Paper  Title  Page 

TUXGBF3  Reduction of the Kicker Impedance Maintaining the Performance of Present Kicker Magnet at RCS in JPARC  616 


The present kicker at RCS in JPARC is designed to make a waveform by superposing the forward and backward currents from the power source to extract beams, so that one terminal of the kicker is shorted and the other one is open. On the other hand, the kicker impedance is the dominant source of the beam instability at the RCS. This report proposes a scheme to reduce the kicker impedance, maintaining the beneficial of the superposition of currents with the present kicker magnet.  
Slides TUXGBF3 [9.951 MB]  
DOI •  reference for this paper ※ https://doi.org/10.18429/JACoWIPAC2018TUXGBF3  
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TUYGBD5 
A 2D SteadyState Space Charge Solver for Azimuthally Symmetric Problems of Arbitrary Degree  


Student poster award talk  
Slides TUYGBD5 [4.670 MB]  
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THPAF036  Longitudinal and Quadrupolar Coupling Impedance of an Elliptical Vacuum Chamber With Finite Conductivity in Terms of Mathieu Functions  3040 


Funding: Work supported by the CERN PSLIU project The resistive wall impedance of an elliptical vacuum chamber in the classical regime with infinite thickness is known analytically for ultrarelativistic beams by means of the Yokoya form factors. Starting from the longitudinal electric field of a point charge moving at arbitrary speed in an elliptical vacuum chamber, which we express in terms of Mathieu functions, in this paper we take into account the finite conductivity of the beam pipe walls and evaluate the longitudinal and quadrupolar impedance for any beam velocity. We also obtain that the quadrupolar impedance of a circular pipe is different from zero, approaching zero only for ultrarelativistic particles. Even if some of the results, in particular in the ultrarelativistic limit, are already known and expressed in terms of form factors, this approach is the first step towards the calculation of the general problem of a multilayer vacuum chamber with different conductivities and of elliptic cross section. 

DOI •  reference for this paper ※ https://doi.org/10.18429/JACoWIPAC2018THPAF036  
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THPAF062  Impact of Superconducting Magnet Protection Equipment on the Circulating Beam in HLLHC  3115 


Funding: Work supported by the HLLHC project. The new superconducting quadrupole and dipole magnets for the High Luminosity LHC (HLLHC) will rely on quench heaters or CouplingLoss Induced Quench (CLIQ) units or a combination of both to protect the magnet coils in case of a quench. After the detection of a quench, the quench heater power supplies will discharge currents of several hundreds of amperes into the quench heater strips glued to the coils, and the CLIQ units will discharge an oscillating current in the order of 1~kA directly into the coils. These currents can have a significant effect on the circulating beam if the discharge occurs before the beam is dumped. In the HLLHC inner triplet quadrupole magnets and 11 T dipole magnets, which will be installed in the collimation region dispersion suppressor, this effect will even be stronger due to the larger number of quench heaters and use of CLIQ units (triplet magnets only) as well as due to the greater value of beta function in comparison with the present LHC. In this paper, the expected effects of quench heater and CLIQ discharges on the circulating beam are summarized, and several mitigation methods are proposed and evaluated. Matthieu. Valette@cern.ch 

DOI •  reference for this paper ※ https://doi.org/10.18429/JACoWIPAC2018THPAF062  
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THPAF087  MultiObjective Optimization of an SRF Photoinjector with Booster Section for High Brightness Beam Performance  3193 
SUSPF071  use link to see paper's listing under its alternate paper code  


Several future accelerator projects, light sources and user experiments require high brightness electron beams. SRF photoinjectors operating in continuouswave (cw) mode hold the potential to serve as an electron source generating beams of high average brightness and short bunch lengths. Different operation and design parameters of the SRF photoinjector impact the beam dynamics and thus the beam brightness. A universal multiobjective optimization program based on a genetic algorithm was developed to extract optimum gun parameter settings from Paretooptimum solutions. After getting the first optimum results, the photoinjector is supplemented with a booster section downstream. The new optimization results are presented. Further, the optimization program is applied to evaluate the impact of the field flatness of the gun cavity on the high brightness performance.  
DOI •  reference for this paper ※ https://doi.org/10.18429/JACoWIPAC2018THPAF087  
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THPAK010  Optimization on the Optical Resonator of CTFEL  3228 


Funding: Program for the National Science Foundation of China (Grant No. 11105019) and the National Science Device Exploitation Foundation of China (Grant No. 2011YQ130018). A high power THz free electron laser (FEL) facility is under construction at China Academy of Engineering Physics (CTFEL) since October, 2011. The radiation frequency of the FEL facility will be tuned in range of 1~3 THz and the average output power is about 10 W. The system mainly consists of a GaAs photoemission DC gun, superconductor accelerator, the hybrid wiggler, optical cavity. The first lasing is obtained on Aug. 29, 2017. The optical resonator of CTFEL is optimized to ensure wavelength tunable in a wide range and high power operation. The FEL power strongly depends on the performance of the optical resonator including output efficiency, gain and roundtrip loss. The optical resonator consists of metalcoated reflect mirror, the centerhole output mirror, waveguide. The influence of waveguide and Rayleigh length on the quality of optical cavity is evaluated by the 3DOSIFEL code. The waveguide size, mirror curvature radius, output hole radius is optimized to different frequencies between 1 THz to 3 THz. 

DOI •  reference for this paper ※ https://doi.org/10.18429/JACoWIPAC2018THPAK010  
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THPAK017  Higher Order Modes in ChinaADS Demo Linac  3240 


Funding: Work supported by Natural Science Foundation of China，No.11505253 The study of higher order modes excited in the ChinaADS Linac has been presented in this paper. The effects of the cryogenic losses and the influence on beam of the higher order modes have been investigated. 

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THPAK051  Computer Simulation of Explosive Emission Electrons Acceleration and Xray Quantum Generation in Pulse Coaxial Diode System with Interior Anode  3333 


Computer simulation of electrons from explosive emission acceleration and Xray quantum generation in pulse coaxial diode system with interior anode, which is used in accelerating tube of compact Xray generator* with Tesla transformer as high voltage source, was done. The results obtained allow us to choose accelerating tube diode system geometry for different running modes. Comparison of numerical results with experimental data of dose rate dependence on the distance from vacuum tube anode and energy at first circuit Tesla transformer was fulfilled.
*Patent RF N71817, 03.10.2007 

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THPAK064  Theoretical Modeling of Electromagnetic Field from Electron Bunches in Periodic Wire Medium  3376 


Funding: Work supported by the Grant from Russian Foundation for Basic Research (No. 175204107). The interaction of relativistic electrons with periodic structures results in radiation by a number of mechanisms. In case of crystals one obtains parametric Xray radiation, its frequency is determined by distance between crystallographic planes and direction of electron beam. If instead of crystal one considers a periodic structure of metallic wires with period of the order of mm, one can expect emission of THz radiation. In the present contribution we consider theoretical approaches for modeling of the distribution of electromagnetic field from electron bunches in lattice formed by metallic wires. The analytical description is possible for the case of wires with small radius, the range of validity is checked by numerical simulations. The intensity of radiation will be significantly increased if the electrons in the bunch could radiate coherently. Two possibilities will be discussed: the prebunching of the beam and the selfmodulation of the beam due to interaction with radiated field. 

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THPAK086  A 2D SteadyState Space Charge Solver for Azimuthally Symmetric Problems of Arbitrary Degree  3431 
SUSPF072  use link to see paper's listing under its alternate paper code  


Correctly and rapidly simulating the steadystate interaction between particle beams and electromagnetic fields is crucial to the design and optimization of accelerator and radiofrequency (RF) source components. Iteratively solving for the selfconsistent interaction between particles and fields can prove challenging and highly susceptible to numerical noise and mesh induced instabilities. We present herein two new approaches to solving the selfconsistent trajectories of particles in the presence of external and self fields. The first method reformulates the integrated self field contribution as a path integral. The second method uses a hybrid Eulerian framework and produces an interpolated continuous current density, resulting in 12 orders of magnitude fewer particles required to obtain an accurate solution. We conclude with benchmarking results which show this method is as accurate as state of the art PIC solvers, while running 80120X faster.  
DOI •  reference for this paper ※ https://doi.org/10.18429/JACoWIPAC2018THPAK086  
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THPAK113  Cavity Characterization Studies With the Latest Revision of YACS  3503 


Funding: Work supported by the BMBF under contract no. 05K13PEB. YACS is a 2.5D finite element method solver capable of solving for the full 3D eigenfrequency spectra of resonant axisymmetric structures while reducing the computational problem to a 2D rotation plane. The most recent revision of YACS now supports arbitrary order basis functions for the geometry and field discretization. In earlier revisions of YACS spurious modes were introduced by increasing the order of either the geometry or field basis functions. To prevent the emergence of spurious modes, YACS now matches the function spaces of the inplane and outplane function basis, and thus yields spurious free solutions. To demonstrate the capabilities of YACS, extensive cavity characterization studies on curved multicell microwave cavities are presented. Due to the combined utilization of the rotation symmetry, higher order basis functions and curved elements, eigenfrequency spectra above 10 GHz for Lband multicell structures can be easily obtained. 

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