Burning plasmas

The fraction of fusion reaction energy that is released in energetic charged ions, such as the alpha particles of the D-T reaction, can be thermalized within the reacting plasma and used to maintain its temperature. This mechanism facilitates the achievement of very high energy multiplication factors Q, but also raises a number of new issues of confinement physics. To ensure satisfactory reactor operation, three areas of energetic ion interaction need to be addressed: (1) single ion transport in imperfectly symmetric magnetic fields or turbulent background plasmas; (2) energetic ion driven (or stabilized) collective phenomena; (3) fusion heat driven collective phenomena. The first of these topics is already being explored in a number of tokamak experiments, and the second will begin to be addressed in the D-T burning phase of TFTR and JET. Exploration of the third topic calls for high-Q operation, which is a goal of proposed next generation plasma burning projects. Planning for future experiments must take into consideration the full range of plasma physics and engineering R and D areas that need to be addressed on the way to fusion power demonstration.