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Title: Beam Position Monitoring with Cavity Higher Order Modes in the Superconducting Linac FLASH

Abstract

FLASH (Free Electron Laser in Hamburg) is a user facility for a high intensity VUV-light source [1]. The radiation wavelength is tunable in the range from about 40 to 13 nm by changing the electron beam energy from 450 to 700 MeV. The accelerator is also a test facility for the European XFEL (X-ray Free Electron Laser) to be built in Hamburg [2] and the project study ILC (International Linear Collider) [3]. The superconducting TESLA technology is tested at this facility, together with other accelerator components.

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
901265
Report Number(s):
SLAC-PUB-12403
TRN: US0702563
DOE Contract Number:
AC02-76SF00515
Resource Type:
Journal Article
Resource Relation:
Journal Name: ICFA Beam Dyn.Newslett.41:9-14,2006; Journal Volume: 41
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ACCELERATORS; BEAM POSITION; ELECTRON BEAMS; ELECTRONS; FREE ELECTRON LASERS; LASERS; LINEAR ACCELERATORS; LINEAR COLLIDERS; MONITORING; RADIATIONS; WAVELENGTHS; Accelerators,ACCPHY

Citation Formats

Baboi, N., Molloy, S., Eddy, N., Frisch, J., Hendrickson, L., Hensler, O., McCormick, D., May, J., Nagaitsev, S., Napoly, O., Paparella, R.C., Petrosian, L., Piccolli, L., Rechenmacher, R., Ross, M., Simon, C., Smith, T., Watanabe, K., Wendt, M., and /DESY /SLAC /Fermilab /DAPNIA, Saclay /KEK, Tsukuba. Beam Position Monitoring with Cavity Higher Order Modes in the Superconducting Linac FLASH. United States: N. p., 2007. Web.
Baboi, N., Molloy, S., Eddy, N., Frisch, J., Hendrickson, L., Hensler, O., McCormick, D., May, J., Nagaitsev, S., Napoly, O., Paparella, R.C., Petrosian, L., Piccolli, L., Rechenmacher, R., Ross, M., Simon, C., Smith, T., Watanabe, K., Wendt, M., & /DESY /SLAC /Fermilab /DAPNIA, Saclay /KEK, Tsukuba. Beam Position Monitoring with Cavity Higher Order Modes in the Superconducting Linac FLASH. United States.
Baboi, N., Molloy, S., Eddy, N., Frisch, J., Hendrickson, L., Hensler, O., McCormick, D., May, J., Nagaitsev, S., Napoly, O., Paparella, R.C., Petrosian, L., Piccolli, L., Rechenmacher, R., Ross, M., Simon, C., Smith, T., Watanabe, K., Wendt, M., and /DESY /SLAC /Fermilab /DAPNIA, Saclay /KEK, Tsukuba. Tue . "Beam Position Monitoring with Cavity Higher Order Modes in the Superconducting Linac FLASH". United States. doi:. https://www.osti.gov/servlets/purl/901265.
@article{osti_901265,
title = {Beam Position Monitoring with Cavity Higher Order Modes in the Superconducting Linac FLASH},
author = {Baboi, N. and Molloy, S. 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 Petrosian, L. and Piccolli, L. and Rechenmacher, R. and Ross, M. and Simon, C. and Smith, T. and Watanabe, K. and Wendt, M. and /DESY /SLAC /Fermilab /DAPNIA, Saclay /KEK, Tsukuba},
abstractNote = {FLASH (Free Electron Laser in Hamburg) is a user facility for a high intensity VUV-light source [1]. The radiation wavelength is tunable in the range from about 40 to 13 nm by changing the electron beam energy from 450 to 700 MeV. The accelerator is also a test facility for the European XFEL (X-ray Free Electron Laser) to be built in Hamburg [2] and the project study ILC (International Linear Collider) [3]. The superconducting TESLA technology is tested at this facility, together with other accelerator components.},
doi = {},
journal = {ICFA Beam Dyn.Newslett.41:9-14,2006},
number = ,
volume = 41,
place = {United States},
year = {Tue Mar 20 00:00:00 EDT 2007},
month = {Tue Mar 20 00:00:00 EDT 2007}
}
  • 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
  • Beam-excited higher order modes (HOMs) can provide remote diagnostics information of the beam position and cavity misalignment. In this paper we report on recent studies on the resolution with specially selected series of modes with custom-built electronics. This constitutes the first report of measurements of these cavities in which we obtained a resolution of 20 micron in beam offset. Details of the setup of the electronics and HOM measurements are provided.
  • Each nine cell superconducting (SC) accelerator cavity in the TESLA Test Facility (TTF) at DESY [1] has two higher order mode (HOM) couplers that efficiently remove the HOM power [2]. They can also provide useful diagnostic signals. The most interesting modes are in the first 2 cavity dipole passbands. They are easy to identify and their amplitude depends linearly on the beam offset from the cavity axis making them excellent beam position monitors (BPM). By steering the beam through an eight-cavity cryomodule, we can use the HOM signals to estimate internal residual alignment errors and minimize wakefield related beam emittancemore » growth. We built and tested a time-domain based waveform recorder system that captures information from each mode in these two bands on each beam pulse. In this paper we present a preliminary experimental study of the single-bunch generated HOM signals at the TTF linac including estimates of cavity alignment precision and HOM BPM resolution.« less
  • 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 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
  • 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