Masters Theses

Date of Award

8-1995

Degree Type

Thesis

Degree Name

Master of Science

Major

Nuclear Engineering

Major Professor

Rafael B. Perez

Committee Members

Laurence F. Miller, Belle R. Upadhyaya

Abstract

The plasma divertor is a device that is used to limit the interaction between a plasma and neighboring material surfaces and guides the escaping plasma into a different chamber where the particles are neutralized. Magnetic confinement has as its principal aim to isolate the hot plasma from the cold first wall that surrounds the plasma. Nevertheless, some plasma comes into contact with the first wall and other surfaces as divertors and limiters. Ion and neutral-atom sputtering is a cause of impurity release from the first walls of a tokamak reactor. The effects of a plasma divertor on the particle confinement time in the Advanced Zoned Tokamak are examined by modeling of a particle, momentum, and energy transport equations in the plasma divertor and the plasma divertor and the particle transport in the main plasma. We have considered a simplified model for neutral-particle transport. Recent experiments have confirmed the formation of cold and dense plasma in a divertor chamber. The divertor plasma has two equilibrium states of the ion flux entering the divertor. It will be investigated that the existence of the two equilibrium states might lead to alteration of the particle confinement characteristics during additional heating. To stabilize and control the operation at the divertor, a control system was developed based on adjusting the pumping rate of neutrals and a proportional integral (PI) controller was introduced in order to accomplish the stability of the system. The stability of the divertor was examined for two power levels (0.5 MW and 2.0 MW) and two regions. These are high temperature and low plasma concentration, and conversely, low temperature and high plasma concentration. It is found that the existence of the two equilibrium states represent the two branches of solution of the present divertor model. The system is marginally stable.

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