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Title: Using higher order modes in superconducting accelerating cavities for beam monitoring

Abstract

Dipole modes have been shown to be successful diagnostics for the beam position in superconducting accelerating cavities at the Free Electron Laser in Hamburg (FLASH) facility at DESY. By help of downmixing electronics the signals from the two higher order mode (HOM) couplers mounted on each cavity are monitored. The calibration, based on sigular value decomposition, is more complicated than in standard position monitors. Position like signals based on this calibration are currently being in the process of being included in the control system. A second setup based on digitizing the spectrum from the HOM couplers has been used for monitoring monopole modes. The beam phase with respect to the RF has been thus monitored. The position calibration measurements and phase monitoring made at the FLASH are presented.

Authors:
; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
924528
Report Number(s):
FERMILAB-CONF-06-512-AD
TRN: US0802909
DOE Contract Number:
AC02-07CH11359
Resource Type:
Conference
Resource Relation:
Conference: Presented at 2006 Linear Accelerator Conference (LINAC 06), Knoxville, Tennessee, 21-25 Aug 2006
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; BEAM MONITORING; BEAM POSITION; CALIBRATION; CAVITIES; CONTROL SYSTEMS; DIPOLES; FREE ELECTRON LASERS; LINEAR ACCELERATORS; MONITORING; MONITORS; MONOPOLES; Accelerators

Citation Formats

Molloy, S., Baboi, N., Eddy, N., Frisch, J., Hendrickson, L., Hensler, O., McCormick, D., May, J., Nagaitsev, S., Napoly, O., Paparella, R.C., and /SLAC /DESY /Fermilab /DSM, DAPNIA, Saclay /KEK, Tsukuba. Using higher order modes in superconducting accelerating cavities for beam monitoring. United States: N. p., 2006. Web.
Molloy, S., Baboi, N., Eddy, N., Frisch, J., Hendrickson, L., Hensler, O., McCormick, D., May, J., Nagaitsev, S., Napoly, O., Paparella, R.C., & /SLAC /DESY /Fermilab /DSM, DAPNIA, Saclay /KEK, Tsukuba. Using higher order modes in superconducting accelerating cavities for beam monitoring. United States.
Molloy, S., Baboi, N., Eddy, N., Frisch, J., Hendrickson, L., Hensler, O., McCormick, D., May, J., Nagaitsev, S., Napoly, O., Paparella, R.C., and /SLAC /DESY /Fermilab /DSM, DAPNIA, Saclay /KEK, Tsukuba. Sun . "Using higher order modes in superconducting accelerating cavities for beam monitoring". United States. doi:. https://www.osti.gov/servlets/purl/924528.
@article{osti_924528,
title = {Using higher order modes in superconducting accelerating cavities for beam monitoring},
author = {Molloy, S. and Baboi, N. and Eddy, N. and Frisch, J. and Hendrickson, L. and Hensler, O. and McCormick, D. and May, J. and Nagaitsev, S. and Napoly, O. and Paparella, R.C. and /SLAC /DESY /Fermilab /DSM, DAPNIA, Saclay /KEK, Tsukuba},
abstractNote = {Dipole modes have been shown to be successful diagnostics for the beam position in superconducting accelerating cavities at the Free Electron Laser in Hamburg (FLASH) facility at DESY. By help of downmixing electronics the signals from the two higher order mode (HOM) couplers mounted on each cavity are monitored. The calibration, based on sigular value decomposition, is more complicated than in standard position monitors. Position like signals based on this calibration are currently being in the process of being included in the control system. A second setup based on digitizing the spectrum from the HOM couplers has been used for monitoring monopole modes. The beam phase with respect to the RF has been thus monitored. The position calibration measurements and phase monitoring made at the FLASH are presented.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}

Conference:
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  • Dipole modes have been shown to be successful diagnostics for the beam position in superconducting accelerating cavities at the Free Electron Laser in Hamburg (FLASH) facility at DESY. By help of downmixing electronics the signals from the two higher order mode (HOM) couplers mounted on each cavity are monitored. The calibration, based on singular value decomposition, is more complicated than in standard position monitors. Position like signals based on this calibration are currently being in the process of being included in the control system. A second setup based on digitizing the spectrum from the HOM couplers has been used formore » monitoring monopole modes. The beam phase with respect to the RF has been thus monitored. The position calibration measurements and phase monitoring made at the FLASH are presented.« less
  • Beam-excited higher order modes (HOM) in accelerating cavities contain transverse beam position information. Previous studies have narrowed down three modal options for beam position diagnostics in the third harmonic 3.9 GHz cavities at FLASH. Localized modes in the beam pipes at approximately 4.1 GHz and in the fifth cavity dipole band at approximately 9 GHz were found, that can provide a local measurement of the beam position. In contrast, propagating modes in the first and second dipole bands between 4.2 and 5.5 GHz can reach a better resolution. All the options were assessed with a specially designed test electronics builtmore » by Fermilab. The aim is to define a mode or spectral region suitable for the HOM electronics. Two data analysis techniques are used and compared in extracting beam position information from the dipole HOMs: direct linear regression and singular value decomposition. Current experiments suggest a resolution of 50 {\mu}m accuracy in predicting local beam position using modes in the fifth dipole band, and a global resolution of 20 {\mu}m over the complete module. Based on these results we decided to build a HOM electronics for the second dipole band and the fifth dipole band, so that we will have both high resolution measurements for the whole module, and localized measurements for individual cavity. The prototype electronics is being built by Fermilab and planned to be tested in FLASH by the end of 2012.« less
  • Higher order modes in the accelerating cavities are expected to drive coupled bunch instabilities in the ALS, which will be overcome by a bunch-by-bunch feedback system. Computations of the cavity higher order modes using the URMEL-T and MAFIA codes are presented. Damping of the higher order modes is achieved by filters in the high power feeder waveguide which is aperture coupled to the cavity. Measurements of the modes in an ALS 500 MHz cavity are presented and compared with computed values for an isolated, un-damped cavity. The resources of the Lambertson Beam Electrodynamics Laboratory of the Center for Beam Physicsmore » at LBL were used to perform these studies.« less