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Title: Nb-on-Cu Cavities for 700-1500 MHZ SRF Accelerators

Abstract

Single crystal films of Nb were grown on MGO; RRR≈570 was measured in ≈4 µm films of Nb; cross-section SEM images showed that macro-particles embedded in the film had the same (100) crystal structure as the bulk film and were well adhered, hence did not pose a problem for vortex penetration. We coated 1.3 GHz cavities inside our vacuum chamber. We showed that we could grow uniform films on such cavities, but the best Qo measured was ~2E8, not acceptable. Next we coated 1.3 GHz cavities when pumping directly on the cavity. Arguing that heaters inside the vacuum chamber might be contaminating the coating, we pumped directly on the cavity so that it could be heated from outside (in air). The best Qo measured was ≈1E9, a record for all our cavity deposition. However, this encouraging result was tempered by Q-slope, which we attributed to impurities in the film due to the dirty (non-clean room) environment at AASC. It was decided to install the CED apparatus at JLab, to assemble, clean and coat under cleaner conditions We next coated 1.3 GHz cavity at JLab. After shipping and installing the CED apparatus at JLab, two coating runs were completed before themore » project ended. Due to arcs inside the vacuum (faulty current leads) the runs ended prematurely, with ≈0.7 µm films. Since we had learned from coupon work that film thickness >2 µm (preferably 4 µm) were essential for good RF performance, the negative results were understandable. Indeed, the quadrupole resonator coatings for Sarah Aull at CERN had also indicated that a 2 µm coating would show adequate RF quality for LHC upgrades and for the ILC. JLab now has acquired the apparatus and knowledge of its operation. It is hoped that JLab will continue this potentially rewarding development and soon show the results that have eluded us.« less

Authors:
 [1];  [1]
  1. Alameda Applied Sciences Corp., San Leandro, CA (United States)
Publication Date:
Research Org.:
Alameda Applied Sciences Corp., San Leandro, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
Contributing Org.:
Thomas Jefferson National Accelerator Facility
OSTI Identifier:
1465024
Report Number(s):
SC0011371Final Report_AASC.docx
DOE Contract Number:  
SC0011371
Type / Phase:
SBIR (Phase II)
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; niobium thinfilms; SRF accelerators

Citation Formats

Krishnan, Mahadevan, and Velas, Katherine. Nb-on-Cu Cavities for 700-1500 MHZ SRF Accelerators. United States: N. p., 2018. Web.
Krishnan, Mahadevan, & Velas, Katherine. Nb-on-Cu Cavities for 700-1500 MHZ SRF Accelerators. United States.
Krishnan, Mahadevan, and Velas, Katherine. Sun . "Nb-on-Cu Cavities for 700-1500 MHZ SRF Accelerators". United States.
@article{osti_1465024,
title = {Nb-on-Cu Cavities for 700-1500 MHZ SRF Accelerators},
author = {Krishnan, Mahadevan and Velas, Katherine},
abstractNote = {Single crystal films of Nb were grown on MGO; RRR≈570 was measured in ≈4 µm films of Nb; cross-section SEM images showed that macro-particles embedded in the film had the same (100) crystal structure as the bulk film and were well adhered, hence did not pose a problem for vortex penetration. We coated 1.3 GHz cavities inside our vacuum chamber. We showed that we could grow uniform films on such cavities, but the best Qo measured was ~2E8, not acceptable. Next we coated 1.3 GHz cavities when pumping directly on the cavity. Arguing that heaters inside the vacuum chamber might be contaminating the coating, we pumped directly on the cavity so that it could be heated from outside (in air). The best Qo measured was ≈1E9, a record for all our cavity deposition. However, this encouraging result was tempered by Q-slope, which we attributed to impurities in the film due to the dirty (non-clean room) environment at AASC. It was decided to install the CED apparatus at JLab, to assemble, clean and coat under cleaner conditions We next coated 1.3 GHz cavity at JLab. After shipping and installing the CED apparatus at JLab, two coating runs were completed before the project ended. Due to arcs inside the vacuum (faulty current leads) the runs ended prematurely, with ≈0.7 µm films. Since we had learned from coupon work that film thickness >2 µm (preferably 4 µm) were essential for good RF performance, the negative results were understandable. Indeed, the quadrupole resonator coatings for Sarah Aull at CERN had also indicated that a 2 µm coating would show adequate RF quality for LHC upgrades and for the ILC. JLab now has acquired the apparatus and knowledge of its operation. It is hoped that JLab will continue this potentially rewarding development and soon show the results that have eluded us.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2018},
month = {4}
}

Technical Report:
This technical report may be released as soon as August 18, 2022
Other availability
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