Dresden 2014 – wissenschaftliches Programm
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VA: Fachverband Vakuumphysik und Vakuumtechnik
VA 3: Vacuum based Manufacturing, Coating and Analysis
VA 3.2: Vortrag
Montag, 31. März 2014, 16:00–16:20, HSZ 105
Glow discharge effects in a field emission vacuum chamber — •Daniela Wenger1,2, Wolfram Knapp3, Bernhard Hensel2, and Sandro F. Tedde1 — 1Siemens AG, Corporate Technology, Erlangen, Germany — 2Center for Medical Physics and Engineering, University Erlangen-Nuremberg, Germany — 3Otto von Guericke University, Magdeburg, Germany
The field emission properties of SWCNT/graphene hybrid samples were investigated in diode mode in a high vacuum chamber (10−8 mbar). For the application in medical X-ray systems for e.g. mammography, long pulses of more than 100 ms are necessary. The maximum current, which was achieved with short pulses, reached 400 mA (0.8 A/cm2). Here, IV characteristics were investigated with long pulse-on times up to 500 ms. The pulse-off time was varied, resulting in duty cycles between 0% (single pulse) and 100%.
During long voltage pulses of more than 100 ms, a significant increase of the current was measured. This indicates a secondary electron emission effect, which increases the initial field emission current. We assume that the field emission electrons ignite the glow discharge of the gas molecules in the gap between cathode and anode. The glow discharge can be observed as glowing plasma between cathode and anode. Since this gap is only 100 µm wide, the local pressure is probably much higher than the chamber pressure due to geometry and outgassing due to electron scattering at the anode.
Experimental evidences of avalanche discharges will be given. The local pressure will be calculated, based on observations of the plasma.