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. Prager September, 2006 FPA Symposium. Why RFP research?. RFP as a fusion configuration For fusion energy science - PowerPoint PPT PresentationTRANSCRIPT
The Reversed Field Pinch:on the path to fusion energy
S.C. PragerSeptember, 2006
FPA Symposium
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)
Why the RFP as a fusion configuration?
Toroidal confinement in the limitBT 0 at the plasma surface
Why the RFP as a fusion configuration?
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
RFP Physics Challenges for Fusion
• Confinement
• Beta limits
• Resistive wall instabilities
• Current sustainment
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)
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
Electron confinement improved
1
1.5
0.5
improved
standard
Te (keV)
MST
Energy confinement increases tenfold
Ion energy increase
• Ions heated by reconnection event(“self-heating”)
• Ion energy retained by initiating improved confinement immediately following event
Ion heating in standard plasma
Ion heating with improved confinement
Improved confinement
reconnectionevent
Ti
(eV)
Ti
(eV)
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
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
Confinement of fast ions
Fast ion confinement time> 20
ms
From neutral beam injection
toroidal angle
radius
ion trajectory
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
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
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
Resistive Wall InstabilitiesRecent: All instabilities suppressed by feedback
(RFX, Italy; T2, Sweden)
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
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
Oscillating field current drive
10% current drive
Ohmic efficiency
Next: increased power,
test efficiency and confinement compatibility
MST
Current RFP Program Emphases
Europe: Resistive wall instabilitiesSingle helicity states
US/Japan: Confinement Beta limitsSustainment
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