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Title: Beam Pipe HOM Absorber for SRF Cavities

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Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
Report Number(s):
DOE Contract Number:
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Resource Relation:
Journal Name: Conf.Proc.C110328:1012-1014,2011; Conference: Particle Accelerator, 24th Conference (PAC'11) 28 Mar - 1 Apr 2011, New York, USA
Country of Publication:
United States

Citation Formats

Neubauer, M., Sah, R., Dudas, A., /MUONS Inc., Batavia, Hoffstaetter, G., Padamsee, H., Liepe, M., Shemelin, V., /Cornell U., Ko, K., Xiao, L., Ng, C., and /SLAC. Beam Pipe HOM Absorber for SRF Cavities. United States: N. p., 2016. Web.
Neubauer, M., Sah, R., Dudas, A., /MUONS Inc., Batavia, Hoffstaetter, G., Padamsee, H., Liepe, M., Shemelin, V., /Cornell U., Ko, K., Xiao, L., Ng, C., & /SLAC. Beam Pipe HOM Absorber for SRF Cavities. United States.
Neubauer, M., Sah, R., Dudas, A., /MUONS Inc., Batavia, Hoffstaetter, G., Padamsee, H., Liepe, M., Shemelin, V., /Cornell U., Ko, K., Xiao, L., Ng, C., and /SLAC. Sun . "Beam Pipe HOM Absorber for SRF Cavities". United States. doi:.
title = {Beam Pipe HOM Absorber for SRF Cavities},
author = {Neubauer, M. and Sah, R. and Dudas, A. and /MUONS Inc., Batavia and Hoffstaetter, G. and Padamsee, H. and Liepe, M. and Shemelin, V. and /Cornell U. and Ko, K. and Xiao, L. and Ng, C. and /SLAC},
abstractNote = {},
doi = {},
journal = {Conf.Proc.C110328:1012-1014,2011},
number = ,
volume = ,
place = {United States},
year = {Sun Jul 24 00:00:00 EDT 2016},
month = {Sun Jul 24 00:00:00 EDT 2016}

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  • During initial testing of the prototype cavities incorporated into the developmental cryomodule Renascence severe thermal stability issues were encountered during CW operation. Additional diagnostic instrumentation was added. This enabled identification of an unanticipated thermal impedance between the HOM coupler probe feedthrough assembly and the cavity beamtube. Subsequent detailed FE analysis successfully modeled the situation and indicated the need for alternate cooling path for the couplers on those cavities. HOM damping was measured to be adequate employing only two of the four HOM couplers. The two pickup probes on the couplers at the input power coupler side of each cavity weremore » removed, the remaining HOM probe feedthroughs were heat stationed to two-phase helium supply piping, and a novel heat sink was added to station both the inner and outer conductors of the remaining HOM rf cables. The characterization measurements, analysis, modifications, and resulting performance are presented.« less
  • This joint project of Muons, Inc., Cornell University and SLAC was supported by a Phase I and Phase II grant monitored by the SBIR Office of Science of the DOE. Beam line HOM absorbers are a critical part of future linear colliders. The use of lossy materials at cryogenic temperatures has been incorporated in several systems. The design in beam pipes requires cylinders of lossy material mechanically confined in such a way as to absorb the microwave energy from the higher-order modes and remove the heat generated in the lossy material. Furthermore, the potential for charge build-up on the surfacemore » of the lossy material requires the conductivity of the material to remain consistent from room temperature to cryogenic temperatures. In this program a mechanical design was developed that solved several design constraints: a) fitting into the existing Cornell load vacuum component, b) allowing the use of different material compositions, c) a thermal design that relied upon the compression of the lossy ceramic material without adding stress. Coating experiments were performed that indicated the design constraints needed to fully implement this approach for solving the charge build-up problem inherent in using lossy ceramics. In addition, the ACE3P program, used to calculate the performance of lossy cylinders in beam pipes in general, was supported by this project. Code development and documentation to allow for the more wide spread use of the program was a direct result of this project was well.« less
  • Higher Order Modes (HOM) excited by the beam in the 3.9 GHz accelerating cavities in FLASH can be used for beam position diagnostics, as in a cavity beam position monitor. Previous studies of the modal choices within the complicated spectrum have revealed several options: cavity modes with strong coupling to the beam, and therefore with the potential for better position resolution, but which are propagating within all 4 cavities, and modes localized in the cavities or the beam pipes, which can give localized position information, but which provide worse resolution. For a better characterization of these options, a set ofmore » test electronics has been built, which can down-convert various frequencies between about 4 and 9 GHz to 70 MHz. The performance of various 20 MHz bands has been estimated. The best resolution of 20 \mu m was found for some propagating modes. Based on this study one band at ca. 5 GHz was chosen for high resolution position monitoring and a band at ca. 9 GHz for localized monitoring.« less
  • JLAB SRF cavities employ waveguide type fundamental power couplers (FPC). The FPC design for the 7-cell upgrade cavities was optimized to minimize the dipole field kick. For continuous wave (CW) operation, the forwarding RF power will be at different magnitude to drive the different beam current and cavity gradient. This introduces some deviation from optimized FPC field for varying beam loading. This article analyzes the beam behavior both in centroid kick and head-tail kick under different beam loading conditions.