1. ARIES Inertial Fusion Chamber Assessment M. S. Tillack, F. Najmabadi, L. A. El-Guebaly, D. Goodin, W. R. Meier, J. Perkins, R. R. Peterson, D. A. Petti, K. R. Schultz, J. Sethian, L. M. Waganer, and the ARIES Team 14th Topical Meeting on the Technology of Fusion Energy Park City, Utah 15-19 October 2000

2. Opportunities for IFE have grown since the IFE studies of 1991-92 Important achievements in key enabling technologies, e.g. – Improved understanding of ion beam propagation & ion-material interactions – Increased efficiency of high-power lasers – Demonstration of effective laser smoothing techniques for direct drive targets – Advances in target physics, including innovative concepts such as close- coupled indirect drive and fast ignition. Declassification and increased international effort on unclassified target physics New impetus following community planning efforts (Snowmass, IFE roadmap, VLT program) and construction of NIF

3. Goals of the Study Analyze & assess integrated, self-consistent IFE chamber concepts. Understand trade-offs and identify design windows for promising concepts. The research is not aimed at developing a point design. Identify existing data base and extrapolations needed for each promising concept. Identify high-leverage items for R&D: –What data is missing and what are the shortcomings of present tools? –For incomplete database, what is being assumed and why? –For incomplete database, what is the acceptable range of data? Would it make a difference to zeroth order, i.e., does it make or break the concept? –Start defining experiments needed to complete the database

4. Project Organization Program Management F. Najmabadi Les Waganer (Operations) Mark Tillack (System Integration) Program Management F. Najmabadi Les Waganer (Operations) Mark Tillack (System Integration) Advisory/Review Committees Advisory/Review Committees OFES Target Fab. (GA, LANL*) Target Inj./Tracking (GA) Materials (ANL) Tritium (ANL, LANL*) Drivers* (NRL*, LLNL*, LBL*) Chamber Eng. (UCSD, UW) CAD (UCSD) Target Physics (NRL*, LLNL*, UW) Chamber Physics (UW, UCSD) Parametric Systems Analysis (UCSD, BA, LLNL) Safety & Env. (INEEL, UW, LLNL) Neutronics, Shielding (UW, LLNL) Final Optics & Transport (UCSD, LLNL, LBL*) Tasks Executive Committee (Task Leaders) Executive Committee (Task Leaders) Fusion Labs Fusion Labs * voluntary contributions

5. Approach To make progress, we divided the activity based on three classes of chambers: –Dry wall chambers; –Solid wall chambers protected with a “sacrificial zone” (such as liquid films); –Thick liquid walls. We plan to research these classes of chambers in series with the entire team focusing on each. The initial effort is focused on dry walls (starting in June). Advanced target designs from NRL and LLNL are used as a starting point – both direct-drive and indirect drive designs.

6. Initial results of dry wall chamber assessment 1.Target output. New, accurate knowledge of target output (x-rays, debris, neutrons) is needed to establish protection requirements. 2.Target injection. Need to establish chamber environment that is consistent with both first wall protection and target injection and tracking. 3.Chamber engineering. Engineered chamber surfaces may expand the design window. 4.Driver/chamber interface. Laser optics compatible with the chamber environment are being studied. (We are also examining propagation of ion beams in dry chambers.) 5.Safety and environment. Safety considerations restrict the design window & choices.

7. Reference Direct and Indirect Target Designs LLNL/LBNL HIF Target NRL Advanced Direct-Drive Targets DT Vapor 0.3 mg/cc DT Fuel CH Foam + DT 1  m CH +300 Å Au.195 cm.150 cm.169 cm CH foam  = 20 mg/cc DT Vapor 0.3 mg/cc DT Fuel CH Foam + DT 5  CH. 122 cm.144 cm.162 cm CH foam  = 75 mg/cc NRL Direct Drive Target Gain Calculations (1-D) have been corroborated by LLNL and UW. Nike experiments at NRL are validating physics of direct drive target design.

8. DT Triple Point Target Heating Limits Wall Temperature & Gas Pressure Chamber-based solutions: Reduced gas pressure Reduced wall temperture Alternate wall protection Target-based solutions: Sabot or wake shield Frost coating Failure criteria: stress triple point (98% reflective surface)

9. Chamber Gas Variations Can Affect the Target Trajectory in an Unpredictable Way Forces on target calculated by DSMC Code “Correction Factor” for full Xe pressure is large (~20 cm) Repeatability of correction factor requires constant conditions or precise measurements 1% density variation causes a change in predicted position of 1000  m (at 0.5 Torr) For manageable effect at 50 mTorr, density variability must be <0.01%. Leads to in-chamber tracking Ex-chamber tracking system

10. A sequence of BUCKY runs varying the Xe density were per- formed for the NRL target in a 6.5m radius graphite chamber. Graphite sublimation is a threshold effect, quickly becoming unacceptably large as Xe density is reduced below 0.1 Torr Assumed Target Yields: Ions 29.7 MJ, X-rays 2.33 MJ

11. Good parallel heat transfer, compliant to thermal shock Tailorable fiber geometry, composition, matrix Already demonstrated for high- power laser beam dumps and ion erosion tests Fibers can be thinner than the x- ray attenuation length. Advanced engineered materials may provide superior damage resistance Carbon fiber velvet in carbonizable substrate 7–10  m fiber diameter 1.5-2.5-mm length 1-2% packing fraction

12. Pyrolytic carbon at 1278˚C: k400 W/m-K  2250 kg/m 3 C p 1900 J/kg-K Characteristic Diffusion time length Prompt X-ray pulse0.1 ns0.1  m Fiber diameter10-30 ns1-10  m Reradiation pulse100  s100  m  = k/  C p  = L 2 /  Enhanced thermal behavior results from extended surface, short diffusion time, & semi-transparency Thermal performance, erosion, plugging and material transport need to be studied A f /A = 4/  (1-  ) L/d ~5 for the ESLI material

13. Laser optics compatible with the chamber environment are needed Prometheus-L reactor building layout (30 m) (SOMBRERO values in red) (20 m)

14. Final Optics Threat Spectra Final Optic ThreatNominal Goal Optical damage by laser>5 J/cm 2 threshold (normal to beam) Nonuniform ablation by x-raysWavefront distortion of < /3 (~100 nm) Nonuniform sputtering by ions 6x10 8 pulses in 2 FPY: 2.5x10 6 pulses/atom layer removed Defects and swelling induced Absorption loss of <1% by  -rays and neutronsWavefront distortion of < /3 Contamination from condensable Absorption loss of <1% materials (aerosol, dust, etc.) >5 J/cm 2 threshold Damage that increases absorption (<1%) Damage that modifies the wavefront – – spot size/position (200  m/20  m) and spatial uniformity (1%) Two main concerns:

15. Mirrors and transmissive wedges are considered Fused silica or CaF 2 wedges Grazing incidence metal mirror  = 80-85˚ Transverse energy 10-20 J/cm 2

16. Reflectivity degradation of damaged or contaminated mirrors is being investigated Concerns include absorption, scattering, interference effects Thin protective coatings (not “tuned” multi-layer coatings) also under review

17.  1 m thick dry wall chamber provides lifetime protection for ceramic insulators of adiabatic lens and chamber wall  In addition to blanket, 35 cm thick local shield is needed to protect FF magnets against radiation  Placing final optics at > 25 m from target alleviates damage by streaming source neutrons Magnet shielding is an important driver/chamber interface concern for HI Fusion Technology Institute University of Wisconsin - Madison

18. Safety and Environmental Activities in ARIES-IFE Chamber Assessment In-vessel Activation Ex-vessel Activation Waste Assessment Waste Metrics Energy Source Radiological and Toxic Release Metrics Evaluation Decay Heat Calculation Tritium and Activation Product Mobilization Debris or Dust Chemical Reactivity Toxic Material (Performed jointly by INEEL, UW, LLNL)

19. Safety and Environmental Activities  Minimization of radiological inventories through smart materials selection and careful design  in the chamber (e.g., tritium, activation products, debris/dust)  in the tritium pellet factory (preliminary estimates of tritium inventory are quite large)  Implementation of radiological confinement in IFE systems, recognizing the large number of penetrations in the chamber  How many barriers, what are the barriers and where are they located ?  Identification of accident scenarios in IFE systems  events that might bypass the confinement system,  ex-vessel events that could propagate into the chamber,  events involving imperfect target fusion (e.g., shrapnel, partial burn)  traditional loss of coolant and loss of flow events  Safety analysis of some of these events based on existing designs (e.g. SOMBRERO, HYLIFE-II)  Waste management assessments of different configurations focusing on both volume and hazard of waste (e.g final focus magnets) Non- nuclear room Bypass line Leakage to the environment

20. Strategy For Establishing a Dry-Wall Chamber Operating Window Reduce target x-ray yield for direct drive targets –2 MJ (vs. 22 MJ for SOMBRERO) has been confirmed with 1D calculations Reduce gas pressure and lower wall temperature to open window for target injection Increased chamber wall radius Divert debris ions with magnetic fields Establish exact response of cryo target to hot environment and explore new target protection schemes –Experiments are planned to establish this Develop damage resistant materials

21. The 3 stages of IFE research * Stage 1: On first inspection, everything looks relatively simple Stage 2:On closer inspection, some challenges appear insurmountable Stage 3: With hard work and creativity, solutions to the challenges are found * courtesy of Dan Goodin