ORNL, Oak Ridge, Tennessee, USA
Contaminants present at top surface of superconducting radio frequency (SRF) cavities can act as field emitters and restrict the cavity accelerating gradient. A room temperature in-situ plasma processing technology for SRF cavities aiming to clean hydrocarbons from inner surface of cavities has been recently developed at the Spallation Neutron Source (SNS). Surface studies of the plasma processed Nb samples by Secondary ion mass spectrometry (SIMS) and Scanning Kelvin Probe (SKP) showed that the NeO2 plasma processing is very effective to remove carbonaceous contaminants from top surface and improves the surface work function by 0.5 to 1.0 eV.
*M. Doleans et al., Proc. 2013 SRF, Paris, France.
**P. V. Tyagi, et al., Proc. Linac14, Geneva, Switzerland.
***M. Doleans et al., These proceedings.
ORNL, Oak Ridge, Tennessee, USA
ORNL RAD, Oak Ridge, Tennessee, USA
The Spallation Neutron Source (SNS) has developed a vertical test area (VTA) for the testing and qualification of superconducting radio frequency cavities. The associated RF System successfully supported the initial commissioning of the VTA system and has been utilized for cavity testing at both 4 and 2 K. As operational experience was gained, improvements to the RF system were implemented to better utilize the dynamic range of the system, and software updates and additions were made to meet the operational needs. The system continues to evolve as we gain better understanding of the testing needs.
THBA01
ORNL, Oak Ridge, Tennessee, USA
A new In-situ plasma processing technique is being developed at the SNS (Spallation Neutron Source) to improve the performance of the cavities in operation. The technique utilizes a reactive low-density room-temperature plasma to remove top-surface hydrocarbons. This increases the work function of the cavity surface and reduces the overall amount of electron activity; In particular it increases the field-emission onset, which enables to operate a cavity at higher accelerating gradient. Development of the basic plasma processing parameters and effect on the Niobium surface can be found elsewhere *,**. Details on the results for in-situ plasma processing of dressed cavities in the SNS HTA (horizontal test apparatus) will be reported here.
* M. Doleans et al. “Plasma processing R&D for the SNS superconducting linac RF cavities” SRF2013 Proceedings
** P. V. Tyagi, et al. “Surface Studies of Plasma Processed Nb samples” These proceedings
ORNL RAD, Oak Ridge, Tennessee, USA
Omega Technical Services, Oak Ridge, Tennessee, USA
ORNL, Oak Ridge, Tennessee, USA
Many of the SRF activities involve interactions to cavities which presents risk for particulate contamination to RF surfaces. In order to understand and reduce contamination in cavities during cleaning, vacuum pumping and purging, and in-situ cryomodule repairs, a Quality Assurance (QA) studies were initiated to evaluate these activities and improve them where possible. This paper covers the results of investigations on the effectiveness of the SNS ultrasonic cleaning systems, particulate control during pumping and purging, procedure development for in-situ cryomodule repairs, the application of these studies to the repair of a linac cryomodule, and discussion of further improvement in these areas.