[Jlabsa_gs] Pizza Seminar Series - Wednesday, March 20, 2013 - A message from Hari Areti
Jodi Patient
patient at jlab.org
Fri Mar 15 09:15:23 EDT 2013
Please let us know if you have any seminar topic suggestions.
Jefferson Lab's Graduate Student and Post-Doc Association Wiki:
https://gspda.jlab.org/wiki/index.php/Main_Page
Please RSVP to: patient at jlab.org by COB on March 18, 2013
Wednesday, March 20, 2013
***CC F113***
12:00-1:00 pm
"Field Emission Studies toward Improving the Performance of DC High Voltage Photoguns"
Mahzad BastaniNejad, Old Dominion University
Abstract
The field emission characteristics of niobium electrodes were compared to those of stainless steel electrodes using a DC high voltage field emission test apparatus. A total of eight electrodes were evaluated: two 304 stainless steel electrodes and six niobium electrodes. Upon the first application of high voltage, the best large-grain and single-crystal niobium electrodes performed better than the best stainless steel electrodes, exhibiting less field emission at comparable voltage and field strength. Of all the electrodes tested, a large-grain niobium electrode performed the best, exhibiting no measurable field emission (< 10 pA) at 225 kV with 20 mm cathode/anode gap, corresponding to a field strength of 18.7 MV/m. Inert gas conditioning was utilized as a way of eliminating/reducing field emission on all cathodes. Two important behavior of the anode current were studied which were “current suppression” due to an increase in the level of work function by the implanted gas ions into the metal surface and the “current amplification” due to current increase because of the ionized gas. As part of this study, both helium and krypton gases at different pairs of gap-pressure were examined and the effectiveness of each gas, pressure and gap were studied. Both gases have shown their effectiveness in general, however helium showed higher effectiveness at shorter gaps and krypton at larger gaps; This behavior was explained using TRIM/SRIM by ions implantation depth calculation where it showed that Helium needs less energy to be implanted at shallower depths where the work function changes are taking place.
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