Global power balance on high density field reversed configurations for use in magnetized target fusion

Richard M Renneke, Purdue University

Abstract

Field Reversed Configuration plasmas (FRCs) have been created in the Field Reversed Experiment-Liner (FRX-L) with density 2–6 × 10 22 m-3, total temperature 300–400 eV, and lifetime on the order of 10 µs. This thesis investigates global energy balance on high-density FRCs for the first time. The zero-dimensional approach to global energy balance developed by Rej and Tuszewski (Phys. Fluids 27, p. 1514, 1984) is utilized here. From the shots analyzed with this method, it is clear that energy loss from these FRCs is dominated by particle and thermal (collisional) losses. The percentage of radiative losses versus total loss is an order of magnitude lower than previous FRC experiments. This is reasonable for high density based on empirical scaling from the extensive database of tokamak plasma experiments. Ohmic dissipation, which heats plasma when trapped magnetic field decays to create electric field, is an important source of heating for the plasma. Ohmic heating shows a correlation with increasing the effective Lundquist number (S*). Empirical evidence suggest S* can be increased by lowering the density, which does not achieve the goals of FRX-L. A better way to improve ohmic heating is to trap more poloidal flux. This dissertation shows that FRX-L follows a semi-empirical scaling law which predicts plasma temperature gains for larger poloidal flux. Flux (τ&phis;) and particle (τN) lifetimes for these FRCs were typically shorter than 10 µs. Approximately 1/3 of the particle and flux lifetimes for these FRCs did not scale with the usual τN ≈ τ&phis; scaling of low-density FRCs, but instead showed τN ≥ τ &phis;. However, scatter in the data indicates that the average performance of FRCs on FRX-L yields the typical (for FRCs) relationship τ N ≈ τ&phis;. Fusion energy gain Q was extrapolated for the shots analyzed in this study using a zero-dimensional scaling code with liner effects. The predicted Q is below the desired value of 0.1 (Schoenberg et al., LA-UR-98-2413, 1998). The situation predicted to lead to Q = 0.1 requires a larger plasma pressure than shown in the present data. This can be accomplished by increasing the plasma density (through larger fill pressure) and maintaining temperature with increased flux trapping. Larger Q and other benefits could be realized by raising the plasma pressure for future FRX-L shots. The innovation inherent in this work performed by the author is the extension of the global power balance model to include a time history of the plasma discharge. This extension required rigorous checking of the power balance model using internal density profiles provided by the multichord interferometer. Typical orders of the parameters calculated by the model are ∼500 MW total loss power, ∼100 MW ohmic heating power, and ∼200 MW total compression (input) power. Radiation was never measured above 5 MW, which is why it was deemed insignificant. It should be noted that these numbers are merely estimates and vary widely between shots.

Degree

Ph.D.

Advisors

Choi, Purdue University.

Subject Area

Nuclear engineering|Plasma physics|Nuclear physics

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