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Title: High gradient superconducting niobium cavities: A review of the present status

Abstract

Superconducting niobium cavities used in particle accelerators are limited in their rf performance by two phenomena: quench field levels below the theoretical limit of the material caused by defects, and field emission loading resulting from artificial contamination of the superconducting surfaces during surface treatment and assembly procedures. In recent years, the community involved in SRF technology developments has successfully improved cavity performances by applying advanced surface treatment methods such as chemical polishing, electropolishing, tumbling, high temperature heat treatment, high pressure rinsing, ``in situ'' high peak power processing, and clean room assembly procedures. In addition, improvements in the material properties such as thermal conductivity by ''solid state'' gettering'' and very strict QA methods, both in material inspection and during cavity fabrication, have resulted in cavity performance levels of E{sub acc} up to 40 MV/m in monocells and gradients in the vicinity of 30 MV/m in multicell structures at Q-values of {approx} 10{sup 10} at a temperature of 2K. More recently the fabrication of ``seamless'' cavities by spinning is being pursued with encouraging results. This process eliminates electron beam welds, which sometimes are the causes of performance degradations.

Authors:
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA (US)
Sponsoring Org.:
USDOE Office of Energy Research (ER) (US)
OSTI Identifier:
755347
Report Number(s):
DOE/ER/40150-1444; JLAB-ACT-98-07
TRN: US0002430
DOE Contract Number:
AC05-84ER40150
Resource Type:
Conference
Resource Relation:
Conference: Conference title not supplied, No location, No date; Other Information: PBD: 1 Sep 1998
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; RF SYSTEMS; ACCELERATORS; SUPERCONDUCTING CAVITY RESONATORS; NIOBIUM; QUENCHING; FIELD EMISSION; SURFACE TREATMENTS; PERFORMANCE; TECHNOLOGY ASSESSMENT

Citation Formats

Peter Kneisel. High gradient superconducting niobium cavities: A review of the present status. United States: N. p., 1998. Web.
Peter Kneisel. High gradient superconducting niobium cavities: A review of the present status. United States.
Peter Kneisel. Tue . "High gradient superconducting niobium cavities: A review of the present status". United States. doi:. https://www.osti.gov/servlets/purl/755347.
@article{osti_755347,
title = {High gradient superconducting niobium cavities: A review of the present status},
author = {Peter Kneisel},
abstractNote = {Superconducting niobium cavities used in particle accelerators are limited in their rf performance by two phenomena: quench field levels below the theoretical limit of the material caused by defects, and field emission loading resulting from artificial contamination of the superconducting surfaces during surface treatment and assembly procedures. In recent years, the community involved in SRF technology developments has successfully improved cavity performances by applying advanced surface treatment methods such as chemical polishing, electropolishing, tumbling, high temperature heat treatment, high pressure rinsing, ``in situ'' high peak power processing, and clean room assembly procedures. In addition, improvements in the material properties such as thermal conductivity by ''solid state'' gettering'' and very strict QA methods, both in material inspection and during cavity fabrication, have resulted in cavity performance levels of E{sub acc} up to 40 MV/m in monocells and gradients in the vicinity of 30 MV/m in multicell structures at Q-values of {approx} 10{sup 10} at a temperature of 2K. More recently the fabrication of ``seamless'' cavities by spinning is being pursued with encouraging results. This process eliminates electron beam welds, which sometimes are the causes of performance degradations.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Sep 01 00:00:00 EDT 1998},
month = {Tue Sep 01 00:00:00 EDT 1998}
}

Conference:
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  • The present study is addressed to the theoretical description of the ultimate gradient limitation in SRF cavities. Our intent is to exploit experimental data to confirm models which provide feed-backs on how to improve the current state-of-art. New theoretical insight on the cavities limiting factor can be suitable to improve the quench field of N-doped cavities, and therefore to take advantage of high Q 0 at high gradients.
  • Tests performed on several Niobium TM/sub 010/ cavities at frequencies of about 2856 MHz using a high-power, pulsed method indicate that, at the end of the charging pulse, peak surface magnetic fields of up to approx. 1300 Oe, corresponding to a peak surface electric field of approx. 68 MV/m, can be reached at 4.2/sup 0/K without appreciable average losses. Further studies of the properties of superconductors under pulsed operation might shed light on fundamental properties of rf superconductivity, as well as lead to the possibility of applying the pulse method to the operation of high-gradient linear colliders. 7 references, 30more » figures, 2 tables.« less
  • We report on the recent progress at Jefferson Lab in developing ultra high gradient and high Q{sub 0} superconducting radio frequency (SRF) cavities for future SRF based machines. A new 1300 MHz 9-cell prototype cavity is being fabricated. This cavity has an optimized shape in terms of the ratio of the peak surface field (both magnetic and electric) to the acceleration gradient, hence the name low surface field (LSF) shape. The goal of the effort is to demonstrate an acceleration gradient of 50 MV/m with Q{sub 0} of 10{sup 10} at 2 K in a 9-cell SRF cavity. Fine-grain niobiummore » material is used. Conventional forming, machining and electron beam welding method are used for cavity fabrication. New techniques are adopted to ensure repeatable, accurate and inexpensive fabrication of components and the full assembly. The completed cavity is to be first mechanically polished to a mirror-finish, a newly acquired in-house capability at JLab, followed by the proven ILC-style processing recipe established already at JLab. In parallel, new single-cell cavities made from large-grain niobium material are made to further advance the cavity treatment and processing procedures, aiming for the demonstration of an acceleration gradient of 50 MV/m with Q{sub 0} of 2-10{sup 10} at 2K.« less
  • We report on the latest results of development on high-efficiency high-gradient superconducting radio frequency (SRF) cavities. Several 1-cell cavities made of large-grain niobium (Nb) were built, processed and tested. Two of these cavities are of the Low Surface Field (LSF) shape. Series of tests were carried out following controlled thermal cycling. Experiments toward zero-field cooling were carried out. The best experimentally achieved results are E acc = 41 MV/m at Q 0 = 6.5×10 10 at 1.4 K by a 1-cell 1.3 GHz large-grain Nb TTF shape cavity and E acc = 49 MV/m at Q 0 = 1.5×10 10more » at 1.8 K by a 1-cell 1.5 GHz large-grain Nb CEBAF upgrade low-loss shape cavity.« less
  • Superconducting (SC) cavities for use in electron storage rings have advanced to the point where several laboratories are making definite plans to use them on a large scale. Laboratory tests of multi-cell SC cavities, including input and higher-order-mode (HOM) couplers, have yielded accelerating fields up to 15.3 MeV/m (CW). Reasons for the improved performance are discussed. Since the 1983 International Accelerator Conference in August, 1983, four SC cavities have been tested in storage rings. The cavities have yielded accelerating gradients up to 6.5 MeV/m, in excess of the frequency-quoted objective of 5 MeV/m. In addition, the average gradient obtained inmore » these four tests was 4 MeV/m, almost twice the average obtained in the four cavities tested in storage rings during 1982 - 1983.« less