SRF2017 - List of Authors (Mitchell, J.A.)

Paper	Title	Page
MOPB079	HOM Coupler Alterations for the LHC DQW Crab Cavity	249
	J.A. Mitchell Lancaster University, Lancaster, United Kingdom G. Burt, N.C. Shipman Cockcroft Institute, Lancaster University, Lancaster, United Kingdom R. Calaga CERN, Geneva, Switzerland S. Verdú-Andrés, Q. Wu, B. P. Xiao BNL, Upton, Long Island, New York, USA
	As part of the High Luminosity Large Hadron Collider (HL-LHC) project, 16 crab cavities are to be installed in the LHC in 2025. The two crab cavity designs are the Double Quarter Wave (DQW) and Radio Frequency Dipole (RFD). Preliminary beam tests in the Super Proton Synchrotron (SPS) are planned for both cavity types, with the DQW scheduled for testing in 2018. In reference to to Higher Order Mode (HOM) damping, the DQW has three identical on-cell HOM couplers. These HOM couplers provide a band-stop response at the frequency of the fundamental mode and act as a transmission path for the cavity HOMs. For the SPS cavity design, several geometric constraints exist. These give rise to dimensional limitations which in-turn impose limitations on the RF performance of the HOM couplers. As such, for the LHC assembly, the HOM coupler design is re-visited to take into account the relaxed geometric limitations, hence allowing the feasibility of an increased RF performance to be investigated. In addition to the RF performance, several geometric alterations were incorporated to ease manufacturing processes, tolerances and costs.
	Poster MOPB079 [2.038 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB079
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TUPB014	In-situ Bulk Residual Resistivity Ratio Measurement on Double Quarter Wave Crab Cavities	415
	N.C. Shipman, A. Castilla, K.G. Hernández-Chahín, A. Macpherson CERN, Geneva, Switzerland I. Ben-Zvi BNL, Upton, Long Island, New York, USA G. Burt, N.C. Shipman Cockcroft Institute, Lancaster University, Lancaster, United Kingdom K.G. Hernández-Chahín Universidad de Guanajuato, División de Ciencias e Ingenierías, León, Mexico J.A. Mitchell Lancaster University, Lancaster, United Kingdom N.C. Shipman UMAN, Manchester, United Kingdom
	A four wire measurement was used to measure the bulk RRR on two DQW Crab Cavities. The measurement procedure is explained and the values obtained for each cavity are compared together with the values obtained from Niobium samples of the same stock from which the cavities were manufactured. Measurement errors and carefully analysed and further improvements to the measurement procedure are suggested.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB014
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TUPB100	Determining BCP Etch Rate and Uniformity in High Luminosity LHC Crab Cavities	635
	T.J. Jones STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom G. Burt Cockcroft Institute, Lancaster University, Lancaster, United Kingdom R. Calaga, O. Capatina, L.M.A. Ferreira, R. Leuxe CERN, Geneva, Switzerland T.J. Jones, J.A. Mitchell Lancaster University, Lancaster, United Kingdom S.M. Pattalwar STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom S. Verdú-Andrés, B. P. Xiao BNL, Upton, Long Island, New York, USA
	The compact SRF Crab Cavities required for HL-LHC have complex geometries making prediction of average and local BCP etch rates a difficult task. This paper describes a series of experiments and simulations used to determine the etch uniformity and rate within these structures. An initial experiment was conducted to determine the correlation between etch rate and flow rate in a Nb tube. These results were then incorporated into Computational Fluid Dynamics simulations of acid flow in the Double Quarter Wave (DQW) cavity to predict etch rates across the surface and allow optimisation of the BCP setup. There were several important findings from the work; one of which is that the flow rate in the relatively large body of the cavity is predominantly driven by natural convection due to the exothermic reaction. During BCP processing of the DQW cavity a significant difference in etching was observed between upper and lower horizontal surfaces which was mitigated by etching in several orientations. Two DQW cavities manufactured by CERN have received a heavy BCP of 200μm followed by 2 light BCPs of 30μm each with subsequent vertical cold tests showing performance exceeding specification.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB100
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THPB059	Simulation and Measurements of Crab Cavity HOMs and HOM Couplers for HL-LHC	881
	J.A. Mitchell, T.J. Jones Lancaster University, Lancaster, United Kingdom R. Apsimon, G. Burt, N.C. Shipman Cockcroft Institute, Lancaster University, Lancaster, United Kingdom I. Ben-Zvi, S. Verdú-Andrés, B. P. Xiao BNL, Upton, Long Island, New York, USA R. Calaga, A. Castilla, A. Macpherson, N.C. Shipman, A. Zwozniak CERN, Geneva, Switzerland T. Powers, H. Wang JLab, Newport News, Virginia, USA N.C. Shipman UMAN, Manchester, United Kingdom
	Two Superconducting Radio-Frequency (SRF) crab cavities are foreseen for the High Luminosity LHC (HL-LHC) upgrade. Preliminary beam tests of the Double Quarter Wave (DQW) crab cavity will take place in the Super Proton Synchrotron (SPS) in 2018. For damping of the cavity's Higher Order Modes (HOMs) the DQW has three identical on-cell, superconducting HOM couplers. The couplers are actively cooled by liquid heluim. In this paper, electromagnetic simulations of the HOMs and HOM couplers are presented. A novel approach to pre-installation spectral analysis of the HOM couplers is then presented, detailing both simulated and measured data. Measurements of the cavity HOMs at warm and in Vertical Test Facilities (VTFs) at both JLAB and CERN are detailed, comparing the measured characteristics of each mode to that of the simulated data-sets. Finally, the measured cavity data is compared with the test box measurements to see by what extent any reduction in damping can be predicted.
	Poster THPB059 [8.192 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB059
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

HOM Coupler Alterations for the LHC DQW Crab Cavity

249

J.A. Mitchell
Lancaster University, Lancaster, United Kingdom
G. Burt, N.C. Shipman
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
R. Calaga
CERN, Geneva, Switzerland
S. Verdú-Andrés, Q. Wu, B. P. Xiao
BNL, Upton, Long Island, New York, USA

As part of the High Luminosity Large Hadron Collider (HL-LHC) project, 16 crab cavities are to be installed in the LHC in 2025. The two crab cavity designs are the Double Quarter Wave (DQW) and Radio Frequency Dipole (RFD). Preliminary beam tests in the Super Proton Synchrotron (SPS) are planned for both cavity types, with the DQW scheduled for testing in 2018. In reference to to Higher Order Mode (HOM) damping, the DQW has three identical on-cell HOM couplers. These HOM couplers provide a band-stop response at the frequency of the fundamental mode and act as a transmission path for the cavity HOMs. For the SPS cavity design, several geometric constraints exist. These give rise to dimensional limitations which in-turn impose limitations on the RF performance of the HOM couplers. As such, for the LHC assembly, the HOM coupler design is re-visited to take into account the relaxed geometric limitations, hence allowing the feasibility of an increased RF performance to be investigated. In addition to the RF performance, several geometric alterations were incorporated to ease manufacturing processes, tolerances and costs.

Poster MOPB079 [2.038 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB079

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPB014

In-situ Bulk Residual Resistivity Ratio Measurement on Double Quarter Wave Crab Cavities

415

N.C. Shipman, A. Castilla, K.G. Hernández-Chahín, A. Macpherson
CERN, Geneva, Switzerland
I. Ben-Zvi
BNL, Upton, Long Island, New York, USA
G. Burt, N.C. Shipman
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
K.G. Hernández-Chahín
Universidad de Guanajuato, División de Ciencias e Ingenierías, León, Mexico
J.A. Mitchell
Lancaster University, Lancaster, United Kingdom
N.C. Shipman
UMAN, Manchester, United Kingdom

A four wire measurement was used to measure the bulk RRR on two DQW Crab Cavities. The measurement procedure is explained and the values obtained for each cavity are compared together with the values obtained from Niobium samples of the same stock from which the cavities were manufactured. Measurement errors and carefully analysed and further improvements to the measurement procedure are suggested.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB014

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPB100

Determining BCP Etch Rate and Uniformity in High Luminosity LHC Crab Cavities

635

T.J. Jones
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
G. Burt
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
R. Calaga, O. Capatina, L.M.A. Ferreira, R. Leuxe
CERN, Geneva, Switzerland
T.J. Jones, J.A. Mitchell
Lancaster University, Lancaster, United Kingdom
S.M. Pattalwar
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
S. Verdú-Andrés, B. P. Xiao
BNL, Upton, Long Island, New York, USA

The compact SRF Crab Cavities required for HL-LHC have complex geometries making prediction of average and local BCP etch rates a difficult task. This paper describes a series of experiments and simulations used to determine the etch uniformity and rate within these structures. An initial experiment was conducted to determine the correlation between etch rate and flow rate in a Nb tube. These results were then incorporated into Computational Fluid Dynamics simulations of acid flow in the Double Quarter Wave (DQW) cavity to predict etch rates across the surface and allow optimisation of the BCP setup. There were several important findings from the work; one of which is that the flow rate in the relatively large body of the cavity is predominantly driven by natural convection due to the exothermic reaction. During BCP processing of the DQW cavity a significant difference in etching was observed between upper and lower horizontal surfaces which was mitigated by etching in several orientations. Two DQW cavities manufactured by CERN have received a heavy BCP of 200μm followed by 2 light BCPs of 30μm each with subsequent vertical cold tests showing performance exceeding specification.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB100

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPB059

Simulation and Measurements of Crab Cavity HOMs and HOM Couplers for HL-LHC

881

J.A. Mitchell, T.J. Jones
Lancaster University, Lancaster, United Kingdom
R. Apsimon, G. Burt, N.C. Shipman
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
I. Ben-Zvi, S. Verdú-Andrés, B. P. Xiao
BNL, Upton, Long Island, New York, USA
R. Calaga, A. Castilla, A. Macpherson, N.C. Shipman, A. Zwozniak
CERN, Geneva, Switzerland
T. Powers, H. Wang
JLab, Newport News, Virginia, USA
N.C. Shipman
UMAN, Manchester, United Kingdom

Two Superconducting Radio-Frequency (SRF) crab cavities are foreseen for the High Luminosity LHC (HL-LHC) upgrade. Preliminary beam tests of the Double Quarter Wave (DQW) crab cavity will take place in the Super Proton Synchrotron (SPS) in 2018. For damping of the cavity's Higher Order Modes (HOMs) the DQW has three identical on-cell, superconducting HOM couplers. The couplers are actively cooled by liquid heluim. In this paper, electromagnetic simulations of the HOMs and HOM couplers are presented. A novel approach to pre-installation spectral analysis of the HOM couplers is then presented, detailing both simulated and measured data. Measurements of the cavity HOMs at warm and in Vertical Test Facilities (VTFs) at both JLAB and CERN are detailed, comparing the measured characteristics of each mode to that of the simulated data-sets. Finally, the measured cavity data is compared with the test box measurements to see by what extent any reduction in damping can be predicted.

Poster THPB059 [8.192 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB059

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)