Smaller & Sooner: How a new generation of superconductors can accelerate fusion’s development Dennis

Whyte

Z. Hartwig, C. Haakonsen, L. Bromberg, H. Barnard, G. Olynyk, M. Greenwald, E. Marmar,

MIT PSFC

& Students of 22.63 Fusion Engineering

Fusion Power Associates

Washington DC December 2012



FPA Whyte Dec. 2012

1

Fusion’s development is impeded by its large single-unit cost

•  The overnight cost of a fission power plant is ~ $4/W.

•  First of kind fusion plants at least $10-20/W

•  Which implies that developing fusion reactors at ~GWe scale requires 10-20 G$ “per try” e.g. ITER

•  Chance of fusion development significantly improved if net thermal/electrical power produced at ~5-10 x smaller i.e. ~ 500 MW thermal.

FPA Whyte Dec. 2012

2

Steady-state tokamak reactor: robust and compact if the achievable B can be ~doubled from its present limitation of B~5-6 T to B~10 T

•  Reactor/DEMO criteria? −2 1) Adequate fusion power areal density  Pf / Ablanket ≥ 4 MW m 2) High fusion (Q > 25) and electrical (Qe~5) gain. 

•  High fusion power density and thermal conversion are not optional  E.g. It would take ITER ~ 1800 years to pay off its principle even if operating 24/7 and selling electricity at 10 c/kW-hr.  Problem? Pfusion / A ~ 0.7 MW/m2 , water-cooled wall and 20B$

•  Robustly non-disruptive steady-state scenarios are also necessary

Ø  Plasma pressure (pth), determines the fusion power density (~pth2), will be ~ 1 MPa in all reactor designs [1]

Ø  So energy density a factor of 4-5 larger than in ITER where damage from disruptions/instabilities seems already unacceptable.

FPA Whyte Dec. 2012

3

The development schedule of fusion power would be greatly accelerated if ‘1st DEMO’ could be designed with two extra criteria

‘1st DEMO’ plant criteria

3) Smallest size/volume, total power output and expense, and,

4) For the leading tokamak concept, robust steady-state operation.

•  The only way to satisfy all of four these criteria is to increase B which can be seen from the simplified relationships at fixed R/a*

Pf Ablanket

⎛ β N2 ⎞ 4 ~⎜ 2 ⎟ RB ⎝q ⎠

Power density

FPA Whyte Dec. 2012

,

⎛ β N H ⎞ 1/2 3 ⎜⎝ q 2 ⎟⎠ R B ≥ C Ignition Gain

* See Appendix of FESAC WP for details

4

Doubling B field to ~9-10 T solves the “Catch-22” of initial DEMOs

•  #1: At standard B~5-6 T the bracketed “plasma physics” must be pushed to and past intrinsic operational limits (e.g. q*~2, Beta_N~5-6) in order to keep size reasonable, R<6 m.

•  #2: Yet exceeding any operational limits becomes essentially unacceptable due to reactor pressure/energy density!

•  Doubling the B field provides x10-16 to simultaneously decrease plasma physics /operational risk (bracketed terms) and size and cost ($ ~ R2-3)



A new generation of superconductors developed over the last decade allow ~doubling of Bmax compared to standard NbSn

FPA Whyte Dec. 2012

5

Sub-cooled high-temperature super-conductors have critical currents with very small degradation versus B field up to ~30 T

Developed for power transmission

Commercially produced in thin tapes with excellent mechanical properties (hastelloy + Cu)

FPA Whyte Dec. 2012

6

HTSC tapes can use intermediate T ~ 20K (H cooling) Design B primarily // to tape in high field regions

FPA Whyte Dec. 2012

7

Recent MIT Design Effort* “Rules”

•  Develop a robust conceptual design based on YBCO magnets of a high gain, net electricity producing magnetic fusion power plant at substantially reduced total thermal power ~ 500 MW (factor of ~5 reduction from typical designs).

Ø No violation of basic core limits: kink, no-wall Troyon Beta, Greenwald to assure stable operation.

Ø Fully non-inductive scenarios but robust external control

Ø Minimize solid waste

Ø Minimize capital cost ~ Surface area of plasma/blanket to assure best fusion economic outlook.

Ø Q_electric > 4

FPA Whyte Dec. 2012

*22.63 MIT fusion design course Spring 2012

8

Acknowledgements

•  22.63 Design Course Students:  S. Arsenyev, J. Ball, J. Goh, C. Kasten, P. Le, F. Mangiarotti,  B. Nield, T. Palmer, J. Sierchio, B. Sorbom, C. Sung, D. Sutherland

•  22.63 Design Course Teaching Assistants: H. Barnard, C. Haakonsen, Z. Hartwig, G. Olynyk

•  MIT professional staff: P. Bonoli, L. Bromberg, M. Greenwald, B. Lipshcultz, E. Marmar, J. Minervini, S. Wolfe

FPA Whyte Dec. 2012

9

The limitation in B field is set by structural stress limits

•  Bcoil,max in regime of 20-25 Tesla has been scoped.

•  Preliminary design identified options for static stress

Ø  Dynamics not addressed.

•  B0 ~9.2 T on axis for R/a~3, 1 m shield

FPA Whyte Dec. 2012

10

HTSC tapes also open the possibility that the SC coils are demountable Design: low resistance normal joints

•  Points

FPA Whyte Dec. 2012

Structures for stress

11

Small size permits reasonable cool/warm time for structures during demounting Different joints design à flexibility vs Pelectric

•  Coil shape tradeoffs.

•  Window-shape: easier design but longer down time + more electric power…use for more FNSF version?

•  D-shape: more complex design, but quicker changes + lower electric power…more DEMO

Ø  Warmup ~ 3 days with dry air

Ø  Cool down ~1-2 days

DEMO-like FPA Whyte Dec. 2012

FNSF-like

12

Analysis confirms high-B path to small size, high gain design away from operational limits

Simultaneously: Qp>25, Pf/A>3 MW/m2, non-inductive

FPA Whyte Dec. 2012

13

Synergistic benefit: aspect ratio optimization allowed by demountablity

Bcoil,max: 13 T

Bcoil,max: 18 T

Pf Ablanket

4 ⎧ ⎫ ⎛ β N2 ⎞ Δ ⎪ ⎛ ⎞ 4 3 2 2⎪ b ~ ⎜ 2 ⎟ RBcoil , max ⎨ ⎜ 1−  − ⎟ (1+ κ ) ⎬ R⎠ ⎝q ⎠ ⎪⎩ ⎝ ⎪⎭

Example 0-D point designs finds R/a~3 in order to minimize Ablanket and $$

FPA Whyte Dec. 2012

Bcoil,max: 22 T

a/R

14

High-field side Lower Hybrid exploits favorable physics for robust penetration + Launcher survivability

•  Developed for 24/7 tokamak to study PMI: VULCAN*

•  Launchers integrated into axisymmetric inner wall

•  Placing launcher at goodcurvature + quiescent SOL à controlled launcher PMI

•  Launch point optimized near null point

Ø  Maximized radial propagation when poloidal field is minimum.

FPA Whyte Dec. 2012

* Fusion Eng. Design 2012

15

Synergistic benefit: High-efficiency  mid-radius current drive à  SS scenario at lower bootstrap fraction ~80%

FPA Whyte Dec. 2012

16

High field permits high fusion gain with reduced scenario requirements à Shifts risk from plasma physics to magnets

ARIES-AT

ARC

ARC

FPA Whyte Dec. 2012

Sips IAEA & Zarnstorff MFE roadmapping

17

B ~ 9.2T + ~ 10 keV + high ηCDà High gain + robust steady-state + Qe~5

FPA Whyte Dec. 2012

18

Demountablity à Liquid immersion blanket à reduce solid waste ~x50

FPA Whyte Dec. 2012

19

Full modular replacement: no connections ever made inside TF Transition FNSF à DEMO

•  •  •  • 

R=3.3m, R/a=3, B=9.2T

Pf/A~3.3 MW/m2, A~180 m2

VV/core can be single lifted

All construction/QA offsite

FPA Whyte Dec. 2012

20

Simplified single-fluid cooling scheme at high temperature like molten-salt reactors Pheat/S~0.65 MW/m2 matched by Alcator C-Mod

•  Point

FPA Whyte Dec. 2012

21

Design activity indicates acceptable  TF lifetime and TBR.  Vacuum vessel has dpa limit rather than blanket

FPA Whyte Dec. 2012

22

New high-T superconductors can provide the path to smaller & sooner fusion: Higher B + Detachable coils

Sub-cooled YBCO tapes

Can nearly double B (up to stress limits of structure)

Small tape-to-tape joints à coils can be demounted

R/2 à Volume/8 à $/8 !

Eliminate sector (pie-wedge) maintenance

Away from operating limits

Modular replacement of smaller internal parts

More easily constructed and maintained fusion device at small size but with reliable high gain

FPA Whyte Dec. 2012

23

Key innovations towards achieving design goals

Integrated YBCO + structure to achieve 9.2 T on axis without large electrical costs

R=3.2 m

FPA Whyte Dec. 2012

24

Key innovations towards achieving design goals

Demountable coils à Modular replacement of vacuum vessel + components à full off-site construction + QA of all internal components à

No connection ever made inside TF

= Paradigm shift to standard sector maintenance

FPA Whyte Dec. 2012

25

Key innovations towards achieving design goals

Immersion liquid FLIBE blanket à No materials radiation damage in blanket à ~50-fold reduction in solid waste à full coverage high-TBR blanket

FLIBE

FPA Whyte Dec. 2012

26

Demountable coils à Attractive liquid immersion blanket

Liquid FLIBE

@ 900 K

FPA Whyte Dec. 2012

Key Features



Tritium breeding ratio: 1.15

Excess T in FPY: ~3 kg



High thermal efficiency

Low recirculating power



30+ year lifetime of coils from radiation damage



Solid waste reduced x50 compared to standard blanket

27

Key innovations towards achieving design goals

Lower Hybrid CD with high-field side launch à near theoretical max. for CD efficiency at midradius à ~20% external control of current profile

FPA Whyte Dec. 2012

28

Key innovations towards achieving design goals

~4 keV pedestal not regulated by ELMs à + high CD efficiency à high fusion gain with moderate bootstrap fraction

= Robust steady-state scenarios producing  ~250 MWe

FPA Whyte Dec. 2012

29

Acknowledgements

•  22.63 Design Course Students:  S. Arsenyev, J. Ball, J. Goh, C. Kasten, P. Le, F. Mangiarotti,  B. Nield, T. Palmer, J. Sierchio, B. Sorbom, C. Sung, D. Sutherland

•  22.63 Design Course Teaching Assistants: H. Barnard, C. Haakonsen, Z. Hartwig, G. Olynyk

•  MIT professional staff: P. Bonoli, L. Bromberg, M. Greenwald, B. Lipshcultz, E. Marmar, J. Minervini, S. Wolfe

FPA Whyte Dec. 2012

30

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