The Reversed Field Pinch: on the path to fusion energy
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Transcript of The Reversed Field Pinch: on the path to fusion energy
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The Reversed Field Pinch:on the path to fusion energy
S.C. PragerSeptember, 2006
FPA Symposium
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Why RFP research?
• RFP as a fusion configuration
• For fusion energy science(magnetic transport, resistive wall instabilities, electrostatic transport with strong shear, high beta instabilities, fast particle instabilities…..)
• For connections to plasma physics and astrophysics(benefits from hot, well-diagnosed fusion plasma)
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Why the RFP as a fusion configuration?
Toroidal confinement in the limitBT 0 at the plasma surface
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Why the RFP as a fusion configuration?
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low magnetic field
High beta
Very high engineering beta (low field at coils)Normal coils, reduced shielding
High mass power density (compact)Efficient maintenance/disassemblyPossibly free choice of aspect ratio
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RFP Physics Challenges for Fusion
• Confinement
• Beta limits
• Resistive wall instabilities
• Current sustainment
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RFP Physics Challenges for Fusion
• Confinementat q < 1, large transport from magnetic fluctuations; the historic RFP obstacle
• Beta limits intrinsically high; limit not yet known
• Resistive wall instabilities multiple modes unstable without a conducting shell
• Current sustainment bootstrap current small (except possibly at low aspect ratio)
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Confinement
Status: Confinement improved by j(r) controlElectron energy increasesEnergy confinement improves ten-foldTokamak-like electron confinementBut, so far demonstrated only transiently
Recent advances: Ion energy and confinement increases large orbit ions very well-confined quasi-single helicity states obtained
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Electron confinement improved
1
1.5
0.5
improved
standard
Te (keV)
MST
Energy confinement increases tenfold
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Ion energy increase
• Ions heated by reconnection event(“self-heating”)
• Ion energy retained by initiating improved confinement immediately following event
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Ion heating in standard plasma
Ion heating with improved confinement
Improved confinement
reconnectionevent
Ti
(eV)
Ti
(eV)
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Ions hotter over entire plasma
0
200
400
600
800
1000
1200
1400
1600
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Following reconnectionWith no reconnection
r/a
Ti
(eV)
r/a
MST
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Confinement
Status: Confinement improvement by j(r) controlElectron energy increasesEnergy confinement improves ten-foldTokamak-like electron confinement, with low BTBut, so far demonstrated only transiently
Recent advances:Ion energy and confinement increaseslarge orbit ions very well-confinedquasi-single-helicity states obtained
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Confinement of fast ions
Fast ion confinement time> 20
ms
From neutral beam injection
toroidal angle
radius
ion trajectory
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Confinement
Status: Confinement improvement by j(r) controlElectron energy increasesEnergy confinement improves ten-foldTokamak-like electron confinement, with low BTBut, so far demonstrated only transiently
Recent advances:Ion energy and confinement increaseslarge orbit ions very well-confinedquasi-single-helicity states obtained
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Beta LimitsStatus
Beta historically high, even with poor confinement,High beta also obtained with improved confinement
Recent With improved confinement, beta increases with pellet injection
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Beta increased, for example, from
€
βtotal =p
V
Bs2 /2μo
≈15%
€
βtotal ≈ 27%
€
βtoroidal =p
V
BT ,vac2 /2μo
≈ 80%
upper limit not yet known
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Resistive Wall InstabilitiesRecent: All instabilities suppressed by feedback
(RFX, Italy; T2, Sweden)
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Resistive Wall Instabilities
Recet: All instabilities suppressed by feedback
(RFX, Italy; T2, Sweden)
-Standard
-With feedback
€
˜ B r
toroidal mode number
Next: optimize for engineering feasibility,
additional programming for enhanced control
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Current Sustainment
• Oscillating field current drive(or ac helicity injection, an oscillating inductive technique,possibly efficient, but possibly degrades confinement)
• Bootstrap-current driven at small aspect ratio
• Pulsed reactor scenarios
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Oscillating field current drive
10% current drive
Ohmic efficiency
Next: increased power,
test efficiency and confinement compatibility
MST
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Current RFP Program Emphases
Europe: Resistive wall instabilitiesSingle helicity states
US/Japan: Confinement Beta limitsSustainment
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RFP Development
• In the next decade, with reasonably enhanced capabilities, the RFP can be advanced to more
fusion-relevant and new physics regimes
• If results are positive, the RFP could influence the fusion vision within the time to DEMO
• In the past decade, the RFP has developed substantially, with modest (but significant) resources