EPFL, Lausanne
CERN, Geneva
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).
UMAN, Manchester
CERN, Geneva
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.
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.
IUCF, Bloomington, Indiana
ORNL, Oak Ridge, Tennessee
SLAC, Menlo Park, California
Recently, discrepancies between model-based and observed linear optics, such as the tune and the closed orbit, have been observed in the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. Accurate accelerator modeling is very important for machine control during the ongoing power ramp up. The Orbit Response Matrix (ORM) method is applied here to find and correct errors in the linear optics of the SNS ring. With the closed orbit data (4472 data points), we are able to calibrate the strength of the steering magnets, the BPM gain factors, and 6 quadrupole power supplies. Current results and remaining challenges will be presented and discussed.
KEK, Ibaraki
The J-PARC Main Ring should provide high beam power with strict limitation of the particle losses during the operation, including the injection and acceleration processes,caused by the machine imperfections and the space charge effects. The linear coupling resonance [1,1,43] has been identified as the most serious resonance for the MR operation, which leads to significant particle losses during the injection process. Effect of the sextupole resonances, caused by the machine imperfection, is much smaller. The 4th order resonances, mainly 4Qx, 4Qy and 2Qx-2Qy, excited by the space charge of the low energy beam, lead to additional particle losses. The correction procedure to minimize the effect of the sum coupling resonance [1,1,43] by using four independent skew quadrupole magnets has been studied. The particle losses for different machine operation scenario have been estimated, including the injection and acceleration processes. The study of the combined effect of the MR imperfections and the space charge of the beam with moderate beam power has been performed by using the PTC_ORBIT code, installed for the KEK super computer HITACHI SR11000.
ORNL, Oak Ridge, Tennessee
UW-Madison, Madison, Wisconsin
An analog wideband feedback system for damping e-p instabilities has been demonstrated at the PSR at Lansce. A mixed signal system is being developed and deployed at SNS. The status and expected performance of the of the system is discussed.
TRIUMF, Vancouver
GSI, Darmstadt
CERN, Geneva
32 papers were presented. Rather than summarizing each one individually, we give a few highlights, conditioned by the items in the working group charge, namely:
- Summarize the state of the art in simulation capabilities. What developments are needed?
- Summarize the state of the art in theory. What developments are needed?
- Summarize recent developments in benchmarking experimental data with simulations. What critical experiments and diagnostic developments are needed to further refine the theory and simulations?
- Summarize the state of the art in instability mitigation techniques. What further technology developments are needed?
- Summarize the primary limitations to beam intensity in existing circular machines.
- Summarize the key beam dynamics questions for high-intensity circular machines
- Summarize opportunities for advancing the field.