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Fusion Driver (CFNS) NSTX - Super U and CFNS

Neutron shield. Poloidal Coils. 100 MW CFNS core. UT-IFS Super-X Divertor. Fusion Driver (CFNS) NSTX - Super U and CFNS. M. Kotschenreuther, S. Mahajan, P.Valanju Institute for Fusion Studies The University of Texas PPPL 30 April, 2009.

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Fusion Driver (CFNS) NSTX - Super U and CFNS

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  1. Neutron shield Poloidal Coils 100 MW CFNS core UT-IFS Super-X Divertor Fusion Driver (CFNS) NSTX - Super U and CFNS M. Kotschenreuther, S. Mahajan, P.Valanju Institute for Fusion Studies The University of Texas PPPL 30 April, 2009

  2. The fusion driver for a hybrid (CFNS) has some differences from ST-CTF Differences have significant consequences • First wall temperature can be lower • Thermal conversion efficiency of fusion blanket is a minor consideration • Low temperature opens a window for liquid Li walls (porous?) • Many first wall problems could be solved by this • MUCH less tolerance for large blanket penetrations for fission • NB may be a “no go” for many fission blanket concepts • RF current drive much more desirable • Cu center post should last longer, so ~ 10 cm shield needed • Even less room for central transformer • Aspect ratio might be slightly increased to make more room

  3. Desirable characteristics of a “super upgrade” of NSTX leading to CFNS • Liquid Metal (LM) wall on porous media • Solves many first wall problems, could be DEMO relevant with some LMs • Room in Vacuum vessel for full Super-X divertor • Need to test SXD with LM wall (Li), higher power than MAST • Single turn water cooled TF for long pulses (possibly with higher field) • Should the first single turn long pulse TF magnet be a multi-Billion CFNS/CTF? • Emphasize RF current drive that would require minimal/no blanket penetrations in a hybrid • EBW (synergy with Li?), HHFW, perhaps high field launch ECCD, LHCD, etc?

  4. Porous LM wall 1 • Success with porous Li limiter on T-11, FTU • Estimate: porous media with pore size ~ T-11 would have sufficient suction to retain Li even in the presence of j x B forces where j is limited by the ion saturation current • Hence Li would not get ejected from the wall into to plasma • It will be, perhaps, possible to develop materials with much lower pore size and hence much higher Li suction, giving much higher margin for wall retention of Li • Estimate: capillary forces (in a ~ 2 T field) suffice to be able to replace the LM over meter sized distances in ~ 1 hour • This should allow rapid enough Li replacement to prevent un-accepable T inventory in the Li in the wall for a CFNS • (T would have to be removed quickly from Li ex-vessel by heating)

  5. Porous LM wall 2 • This could provide a solution to many PMI problems plus allow the benefits of Lithium operation • PMI problems avoided- first wall T retention • Erosion/ re-deposition • Flaking of solid PFC materials into the plasma • Bubble formation in solid PFC/ unacceptable evolution of solid surfaces • Dust formation • Robustness to transient events, etc. • A higher temperature operating window could be provided by high recycling LMs • Tin-Lithium (effectively a low Z PFC) • Gallium or Tin (high Z PFCs, low vapor pressure at high temperature > 500 C) • This higher temperature operating window could be desirable for DEMO

  6. Single turn water cooled TF • Magnet engineers at UT (Center for Electromechanics) indicate this should be much lower cost, higher strength than a traditional TF designs • Main engineering issues: high current low voltage power supplies and sliding joint • Two options for power supply • unconventional semiconductor power supplies • homopolars with LM brushes for very long pulse lengths (> 1000s seconds), conventional brushes for pulse lengths of 100s seconds • Magnet engineering is not so certain than it should not be tested • Do we want the first test of a single turn long pulse TF to be on a multi-billion dollar device with DT? • This would also provide a long pulse length, high field capability for plasma operation

  7. RF current drive • Fission blankets are FAR less tolerant of penetrations than fusion blankets • Heating power density is 1 1/2 orders of magnitude higher • Much more serious safety issues if cooling is less than absolutely reliable • Fission products are much more easily released, but must be retained even in accidents • Large penetrations of a fission blanket are highly undesirable for all these reasons • MHD drag on coolant makes a penetration even more problematic • Ways of driving current without penetrating the fission blanket or interfering with fission coolant paths are highly desirable-may even be a practical requirement for licensing • RF current drive options that could meet these demands must be emphasized • EC based options (EBW, inboard ECCD), HHFW, LHCD launched in high field, etc.

  8. Back-up Slides

  9. Reference Hybrid Design with CFNS “Module” • “Real” fusion plasma design using CORSICA+SOLPS codes • Conservative (credible) plasma parameters give required neutron flux • Super-X divertor needed to (and can) handle huge heat and neutron fluxes • “Real” fission blanket design using MCNPX code • Based on standard reactor designs, so quite credible • Huge fusion neutron flux allows very safely burning the worst nuclear waste

  10. Super X Divertor: Community Response • Worldwide plans are in motion to test Super X Divertor- designs are underway • MAST upgrade (Culham, UK) • NSTX (PPPL) • DIII-D, possibly this year (GA) • Long-pulse superconducting tokamak SST (India) Super X Divertor for MAST Upgrade

  11. A B Replaceable Fusion Driver Concept • Due to SXD, the whole CFNS is small enough to fit inside fission blanket • CFNS driver to last about 1-2 full power years • It can be replaced by another CFNS driver and refurbished away from hybrid • CFNS driver itself is small fraction of cost, so a spare is affordable

  12. A B Replaceable Fusion Driver Concept • Pull CFNS driver A out to service bay once every 1-2 years or so - at the same time when fission blanket maintenance is usually done • Refurbish driver A in service bay - much easier than in-situ repairs

  13. A B Replaceable Fusion Driver Concept • Put driver B into fission blanket • This can coincide with fission blanket maintenance • Use driver B while driver A is being repaired

  14. Neutron shield Poloidal Coils 100 MW CFNS core UT-IFS Super-X Divertor: The Key How compact is compact? ITER (the next fusion flagship) and Hybrid (on same scale) Neutron Reflector Neutron Reflector 3 GW Fission Blanket Fission Waste& Coolant CFNS “Module” in Hybrid Reactor

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