The effects of magnetic field errors on reversed field pinch plasma

Technical Report · Sat Dec 01 04:00:00 EST 1990

OSTI ID:5569789

Almagri, A F

Studies of magnetic field error effects on Reversed Field Pinch plasma were carried out on the Madison Symmetric Torus. Magnetic field errors at the poloidal gap were reduced by 18% in rms value. This modest reduction of field errors resulted in improved plasma discharges. The plasma loop voltage was reduced by about 31%, and the plasma resistivity was reduced by 36%. Reversal duration increased by 16%. The character of the sawtooth activity as seen on the toroidal field at the wall changed considerably when field errors were reduced. These results suggest improved plasma confinement. Field errors were reduced further by a factor of six in rms value. With this reduction of field errors, plasma loop voltage was reduced by about a factor of two. The discharge duration doubled. At this low level of field errors, the plasma exhibited coherent magnetic fluctuations. These fluctuations have a poloidal mode number m = 1 and toroidal mode number n = 5 - 10. These modes are typically phase-locked to one another to form a localized perturbation. This perturbation rotates toroidally in the ion-diamagnetic drift direction with a speed of about 10{sup 6} cm/sec. Occasionally these modes are observed to lock to the conducting wall. This locking is believed to be caused by the poloidal gap field errors. These locked discharges tend to be much shorter in duration and to have larger loop voltage. The behavior of locked discharges can be explained by a field-error instability. Some estimates of the internal radial magnetic fields and the resulting magnetic islands are calculated. These calculations show that the field errors need to be reduced to less than 2% of the poloidal field at the wall to reduce islands overlap.

• Research Organization: Wisconsin Univ., Madison, WI (USA)
• Sponsoring Organization: DOE; USDOE, Washington, DC (USA)
• DOE Contract Number: FG02-85ER53198
• OSTI ID: 5569789
• Report Number(s): DOE/ER/53198-171; ON: DE91013636
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
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CONFINEMENT
ERRORS
FLUCTUATIONS
MAGNETIC FIELD CONFIGURATIONS
MAGNETIC FIELDS
MAGNETIC ISLANDS
OSCILLATIONS
PINCH EFFECT
PLASMA CONFINEMENT
PLASMA DIAGNOSTICS
REVERSE-FIELD PINCH
SAWTOOTH OSCILLATIONS
VARIATIONS