A   B   C   D   E   F   H   I   K   L   M   N   O   P   Q   R   S   T   V   W  

impedance

Paper Title Other Keywords Page
OPL03 Intensity Upgrade Plans for CERN-LHC Injectors injection, linac, emittance, extraction 16
 
  • E.N. Shaposhnikova
    CERN, Geneva
 
 

With LHC coming into operation very soon an upgrade plan for the whole CERN accelerator complex has been proposed to allow full exploitation of the LHC potential in the future as well as giving increased support to traditional and possible new experiments at lower beam energies. This plan foresees replacing during the period 2011 - 2017 all the accelerators in the LHC injector chain (Linac2, Booster, PS) by new machines (Linac4, SPL and PS2) except for the last - the SPS. In this scenario the SPS should be able to reliably accelerate twice higher beam intensity than achieved so far and therefore significant improvements to the machine performance, in addition to the increased injection energy due to PS2, should be found and implemented at the same time scale. The present status of proposals and ongoing studies for all accelerator injector chain is described with main emphasis on the SPS challenges and upgrade plans.

 

slides icon

Slides

 
WGA01 Impedance and Beam Instability Issues at J-PARC Rings kicker, resonance, damping, synchrotron 40
 
  • Y.H. Chin, K. Takata, T. Toyama
    KEK, Ibaraki
  • J. Kamiya, Y. Shobuda
    JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
 
 

This talk will review the impedance and beam instabilities study for the J-PARC RCS and MR rings. RCS is possibly the first synchrotron employing a massive amount of ceramic chambers to reduce the eddy current effects on the chambers. The resulting RF shields on the chambers to reduce the beam impedance required new considerations on impedance calculation procedure. MR, on the other hand, uses conventional stain-less steel chambers due to its relatively small rep rate (0.3Hz), but then induces huge resistive-wall impedance. The recent study of resistive-wall impedance shows that the actual impedance will be even larger than the calculated one using the conventional formula, when the typical skin depth becomes comparable to the thickness of the chamber. In my talk, I will also touch on the issues of kicker impedances and their possible cures.

 

slides icon

Slides

 
WGA02 Transverse Mode-Coupling Instability in the CERN SPS: Comparing HEADTAIL Simulations with Beam Measurements simulation, coupling, kicker, injection 45
 
  • B. Salvant
    EPFL, Lausanne
  • G. Arduini, E. Métral, G. Papotti, D. Quatraro, G. Rumolo, R.J. Steinhagen, R. Tomás
    CERN, Geneva
  • R. Calaga
    BNL, Upton, Long Island, New York
 
 

Since 2003, single bunches of protons with high intensity and low longitudinal emittance have been observed to suffer from heavy losses in less than one synchrotron period after injection in the CERN Super Proton Synchrotron (SPS) when the vertical chromaticity is corrected. This fast instability does not limit the current performance of the SPS, but would be a major limitation in case of an anticipated upgrade of the SPS, which requires bunches of 4·1011 protons (p). Besides, the characteristics of this instability are also complementary indicators of the value of the SPS beam coupling impedance. MOSES analytical calculations, HEADTAIL macroparticle tracking simulations, as well as several measurement campaigns in the SPS indicate that this instability may be due to a coupling between transverse modes ‘-2’ and ‘-3’. The aim of this contribution is to report improvements of the SPS impedance model used by HEADTAIL simulations, and to find out more characteristics of the measured instability in order to assess whether the observed instability in the SPS is indeed a Transverse Mode Coupling Instability (TMCI).

 

slides icon

Slides

 
WGA03 Measurement of the Transverse Resistive Wall Impedance of a LHC Graphite Collimator at Low Frequency coupling, simulation, HOM, luminosity 48
 
  • F. Roncarolo
    UMAN, Manchester
  • F. Caspers, T. Kroyer, E. Métral
    CERN, Geneva
  • B. Salvant
    EPFL, Lausanne
 
 

The largest contribution to the LHC transverse resistive wall impedance is given by the graphite collimators. Such a contribution is predicted by analytical calculations. A series of laboratory measurements were performed to experimentally validate the analytical results in the case of small gaps and in a low frequency regime where the skin depth becomes comparable to the collimator thickness. The measurement method consists in determining the dependence of a probe coil input impedance on the surrounding materials and was applied to sample graphite plates, stand alone LHC collimator jaws and a full collimator assembly. After reviewing the measurement procedures, problematics and stages, the results are compared to analytical predictions and numerical simulations.

 

slides icon

Slides

 
WGA05 Transverse Instabilities of Coasting Beams With Space Charge damping, space-charge, lattice, octupole 58
 
  • V.A. Lebedev, A.V. Burov
    Fermilab, Batavia, Illinois
 
 

If large enough the beam space charge strongly affects the beam stability in a circular accelerator. It results in a separation of coherent and incoherent tunes and, consequently, instability. Effects of space charge on the beam stability are considered in application to Fermilab Booster, Main injector and Recycler.

 
WGA07 Simulation Study of Transverse Coherent Instabilities in Intense Bunches with Space Charge and Image Currents simulation, synchrotron, space-charge, wakefield 66
 
  • V. Kornilov, O. Boine-Frankenheim
    GSI, Darmstadt
 
 

The head-tail instability is a well known intensity limitation for hadron bunches in synchrotrons. The instability has been observed in several synchrotrons and storage rings. Also for the FAIR synchrotrons the head-tail instability represents a potential intensity limitation. In the SIS-18 and SIS-100 synchrotrons space charge effects together with image currents play an important role for the determination of the instability threshold. In this work we study head-tail modes using 3D particle simulations for SIS100 beam parameters. The unstable modes are driven by the resistive wall impedance. Space-charge and image currents are taken into account. The possibility to include space charge into long-term simulations, which are necessary for head-tail instability studies, is investigated using the HEADTAIL code and the PATRIC code, developed at GSI. Potential instability cures will be discussed.

 
WGA14 Coupling and its Effects on Beam Dynamics coupling, betatron, emittance, kicker 85
 
  • V.A. Lebedev, A.V. Burov
    Fermilab, Batavia, Illinois
 
 

Coupling between different degrees of freedom complicates analysis of beam dynamics in a ring. Nevertheless appropriate choice of dynamic variables often allows reducing a problem to uncoupled case. Effects of coupling on the beam instabilities and their damping are considered. As examples the X-Y coupling in Tevatron and the coupling of longitudinal and horizontal motion in FNAL Booster are considered.

 
WGA30 Space Charge Effect in Isochronous Rings space-charge, optics, simulation, vacuum 157
 
  • E. Pozdeyev
    BNL, Upton, Long Island, New York
  • F. Marti, R.C. York
    NSCL, East Lansing, Michigan
  • J.A. Rodriguez
    CERN, Geneva
 
 

Isochronous cyclotrons, rings for precise nuclear mass spectrometry, and some isochronous-optics light sources with extremely short bunches are operated or proposed to be operated in the isochronous or almost isochronous regime. Also, many hadron synchrotrons run in the isochronous regime for a short period of time each acceleration cycle during transition crossing. The longitudinal motion is “frozen” in the isochronous regime that leads to accumulation of the integral of the longitudinal space charge force. In low-gamma hadron machines, this can cause a fast growth of the beam energy spread even at modest beam intensities. In this paper, I discuss specifics of space charge in the isochronous regime and present experimental results obtained in the Small Isochronous Ring, developed at Michigan State University specifically for studies of space charge in the isochronous regime.

 

slides icon

Slides

 
WGA32 Landau Damping of Space-Charge Dominated Fermilab Booster Beam space-charge, octupole, electron, booster 168
 
  • K.Y. Ng
    Fermilab, Batavia, Illinois
 
 

The stable region of the Fermilab Booster beam in the complex coherent-tune-shift plane appears to have been shifted far away from the origin by its intense space charge making Landau damping appear impossible. However, it is shown that the bunching structure of the beam reduces this space-charge shift. As a result, the beam can be stabilized by suitable octupole driven tune spread.