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Title: Automatic Phase Calibration for RF Cavities using Beam-Loading Signals

Abstract

Precise calibration of the cavity phase signals is necessary for the operation of any particle accelerator. For many systems this requires human in the loop adjustments based on measurements of the beam parameters downstream. Some recent work has developed a scheme for the calibration of the cavity phase using beam measurements and beam-loading however this scheme is still a multi-step process that requires heavy automation or human in the loop. In this paper we analyze a new scheme that uses only RF signals reacting to beam-loading to calculate the phase of the beam relative to the cavity. This technique could be used in slow control loops to provide real-time adjustment of the cavity phase calibration without human intervention thereby increasing the stability and reliability of the accelerator.

Authors:
 [1];  [1]
  1. Fermilab
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1414396
Report Number(s):
FERMILAB-CONF-17-565-AD
1644044
DOE Contract Number:
AC02-07CH11359
Resource Type:
Conference
Resource Relation:
Conference: Low Level Radio Frequency Workshop 2017, Barcelona, Catalonia, Spain, 10/16-10/19/2017
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS

Citation Formats

Edelen, J. P., and Chase, B. E. Automatic Phase Calibration for RF Cavities using Beam-Loading Signals. United States: N. p., 2017. Web.
Edelen, J. P., & Chase, B. E. Automatic Phase Calibration for RF Cavities using Beam-Loading Signals. United States.
Edelen, J. P., and Chase, B. E. 2017. "Automatic Phase Calibration for RF Cavities using Beam-Loading Signals". United States. doi:. https://www.osti.gov/servlets/purl/1414396.
@article{osti_1414396,
title = {Automatic Phase Calibration for RF Cavities using Beam-Loading Signals},
author = {Edelen, J. P. and Chase, B. E.},
abstractNote = {Precise calibration of the cavity phase signals is necessary for the operation of any particle accelerator. For many systems this requires human in the loop adjustments based on measurements of the beam parameters downstream. Some recent work has developed a scheme for the calibration of the cavity phase using beam measurements and beam-loading however this scheme is still a multi-step process that requires heavy automation or human in the loop. In this paper we analyze a new scheme that uses only RF signals reacting to beam-loading to calculate the phase of the beam relative to the cavity. This technique could be used in slow control loops to provide real-time adjustment of the cavity phase calibration without human intervention thereby increasing the stability and reliability of the accelerator.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month =
}

Conference:
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  • Beam loading of RF cavities is a subject of great concern for the design and operation of high current circular accelerators and storage rings. The steady state and transient perturbations of the accelerating voltage by the beam current lead to undesirable beam behaviour, like for instance the onset of instabilities or particle loss by lack of longitudinal acceptance. To some extent, it is possible to alleviate or even completely suppress these effects by a proper control of the RF power amplifier - cavity combination, using feedback or feedforward techniques. Several new developments in this field have taken place during themore » past years. For instance, the implementation of fast feedback technology, the use of cavity compensation schemes or digital filtering of signals in long delay feedback systems have resulted in considerably improved machine performance. Such techniques will be reviewed in this paper and their performance and limitations will be presented.« less
  • Making use of Maxwell`s equations, a first principles analysis of the beam-deflection cavity interaction in a magnicon is presented. For a driven cavity this leads to a dispersion relation wherein the interaction modifies the unloaded Q (beam loading) and the resonance frequency (detuning). In terms of a lumped-parameter equivalent circuit, the interaction corresponds to a complex-valued beam admittance, Y{sub e}, in parallel with the cavity shunt impedance. The response of the gain cavities is modified by the same admittance, Y{sub e}. In a magnicon, Y{sub e} is a sensitive function of the solenoidal focusing magnetic field, B{sub 0}. In fact,more » when the relativistic gyrofrequency is twice the RF frequency, Im (Y{sub e}) = 0 and the beam does load the cavity. This provides a convenient means of adjusting the cavity properties in experiments. A detailed description of the variation of the detuning, instantaneous bandwidth (i.e., loaded Q) and gain with B{sub 0} is presented. Recent results of the NRL X-band magnicon experiment are examined in the light of the analysis.« less
  • A method is proposed for using adjustable, waveguide stub-line tuners to match the load impedance of the cavity plus beam to the power source, without the need to detune the cavity. Adjustable stub-line tuners are shown to be able to completely match the resistive and reactive parts of the load impedance to a generator under all conditions of beam loading, ensuring optimum power transfer between generator and cavity. This technique may have advantages in high-current storage rings such as the SLC damping rings and the new PEP II storage rings. The coupled-bunch instability driven by the fundamental mode of themore » cavity is reappraised in this coupling scheme in which the cavity is no longer detuned. The consequences of this matching scheme are also considered for the beam loading stability limit.« less
  • A narrowband beam loading compensation system was installed for the Main Injector Accelerating Cavities. This feedback operates solely on the fundamental resonant mode of the cavity. This paper describes modifications to the high level Radio Frequency system required to make the system operational. These modifications decreased the effect of steady-state beam loading by a factor of 10 and improved the reliability of paraphasing for coalescing.