Keyword: focusing
Paper Title Other Keywords Page
MOP217 MEBT2 Design for the C-ADS Linac emittance, linac, space-charge, proton 93
 
  • Z. Guo, H. Geng, Z. Li, J.Y. Tang
    IHEP, Beijing, People's Republic of China
 
  The C-ADS linac is composed by two parallel injectors and a main linac, a section of Medium Energy Beam Line (MEBT2) is designed to guide and match beams from two injectors to the main linac. The two injectors are hot-spare for each other in order to satisfied the requirement of high availability and reliability. The beam in online operation mode will be directed to the main linac from one injector, while the beam in the offline mode with low repetition frequency from the other injector, will be directed to a beam dump through an auxiliary beam line. With a long drift distance and in the presence of space charge force for 10 mA 10 MeV proton beam, the debunching effect is very strong and it requires very strict control over beam losses and emittance growth. It is difficult to obtain satisfactory longitudinal matching without bunchers in the bending section. An analytical study using transfer matrix shows that with two bunchers of same voltage in the bending section the achromatism can be maintained if the effective voltage is inversely proportional to the distance between the two bunchers. It is also under consideration if and how a beam collimation can be implanted in MEBT2.  
 
MOP218 Dynamics of Particles in a Tilted Solenoidal Focusing Channel emittance, linac, solenoid, alignment 97
 
  • H. Jiang, S. Fu
    IHEP, Beijing, People's Republic of China
 
  We use the paraxial ray approximation equations to analysis the dynamics of particles in a tilted solenoidal focusing channel. In this case, the particles' initial canonical angular momentum is nonzero, so we need to add the term of centrifugal potential to the dynamics equation of particles. And in the dynamics equation this centrifugal potential term is nonlinear, which results in the emittance growth. In practice, we also need to consider the spherical aberration's effect on emittance growth and the linear part of the space-charge force of a Kapchinskij-Vladimirskij distribution beam in the dynamics equation of particles.  
 
MOP220 Local Compensation-rematch for Major Element Failures in the C-ADS Accelerator cavity, solenoid, quadrupole, emittance 102
 
  • B. Sun, Z. Li, J.Y. Tang, F. Yan
    IHEP, Beijing, People's Republic of China
 
  In order to achieve the required reliability and availability for the C-ADS accelerator, a fault tolerance design is pursued. The effects of cavity failure in different locations have been studied and the schemes of compensation by means of local compensation have been investigated. After one cavity failure, by adjusting the settings of the neighboring cavities and the focusing elements to make sure that the Twiss parameters and energy are approximately recovered to that of the nominal ones at the matching point. We find the normalized RMS emittance and emittances including 99.9% and 100% particles have no obvious growth after applying the compensation with the RMS rematching in each section of the main linac. However, the conclusions above are drawn from the simulation results with the TraceWin code, which doesn't consider the phase difference. A code based on Matlab is under developing. By applying the code on the cavity failure in the middle part of spoke021 section, a fully compensated scheme with good dynamics results is obtained. The space charge effect is still not implanted in the code, and further study and optimization of the code will be performed in the next step.  
 
TUO1A03 Space Charge Effects in Isochronous FFAGs and Cyclotrons space-charge, cyclotron, TRIUMF, simulation 231
 
  • T. Planche, R.A. Baartman, Y.-N. Rao
    TRIUMF, Vancouver, Canada
 
  Effects of space charge forces on the beam dynamics of isochronous rings will be discussed. Two different kinds of phenomena will be introduced through a brief review of the literature on the topic. The first one is a consequence of the very weak vertical focusing found in the low energy region of most cyclotrons. The space charge tune shift further reduces the vertical focusing, setting an upper limit on instantaneous current. The second one arises from the fact that longitudinal phase space is frozen in isochronous rings. This leads to effects of space charge forces which are very peculiar to isochronous machines. We will finally present the simulation tools being developed at TRIUMF to study these effects.  
slides icon Slides TUO1A03 [0.974 MB]  
 
WEO1C05 Longitudinal Space Charge Phenomena in an Intense Beam in a Ring space-charge, induction, electron, injection 447
 
  • R.A. Kishek, B.L. Beaudoin, D.W. Feldman, I. Haber, T.W. Koeth, Y. Mo
    UMD, College Park, Maryland, USA
 
  Funding: Supported by the US Dept. of Energy, Offices of High Energy Physics and Fusion Energy Sciences, and by the US Dept. of Defense, Office of Naval Research and the Joint Technology Office.
The University of Maryland Electron Ring (UMER) uses nonrelativistic, high-current electron beams to access the intense space charge dynamics applicable to hadron beams. The UMER beam parameters correspond to space charge incoherent tune shifts, at injection, in the range of 1-5.5 integers. Longitudinal induction focusing is used to counteract the space charge force at the edges of a long rectangular bunch, confining the beam for 100s of turns. We report on two recent findings: (1) The formation and propagation of solitons from large amplitude longitudinal perturbations, observed experimentally and reproduced in WARP* simulations. (2) The evolution of a longitudinal multi-streaming instability when the space-charge force is allowed to lengthen the bunch ends. The expanding bunch ends fill the ring, interpenetrate, and wrap repeatedly, forming multiple streams at any one location, each with its unique velocity. The resulting multi-stream instability is investigated over a wide range of beam currents and initial pulse lengths, and experimental observations are in good agreement with WARP simulations and an analytical theory that successfully predicts the onset of the instability.
* D.P. Grote, A. Friedman, I. Haber, S. Yu, Fus. Eng. & Des. 32-33, 193-200 (1996).
 
slides icon Slides WEO1C05 [5.868 MB]