1. ARIES-IFE: An Integrated Assessment of Chamber Concepts for IFE Power Plants Mark Tillack for the ARIES Team 19th IEEE/NPSS SOFE January 22-25, 2002 Atlantic City, NJ http://aries.ucsd.edu/ARIES

2. Goals:  Analyze & assess integrated and 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. ARIES Integrated IFE Chamber Analysis and Assessment Research -- Goals Approach:  Several classes of target were identified. Advanced target designs from NRL (laser-driven direct drive) and LLNL (Heavy-ion-driven indirect-drive) are used as references.  To make progress, we divided the activity based on three classes of chambers: Dry wall chambers; Solid wall chambers protected with a “sacrificial zone” (e.g., liquid films); Thick liquid walls.  We are examining these three classes of chambers in series with the entire team focusing on each concept.

3. 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 D. A. Callahan-Miller and M. Tabak, “A Distributed Radiator, Heavy- Ion Target Driven by Gaussian Beams in a Multibeam Illumination Geometry,” Nuclear Fusion 39(7) July 1999. S. E. Bodner, D. G. Colombant, A. J. Schmitt, and M. Klapisch, “High- Gain Direct-Drive Target Design for Laser Fusion,” Physics of Plasmas 7(6), June 2000, pp. 2298-2301. (NRL 1-D Direct Drive Target Gain Calculations have been corroborated by both LLNL and UW.) LLNL/LBNL HIF Target Reference Direct and Indirect Target Designs

4.  Little energy in the X-ray channel for NRL direct-drive target NRL Direct Drive Target (MJ) HI Indirect Drive Target (MJ) X-rays 2.14 (1%) 115 (25%) Neutrons 109 (71%) 316 (69%) Gammas0.0046 (0.003%) 0.36 (0.1%) Burn product fast ions 18.1 (12%) 8.43 (2%) Debris ions kinetic energy 24.9 (16%) 18.1 (4%) Residual thermal energy 0.0130.57 Total154458 Detailed target spectrum available on ARIES Web site http://aries.ucsd.edu/ARIES/ X-ray and Ion Spectra from Reference Direct and Indirect-Drive Targets Are Computed

5.  Analysis of design window for successful injection of direct and indirect drive targets in a gas-filled chamber (e.g., Xe) is completed. No major constraints for indirect-drive targets (Indirect-drive target is well insulated by hohlraum materials) Narrow design window for direct-drive targets due to heating: Target Injection Design Window Naturally Leads to Certain Research Directions  (Pressure < ~50 mTorr, Wall temperature < ~900 o C) Chamber Pressure, Torr

6. In-chamber tracking may be needed  Repeatable, high-precision placement (  5 mm).  Indirect/direct requires tracking and beam steering to  200/20  m.  For Ex-Chamber Tracking: 1% density variation in chamber gas causes a change in predicted position of 1000 mm (at 0.5 Torr) For manageable effect at 50 mTorr, density variability must be <0.01%.  Need both low gas pressure and in-chamber tracking. Variations in the Chamber Environment Affect the Target Trajectory in an Unpredictable Way

7. Ion power on chamber wall (6.5-m radius chamber in vacuum)  Photon and ion energy deposition falls by 1-2 orders of magnitude within 0.1 mm of surface  Most of heat flux due to fusion fuel and fusion products (for direct-drive). Photon and Ion Attenuations in C and W Slabs (NRL Direct Drive Target)  Time of flight of ions spread the temporal profile of energy flux on the wall over several  s (resulting heat fluxes are much lower than predicted previously). Details of Target Spectra Have a Strong Impact on the Thermal Response of the Wall

8. Coolant at 500°C 3-mm thick W Chamber Wall Energy Front Evaporation heat flux B.C at incident wall Convection B.C. at coolant wall: h= 10 kW/m 2 -K  Significant margin for design optimization (a conservative limit for tungsten is to avoid reaching the melting point at 3,410°C).  Similar margin for C slab.  Thermal response of a W flat wall to NRL direct-drive target (6.5-m chamber with no gas protection): Is Any Gas Necessary to Product Solid Walls (for NRL Direct-Drive Targets)? 100  m 1506 °C peak surface temperature 20  m depth 10  m 5m5m

9. Depth (mm): 00.021 3 Typical T Swing (°C):~1000~300~10 ~1 Coolant ~ 0.2 mm Armor 3-5 mm Structural Material Armor is optimized to handle particle and heat flux. First wall is optimized for efficient heat removal. Most neutrons are deposited in the back where temperatures will be quasi-steady state Therefore: Focus IFE effort on armor design and material issues Blanket design can be adapted from MFE blankets All of the Action Takes Place within 0.1-0.2 mm of Surface. Conclusion: Use an Armor Candidate Dry Chamber Armor Materials  Carbon (and CFC composites) Key Issues: erosion, fabrication, tritium retention (co-dep.), oxidation, safety  Tungsten & Other Refractories Key Issues: fabrication/bonding and integrity under IFE conditions  “Engineered Surfaces” to increase effective incident area. E.g., Carbon velvet.

10. Specimen fractured to reveal interior Under the velvet pile, the substrate shows little erosion (epoxy coating over aluminum survives) Samples tested in RHEPP ion-beam facility (25 shots) POCO graphite: Exposed surface recedes ~50  m at high-flux location POLYMER MASK Why so much less erosion? Each pulse is spread over 15x more area, so that <0.1  m is ablated The ablated material may redeposit on the nearby fibers: recycling Thermal penetration into vertical fibers may be providing effective cooling on this time scale Example of Engineered Material: ESLI Fiber-Infiltrated Substrate

11. IFE Armor Conditions are similar to those for MFE PFCs (ELM, VDE, Disruption)  We should make the most of existing R&D in MFE (and other areas) since conditions can be similar (ELM’s vs IFE)

12. Use of an Armor Allows Adaptation of Efficient MFE Blankets for IFE Applications  Simple, low pressure design with SiC structure and LiPb coolant and breeder.  Innovative design leads to high LiPb outlet temperature (~1100 o C) while keeping SiC structure temperature below 1000 ˚ C leading to a high thermal efficiency of ~ 55%.  Plausible manufacturing technique.  Very low afterheat.  Class C waste by a wide margin. Outboard blanket & first wall  As an example, we considered a variation of ARIES-AT blanket as shown:

13. Thermal design window Pumping requirements are reasonable for chamber pressures of ~10-50 mTorr. Design Windows for Direct-Drive Chambers Laser propagation design window(?) Target injection/tracking design window

14.  Gas pressure of  0.1-0.2 Torr is needed (due to large power in x- ray channel).  Similar Results for W.  Operation at high gas pressure may be needed to stop all of the debris ions and recycle the target material.  No major constraint from injection/tracking.  Heavy-ion stand-off issues: Pressure too high for non- neutralized transport. Pinch transport (self or pre-formed pinch) Graphite Wall, 6.5m radius Direct-drive Indirect-drive Thermal Design Window Design Window for Indirect-Drive Chambers

15. Beam Transport Option for Heavy-Ion Driver

16.  National program started in June 2000, planned be completed by Dec. 2002.  Assessment of “wetted-wall” chambers is now in progress.  Assessment of thick liquid walls will start in 2002. ARIES-IFE Goals and Plans

17. Self-pinched Transport Offers Attractive Power Plant Scenario  Advantages include small chamber entrance holes, eases chamber focus requirements, and reduces accelerator costs. Uses ~2-100 beams and operates in a low-pressure range of ~1-100 mTorr.  Main issues are beam front erosion, aiming/tracking, multiple beam effects, and beam/plasma stability (ARIES-IFE studies are continuing). 6 meters

18. Channel Transport (“Assisted Pinch”)  Advantages: offers small chamber entrance holes, eases chamber focusing requirements, and reduces accelerator costs. Uses ~2 beams and operates in a high-pressure range of ~1-10 Torr. Requires laser or z-pinch discharge.  Main issues are the insulator at the chamber entrance, and beam/channel stability (recent ARIES-IFE studies on both are favorable).