A new large area lanthanum hexaboride plasma source
Abstract
A new 18×18 cm2 active area lanthanum hexaboride (LaB6) plasma source for use in a dc discharge has been developed at UCLA. The cathode consists of four tiled LaB6 pieces indirectly heated to electron emission (1750 °C) by a graphite heater. A molybdenum mesh anode 33 cm in front of the LaB6 accelerates the electrons, ionizing a fill gas to create a 20×20 cm2 nearly square plasma. The source is run in pulsed operation with the anode biased up to +400 V dc with respect to the cathode for up to 100 ms at a 1 Hz repetition rate. Both the cathode and anode "float" electrically with respect to the chamber walls. The source is placed in a toroidal chamber 2 m wide and 3 m tall with a major radius of 5 m. Toroidal and vertical magnetic fields confine the current-free plasma which follows the field in a helix. The plasma starts on the bottom of the machine and spirals around it up to four times (120 m) and can be configured to terminate either on the top wall or on the neutral gas itself. The source typically operates with a discharge current up to 250 A in helium making plasmas with Te<30 eV, Ti<16 eV, and ne<3×1013 cm-3 in a background field of 100 G<Bo<320 G, giving a magnetized plasma with 0.1<β<1.
- Publication:
-
Review of Scientific Instruments
- Pub Date:
- August 2010
- DOI:
- 10.1063/1.3471917
- Bibcode:
- 2010RScI...81h3503C
- Keywords:
-
- discharges (electric);
- helium;
- lanthanum compounds;
- plasma sources;
- plasma toroidal confinement;
- 52.50.Dg;
- 52.55.Fa;
- 52.80.-s;
- Plasma sources;
- Tokamaks spherical tokamaks;
- Electric discharges