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FIZIKA A 14 (2005) 3, 225 - 232
 
CHARACTERISTICS OF DC PSEUDO-ELECTRIC (VIRTUAL CATHODE) DISCHARGE IN
HELIUM GAS
M. A. SAUDYa, A. I. EATAHa and M. M. MASOUDb
aPhysics Department, Faculty of Science, Ain Shams
University, Cairo, Egypt
bAtomic Energy Authority, Egypt
Received 5 May 2004 ; revised manuscript received 14 March
2005
Accepted 2 May 2005 Online 6 February 2006
The plasma properties of a DC pseudo-discharge have been studied in helium as working
gas. The discharge takes place between a disc cathode and a mesh anode, similar to a
pulsed virtual-cathode oscillator. It has been found that breakdown characteristics
essentially deviate from the expected regular Paschen curves. The current-voltage
characteristics of the DC discharge show that it occurs in the region of abnormal glow.
The breakdown voltage increases with the decrease of working gas pressure. When the
electron beam density increases, the plasma covers the whole surface of the discharge cell
outside the electrodes. The plasma has a negative potential with respect to the mesh and
the location of the virtual cathode has been measured at around 1 cm from the mesh anode.
The axial and radial distributions of electron temperature and ion density have been
measured using a double electric probe. The electron temperature has been found to vary
between 0.4 and 1 eV and the ion density from 2.8 ×1010 to 4.5 ×1010
cm-3, outside the electrodes. The plasma electron
temperature was nearly constant along the axial and radial directions. The plasma density
has been found to decrease with axial distance due to electron beam energy loss, and also
decreased in the radial position due to diffusion to the discharge walls.
PACS numbers: 51.50.+v, 52.80.Hc
UDC 537.525
Keywords: DC pseudo-discharge in helium, breakdown characteristics, abnormal glow,
electron temperature, ion density
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