Stationary uniform plasmas by electron cyclotron heating in a linear multipole

• Published in: Review of scientific instruments 2000-09, Vol.71 (9), p.3402-3408
• Main Authors: Fukao, Masayuki, Mizuno, Tamotsu, Saito, Yoshiharu, Matsuo, Hironobu
• Format: Article
• Language: English
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/1.1287630

A description is given of experimental results on stationary plasmas produced by 430 MHz electron cyclotron heating (ECH) in a linear multipole (hexadecapole). A uniform and stable plasma was produced with 200 W rf power in the magnetic-field-free central region over a large area (20 cm in diameter) and with an electron density of up to 1.5×10 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 the axis. The depletion in electron density due to the insertion was small and radial uniformity was well maintained. The changes in field-free zone area and current density required to produce a stable confinement magnetic field with strong enough intensity for ECH application are described for the case when the number of current rods on a constant circumference is increased. It is concluded that in principle the uniform plasma area can be widened without limit by increasing the pole number while maintaining the same interval between adjacent rods.