Design of compact loop antennas for present and future fusion heating experiments

The goal of the supplemental radio-frequency (rf) heating of fusion plasmas is to deliver power at high efficiencies deep within the plasma interior. Because the different plasma particle species give rise to a range of characteristic resonance frequencies, many options are available for heating a plasma through the absorp tion of energy from rf waves. Ion cyclotron resonant heating (ICRH) is one of the prime candidates for supplementary heating. The technology of ICRH haw reached the point of requiring "proof-of-performance" demonstrations of specific antenna designs. A functional understanding and utilization of aspects of plasma engi neering, electrical engineering, and mechanical engineering are necessary to design and evaluate ICRH antennas. The objective of this thesis is to identify these aspects and demonstrate their integration into the design process of a compact loop antenna.

The feasibility of wave excitation and energy deposition to a plasma can be established from the theories of plasma physics. The coupling and propagation, specifically of ICRH waves, are described. Once the theoretical rationale of ICRH is established, a logical progression toward the technology of its implementation is presented.

ICRH antennas can have different electrical configurations, each with characteristic advantages and limitations. A review of past and presently pursued concepts is presented, along with a comparison of the operating parameters for these concepts. Ultimately, the choice of a specific configuration will depend on the technological feasibility of achieving adequate coupling, lifetime, and reliability.

The technology of rf antennas is governed by a closely meshed interaction between electrical and mechanical requirements and constraints. The design of the Oak Ridge National Laboratory (ORNL) version of the antenna configuration chosen for the Tokamak Fusion Test Reactor (TFTR) is used to characterize rf antenna technology.

As with any design process, the requirements and target parameters are first defined. These design criteria are presented in terms of plasma, electrical, and me chanical considerations. Once the requirements are established, a comprehensive description of the antenna configuration and the functional purpose of individual components is presented. Individual components are evaluated for specific functionality as dictated by electrical, thermal, structural, and material compatibility requirements.

The rf technology developed for present fusion experiments must be extended for the design of antennas of future devices. These future machines will impose new requirements that must be addressed. The final subject is a survey of future antenna design considerations as an extension of present technology, including reactor-relevant plasma heating and nuclear environments.