An investigation and minimization of the tau = 1/2 magnetic islands on the compact Auburn torsatron. Ph.D. Thesis

Thesis/Dissertation · Fri Dec 31 04:00:00 EST 1993

OSTI ID:135426

Hartwell, G JOSEPH

In toroidal magnetic fusion confinement devices, such as tokamaks and stellarators, the formation of magnetic islands is possible. Magnetic islands are formed when magnetic field errors, or perturbations, exist which resonate with magnetic flux surfaces having rational rotational transforms. Knowledge of and minimization of magnetic islands is important because the presence of magnetic islands enhances the plasma transport from regions bounded by the magnetic islands to regions outside of the magnetic islands. The Compact Auburn Torsatron (CAT) is an example of an optimized torsatron in the stellarator class of magnetic confinement devices. The unique feature of CAT is that the magnetic fields are produced by two main helical windings which allows the variation of the rotational transform profile in CAT. In this experiment, the tau = 1/2 magnetic islands are studied under the assumption that the magnetic islands can be described as a Hamiltonian system, much like that of a simple pendulum. Momentum-like, frequency-like and mass-like terms are measured and are related to the toroidal flux, local rotational transform and shear respectively. The variation of these quantities is investigated as a function of the magnetic error fields producing the islands. The magnitude and phase of the error field is controlled with the use of two separate sets of correction coils. The first correction coil configuration consists of a pair of Helmholtz coils which produce orthogonal horizontal fields. The second configuration consists of a set of helical correction coils that produces a magnetic field which resonates strongly with the tau = 1/2 magnetic island. The electron-beam, phosphor-screen method was used to investigate the magnetic flux surfaces. The applicability and limitations of the Hamiltonian theory are discussed.

• Research Organization: Auburn Univ., AL (United States)
• OSTI ID: 135426
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
CONTROL
MAGNETIC FIELDS
MAGNETIC FLUX
MAGNETIC ISLANDS
OPTIMIZATION
TORSATRON STELLARATORS