(Step 1: Identifying critical gaps) (Step 2: Options to fill the critical gaps…initiated) (Step 3: Success…not yet) Clement P.C. Wong General Atomics Fusion Nuclear Science and Technology Annual Meeting August 2, 2010 Rice Conference Room, UCLA Critical Gaps between Tokamak Physics and Nuclear Science
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Critical Gaps between Tokamak Physics and Nuclear Science › FNST › FNST-PFC-2-6-Aug-2010 › ... · (Step 1: Identifying critical gaps) (Step 2: Options to fill the critical gaps…initiated)
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(Step 1: Identifying critical gaps)(Step 2: Options to fill the critical gaps…initiated)
Impact of T burn-up fraction in plasma on start-up T inventory for new power plant
L. El-Guebaly, UW
Implications of tritium burn-up fraction for ITER ~ 0.3%
A power reactor consumes ~ 0.5 kg per day, and if ttp is ~ 24 hours like TSTA, then the tritium inventory in the fuel storage will be > 160 kg!! Totally unacceptable. If ttp is reduced
to 4 hours, it will be ~ 27 kg. Still too high!!
A power reactor with the same as ITER would be unacceptable!
ITER is designed with a burn-up fraction of 0.3%Low tritium burn-up fraction will need large tritium startup inventoryThe key is to optimize burn-up fraction and tritium processing, ttp
M. Abdou, UCLA, 2007
Divertor configuration and peak heat flux reduction
• Tritium supply, burnup fraction, tritium processing and TBR
• Divertor configuration and peak heat flux reduction
• Transient events: disruptions, ELMs and runaway electrons
• First wall heat flux and design
• Plasma surface material
Critical areas that will have major impacts to the feasibility of fusion power
Most divertors are designed to a peak heat flux of 10 MW/m2
M. Kotschenreuther, ARIES Workshop, San Diego, CA, May 20-21 2010
Peak heat flux for DEMO is very uncertainNew divertor configurations should be considered
D. Ryutov, ARIES Workshop, San Diego, CA, May 20-21 2010
Transient events: disruptions, ELMs and runaway electrons
• Tritium supply, burnup fraction, tritium processing and TBR
• Divertor configuration and peak heat flux reduction
• Transient events: disruptions, ELMs and runaway electrons
• First wall heat flux and design
• Plasma surface material
Critical areas that will have major impacts to the feasibility of fusion power
However even with prefect disruption mitigation, a power reactor will need to be designed to withstand a few unforeseeable events
First wall heat flux and design
• Tritium supply, burnup fraction, tritium processing and TBR
• Divertor configuration and peak heat flux reduction
• Transient events: disruptions, ELMs and runaway electrons
• First wall heat flux and design
• Plasma surface material
Critical areas that will have major impacts to the feasibility of fusion power
ReNeW PFC panel generated unexpected surprises
• ITER First wall panels are designed to
1 MW/m2 and 5 MW/m2 heat flux
while steady state radiation is only 0.5 MW/m2
• Why???
R. Nygren SNL, 2010
R. Nygren SNL, 2010
Correct question: Can physicists manage without such a requirements ?
Main chamber ELM loads• Clearly present in higher
triangularity configurations
DIII-D
#13
82
19
Before ELM
During ELM
IR TV
DIII-DSecondary
strike
See J. G. Watkins, Poster P2-66, Tuesday68193, 57 s
• Should be able to control tritium inventory at temperature ~1000 °C (#7)
• Suitable real time siliconization could be used to replenish Si when and
where needed (#10)
(Satisfying requirements #12 TBD)
W-buttons
W-buttons
filled with Si
Si filled W-buttons W-buttons with
1 mm dia. indentsLoaded DiMES sample
2 Si-W, 3 graphite, 2 W buttons
Initial Results of Transient Tolerant Si-filled W-buttons
Sample exposed
To 4 LSN dischargesAfter one additional disruption,
but not fully thermally loaded
Exposed in
DIII-D lower divertor
Shot 14261-14264Shot 142706
Si-W Buttons Exposure Observations
• As expected Si on the W button surface got removed during normal
discharges easily via sputtering or vaporization
• Favorable result shows much of the Si is retained in the indents even
under relatively high heat and particle flux
• Retained Si could demonstrate the vapor shielding effect to protect
the W-button surface from melting
• Initial results show expected results in the performance of Si-filled W-
surface to fulfill its function, much more development and testing will
be needed
Conclusions
From ITER to FNSF critical gaps have been identified between Tokamak Physics and Nuclear Science
and they can only be resolved with close interactions between physics, material, technology and design communities
Examples are:
• Tritium supply, burnup fraction, tritium processing and TBR• Divertor configuration and peak heat flux reduction• Transient events: disruptions, ELMs and runaway electrons• First wall heat flux and design• Plasma surface material
Conclusions-Solutions
• Tritium supply, burnup fraction, tritium processing and TBR
Higher T burnup fraction >>0.3% is needed, furthermore a net tritium producing device like FNSF is needed before the tritium supply runs out
• Divertor configuration and peak heat flux reduction
New divertor configuration and with radiation to maintain acceptable peak heat flux is needed for a robust FNSF design with design margin
• Transient events: disruptions, ELMs and runaway electrons
Different schemes of radiation are needed to mitigate damaging peak power flux impacts to surface material
• First wall heat flux and design
Radiation to spread the peak heat flux and ELM-free operation, like QH mode are needed
• Plasma surface material
Si-filled W-surface, which uses radiation to mitigate surface material damage is a possible transient tolerance approach and should be developed
Conclusions-Radiation is the key
We will need FNSF soon, and radiation is the key to control the damaging transient events. Si-filled W-surface design is proposed as a possible PFM for steady state operation of FNSF and should be organized for more systematic studies.
• Tritium supply, burnup fraction, tritium processing and TBR
Higher T burnup fraction >>0.3% is needed, furthermore a net tritium producing device like FNSF is needed before the tritium supply runs out
• Divertor configuration and peak heat flux reduction
New divertor configuration and with radiation to maintain acceptable peak heat flux is needed for a robust FNSF design with design margin
• Transient events: disruptions, ELMs and runaway electrons
Different schemes of radiation are needed to mitigate damaging peak power flux impacts to surface material
• First wall heat flux and design
Radiation to spread the peak heat flux and ELM-free operation, like QH mode are needed
• Plasma surface material
Si-filled W-surface, which uses radiation to mitigate surface material damage is a possible transient tolerance approach and should be developed