50 Years of Electron Cyclotron Emission Research

Electron cyclotron emission (ECE) has been of interest in fusion research since the beginning, in the late 1950s, of the worldwide effort to realize fusion energy. The initial interest was in its contribution to the power loss, which under some conditions was predicted to be a possible impediment to achieving net power generation from fusion. The current interest centers on the use of measurements of the emission as a powerful means of determining the value of some of the main parameters of the plasma: Most modern tokamaks and stellarators are equipped with extensive ECE measurement systems. Creativity, surprises, debate, careful experimentation, and solid theoretical work characterize the path in between, which has not always been smooth but through the diagnostic applications has ultimately been very successful. In this paper, we trace that path by identifying and illustrating the main developments. We also take a brief look forward. The transport of energy due to ECE is expected to play a significant role in the burn dynamics of fusion plasmas, and this role is outlined. Measurements of ECE are expected to play an important role in the diagnosis of future fusion machines, like ITER, that will achieve thermonuclear conditions. There are significant benefits and challenges associated with making measurements of ECE on such plasmas, and these are briefly summarized.