EXPERIMENTAL-STUDY OF CURVATURE-DRIVEN FLUTE INSTABILITY IN THE GAS-DYNAMIC TRAP

A curvature-driven flute instability will be excited in the magnetized plasmas if the magnetic field lines curve toward the entire plasma bo undary. Conditions under which it can be effectively stabilized in axi symmetric geometry have been experimentally studied in a gas-dynamic t rap (GDT) at Novosibirsk. Flexible design of the experimental device a nd the availability of neutral beams and ion cyclotron heating enabled the pressure-weighted curvature to be varied over a wide range. The s tability limits were thus measured and compared with those predicted b y the modified Rosenbluth-Longmire criterion. Characteristics of unsta ble curvature-driven flute modes were also measured and found to confo rm to a theory including finite ion Larmor radius (FLR) effects. Stabl e operation during neutral beam injection was achieved with a cusp end cell, resulting in an increase in T(e) to 45 eV, limited by end losse s rather than anomalous power losses.