University of Texas Confidential, Patents pending 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 UT-IFS Super-X Divertor Neutron shield Poloidal Coils 100 MW CFNS core

University of Texas Confidential, Patents pending 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

University of Texas Confidential, Patents pending 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? Desirable characteristics of a “super upgrade” of NSTX leading to CFNS

University of Texas Confidential, Patents pending 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) Porous LM wall 1

University of Texas Confidential, Patents pending 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 Porous LM wall 2

University of Texas Confidential, Patents pending 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 Single turn water cooled TF

University of Texas Confidential, Patents pending 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. RF current drive

University of Texas Confidential, Patents pending Back-up Slides

University of Texas Confidential, Patents pending 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

University of Texas Confidential, Patents pending 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

University of Texas Confidential, Patents pending 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 BA

University of Texas Confidential, Patents pending 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 BA

University of Texas Confidential, Patents pending 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 BA

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