Engineering Papers⌕ Search

Engineering topics

Powers, Thomas

Publications and source records attributed to Powers, Thomas.

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

AN OVERVIEW OF PLASMA PROCESSING OF SRF CAVITIES AT JLAB

Plasma processing is a common technique where the free oxygen produced in a low-pressure RF plasma breaks down and removes hydrocarbons from surfaces. This increases the work function and reduces the secondary emission coefficient of the treated surfaces. Jefferson Lab has an ongoing R&D program in plasma processing. The experimental program investigated processing using argon/oxygen and helium/oxygen gas mixtures. The initial focus of the effort was processing C100 cavities by injecting RF power into the HOM coupler ports. We also developed the methods for establishing a plasma C75 cavities where the RF power is injected via the fundamental power-coupler. As part of the process development we processed, three C100 cryomodules in our off-line cryomodule test facility. In May 2023 we processed four C100 cryomodules in-situ in the CEBAF accelerator with the cryomodules returning to an operational status in Sept. 2023. The cumulative improvement in field emission free operation, as measured on a cavity by cavity basis, was 59 MeV or 24%. We recently started processing 7 cryomodules in the CEBAF accelerator in August 2024. Methods systems and results from processing cryomodules and individual cavities in the vertical test will be presented. Current status and future plans will also be presented.

Ganey, Tiffany↗
DOE OSTI2023

IN SITU PLASMA PROCESSING OF SUPERCONDUCTING CAVITIES AT JLAB, 2023 UPDATE

Jefferson Lab has an ongoing R&D program in plasma processing which just completed a round of production processing in the CEBAF accelerator. Plasma processing is a common technique for removing hydrocarbons from surfaces, which increases the work function and reduces the secondary emission coefficient. The initial focus of the effort was processing C100 cavities by injecting RF power into the higher order mode (HOM) coupler ports. Results from processing cryomodules in the CEBAF accelerator as well as vertical test results will be present-ed. The goal of in-situ processing is to improve the operational gradients and the energy margin of the linacs. This work will describe the systems and methods used at JLAB for processing cavities using an argon-oxygen gas mixture as well as a helium-oxygen gas mixture. Before and after plasma processing results will also be presented.

Powers, Thomas↗
DOE OSTI2023

Simulation of the dynamics of gas mixtures during plasma processing in the C75 Cavity

Plasma processing using a mixture of noble gas and oxygen is a technique that is currently being used to reduce field emission and multipacting in accelerating cavities. Plasma is created inside the cavity when the gas mixture is exposed to an electromagnetic field that is generated by applying RF power through the fundamental power or higher-order mode couplers. Oxygen ions and atomic oxygen are created in the plasma which breaks down the hydrocarbons on the surface of the cavity and the residuals from this process are removed as part of the process gas flow. Removal of hydrocarbons from the surface increases the work function and reduces the secondary emission coefficient. This work describes the initial results of plasma simulation, which provides insight into the ignition process, distribution of different species, and interactions of free oxygen and oxygen ions with the cavity surfaces. The simulations have been done with an Ar/?2 plasma using COMSOL® multiphysics. These simulations help in understanding the dynamics and control of plasma inside the cavity and the exploration of different gas mixtures.

Dhakal, Pashupati↗
DOE OSTI2023

Development of a Prototype Superconducting Radio-Frequency Cavity for Conduction-Cooled Accelerators

Recent progress in the development of high-quality Nb?Sn film coatings along with the availability of cryocoolers with high cooling capacity at 4 K makes it feasible to operate SRF cavities cooled by thermal conduction at relevant accelerating gradients for use in accelerators. We have developed a prototype single-cell cavity to prove the feasibility of operation up to the accelerating gradient required for 1 MeV energy gain, cooled by conduction with cryocoolers. The cavity has a ~3 ¿m thick Nb?Sn film on the inner surface, deposited on a ~4 mm thick bulk Nb substrate and a bulk ~7 mm thick Cu outer shell with three Cu attachment tabs. The cavity was tested up to a peak surface magnetic field of 53 mT in liquid He at 4.3 K. A horizontal test cryostat was designed and built to test the cavity cooled with three cryocoolers. The rf tests of the conduction-cooled cavity achieved a peak surface magnetic field of 50 mT and stable operation was possible with up to 18.5 W of rf heat load. The peak frequency shift due to microphonics was 23 Hz. These results represent the highest peak surface magnetic field achieved in a conduction-cooled SRF cavity to date

Ciovati, Gianluigi↗