2011 Particle Accelerator Conference - Classification: Accelerator Technology / Dynamics 05: Code Development and Simulation Techniques

Paper

Title

Page

Study of Robinson Instabilities with a Higher-Harmonic Cavity for HLS Phase II Project

808

Y. Zhao, W. Li, L. Wang, C.-F. Wu
USTC/NSRL, Hefei, Anhui, People's Republic of China

In the phase II project of Hefei Light Source, a fourth-harmonic “Landau” cavity will be operated in order to suppress coupled-bunch instabilities and increase the beam lifetime of Hefei Storage Ring. Instabilities limit the utility of the higher-harmonic cavity when the storage ring is operated with a small momentum compaction. Analytical modeling and simulations show that the instabilities result from Robinson mode coupling. In the analytic modeling, we operate an algorithm to consider Robinson instabilities. To study the evolution of unstable behavior, simulations have been performed in which macroparticles are distributed among the buckets. Both the analytic modeling and simulations agree for passive operation of the harmonic cavity.

TUP003

Beam Stop of Spiral2 Facility: Activation and Residual Dose Rate Calculations

811

A. Mayoral, M. García, D. López, F. Ogando, J. Sanz, P. Sauvan
UNED, Madrid, Spain

Funding: *SPIRAL 2 Preparatory Phase. European Strategy Forum on Research Infrastructures. Seventh Framework Programme Ref 212692 **The Spanish Ministery of Science and Innovation. Project ENE2009-07572
SPIRAL2 facility is expected to produce 5mA of deuterons at 40 MeV. A beam dump device (BD) has been designed to stop the beam. In this paper we assess the residual dose rates (RDR) in the BD room during beam-off phases. MCNPX was used to deal with deuterons transport and production and transport of secondary neutrons. Deuteron and neutron induced activation were computed using ACAB* and EAF2007. Decay gammas were transported using MCNPX to compute RDR. Dose rates at cooling times up to one year are presented, showing that it is mainly due to BD copper induced activation. The uncertainties in the results can be attributed to: i) the reliability of the d-Cu activation cross sections reactions, ii) the computational approach used to assess the neutron source. The troublesome radioisotopes from d-Cu and their formation reactions were identified. EAF2007 cross sections for these reactions were compared with the available experimental data. Regarding the computational approach to determine the neutron source from d-Cu interactions two options were used: i) built-in nuclear models of MCNPX, ii) TENDL** and MCUNED***. The available experimental data were used for benchmarking.
* J. Sanz et al. ACAB. User’s manual NEA-1839 (2009)
** A.J. Koning et al. TENDL2008 http://www.talys.eu/tendl-2008/
*** P.Sauvan et al. Nucl. Instr.and Meth. A 614 (2010)3 323-330.

TUP004

GEANT4 Modelling of Heat Deposition into the ISIS Muon Target

814

A. Bungau, R. Cywinski
University of Huddersfield, Huddersfield, United Kingdom
R.J. Barlow
Cockcroft Institute, Warrington, Cheshire, United Kingdom
C. Bungau
Manchester University, Manchester, United Kingdom
P.J.C. King, J.S. Lord
STFC/RAL, Chilton, Didcot, Oxon, United Kingdom

The energy deposition on the ISIS muon target and the temperature profiles are analysed in this paper. The thermal modelling is performed using the GEANT4 Monte Carlo code. Heat deposition patterns are also simulated for alternative target geometries. Energy deposition in the collimators is also discussed.

TUP005

Comparison of Back-scattering Properties of Electron Emission Materials

817

Z. Insepov, V. Ivanov, S.J. Jokela, M. Wetstein
ANL, Argonne, USA

We use “microscopic” Monte Carlo (MC) simulations, empirical theories, and comparison with experiments to identify the influence of back-scattered electrons and the saturation effect on the emissive properties of materials and to study the gain and transit times for various microchannel plates (MCPs). We have applied this method to Al2O3 and MgO emissive materials of various thickness and surface quality. The experimental secondary emission yield (SEY) data were obtained at normal electron impacts and were used as the reference data for adjusting our MC simulations. The SEY data were calculated at oblique angles of the primary electrons in the interval of 0-80 degrees. The energy dependence of backscattered electron coefficients (BSCs) for various primary electron incidence angles was calculated by MC for both materials, and the results were compared with experimental “average” values obtained in the literature. Both SEY and BSC data were used as input files to our “macroscopic” trajectory simulation, which models MCP amplifiers as whole devices and is capable of gain and transit time calculations.

TUP008

Update on Multipactor in Coaxial Waveguides using CST Particle Studio

820

G.V. Romanov
Fermilab, Batavia, USA

CST Particle Studio combines electromagnetic field simulation, multiparticle tracking, adequate post-processing and advanced probabilistic emission model, which is the most important new capability in multipactor simulation. The emission model includes in simulation the stochastic properties of emission and adds primary electron elastic and inelastic reflection from the surfaces. The simulation of multipactor in coaxial waveguides have been performed to study the effects of the innovations on the multipactor threshold and the range over which multipactor can occur. The results compared with available previous experiments and simualtions as well as the technique of MP simulation with CST PS are presented and discussed.

TUP009

A Computational Model for Muons Passing Gas and Plasma Targets: Beam Emittance.

823

A. Samolov, A.L. Godunov
ODU, Norfolk, Virginia, USA

A good understanding of interaction of muon beams with gas targets is crucial for attaining high acceleration gradients in gas pressured RF cavities. This physics includes a number of challenging problems. Our objective has been to develop a computational model for studying the most important effects within the same level of accuracy. The computational model simulates scattering of a bunch of charged particles on multiple atomic, molecular and ionic centers. The interaction potentials have been calculated using Hartree-Fock method for atomic targets, and Molecular Orbital method for molecular targets. Target particles are populated randomly to simulate either a gas in a pressured RF cavity with a particular material density, or liquid hydrogen. In the present work the following effects on beam emittance have been studied: effect of multiple scattering (comparing to single particle tracking models), effect of various degree of target ionization (beam-plasma interaction), space charge screening in plasma, effect of strong magnetic fields. Our preliminary results demonstrate that the degree of plasma ionization has a strong effect of the beam emittance.

TUP010

Code TESLA for Modeling and Design of High-Power, High-Efficiency Klystrons

826

I.A. Chernyavskiy
SAIC, McLean, USA
T.M. Antonsen
UMD, College Park, Maryland, USA
S.J. Cooke, B. Levush, A.N. Vlasov
NRL, Washington, DC, USA

Funding: This work was supported by the U.S. Office of Naval Research (ONR).
This work gives an overview of the main features of the 2.5D large-signal code TESLA and its capabilities for the modelling single-beam and multiple-beam klystrons as high-power RF sources. These sources are widely used or proposed to be used in accelerators in the future. Comparison of TESLA modelling results with experimental data for a few multiple-beam klystrons are shown.

TUP011

Multipactor Dynamics in Dielectric-loaded Accelerator Structures

829

O.V. Sinitsyn, T.M. Antonsen, G.S. Nusinovich
UMD, College Park, Maryland, USA

Funding: This work has been supported by the Office of High Energy Physics of the U.S. Department of Energy.
In this paper the authors present results of threedimensional analysis of multipactor in dielectric-loaded accelerator structures. The studies are aimed at checking some assumptions that were used in previous two-dimensional theory. In particular, it is demonstrated that the spatial distribution of charged particles can be azimuthally non-uniform which suggests using a more complex space charge model in some cases. Also, it is shown that the particle axial velocity components can be making a substantial contribution to particle energy and should not be ignored in future studies.

WEOCS4

Integrated EM & Thermal Simulations with Upgraded VORPAL Software

1463

D.N. Smithe, D. Karipides, P. Stoltz
Tech-X, Boulder, Colorado, USA
G. Cheng, H. Wang
JLAB, Newport News, Virginia, USA

Funding: This work supported by a DOE Phase II SBIR.
Nuclear physics accelerators are powered by microwaves which must travel in waveguides between room-temperature sources and the cryogenic accelerator structures. The ohmic heat load from the microwaves is affected by the temperature-dependent surface resistance and in turn affects the cryogenic thermal conduction problem. Integrated EM & thermal analysis of this difficult non-linear problem is now possible with the VORPAL finite-difference time-domain simulation tool. We highlight thermal benchmarking work with a complex HOM feed-through geometry, done in collaboration with researchers at the Thomas Jefferson National Accelerator Laboratory, and discuss upcoming design studies with this emerging tool. This work is part of an effort to generalize the VORPAL framework to include generalized PDE capabilities, for wider multi-physics capabilities in the accelerator, vacuum electronics, plasma processing and fusion R&D fields, and we will also discuss user interface and algorithmic upgrades which facilitate this emerging multiphysics capability.

Slides WEOCS4 [0.996 MB]

WEODS1

Design and Optimization of Future X-ray FELs based on Advanced High Frequency Linacs

1491

F. Wang
SLAC, Menlo Park, California, USA

To drive future XFELs, normal-conducting linacs at various rf freqencies are being considered. With optimized accelerator structures and rf systems, a higher rf frequency linac has several advantages, such as high acceleration gradient and high rf-to-beam efficiency. This paper presents a comparison of possible S-band, C-band and X-band linac designs for two cases, single bunch operation and multibunch operation, where the bunch train length is longer than the structure fill time and the beam loading is small. General scaling laws for the main linac parameters, which can be useful in the design such linacs, are derived.

Slides WEODS1 [5.795 MB]

Paper	Title	Page
TUP002	Study of Robinson Instabilities with a Higher-Harmonic Cavity for HLS Phase II Project	808
	Y. Zhao, W. Li, L. Wang, C.-F. Wu USTC/NSRL, Hefei, Anhui, People's Republic of China
	In the phase II project of Hefei Light Source, a fourth-harmonic “Landau” cavity will be operated in order to suppress coupled-bunch instabilities and increase the beam lifetime of Hefei Storage Ring. Instabilities limit the utility of the higher-harmonic cavity when the storage ring is operated with a small momentum compaction. Analytical modeling and simulations show that the instabilities result from Robinson mode coupling. In the analytic modeling, we operate an algorithm to consider Robinson instabilities. To study the evolution of unstable behavior, simulations have been performed in which macroparticles are distributed among the buckets. Both the analytic modeling and simulations agree for passive operation of the harmonic cavity.

TUP003	Beam Stop of Spiral2 Facility: Activation and Residual Dose Rate Calculations	811
	A. Mayoral, M. García, D. López, F. Ogando, J. Sanz, P. Sauvan UNED, Madrid, Spain
	Funding: SPIRAL 2 Preparatory Phase. European Strategy Forum on Research Infrastructures. Seventh Framework Programme Ref 212692 The Spanish Ministery of Science and Innovation. Project ENE2009-07572 SPIRAL2 facility is expected to produce 5mA of deuterons at 40 MeV. A beam dump device (BD) has been designed to stop the beam. In this paper we assess the residual dose rates (RDR) in the BD room during beam-off phases. MCNPX was used to deal with deuterons transport and production and transport of secondary neutrons. Deuteron and neutron induced activation were computed using ACAB and EAF2007. Decay gammas were transported using MCNPX to compute RDR. Dose rates at cooling times up to one year are presented, showing that it is mainly due to BD copper induced activation. The uncertainties in the results can be attributed to: i) the reliability of the d-Cu activation cross sections reactions, ii) the computational approach used to assess the neutron source. The troublesome radioisotopes from d-Cu and their formation reactions were identified. EAF2007 cross sections for these reactions were compared with the available experimental data. Regarding the computational approach to determine the neutron source from d-Cu interactions two options were used: i) built-in nuclear models of MCNPX, ii) TENDL and MCUNED. The available experimental data were used for benchmarking. J. Sanz et al. ACAB. User’s manual NEA-1839 (2009) A.J. Koning et al. TENDL2008 http://www.talys.eu/tendl-2008/ * P.Sauvan et al. Nucl. Instr.and Meth. A 614 (2010)3 323-330.

TUP004	GEANT4 Modelling of Heat Deposition into the ISIS Muon Target	814
	A. Bungau, R. Cywinski University of Huddersfield, Huddersfield, United Kingdom R.J. Barlow Cockcroft Institute, Warrington, Cheshire, United Kingdom C. Bungau Manchester University, Manchester, United Kingdom P.J.C. King, J.S. Lord STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
	The energy deposition on the ISIS muon target and the temperature profiles are analysed in this paper. The thermal modelling is performed using the GEANT4 Monte Carlo code. Heat deposition patterns are also simulated for alternative target geometries. Energy deposition in the collimators is also discussed.

TUP005	Comparison of Back-scattering Properties of Electron Emission Materials	817
	Z. Insepov, V. Ivanov, S.J. Jokela, M. Wetstein ANL, Argonne, USA
	We use “microscopic” Monte Carlo (MC) simulations, empirical theories, and comparison with experiments to identify the influence of back-scattered electrons and the saturation effect on the emissive properties of materials and to study the gain and transit times for various microchannel plates (MCPs). We have applied this method to Al2O3 and MgO emissive materials of various thickness and surface quality. The experimental secondary emission yield (SEY) data were obtained at normal electron impacts and were used as the reference data for adjusting our MC simulations. The SEY data were calculated at oblique angles of the primary electrons in the interval of 0-80 degrees. The energy dependence of backscattered electron coefficients (BSCs) for various primary electron incidence angles was calculated by MC for both materials, and the results were compared with experimental “average” values obtained in the literature. Both SEY and BSC data were used as input files to our “macroscopic” trajectory simulation, which models MCP amplifiers as whole devices and is capable of gain and transit time calculations.

TUP008	Update on Multipactor in Coaxial Waveguides using CST Particle Studio	820
	G.V. Romanov Fermilab, Batavia, USA
	CST Particle Studio combines electromagnetic field simulation, multiparticle tracking, adequate post-processing and advanced probabilistic emission model, which is the most important new capability in multipactor simulation. The emission model includes in simulation the stochastic properties of emission and adds primary electron elastic and inelastic reflection from the surfaces. The simulation of multipactor in coaxial waveguides have been performed to study the effects of the innovations on the multipactor threshold and the range over which multipactor can occur. The results compared with available previous experiments and simualtions as well as the technique of MP simulation with CST PS are presented and discussed.

TUP009	A Computational Model for Muons Passing Gas and Plasma Targets: Beam Emittance.	823
	A. Samolov, A.L. Godunov ODU, Norfolk, Virginia, USA
	A good understanding of interaction of muon beams with gas targets is crucial for attaining high acceleration gradients in gas pressured RF cavities. This physics includes a number of challenging problems. Our objective has been to develop a computational model for studying the most important effects within the same level of accuracy. The computational model simulates scattering of a bunch of charged particles on multiple atomic, molecular and ionic centers. The interaction potentials have been calculated using Hartree-Fock method for atomic targets, and Molecular Orbital method for molecular targets. Target particles are populated randomly to simulate either a gas in a pressured RF cavity with a particular material density, or liquid hydrogen. In the present work the following effects on beam emittance have been studied: effect of multiple scattering (comparing to single particle tracking models), effect of various degree of target ionization (beam-plasma interaction), space charge screening in plasma, effect of strong magnetic fields. Our preliminary results demonstrate that the degree of plasma ionization has a strong effect of the beam emittance.

TUP010	Code TESLA for Modeling and Design of High-Power, High-Efficiency Klystrons	826
	I.A. Chernyavskiy SAIC, McLean, USA T.M. Antonsen UMD, College Park, Maryland, USA S.J. Cooke, B. Levush, A.N. Vlasov NRL, Washington, DC, USA
	Funding: This work was supported by the U.S. Office of Naval Research (ONR). This work gives an overview of the main features of the 2.5D large-signal code TESLA and its capabilities for the modelling single-beam and multiple-beam klystrons as high-power RF sources. These sources are widely used or proposed to be used in accelerators in the future. Comparison of TESLA modelling results with experimental data for a few multiple-beam klystrons are shown.

TUP011	Multipactor Dynamics in Dielectric-loaded Accelerator Structures	829
	O.V. Sinitsyn, T.M. Antonsen, G.S. Nusinovich UMD, College Park, Maryland, USA
	Funding: This work has been supported by the Office of High Energy Physics of the U.S. Department of Energy. In this paper the authors present results of threedimensional analysis of multipactor in dielectric-loaded accelerator structures. The studies are aimed at checking some assumptions that were used in previous two-dimensional theory. In particular, it is demonstrated that the spatial distribution of charged particles can be azimuthally non-uniform which suggests using a more complex space charge model in some cases. Also, it is shown that the particle axial velocity components can be making a substantial contribution to particle energy and should not be ignored in future studies.

WEOCS4	Integrated EM & Thermal Simulations with Upgraded VORPAL Software	1463
	D.N. Smithe, D. Karipides, P. Stoltz Tech-X, Boulder, Colorado, USA G. Cheng, H. Wang JLAB, Newport News, Virginia, USA
	Funding: This work supported by a DOE Phase II SBIR. Nuclear physics accelerators are powered by microwaves which must travel in waveguides between room-temperature sources and the cryogenic accelerator structures. The ohmic heat load from the microwaves is affected by the temperature-dependent surface resistance and in turn affects the cryogenic thermal conduction problem. Integrated EM & thermal analysis of this difficult non-linear problem is now possible with the VORPAL finite-difference time-domain simulation tool. We highlight thermal benchmarking work with a complex HOM feed-through geometry, done in collaboration with researchers at the Thomas Jefferson National Accelerator Laboratory, and discuss upcoming design studies with this emerging tool. This work is part of an effort to generalize the VORPAL framework to include generalized PDE capabilities, for wider multi-physics capabilities in the accelerator, vacuum electronics, plasma processing and fusion R&D fields, and we will also discuss user interface and algorithmic upgrades which facilitate this emerging multiphysics capability.
	Slides WEOCS4 [0.996 MB]

WEODS1	Design and Optimization of Future X-ray FELs based on Advanced High Frequency Linacs	1491
	F. Wang SLAC, Menlo Park, California, USA
	To drive future XFELs, normal-conducting linacs at various rf freqencies are being considered. With optimized accelerator structures and rf systems, a higher rf frequency linac has several advantages, such as high acceleration gradient and high rf-to-beam efficiency. This paper presents a comparison of possible S-band, C-band and X-band linac designs for two cases, single bunch operation and multibunch operation, where the bunch train length is longer than the structure fill time and the beam loading is small. General scaling laws for the main linac parameters, which can be useful in the design such linacs, are derived.
	Slides WEODS1 [5.795 MB]