FIZIKA A 14 (2005)  3, 225 - 232

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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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