Stability and operation of large anode fireball in magnetically constricted anode

Summary form only given. The electron sheath and anode double layer are interesting nonlinear structures that usually forms near small anode or a probe biased more positive than plasma potential. The anode fireball and electron sheath is subject to various instabilities and becomes unstable. We devised an experiment with magnetized anode to produce large sized fireball without having to use any biased grid structure ¹ . The DC glow discharge is formed by biasing the anode to positive few hundred volts with respect to grounded chamber. The discharge is operated in the range of 5 × 10 ^-3 mbar to 5 × 10 ^-2 mbar, keeping the discharge current in the range of 1 and 10 mA. The plasma shows formation of anode double layer and corresponding electron sheath. The size of fireball varies with pressure and voltage and can be explained by current balance. Typical plasma density is 1 × 10 ⁹ cm ^-3 and electron temperature is 3 eV, with about one order change in plasma density across the ionizing double layer. The discharge as a whole shows different behavior in different pressure regime with its own characteristic I-V curve. The low current regime is confined to central glow mode (C-Mode) whereas the high current branch is associated with peripheral mode (P-Mode). C-Mode is stable at low pressure and abruptly jumps to P-Mode at critical pressure and voltage. The discharge shows characteristic anode double layer oscillations in each mode with hysteresis in its appearance. The oscillations are typically in the range of few tens to few hundreds of kHz. The oscillations are present globally in floating potential and discharge current and increases in frequency with discharge voltage.