Paper  Title  Page 

THP2WB01 
Revisiting the Longitudinal 90 Degree Limit for Superconducting Linear Accelerators  


In the design of highintensity linear accelerators one of the generally adopted criteria is not to exceed a zerocurrent phase advance per focusing period of 90 degrees in order to avoid the space charge driven envelope instability, or a coinciding fourth order space charge resonance. Recently it was claimed that in certain structures, predominantly applicable to superconducting linac lattices  such a constraint is not always necessary in the longitudinal plane (I. Hofmann and O. BoineFrankenheim, Phys. Rev. Lett. 118, 2017). This applies primarily to such focusing structures, where the transverse focusing period only induces a weak space charge dependent modulation in the longitudinal plane, and a different periodicity is applicable to the longitudinal plane. Hence the longitudinal 90 degree stopband is practically absent, and phase advances significantly above 90 degrees should be possible in such structures, with a corresponding additional design freedom. As a consequence, we suggest that the 90 degree rule should no longer be taken as standard criterion in the longitudinal plane of linac design.  
Slides THP2WB01 [5.179 MB]  
THP2WB02  HighIntensity Beam Dynamics Simulation of the IFMIFlike Accelerators  1 


Funding: This research was supported by the National Research Foundation of Korea (Grant No. NRF2017M1A7A1A02016413). The IFMIF (International Fusion Material Irradiation Facility) project is being considered to build fusion material test facility. The IFMIF will use two accelerators to generate high energy neutrons. However, the IFMIF accelerators have been designed to have much higher beam power and beam current than the existing accelerators, so space charge effect is very strong. This raises big concerns about beam loss and beam transport stability, thus detailed highintensity beam dynamics study of the IFMIFlike accelerators is indispensable. This research aims to perform source to target simulation of the IFMIFlike accelerator. The simulation has been carried out by two different kinds of simulation codes because the IFMIF accelerator has distinctive features. One is TRACEWIN simulation code which was used in IFMIF initial design. The other is WARP 3D PIC code which can precisely calculate space charge effects. This presentation will focus on beam simulations for LEBT, RFQ, and MEBT of the IFMIF accelerator 

Slides THP2WB02 [10.583 MB]  
THP2WB03  Influence of the Cavity Field Flatness and Effect of the Phase Reference Line Errors on the Beam Dynamics of the ESS Linac  1 


The particle longitudinal dynamics is affected by errors on the phase and amplitude of the electromagnetic field in each cavity that cause emittance growth, beam degradation and losses. One of the causes of the phase error is the change of the ambient temperature in the LINAC tunnel, in the stub and in the klystron gallery that induces a phase drift of the signal travelling through the cables and radio frequency components. The field flatness error of each multiple cell cavity is caused by volume perturbation, cell to cell coupling, tuner penetration, etc.. In this paper it is studied the influences of these two types of errors on the beam dynamics and it is determined their tolerances such that the beam quality is kept within acceptable limits.  
Slides THP2WB03 [1.556 MB]  
THP2WB04  Longitudinal Dynamics of Low Energy Superconducting Linac  1 


Funding: funded by NSFC(11375122, 11511140277) The superconducting linac is composed of short independent cavities, and the cavity occupies only a small portion (1/4 to 1/6) of the machine compared with the normal conducting one. When phase advance per period is greater than 60 degrees, the smooth approximation is no longer valid and the longitudinal motion has to be described by time dependent system. With the help of Poincare map, the single particle nonlinear time dependent longitudinal motion is investigated. The study shows that when phase advance per period is less than 60 degrees, the system can be well described by smooth approximation, that means there is a clear boundary (separatrix) between stable and unstable area; when phase advance is greater than 60 degrees, the system shows a quite different dynamic structures and the phase acceptance is decreased significantly compared with the smooth approximation theory predicated, especially when phase advance per period is greater than 90 degrees. The results show that even for low current machine, the zero current phase advance should be kept less than 90 degrees to make sure there is no particle loss because of the shrink of the longitudinal acceptance. 

Slides THP2WB04 [1.061 MB]  
THP2WB05  Halo Formation of the High Intensity Beams in a Periodic Solenoidal Fields  1 


Funding: This research was supported by the National Research Foundation of Korea (Grant No. NRF2017M1A7A1A02016413). Transport of intense beams over long distances can be restricted by spacecharge fields which force the trajectories of charged particles to deviate from the stable regions of propagation. The spacecharge fields can be calculated from the density distribution of the beam particles, and Poisson's equation. As the spacecharge term is put in the equations of motion, it affects the envelope equations and betatron wave number of a charged particle in the beam. Also, with different initial conditions of the beam particles, there can be perturbations on the matched beam envelopes which can generate a resonant interaction between the beam core and test particles. Unlike for the KV beam, for nonuniform density beams such as Gaussian beams in the periodic quadrupole or solenoidal focusing fields, there exists higher order terms and nonperiodic solutions of beam particle oscillations, which can generate halo regions and chaotic motions during the beam propagation. In this study, we have investigated the higher order resonances and nonperiodic solutions of the Gaussian beam in the solenoidal focusing fields to understand halo formation mechanisms of the intense beams. 

Slides THP2WB05 [2.295 MB]  
THP2WB06 
The Beam Dynamics Design of HIAF Superconducting Injector  


A new heavy ion superconducting linac, named SuperConducting Ion Linac(iLinac) has been proposed and designed in the Institute of Modern physics of China. As the injector of High intensity heavy Ion accelerator facility (HIAF), iLinac will accelerate the 1 mA 238U^{45+} beam to 17 MeV/u. In this paper, we will focus on the physics design study together with the design principles and the simulation results with machine errors.  
Slides THP2WB06 [1.938 MB]  