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Title: Role of magnetic flux expulsion to reach Q 0 > 3 × 10 10 in superconducting rf cryomodules

Abstract

When a superconducting radiofrequency cavity is cooled through its critical temperature, ambient magnetic flux can become "frozen in" to the superconductor, resulting in degradation of the quality factor. This is especially problematic in applications where quality factor is a cost driver, such as in the CW linac for LCLS-II. Previously, it had been unknown how to prevent flux from being trapped during cooldown in bulk niobium cavities, but recent R&D studies showed near-full flux expulsion can be achieved through high temperature heat treatment and cooling cavities through the superconducting transition with a spatial thermal gradient over the surface. In this paper, we describe the first accelerator implementation of these procedures, in cryomodules that are currently being produced for LCLS-II. We compare the performance of cavities under different conditions of heat treatment and thermal gradient during cooldown, demonstrating a substantial improvement in performance when both are applied, enabling cryomodules to reach and, in many cases, exceed a Q 0 of ~3x10^10.

Authors:
ORCiD logo [1]; ORCiD logo [1];  [1];  [1];  [1];  [1];  [1];  [1];  [2];  [3];  [3]
  1. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  2. Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
  3. SLAC National Accelerator Lab. (SLAC), Menlo Park, CA (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab. (SLAC), Menlo Park, CA (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Jefferson Science Associates, Washington D.C. (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1499075
Alternate Identifier(s):
OSTI ID: 1502826; OSTI ID: 1529398
Report Number(s):
FERMILAB-PUB-19-080-TD
Journal ID: ISSN 2469-9888; 1708045
Grant/Contract Number:  
AC02-76F00515; AC02-07CH11359; AC05-06OR23177; AC05-06OR23177 (Fermilab); AC05-06OR23177 (Jefferson Lab)
Resource Type:
Journal Article: Published Article
Journal Name:
Physical Review Accelerators and Beams
Additional Journal Information:
Journal Volume: 22; Journal Issue: 3; Journal ID: ISSN 2469-9888
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS

Citation Formats

Posen, S., Wu, G., Grassellino, A., Harms, E., Melnychuk, O. S., Sergatskov, D. A., Solyak, N., Romanenko, A., Palczewski, A., Gonnella, D., and Peterson, T. Role of magnetic flux expulsion to reach Q0>3×1010 in superconducting rf cryomodules. United States: N. p., 2019. Web. doi:10.1103/PhysRevAccelBeams.22.032001.
Posen, S., Wu, G., Grassellino, A., Harms, E., Melnychuk, O. S., Sergatskov, D. A., Solyak, N., Romanenko, A., Palczewski, A., Gonnella, D., & Peterson, T. Role of magnetic flux expulsion to reach Q0>3×1010 in superconducting rf cryomodules. United States. doi:10.1103/PhysRevAccelBeams.22.032001.
Posen, S., Wu, G., Grassellino, A., Harms, E., Melnychuk, O. S., Sergatskov, D. A., Solyak, N., Romanenko, A., Palczewski, A., Gonnella, D., and Peterson, T. Tue . "Role of magnetic flux expulsion to reach Q0>3×1010 in superconducting rf cryomodules". United States. doi:10.1103/PhysRevAccelBeams.22.032001.
@article{osti_1499075,
title = {Role of magnetic flux expulsion to reach Q0>3×1010 in superconducting rf cryomodules},
author = {Posen, S. and Wu, G. and Grassellino, A. and Harms, E. and Melnychuk, O. S. and Sergatskov, D. A. and Solyak, N. and Romanenko, A. and Palczewski, A. and Gonnella, D. and Peterson, T.},
abstractNote = {When a superconducting radiofrequency cavity is cooled through its critical temperature, ambient magnetic flux can become "frozen in" to the superconductor, resulting in degradation of the quality factor. This is especially problematic in applications where quality factor is a cost driver, such as in the CW linac for LCLS-II. Previously, it had been unknown how to prevent flux from being trapped during cooldown in bulk niobium cavities, but recent R&D studies showed near-full flux expulsion can be achieved through high temperature heat treatment and cooling cavities through the superconducting transition with a spatial thermal gradient over the surface. In this paper, we describe the first accelerator implementation of these procedures, in cryomodules that are currently being produced for LCLS-II. We compare the performance of cavities under different conditions of heat treatment and thermal gradient during cooldown, demonstrating a substantial improvement in performance when both are applied, enabling cryomodules to reach and, in many cases, exceed a Q0 of ~3x10^10.},
doi = {10.1103/PhysRevAccelBeams.22.032001},
journal = {Physical Review Accelerators and Beams},
issn = {2469-9888},
number = 3,
volume = 22,
place = {United States},
year = {2019},
month = {3}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1103/PhysRevAccelBeams.22.032001

Figures / Tables:

FIG. 1 FIG. 1: LCLS-II helium vessel designed to minimize thermocurrents induced by temperature differences between the two ends of the nine-cell cavities, with symmetric helium inlets and central connection to the helium return line. For the prototype cryomodule, temperature sensors and fluxgate magnetometers were installed on four of the eight cavities.

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