# Maintenance of a stable current profile in a reversed field pinch

## Abstract

Externally produced magnetic fields could be used to maintain the reversed field pinch (RFP) plasma confinement configuration in a stable current, j{sub parallel}/B, profile. This would be accomplished by the creation of stochastic magnetic field regions in the vicinity of rational surfaces on which the safety factor q is the reciprocal of an integer N. External coils simultaneously excite the poloidal mode number unity and toroidal mode number N and N-1 helical fields from N=N{sub max} on down in a peristaltic manner, where N{sub max} is given by the maximal value of q in the RFP plasma. The time scale for turning off and on the N and N-1 pairs of coils is given by {tau}{sub w}{identical_to}({mu}{sub o}/{eta})w{sup 2}, where w=a/2N{sub max} is a typical island half-width required for island overlap, which implies local magnetic stochasticity, and a is the minor radius of the plasma. The total time scale for a complete current spreading cycle is N{sub max}{tau}{sub w}=({mu}{sub 0}/{eta})a{sup 2}/4N{sub max}, which is a factor of N{sub max}{approx_equal}10 faster than the time scale for the overall relaxation of the j{sub parallel}/B profile.

- Authors:

- Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)

- Publication Date:

- OSTI Identifier:
- 20974953

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 4; Other Information: DOI: 10.1063/1.2719628; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CONFIGURATION; CURRENTS; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; MAINTENANCE; MODE RATIONAL SURFACES; PLASMA; PLASMA CONFINEMENT; RELAXATION; REVERSE-FIELD PINCH; REVERSED-FIELD PINCH DEVICES; STOCHASTIC PROCESSES

### Citation Formats

```
Boozer, Allen H.
```*Maintenance of a stable current profile in a reversed field pinch*. United States: N. p., 2007.
Web. doi:10.1063/1.2719628.

```
Boozer, Allen H.
```*Maintenance of a stable current profile in a reversed field pinch*. United States. doi:10.1063/1.2719628.

```
Boozer, Allen H. Sun .
"Maintenance of a stable current profile in a reversed field pinch". United States.
doi:10.1063/1.2719628.
```

```
@article{osti_20974953,
```

title = {Maintenance of a stable current profile in a reversed field pinch},

author = {Boozer, Allen H.},

abstractNote = {Externally produced magnetic fields could be used to maintain the reversed field pinch (RFP) plasma confinement configuration in a stable current, j{sub parallel}/B, profile. This would be accomplished by the creation of stochastic magnetic field regions in the vicinity of rational surfaces on which the safety factor q is the reciprocal of an integer N. External coils simultaneously excite the poloidal mode number unity and toroidal mode number N and N-1 helical fields from N=N{sub max} on down in a peristaltic manner, where N{sub max} is given by the maximal value of q in the RFP plasma. The time scale for turning off and on the N and N-1 pairs of coils is given by {tau}{sub w}{identical_to}({mu}{sub o}/{eta})w{sup 2}, where w=a/2N{sub max} is a typical island half-width required for island overlap, which implies local magnetic stochasticity, and a is the minor radius of the plasma. The total time scale for a complete current spreading cycle is N{sub max}{tau}{sub w}=({mu}{sub 0}/{eta})a{sup 2}/4N{sub max}, which is a factor of N{sub max}{approx_equal}10 faster than the time scale for the overall relaxation of the j{sub parallel}/B profile.},

doi = {10.1063/1.2719628},

journal = {Physics of Plasmas},

number = 4,

volume = 14,

place = {United States},

year = {Sun Apr 15 00:00:00 EDT 2007},

month = {Sun Apr 15 00:00:00 EDT 2007}

}