university of texas confidential, patents pending fusion driver (cfns) nstx - super u and cfns m....

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

Neutronshield

PoloidalCoils

100 MW CFNS core


The fusion driver for a hybrid (CFNS) has some differences

from ST-CTFDifferences 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


• 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


• 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


• 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


• 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


• 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


Back-up Slides


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


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


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

B A



• 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

B A



• Put driver B into fission blanket

• This can coincide with fission blanket maintenance

• Use driver B while driver A is being repaired

B A


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

Neutronshield

PoloidalCoils

100 MW CFNS core

university of texas confidential, patents pending fusion driver (cfns) nstx - super u and cfns m....

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