ORNL, Oak Ridge, Tennessee, USA
ORNL RAD, Oak Ridge, Tennessee, USA
The SNS linac output energy has increased since the start of neutron production in FY2007. The various improvements that contributed to the increase of the linac output energy are LLRF/control system improvement, high voltage converter modulator system improvement, high-power RF system improvement, cryomodule repairs, spare cryomodule development and accelerating gradient improvement through in-situ plasma processing. In this paper, the history of the SNS SCL output energy is reported, and plans for the near-term future and for the Proton Power Upgrade (PPU) project are also presented.
Fermilab, Batavia, Illinois, USA
ORNL, Oak Ridge, Tennessee, USA
SLAC, Menlo Park, California, USA
SRF cavities performance preservation is crucial, from vertical test to accelerator operation. Field emission is still one of the main problems to overcome and plasma cleaning has been proven successful by SNS, in cleaning field emitters and increasing the work function of Nb. A collaboration has been established between FNAL, SLAC and ORNL with the purpose of applying plasma processing to LCLS-II cavities, in order to minimize and overcome field emission without affecting the high Q of N-doped cavities. The recipe will follow the neon-oxygen active plasma adopted at SNS, allowing in-situ processing of cavities and cryomodules from hydrocarbon contaminants. A novel method for plasma ignition has been developed at FNAL: a plasma glow discharge is ignited using high order modes to overcome limitations imposed by the fundamental power coupler. The results of experiments on 9-cell LCLS-II cavity are presented, along with plasma ignition studies. In addition the RF system is shown and N-doped Nb samples studies are discussed.
ORNL, Oak Ridge, Tennessee, USA
Fermilab, Batavia, Illinois, USA
Work function and surface chemistries of SiC-polished, electropolished, and nitrogen-doped niobium coupons were analyzed before and after plasma processing using a neon-oxygen gas mixture. These studies represent an initial enquiry into the feasibility of applying the plasma processing technique designed at ORNL for the Spallation Neutron Source (SNS) to the nitrogen-doped Nb cavities for the Coherent Light Source II (LCLS-II). Work function of all measured samples was increased after plasma processing, which indicates the strong potential of the plasma processing technique as a tool for increasing the accelerating gradient of nitrogen-doped cavities.