low shot counts (~10 3 shots) -Individual "nuggets" (with higher roughness) appear over the high shot counts (~10 5 shots). Samples at the higher base temperature show less damage. For example for 1,000 shots and a  T of ~2,500°C, a sample at 500°C base temperature shows almost no damage whereas a RT sample shows clear damage. This is also seen with higher shot counts but the difference between the two samples is less marked. Future effort will help to understand better these preliminary observations and to observe the effect of testing with higher shot counts on sample roughening. 530mJ (~2500 o C  T), RT 10 3 shots 10 4 shots10 5 shots 530mJ (~2500 o C  T), 500 o C 10 3 shots 10 4 shots10 5 shots

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 15 Example of Modeling Performed to Better Understand the W Thermal Stress Behavior and Crack Initiation and Growth ANSYS calculations of the stress intensities for crack depths ranging from 15  m to 150  m (and spacing of 1 mm) - The stress intensity falls from ~10 MPa-m 1/2 for the 15  m crack to ~2.6 MPa-m 1/2 for the 150  m crack, and to zero for deeper cracks with smaller spacings. -Thisindicates that cracks that initiate at the surface may stop before reaching the armor/steel interface (within ~100  m from the surface). -Limited fracture mechanics data for thin tungsten films make prediction of fracture behavior is difficult (must rely on experiments). Coolant FS W q High cycle fatigue in FS substrate - Data for F82H indicate lifetime >10 6 cycles for stress amplitudes of ~400 MPa -Data from other steels (such as 12Cr-2W FS) indicate lifetime over 10 8 cycles (HAPL level) at stress amplitudes ~300 MPa at 400 °C - Hence, there seems to be margin in the steel stress levels since the tensile stresses in a typical HAPL cycle are not as high as the compressive stresses, whereas the tests are done with a mean stress of 0.

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 16 He Studies Focused on Investigating He Retention and Surface Blistering Characteristics of W Goal is to determine if He retention can be mitigated by the pulsed nature of He implantation in combination with the high temperature spikes within the IFE reactor Experimental activities: -He implantation/anneal cycle experiment(ORNL+UNC) -~850°C base T, ~1.3 MeV He, pulsed implantation and anneals at 2000°C over ~ 1000 cycles to fluences of ~10 20 He/m 2 -He + D implantation in IEC facility (UW) -~800°C base T, ~ keV ion, pulsed implantation to fluences of ~10 22 He/m 2 Modeling activities: -HEROS code (UCLA) Engineered material also considered to enhance He release and provide stress relief -W foam (Ultramet/UCLA) -Vacuum plasma spray porous W with ~ nm microstructure (PPI/UCSD)

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 17 IFE Conditions May Mitigate He Retention Effect He retention decreases drastically when a given He dose is spread over an increasing number of pulses, each one followed by W annealing to 2000°C, to the extent that there would be no He retention below a certain He dose per pulse. For SC, this threshold would be ~ ions/m 2 per shot (lower for PC W) This threshold is still too low as the IFE He dose per shot is ~10 17 ions/m 2. However, for the IFE case the W armor surface temperature would be closer to 2400°C which would significantly increase the He mobility and should increase the per-shot threshold. Thus, the trends are very promising but more R&D is required to make a better assessment of He behavior in the IFE case.

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 18 Required P Xe as a Function of Yield to Maintain T W,max <2400°C for 1800 MW Fusion Power and Different R chamber Armor Survival Constraints Impact the Overall IFE Chamber Design and Operation W temperature limit of 2400°C assumed for illustration purposes (~1.2 J/cm 2 roughening threshold from RHEPP results) Limit to be revisited as R&D data become available Example chamber parameters for 0 gas pressure: -Yield = 350 MJ; R=10.5 m; Rep. rate ~ 5 for 1750 MW fusion Integrated IFE chamber design under way Desirable to avoid protective chamber gas based on target survival and injection considerations

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 19 Conclusions (I) The HAPL program is aimed at developing Laser IFE based on a laser driver, direct drive targets and a solid wall chamber. The design and R&D effort in the chamber and material area is focused toward the key issues affecting the W/FS armor/FW survival under the ion and photon threat spectra. Initial testing of armor thermal response have been performed in a range of facilities. -Possible threshold for armor roughening, which needs to be fully characterized for IFE conditions. -To be determined is whether roughening saturates after a number of cycles or whether it leads to mass loss. -Generally, single crystal W shows less roughening than powder-met W, and W-Re alloy shows much better resistance to roughening than W; -Armor samples at a higher base temperature tend to show less damage (as compared to room temperature samples)

HAPL May 22-27, 2005 ISFNT-7, Tokyo, Japan 20 Conclusions (II) Initial results from fatigue testing of the W/FS bond indicate good adhesion of the coating (no spalling). Long term thermal stability studies are under way. Modeling studies indicate the possibility of cracks initiating at the armor surface but propagating to < 100  m from the surface. Castellating the armor would help accommodate the stresses and reduce crack propagation concerns. There seems to be a significant margin in the FS stress levels to accommodate the cyclic stress without crack formation in the FS substrate. Initial results indicate that there might be a He flux per shot threshold below which the implanted He will be released during the temperature excursion. This threshold is lower for single crystal W as compared to powder met W. Future modeling and experimental effort should help to better understand this effect under IFE prototypical conditions. Overall, although some major issues still need to be resolved, results are encouraging for the possibility of utilizing a W-armored chamber. The major chamber armor and wall issues have been identified and are being addressed through a combination of modeling and experimental R&D.