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Title: Symplectic modeling of beam loading in electromagnetic cavities

Abstract

Simulating beam loading in radio frequency accelerating structures is critical for understanding higher-order mode effects on beam dynamics, such as beam break-up instability in energy recovery linacs. Full wave simulations of beam loading in radio frequency structures are computationally expensive, and while reduced models can ignore essential physics, it can be difficult to generalize. Here, we present a self-consistent algorithm derived from the least-action principle which can model an arbitrary number of cavity eigenmodes and with a generic beam distribution. It has been implemented in our new Open Library for Investigating Vacuum Electronics (OLIVE).

Authors:
 [1];  [1];  [1]
  1. Radiasoft LLC, LLC, Boulder, CO (United States)
Publication Date:
Research Org.:
Radiasoft LLC, LLC, Boulder, CO (United States); RadiaSoft LLC., Boulder, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
OSTI Identifier:
1358126
Grant/Contract Number:
SC0015211; FA9550-15-C-0031
Resource Type:
Journal Article: Published Article
Journal Name:
Physical Review Accelerators and Beams
Additional Journal Information:
Journal Volume: 20; Journal Issue: 5; Journal ID: ISSN 2469-9888
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 43 PARTICLE ACCELERATORS

Citation Formats

Abell, Dan T., Cook, Nathan M., and Webb, Stephen D. Symplectic modeling of beam loading in electromagnetic cavities. United States: N. p., 2017. Web. doi:10.1103/PhysRevAccelBeams.20.052002.
Abell, Dan T., Cook, Nathan M., & Webb, Stephen D. Symplectic modeling of beam loading in electromagnetic cavities. United States. doi:10.1103/PhysRevAccelBeams.20.052002.
Abell, Dan T., Cook, Nathan M., and Webb, Stephen D. 2017. "Symplectic modeling of beam loading in electromagnetic cavities". United States. doi:10.1103/PhysRevAccelBeams.20.052002.
@article{osti_1358126,
title = {Symplectic modeling of beam loading in electromagnetic cavities},
author = {Abell, Dan T. and Cook, Nathan M. and Webb, Stephen D.},
abstractNote = {Simulating beam loading in radio frequency accelerating structures is critical for understanding higher-order mode effects on beam dynamics, such as beam break-up instability in energy recovery linacs. Full wave simulations of beam loading in radio frequency structures are computationally expensive, and while reduced models can ignore essential physics, it can be difficult to generalize. Here, we present a self-consistent algorithm derived from the least-action principle which can model an arbitrary number of cavity eigenmodes and with a generic beam distribution. It has been implemented in our new Open Library for Investigating Vacuum Electronics (OLIVE).},
doi = {10.1103/PhysRevAccelBeams.20.052002},
journal = {Physical Review Accelerators and Beams},
number = 5,
volume = 20,
place = {United States},
year = 2017,
month = 5
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1103/PhysRevAccelBeams.20.052002

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  • Simulating beam loading in radio frequency accelerating structures is critical for understanding higher-order mode effects on beam dynamics, such as beam break-up instability in energy recovery linacs. Full wave simulations of beam loading in radio frequency structures are computationally expensive, while reduced models can ignore essential physics and can be difficult to generalize. Here, we present a self-consistent algorithm derived from the least-action principle which can model an arbitrary number of cavity eigenmodes and with a generic beam distribution. We implemented it in our new Open Library for Investigating Vacuum Electronics (OLIVE).
  • Simulating beam loading in radio frequency accelerating structures is critical for understanding higher-order mode effects on beam dynamics, such as beam break-up instability in energy recovery linacs. Full wave simulations of beam loading in radio frequency structures are computationally expensive, and while reduced models can ignore essential physics, it can be difficult to generalize. Here, we present a self-consistent algorithm derived from the least-action principle which can model an arbitrary number of cavity eigenmodes and with a generic beam distribution. It has been implemented in our new Open Library for Investigating Vacuum Electronics (OLIVE).
  • The radio frequency (RF) source for the next linear collider (NLC) is required to generate a power of 1/2--1 GW per tube in a 200-ns pulse, or 100--200 J of energy in a pulse of up to a few {micro}s in duration, at a frequency of 10--20 GHz. A variety of RF sources are under investigation at the present time aimed at fulfilling the needs of the NLC. These include the X-band klystron, Gyroklystron, traveling-wave tube, harmonic convertor, chopper-driven traveling-wave tube, and magnicon. Here, analysis of the beam-deflection cavity interaction in a magnicon is presented and compared with experiment. Formore » a driven cavity a dispersion relation is obtained wherein the interaction modifies the cold-cavity factor and the resonance frequency. In terms of a lumped-parameter equivalent circuit the interaction corresponds to a complex-values beam admittance Y{sub b} in parallel with the cavity admittance. The response of the gain cavities is modified by the same admittance. In a magnicon, Y{sub b} is a sensitive function of the solenoidal focusing magnetic field B{sub 0}, thus providing a convenient means of adjusting the cavity properties in experiments. When the relativistic gyrofrequency is twice the drive frequency, ImY{sub b} = 0 and the beam does not load the cavity. Analytical expressions of the variation of the detuning, instantaneous bandwidth (i.e., loaded quality factor) and gain with B{sub 0} are derived. Simulation results are presented to verify the linear analysis with ideal beams and to illustrate the modifications due to finite beam emittance. Results of the magnicon experiment at the Naval Research Laboratory are examined in the light of the analysis.« less
  • Quantitative knowledge of beam loading and detuning is necessary for the prediction of the bandwidth and operating frequency of an electron device that has resonant interactions. The authors present a method for calculating the loaded Q and beam detuning of a passive (gain or idler) cavity in an electron device. The method is based on the determination of induced current by a technique often referred to as Ramo's theorem. They use the induced current in conjunction with a lumped equivalent circuit representing the cavity. This leads to a solution for the self-consistent cavity fields. Although the induced-current expression is usuallymore » developed from low-frequency models, they show that Ramo's theorem is valid for high-frequency, steady-state analysis when the unloaded passive cavity Q is high. They use the method to calculate the loaded Q of the passive cavity of a new type of gyro-resonant electron device, the magnicon.« less
  • An explicit fourth-order finite-difference time-domain (FDTD) scheme using the symplectic integrator is applied to electromagnetic simulation. A feasible numerical implementation of the symplectic FDTD (SFDTD) scheme is specified. In particular, new strategies for the air-dielectric interface treatment and the near-to-far-field (NFF) transformation are presented. By using the SFDTD scheme, both the radiation and the scattering of three-dimensional objects are computed. Furthermore, the energy-conserving characteristic hold for the SFDTD scheme is verified under long-term simulation. Numerical results suggest that the SFDTD scheme is more efficient than the traditional FDTD method and other high-order methods, and can save computational resources.