# Presentation: 334756

## 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
- 	(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 limit
- 			BT 	  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/disassembly
Possibly free choice of aspect ratio

- 
- High beta
- Very high engineering beta (low field at coils)
- Normal coils, reduced shielding
- High mass power density (compact)
- Efficient maintenance/disassembly
- Possibly free choice of aspect ratio

## RFP Physics Challenges for Fusion

- Confinement
- Beta limits
- Resistive wall instabilities
- Current sustainment

## RFP Physics Challenges for Fusion

- Confinement
- 	at 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) control
- 	Electron energy increases
- 	Energy confinement improves ten-fold
- 	Tokamak-like electron confinement
- 	But, 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

- Ti (eV)

- r/a

- MST

## Confinement

- Status:
- 	Confinement improvement by j(r) control
- 	Electron energy increases
- 	Energy confinement improves ten-fold
- 	Tokamak-like electron confinement, with low BT
- 	But, so far demonstrated only transiently
- Recent advances:
- 	Ion energy and confinement increases
- 	large orbit ions very well-confined
- 	quasi-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) control
- 	Electron energy increases
- 	Energy confinement improves ten-fold
- 	Tokamak-like electron confinement, with low BT
- 	But, so far demonstrated only transiently
- Recent advances:
- 	Ion energy and confinement increases
- 	large orbit ions very well-confined
- 	quasi-single-helicity states obtained

## Beta Limits

- Status
- 	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 

*upper limit not yet known*

## Resistive Wall Instabilities

- Recent: 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

- 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 instabilities
- 			Single helicity states
- US/Japan:	Confinement
- 			Beta limits
- 			Sustainment

## 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