IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Engineering Tuesday Sessions
       Session SE-TuM

Paper SE-TuM3
Surface Processing of Large-scale FEL SS Test Electrodes by PSII/PVD to Suppress Field Emission

Tuesday, October 30, 2001, 9:00 am, Room 132

Session: Surface Engineering II: Cleaning, Modification, and Finishing
Presenter: L. Wu, College of William and Mary
Authors: L. Wu, College of William and Mary
D.M. Manos, College of William and Mary
F. Dylla, Thomas Jefferson National Accelerator Facility
C. Sinclair, Thomas Jefferson National Accelerator Facility
T. Siggins, Thomas Jefferson National Accelerator Facility
Correspondent: Click to Email
Large-scale highly polished stainless steel test electrodes for FEL electron injection gun have been processed by an integrated PSII/PVD system to suppress field emission. Hand polishing, which is very time-consuming and difficult, has been the main technique used to reduce field emission from these large 3-D electrode structures. Even after extensive polishing, the performance of the electrodes has been found to be unpredictable, with turn-on voltages varying by factors of 2 or more for similarly prepared electrodes. Prior to this work, the maximum practical operating field gradient was 3-6 MV/m, with a dark current of several nA. With a 0.61 m I.D. chamber, 0.57 m I.D. quartz window, and 0.43 m I. D. RF antenna, the PSII/PVD system used in this study is capable of large-area plasma source ion implantation and also of PVD of high purity SiO2 films over stainless steel, with adjustable nitrogen concentrations. Both the PSII and PVD processes are performed at low substrate temperatures, critical to keeping the original electrode surface profile and surface finish. Two recipes were developed, using DC glow discharge cleaning prior to HV pulse implanting to condition the electrode surface and to prevent arcing during implantation. In addition to the test electrodes, witness samples processed under similar conditions were studied by AES depth profiling, SIMS, variable angle spectroscopic ellipsometry, and micro-hardness testing. Results will be reported in detail. Field emission tests of the processed large-area electrodes showed that the electrodes were able to quickly achieve a field of 30 MV/m after minimal conditioning, and to hold this field for long periods with a dark current of only 160 pA. The implications for accelerator structures will be described.