| Paper | Title | Page |
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| MOP085 | The Destructive Effects to the RF Coupler by the Plasma Discharge | 285 |
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| The low temperature RF plasma was proved an effec-tive method to clean the niobium surface and relieve the field emission effect for the SRF cavities. In the case of half-wave resonators, these cavities were usually powered via the fundamental coupler with the electric coupling. Thus, coupler antennas were fixed in the intense electric field region, and this region was where the plasma rou-tinely ignited. Therefore, the ceramic window of coupler taken the risk of breakdown under the sputtering of ions and heating loads that may be caused by the plasma drift and diffusion from the electric field region. In this paper, the plasma ignition for surface cleaning on the HWR cavity and its coupler was investigated, and the power transmission, temperature raising and vacuum degradation were tested to characterize the adverse impacts on the ceramic window. Finally, the solution was proposed to figure these issues. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP085 | |
| About • | paper received ※ 22 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019 | |
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| THP010 | The Mechanism of Electropolishing of Niobium from Choline Chloride-based Deep Eutectic Solvents | 852 |
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Funding: National Natural Science Foundation (11705252) The mechanism of electropolishing of niobium (Nb) from choline chloride-based deep eutectic solvent (DES) was studied by anodic polarization tests and electrochemical impedance spectroscopy (EIS) using a Nb rotating disk electrode (RDE). Based on the results of an anodic polarisation test, the electropolishing of Nb is mass transport controlled. EIS results are consistent with the compact salt film mechanism for niobium electropolishing in this electrolyte. The influence of rotation rate, applied potential and electrolyte temperature on the electropolishing mechanism of Nb was investigated. As the applied potential positively shift, Rct, Rp and L increase, CPE decrease and Rs unchanged. The increase in rotation rate and electrolyte temperature leads to a decrease of Rs, Rct, Rp and L, and an increase of CPE. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP010 | |
| About • | paper received ※ 18 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019 | |
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| THP064 | The Cryostat Results of Carbon Contamination and Plasma Cleaning for the Field Emission on the SRF Cavity | 1038 |
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| The field emission effect is the mainly limitation for the operating of SRF cavities in higher gradient with stability. In this paper, the experiments were performed to evaluate the impact of the carbon contaminants and plasma cleaning on the performance of SRF cavity. Contamination mechanism was classified into cryogenic adsorption with weak strength and chemical deposition with strong strength. For the weak strength condition, the methane was injected into the SRF cavity during vertical test to make a cryogenic adsorption layer on the inner surface of the cavity. The results revealed that the performance of SRF cavity degraded by methane physical adsorption, but the performance can be recovered by thermal cycle the cavity to 300K and pump methane out. For the strong strength condition, the chemical deposited dirty layer of carbon contamination was produced by using of Ar/CH4 mixed PECVD method, and the SRF cavity performance was deteriorated by the severe field emission. Finally, carbon deposited cavity was treated by the Ar/O2 plasma, and its results revealed that the field emission removed greatly and the gradient was increased. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP064 | |
| About • | paper received ※ 20 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019 | |
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| FRCAB6 | The Effect of Helium Processing and Plasma Cleaning for Low Beta HWR Cavity | 1228 |
| THP065 | use link to see paper's listing under its alternate paper code | |
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| The commissioning of the 25 MeV high power and high intensity proton Linac demo for CiADS showed that the performance of the SRF cavities was mainly limited by field emission inside the cavities. Therefore, the techniques of helium processing and reactive oxygen plasma cleaning have been developed to mitigate field emission issues. We performed an experiment with a low beta HWR cavity exposed to air directly and processed by helium and reactive oxygen. In this paper, the details of the experiment will be described, the efficiency of helium processing and plasma cleaning will be compared and discussed | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-FRCAB6 | |
| About • | paper received ※ 23 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019 | |
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