LINAC2014 - List of Authors (McMahan, C.J.)

Paper	Title	Page
MOPP115	Plasma Processing of Nb Surfaces for SRF Cavities	323
MOPOL10	use link to see paper's listing under its alternate paper code
	P.V. Tyagi, M. Doleans, S.-H. Kim ORNL, Oak Ridge, Tennessee, USA R. Afanador, C.J. McMahan ORNL RAD, Oak Ridge, Tennessee, USA
	Funding: This work is supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE. Field emission is one of the most critical issues to achieve high performances of niobium (Nb) superconducting radio frequency (SRF) cavities. Field emission is mainly related to contaminants present at top surface of SRF cavities that act as electron emitters at high gradient operation and limit the cavity accelerating gradient. An R&D program at the Spallation Neutron Source (SNS) is in place* aiming to develop an in-situ plasma processing technique to remove some of the residual contaminants from inner surfaces of Nb cavities and improve their performance. The plasma processing R&D has first concentrated on removing hydrocarbon contamination from top surface of SRF cavities. Results from the surface studies on plasma processed Nb samples will be presented in this article and showed the removal of hydrocarbons from Nb surfaces as well as improvement of the surface workfuntion (WF). *M. Doleans et al. “Plasma processing R&D for the SNS superconducting linac RF cavities” Proceedings of 2013 SRF workshop, Paris, France
	Slides MOPP115 [1.405 MB]

THPP109	History of Cryomodule Repairs at SNS	1108
	M.P. Howell, M. Doleans, D.L. Douglas, S.-H. Kim ORNL, Oak Ridge, Tennessee, USA R. Afanador, B. DeGraff, B.S. Hannah, C.J. McMahan, T.S. Neustadt, S.W. Ottaway, J. Saunders, P.V. Tyagi, D.M. Vandygriff ORNL RAD, Oak Ridge, Tennessee, USA
	The operation of the Superconducting linear accelerator (SCL) has matured and now averages less than one trip per day. The availability of the SCL including radiofrequency systems, high voltage converter modulators, controls, vacuum and other support systems over the last three years is approximately 98%. The SNS has been in operation for ten years including the commissioning period. In support of achieving the stability of operation, multiple cryomodule repairs have been performed. Repairs to cryomodules have included instruments, helium leaks, valve actuators, cavity tuners, insulating vacuum repairs and upgrades, power supplies, higher order mode (HOM) feedthroughs, coupler windows, and coupler cooling components. Performance degradation has been experienced in multiple cavities. This has been corrected by thermal cycling the cryomodules with the affected cavities. Only two cavities have displayed slight permanent degradation that could not be corrected by thermal cycling. Repairs made to the SNS cryomodule will be detailed in this paper.

Paper

Title

Page

MOPP115

Plasma Processing of Nb Surfaces for SRF Cavities

323

MOPOL10

use link to see paper's listing under its alternate paper code

P.V. Tyagi, M. Doleans, S.-H. Kim
ORNL, Oak Ridge, Tennessee, USA
R. Afanador, C.J. McMahan
ORNL RAD, Oak Ridge, Tennessee, USA

Funding: This work is supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE.
Field emission is one of the most critical issues to achieve high performances of niobium (Nb) superconducting radio frequency (SRF) cavities. Field emission is mainly related to contaminants present at top surface of SRF cavities that act as electron emitters at high gradient operation and limit the cavity accelerating gradient. An R&D program at the Spallation Neutron Source (SNS) is in place* aiming to develop an in-situ plasma processing technique to remove some of the residual contaminants from inner surfaces of Nb cavities and improve their performance. The plasma processing R&D has first concentrated on removing hydrocarbon contamination from top surface of SRF cavities. Results from the surface studies on plasma processed Nb samples will be presented in this article and showed the removal of hydrocarbons from Nb surfaces as well as improvement of the surface workfuntion (WF).
*M. Doleans et al. “Plasma processing R&D for the SNS superconducting linac RF cavities” Proceedings of 2013 SRF workshop, Paris, France

Slides MOPP115 [1.405 MB]

THPP109

History of Cryomodule Repairs at SNS

1108

M.P. Howell, M. Doleans, D.L. Douglas, S.-H. Kim
ORNL, Oak Ridge, Tennessee, USA
R. Afanador, B. DeGraff, B.S. Hannah, C.J. McMahan, T.S. Neustadt, S.W. Ottaway, J. Saunders, P.V. Tyagi, D.M. Vandygriff
ORNL RAD, Oak Ridge, Tennessee, USA

The operation of the Superconducting linear accelerator (SCL) has matured and now averages less than one trip per day. The availability of the SCL including radiofrequency systems, high voltage converter modulators, controls, vacuum and other support systems over the last three years is approximately 98%. The SNS has been in operation for ten years including the commissioning period. In support of achieving the stability of operation, multiple cryomodule repairs have been performed. Repairs to cryomodules have included instruments, helium leaks, valve actuators, cavity tuners, insulating vacuum repairs and upgrades, power supplies, higher order mode (HOM) feedthroughs, coupler windows, and coupler cooling components. Performance degradation has been experienced in multiple cavities. This has been corrected by thermal cycling the cryomodules with the affected cavities. Only two cavities have displayed slight permanent degradation that could not be corrected by thermal cycling. Repairs made to the SNS cryomodule will be detailed in this paper.