Plasma Physics Seminar ( Phys 769)

Prof. Thomas Pedersen, Columbia University Non-neutral plasmas in the CNT stellerator The Columbia Non-neutral Torus (CNT) is a stellarator devoted to the studies of non-neutral and electron-positron plasmas on magnetic surfaces. CNT has been in operation for two years now. Our first result was the verification, by field line mapping, of having created the lowest aspect ratio stellarator ever built. Small Debye-length, macroscopically stable pure electron plasmas have been created, and are now being studied. The confinement time of these plasmas can be up to 20 msec. Presently, electron confinement is limited by two transport processes - electron-neutral collisions, and transport driven by the perturbing presence of internal probe rods. Instabilities are seen when operating at a finite ion fraction, perhaps indicating that CNT has a helical analogue of the 'ion resonant instability' seen in Penning traps. Confinement jumps are observed at very low B-fields and high bias voltages. These results will be presented and discussed, as will our future plans for electron-positron plasma research.