EFFECTS OF FUELLING PROFILES ON PLASMA TRANSPORT

A one-dimensional (1-D), multifluid transport model is used to investigate the effects of particle fuelling profiles on plasma transport in an ignition-sized tokamak. The neutral-beam injection power required to reach ignition is used as a measure of the conduction and convection energy losses. Normal diffusive properties of plasmas are likely to maintain the density at the centre of the discharge even if no active fuelling is provided there; this significantly relaxes the requirements for fuel penetration. Not only is lower fuel penetration easier to achieve, but it may have the advantage of reducing or eliminating density-gradient-driven trapped-particle microinstabilities. Simulation of discrete pellet fuelling indicates that relatively low-velocity (ℼ 103 m·s™1) pellets may be sufficient to (1) fuel a device of this size (ℼ 1.25m minor radius), (2) produce a relatively broad, and cool edge region of plasma which should reduce the potential for sputtering, and (3) reduce the likelihood of trapped-particle-mode-dominated transport. Low-penetrating pellets containing up to 10-20% of the total plasma ions can produce fluctuations in density and temperature at the plasma edge, but the pressure profile and fusion alpha production remain almost constant. © 1979 IOP Publishing Ltd.