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 τα is long (1.0 s) and in which the alpha particle source rate Sα is enhanced because of beam-target and beam-beam reactions (by a factor of 2-4). Near reactor-level alpha instability parameters, βα(0)nα(0)/ne(0)1%, are predicted by simulation codes with Q0.5; present TFTR 'supershots' already have βα(0)nα(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.