Alpha storage regime in high temperature sub-ignited D-T tokamaks

Alpha particle parameters in sub-ignited D-T tokamaks such as TFTR can be optimized in a high temperature 'alpha storage regime' in which the alpha particle thermalization time ??is long (?1.0 s) and in which the alpha particle source rate S?is enhanced because of beam-target and beam-beam reactions (by a factor of ?2-4). Near reactor-level alpha instability parameters, ??(O)? n?(0)/ne(0) ? 1%, are predicted by simulation codes when Q 0.5; present TFTR 'supershots' already have ??(O) ? n?(0)/ne(0)? 0.1-0.2%. This alpha storage regime can be used for the first time to test theories of collective alpha instabilities and can also be used to provide a strong (but transient) alpha heating pulse. An experimental scenario to exploit this regime is described.