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Heat pulse propagation studies in TFTR

The time-scales for sawtooth repetition and heat pulse propagation are much longer (tens of milliseconds) in the large tokamak TFTR than in previous, smaller tokamaks. This extended time-scale, coupled with more detailed diagnostics, has led us to revisit the analysis of heat pulse propagation as a method to determine the electron heat diffusivity χe in the plasma. A combination of analytic and computer solutions of the electron heat diffusion equation is used to clarify previous work and to develop new methods for determining χe. Direct comparison of the predicted heat pulses with soft-X-ray and ECE data indicates that the space-time evolution is diffusive. However, the χe determined from heat pulse propagation usually exceeds that determined from background plasma power balance considerations by a factor ranging from two to ten. Some hypotheses for resolving this discrepancy are discussed.