Grid-controlled electron emission from a hollow-anode electron source

Summary form only given. The operation of a hollow-anode (HA) electron source with a biased output grid and an incorporated ferroelectric plasma source (FPS) in a diode powered by a 200 kV, 400 ns pulse is described. It was found that the FPS allows reliable ignition and sustaining of the HA discharge with current amplitude /spl les/1.2 kA and pulse duration /spl les/2/spl times/10/sup -5/ s at N/sub 2/ gas pressure of (1-3)/spl times/10/sup -4/ Torr. Parameters of the hollow-anode plasma were studied by different electrical, optical and spectroscopic diagnostics. It was found that the plasma density is /spl sim/2/spl times/10/sup 14/ cm/sup -3/ and /spl sim/4/spl times/10/sup 12/ cm/sup -3/ at the vicinity of the ferroelectric surface and at the output anode grid, respectively. Three different electrical schemes for the hollow-anode grid bias were tested and compared. The use of an auto-bias grid allows electron beam extraction with current I/sub b//spl les/1.2 kA in an emission-limited mode and insignificant plasma pre-filling of the accelerating gap. The use of an externally biased hollow-anode grid (either with a positive or negative potential) showed the possibility to control the plasma emission properties (I/sub b//spl les/2 kA) without changing the amplitude of the discharge current. Drastic changes in the parameters of the plasma were obtained during the accelerating pulse. The applied accelerating pulse causes a significant increase of the plasma potential (/spl phi//sub pl/) inside the hollow anode. For a discharge current amplitude of 0.3-1 kA, /spl phi//sub pl/ increases relative to the hollow-anode electrode as 6.6-3.1 kV, relative to the ferroelectric plasma source as 0.2-0.4 kV, and relative to the hollow-anode grid as 2.9-1.2 kV. A model which explains the electron emission from the positively charged plasma is proposed. The model suggests screening of the hollow-anode grid potential by the space charge of ions oscillating through the hollow-anode - utput grid. These oscillations occur inside the potential well formed between the hollow-anode plasma boundary and a virtual anode formed inside the accelerating gap. Generation and characterization of a high-current electron beam with current amplitude of /spl sim/1.2 kA was achieved under an accelerating pulse amplitude /spl les/300 kV and /spl sim/400 ns pulse duration.