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Title: Effect of self-bias on cylindrical capacitive discharge for processing of inner walls of tubular structures—Case of SRF cavities

Cylindrical capacitive discharge is a convenient medium for generating reactive ions to process inner walls superconductive radio-frequency (SRF) cavities. These cavities, used in particle accelerators, present a three-dimensional structure made of bulk Niobium, with axial cylindrical symmetry. Manufactured cavity walls are covered with Niobium oxides and scattered particulates, which must be removed for desired SRF performance. Cylindrical capacitive discharge in a mixture of Ar and Cl 2 is a sole and natural non-wet acid choice to purify the inner surfaces of SRF cavities by reactive ion etching. Coaxial cylindrical discharge is generated between a powered inner electrode and the grounded outer electrode, which is the cavity wall to be etched. Plasma sheath voltages were tailored to process the outer wall by providing an additional dc current to the inner electrode with the help of an external compensating dc power supply and corrugated design of the inner electrode. The dc bias potential difference is established between two electrodes to make the set-up favorable for SRF wall processing. To establish guidelines for reversing the asymmetry and establishing the optimal sheath voltage at the cavity wall, the dc self-bias potential and dc current dependence on process parameters, such as gas pressure, rf powermore » and chlorine content in the Ar/Cl 2 gas mixture was measured. In conclusion, the process is potentially applicable to all concave metallic surfaces.« less
Authors:
 [1] ;  [1] ; ORCiD logo [1] ;  [2] ;  [1]
  1. Old Dominion Univ., Norfolk, VA (United States)
  2. Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
Publication Date:
Report Number(s):
JLAB-ACC-18-2843; DOE/OR/23177-4562
Journal ID: ISSN 2158-3226
Grant/Contract Number:
SC0007879; AC05-06OR23177
Type:
Accepted Manuscript
Journal Name:
AIP Advances
Additional Journal Information:
Journal Volume: 8; Journal Issue: 8; Journal ID: ISSN 2158-3226
Publisher:
American Institute of Physics (AIP)
Research Org:
Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
OSTI Identifier:
1477748
Alternate Identifier(s):
OSTI ID: 1463754

Upadhyay, Janardan, Peshi, J., Popovic, Svetozar, Valente-Feliciano, Anne-Marie, and Vuskovic, Leposova. Effect of self-bias on cylindrical capacitive discharge for processing of inner walls of tubular structures—Case of SRF cavities. United States: N. p., Web. doi:10.1063/1.5045692.
Upadhyay, Janardan, Peshi, J., Popovic, Svetozar, Valente-Feliciano, Anne-Marie, & Vuskovic, Leposova. Effect of self-bias on cylindrical capacitive discharge for processing of inner walls of tubular structures—Case of SRF cavities. United States. doi:10.1063/1.5045692.
Upadhyay, Janardan, Peshi, J., Popovic, Svetozar, Valente-Feliciano, Anne-Marie, and Vuskovic, Leposova. 2018. "Effect of self-bias on cylindrical capacitive discharge for processing of inner walls of tubular structures—Case of SRF cavities". United States. doi:10.1063/1.5045692. https://www.osti.gov/servlets/purl/1477748.
@article{osti_1477748,
title = {Effect of self-bias on cylindrical capacitive discharge for processing of inner walls of tubular structures—Case of SRF cavities},
author = {Upadhyay, Janardan and Peshi, J. and Popovic, Svetozar and Valente-Feliciano, Anne-Marie and Vuskovic, Leposova},
abstractNote = {Cylindrical capacitive discharge is a convenient medium for generating reactive ions to process inner walls superconductive radio-frequency (SRF) cavities. These cavities, used in particle accelerators, present a three-dimensional structure made of bulk Niobium, with axial cylindrical symmetry. Manufactured cavity walls are covered with Niobium oxides and scattered particulates, which must be removed for desired SRF performance. Cylindrical capacitive discharge in a mixture of Ar and Cl2 is a sole and natural non-wet acid choice to purify the inner surfaces of SRF cavities by reactive ion etching. Coaxial cylindrical discharge is generated between a powered inner electrode and the grounded outer electrode, which is the cavity wall to be etched. Plasma sheath voltages were tailored to process the outer wall by providing an additional dc current to the inner electrode with the help of an external compensating dc power supply and corrugated design of the inner electrode. The dc bias potential difference is established between two electrodes to make the set-up favorable for SRF wall processing. To establish guidelines for reversing the asymmetry and establishing the optimal sheath voltage at the cavity wall, the dc self-bias potential and dc current dependence on process parameters, such as gas pressure, rf power and chlorine content in the Ar/Cl2 gas mixture was measured. In conclusion, the process is potentially applicable to all concave metallic surfaces.},
doi = {10.1063/1.5045692},
journal = {AIP Advances},
number = 8,
volume = 8,
place = {United States},
year = {2018},
month = {8}
}