Advanced Chamber Concept with Magnetic Intervention: - Ion Dump with Phase Change (including Cu, Pb-17Li, Flibe) - SiC

1. Advanced Chamber Concept with Magnetic Intervention:- Ion Dump with Phase Change (including Cu, Pb-17Li, Flibe) - SiCf/SiC + Pb-17Li or Flibe Blanket A. René Raffray UCSD With contributions from: M. Sawan, G. Sviatoslavsky, I. Sviatoslavsky UW HAPL Meeting PPPL, Princeton, NJ December 12-13, 2006 HAPL meeting, PPPL

2. Outline • Possible options for large chamber in case W armor does not work include (follow-up from last meeting): • Allowing melt layer; momentary liquid wall (Look at possibility of Cu in addition to W and example be case presented before) • Moving solid wall (L. Snead) • Engineered W armor samples provided by PPI to UNC & ORNL to be tested; provision of samples for additional testing elsewhere to follow. • Separate ion dump chamber for magnetic intervention case • Possibility of solid armor with phase change (W, Be, Cu) • Possibility of wetted walls (Pb, Pb-17Li, flibe) • SiCf/SiC blanket for magnetic intervention case • Pb-17Li and flibe (see also posters) • In the process of evolving chamber core of MI case with a number of other contributors HAPL meeting, PPPL

3. 10%W/90%Cu W Structure Coolant Momentary Liquid Walls (allowing solid to melt and resolidify) • Allowing W armor itself to melt is an option but concerns about stability of melt layer and integrity of high temperature solid W under melt layer • Other possibility is to use a lower MP material in a W structure - e.g. >90%Cu in <10% W structure - How to fabricate it? - Structure size to provide good melt layer retention through capillarity (microstructure size to be optimized for melt layer retention and integrity) HAPL meeting, PPPL

4. Histories of Temperature and Phase Change Thickness for a Cu Armor as a Function of the Chamber Sizes for the 350 MJ Target • 1-mm Cu on 3.5 mm FS at 580 °C • No chamber gas • Can the W mesh be maintained at a reasonable temperature acceptable lifetime? (~1250°C for 10.75 m chamber) • Stability of ~3-10 m melt layer of Cu • Minimal evaporation, ~0.0001 nm on average per shot for 10.75 m chamber, ~ 1 g per shot HAPL meeting, PPPL

5. Magnetic Intervention: Utilizing a Cusp Field to Create a Magnetic Bottle Preventing the Ions from Reaching the Wall and Guiding them to Specific Locations at the Equator and Ends • Utilization of a cusp field for such magnetic diversion has been experimentally demonstrated previously - 1980 paper by R.E. Pechacek et al., • Following the micro-explosion, the ions would compress the field against the chamber wall, the latter conserving the flux. Because of this flux conservation, the energetic ions would never get to the wall. • One possibility would be to dissipate the magnetic energy resistively in the FW/blanket, which reduces the energy available to recompress the plasma and reduces the load on the external dumps - about 70% of ion energy dissipated in blanket - about 30% of ion energy in dump region HAPL meeting, PPPL

6. Seems Advantageous to Position Dump Plate In Separate Smaller Chamber • Dry wall main chamber to satisfy target and laser requirements. • Separate phase-change dry wall or wetted wall chamber to accommodate ions and provide long life. • Have to make sure no unacceptable contamination of main chamber HAPL meeting, PPPL

7. Scoping Analysis of an Example Ion Dump Ring Chamber Armor Structure Coolant Rmajor Rmin • Some flexibility in setting chamber major and minor radii so as not to interfere with laser beams • e.g., with Rmajor/Rminor =8/2.7 or 9/2.4 m, and assuming 35% of wetted wall area sees ion flux with a peaking factor of 1: - Ion dump area = 300 m2 - From 0 to 0.5 s, q’’ = 4.51x1010 W/m2 - From 0.5 to 1.5 s, q’’= 6.53x1010 W/m2 • Dry Wall Armor with Phase Change - Example results for W and Be previously presented. - New case analyzed with Cu, possibly within high porosity W microstructure (~80-90%) for integrity and Cu melt layer retention • Wetted Wall - Example results for Pb previously presented - New cases with Pb-17Li and flibe analyzed HAPL meeting, PPPL

8. Temperature and Phase Change Thickness Histories for W, Be, Cu, Pb, Pb-17Li and Flibe for Example Case • 350 MJ target (ion energy = 87.8 MJ) • Ion dump area = 300 m2 • From 0 to 0.5 s, q’’ = 4.51x1010 W/m2 (7.7% of ion energy) • From 0.5 to 1.5 s, q’’= 6.53x1010 W/m2 (22.3% of ion energy) HAPL meeting, PPPL

9. Maximum Temperature and Phase Change Thicknesses for W, Be, Cu, Pb, Pb-17Li and Flibe as a Function of Ion Dump Area • 350 MJ target (ion energy = 87.8 MJ) • Evaporation loss per shot relatively modest for W but could be a concern for Cu or Be (1 nm/shot ~ 0.43 mm/day) • Stability of melt layer is a concern (~10m for Cu or Be; ~ 1 m for W) • For wetted wall in particular, the evaporated material (~10 m for Pb-17Li, Pb or flibe) must recondense within a shot and not contaminate main chamber HAPL meeting, PPPL

10. Wetted-Wall Concept Could Consist of a Porous Mesh Through Which Liquid (Pb-17Li or flibe) Oozes to Form a Protective Film Liquid film Porous mesh Liquid flow Pump Liquid recycling • Need to make sure that protective film is reformed prior to each shot - radial flow through porous mesh - circumferential flow of recondensed liquid - no concern about any droplets falling in chamber HAPL meeting, PPPL

11. Film Condensation in Ion Dump Chamber for Pb-17Li and Flibe • Scoping calculations previously done for Pb as example. • Now extended to Pb-17Li and Flibe as they are used as breeder/coolant in the blanket. • Ion energy from 350 MJ target = 87.8 MJ - 7.7% of ion energy to dump over 0-0.5 s - 22.3% of ion energy over 0.5-1.5 s • Evaporated thickness and vapor temperature rise from ion energy deposition in ion dump chamber. • Assume ion deposition area = 300 m2 - e.g. 35% of chamber with Rmajor = 9 m and Rminor = 2.4 m jevap Pg Tg Tf jcond jnet = net condensation flux (kg/m2-s) M = molecular weight (kg/kmol) R = Universal gas constant (J/kmol-K) G = correction factor for vapor velocity towards film sc, se = condensation and evaporation coefficients Pg, Tg = vapor pressure (Pa) and temperature (K) Pf, Tf = saturation pressure (Pa) and temperature (K) of film HAPL meeting, PPPL

12. Scoping Analysis of Pb-17Li Condensation in Example Ring Chamber • Characteristic condensation time very fast, < 0.024 s • It takes < 0.24 s for vapor density to reach saturation for final vapor temperature > 773 K (assuming linear temporal decrease of vapor temperature from initial to final value). HAPL meeting, PPPL

13. Scoping Analysis of Flibe Condensation in Example Ring Chamber • Characteristic condensation time very fast, < 0.02 s • It takes < 0.202 s is for vapor density to reach saturation for final vapor temperature > 773 K (assuming linear temporal decrease of vapor temperature from initial to final value). HAPL meeting, PPPL

14. Blanket Study for Magnetic Intervention Chamber • More detailed study of blanket using SiCf/SiC + Pb-17Li or Flibe - Layout and thermal-hydraulics - Neutronics - Fabrication - Assembly and maintenance (presented by M. Sawan) (presented by G. Sviatoslavsky) HAPL meeting, PPPL

15. Conical Chamber Well Suited to Cusp Coil Geometry and Utilizing SiCf/SiC for Resistive Dissipation • Armored ion dumps - designed for easier replacement than blanket - shown inside the chamber but could also be in separate ring chamber • SiCf/SiC blanket with liquid breeder - TBR ~ 1.3 for Pb-17Li • Water-cooled steel shield / vacuum vessel (~0.5m thick) is lifetime component and protects the coil. • Design accommodates laser ports. Example Chamber Layout • Maintenance performed from the top by removing the upper shield and the blanket modules from the different region without having to move the coils. HAPL meeting, PPPL

16. Self-Cooled Pb-17Li +SiCf/SiC Blanket Optimized for High Cycle Efficiency • Simple annular submodule design builds on ARIES-AT concept • Pb-17Li flows in two-pass: first pass through the annular channel to cool the structure; and a slow second pass through the large inner channel where the Pb-17Li is superheated • This allows for decoupling of the outlet Pb-17Li temperature from the maximum SiCf/SiC temperature limit HAPL meeting, PPPL

17. Submodule Configuration for Upper Mid-Blanket Region • Submodule cross-section changes because of conical geometry • Pb-17Li enters through annular channel at equator (C-C), turns at top (A-A), flows through inner channel and exits at A-A. • 5 submodules joined (e.g. by brazing) to form a modular unit for assembly and maintenance • Tight fit assembly so that all submodules are pressure-balanced by adjacent modules to avoid large stresses associated with long radial span (particularly at A-A) radial/toroidal dimensions: A-A: 1.06/0.196 m B-B: 0.88/0.33 m C-C: 0.7/0.47 m HAPL meeting, PPPL

18. Submodules Shaped at Module End for Tight Fit Assembly (Resistive Dissipation and Pressure-Balancing of All Submodules) 1 2 3 End sub-module profiles of neighboring modules allows natural fit • Concerns exist about the possible domino effect on all submodules in case of a catastrophic failure of a submodule. • Possible solutions include isolating a limited number of modules by including structurally independent wedges and/or using pressure-sensitive valve system to drain and decompress the coolant in such an accident case. Module A Module C Module B HAPL meeting, PPPL

19. 2-D Stress Analysis of First Wall Performed with ANSYS • At B-B, maximum heat loads: q’’=0.11 MW/m2; qSiC’’’ = 31 MW/m3 • Pb-17Li pressure is ~1 MPa (accounting for hydrostatic pressure ~0.74 MPa for ~9 m elevation, Pblkt ~0.2 MPa and some margin). • tot increases sharply as the wall thickness is increased, indicating the dominating effect of the increasing thermal over the decreasing pressure. • For the present scoping design analysis, it seems reasonable to choose FW ~5 mm; the corresponding tot ~100 MPa for plane stress and ~230 MPa for plane strain , compared to an assumed limit of ~190 MPa for SiCf/SiC. • If more margin is needed in the future, a slightly thinner wall of larger chamber could be used. Chamber dimension = 6m HAPL meeting, PPPL

20. Possible Submodule Fabrication Method(rectangular submodules shown for illustration) Issue:Complex concentric walls prevent assembly of inner and outer channels Solution: Expendable core form fabrication 1. inner channel form 2. Lay-up & infiltrate inner channel 3. Two-piece form fitted over inner channel 4. Lay-up & infiltrate outer channel 6. Braze end caps 5. Consume both forms via chemical or thermal process 7. Braze 5 submodules together to form module HAPL meeting, PPPL

21. Self-Cooled Pb-17Li + SiCf/SiC Blanket Coupled to a Brayton Cycle though a Pb-17Li/He HX • 3 Compressor stages (with 2 intercoolers) + 1 turbine stage; DP/P~0.05; 1.5 < rp< 3.5 - DTHX ~ 30°C - hcomp = 0.89 - hturb = 0.93 - Effect.recup = 0.95 HAPL meeting, PPPL

22. Thermal-Hydraulic Optimization Procedure • Set blanket design parameters. - SiCf/SiC FW=0.5 cm; annulus=0.5 cm - only the blanket length is adjusted based on the chamber size • Simple MHD assumption based on assumed 1 T field and flow laminarization with conduction only (probably conservative). • For given chamber size and fusion power, calculate combination of inlet and outlet Pb-17Li temperatures that would maximize the cycle efficiency for given SiCf/SiC temperature limit and/or Pb-17Li/SiC interface temperature limit. - SiCf/SiC Tmax<1000°C - Pb-17Li/SiC Tmax<950°C - Assume conservatively k=15 W/m-K for SiCf/SiC HAPL meeting, PPPL

23. Brayton Cycle Efficiency as a Function of Cone-Shaped Chamber Size and Corresponding Outlet and Inlet Pb-17Li Temperatures • Pb-17Li/SiC Tmax < 950°C is more constraining than SiCf/SiC Tmax <1000°C • Both P and Ppump show minima at a chamber dimension of 6 m corresponding to the largest T between Pb-Li inlet and outlet temperatures (and lowest flow rate). • For a 6 m chamber, Pb-17Li Tout~1125°C; Brayton ~0.59 • Such a high-temperature also allows for the possibility of H2 production • Question about whether such a high Pb-17Li Tout can be handled in out of reactor annular piping and in heat exchanger. HAPL meeting, PPPL

24. Effect of Varying the Pb-17Li/SiC Interface Temperature Limit • It is not clear what the allowable SiC/Pb-17Li Tmax really is as it depends on a number of conditions. • Earlier experimental results at ISPRA indicated no compatibility problems at 800°C, whereas more recent results indicate a higher limit. • Decreasing the SiC/Pb-17Li Tmax from 950°C to 800°C results in a marked reduction in cycle efficiency, from ~59% to ~50%. • Interestingly, the pressure drop and pumping power minima correspond to an interface limit of 950°C, and both increase significantly as the interface temperature limit is decreased and an increased in flow rate is required. HAPL meeting, PPPL

25. Adapting the Blanket for Flibe Requires a Be region for Tritium Breeding • Flibe electrical resistivity well suited for resistive dissipation of magnetic energy • 1-1.5 cm Be region sufficient for TBR~1.1 • A Be plate can be included in the previous submodule design • Be also used for chemistry control of flibe • The flibe flows in two-pass: a first pass through the annular channel to cool the structure; and a slow second pass through the large inner channel where the flibe is superheated HAPL meeting, PPPL

26. Effect of Varying the Flibe/SiC Interface Temperature Limit • Flibe Tout < Pb-17Li Tout mostly because of its poorer heat transfer properties • For 6 m conical chamber and 1000°C limit: Flibe Tin/Tout = 673/1000°C; Be Tmax = 840 °C P = 0.16 MPa; Ppump = 0.27 MW Brayton = 0.57 • High temperature also allows for possibility of H2 production • Lower density of flibe results in lower primary stresses in module (design pressure ~0.4-0.5 MPa compared to ~1 MPa for Pb-17Li) 6 m chamber SiCf/SiC Tmax < 1000°C: HAPL meeting, PPPL

27. Summary • Scoping study of self-cooled Pb-17Li or flibe + SiCf/SiC blanket concept for use in the magnetic-intervention cone-shaped chamber geometry performed • Separate dump chamber with melted solid wall (W, Cu, Be) or wetted wall (Pb-17Li, flibe, Pb) assessed for magnetic intervention case - Much relaxed atmosphere requirements for separate dump chamber - Encouraging results as condensation is very fast - Need to ensure no unwanted contaminants in main chamber • Future work - Complete overall chamber layout of MI core - More detailed design of separate dump chamber HAPL meeting, PPPL

28. Summary of Blanket Study for MI Case • A scoping design analysis has been performed of a self-cooled Pb-17Li + SiCf/SiC blanket concept for use in the magnetic-intervention cone-shaped chamber geometry - Simple geometry with ease of draining and accommodation of 40 rectangular laser ports with vertical aspect ratio - Good performance, with the possibility of a cycle efficiency >50% depending on chamber size and SiCf/SiC properties and temperature limits - Submodule side walls are pressure-balanced; only the first wall and back wall are designed to accommodate the loads - Must be noted that SiCf/SiC is an advanced material requiring substantially more R&D than more conventional structural material (e.g. FS) - Submodule design can be adapted to flibe as breeder by adding a layer of Be to ensure a TBR of 1.1 and provide for chemistry control - The high coolant temperatures result in high cycle efficiency and could also be used for H2 production - However, issues of what outside coolant tube and HX material(s) to use at these temperatures need to be further investigated HAPL meeting, PPPL