Impurity and deuterium pellet studies on TFTR

Medium speed lithium and carbon pellets (v_p=0.4-0.8 km/s) and solid deuterium pellets (v_p=1.3-1.5 km/s) have been injected into Ohmic, L-mode, and supershot TFTR plasmas. They have been used to study fueling, profile modification, particle and energy transport, and the dependence of confinement on density peakedness and heating power profile. Injection of Li and C pellets approximately 1 s before the neutral beams into low recycling, supershot target plasmas has resulted in a significant increase (5-20%) in the neutron rate during the beam heated portion of the discharge. In addition, injection of Li pellets and the use of Zeeman polarimetry on line emission from the Li ablation cloud have allowed measurement of internal poloidal magnetic field profiles. Multiple D₂ pellets have been used to fuel neutral beam heated discharges to densities of 5×10²⁰m^-3 without disruption or indication of enhanced core particle transport. Plasma current and power scaling studies of deuterium pellet densified, ³He-minority ICRF heated discharges have been performed. Reduced core transport is observed at both plasma currents studied. Global energy confinement measured at the maximum of the stored energy exhibits L-mode type scaling. Interferometric measurements of the prompt (approximately 100 μs) responses of the electron density to these pellets are also reported. A long-lived, localized region of high electron density ablatant is routinely observed in the leading edge of the ablatant wake. These high density perturbations propagate at velocities of approximately 10⁴-10⁵ m/s and, at least for D₂ pellets, appear to travel along field lines.