Stationary uniform plasmas by electron cyclotron heating in a linear multipole

A description is given of experimental results on stationary plasmas produc ed by 430 MHz electron cyclotron heating (ECH) in a linear multipole (hexad ecapole). A uniform and stable plasma was produced with 200 W rf power in t he magnetic-field-free central region over a large area (20 cm in diameter) and with an electron density of up to 1.5x10(11) cm(-3). This corresponds to more than 60 times the cutoff density for rf power at a frequency of 430 MHz. A silicon substrate was inserted into the midplane perpendicular to t he axis. The depletion in electron density due to the insertion was small a nd radial uniformity was well maintained. The changes in field-free zone ar ea and current density required to produce a stable confinement magnetic fi eld with strong enough intensity for ECH application are described for the case when the number of current rods on a constant circumference is increas ed. It is concluded that in principle the uniform plasma area can be widene d without limit by increasing the pole number while maintaining the same in terval between adjacent rods. (C) 2000 American Institute of Physics. [S003 4-6748(00)02809-4].