KEK, Ibaraki
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.
Fermilab, Batavia, Illinois
While a beam is being bunched, a coherent synchrotron frequency grows from zero to a maximal value, crossing many synchro-betatron resonances of the bunch motion. If a related driving force is high enough, the beam can get unstable. This phenomenon is important at Fermilab Booster, presumably being driven by dispersion in the cavities. To stabilize the beam, high chromaticities are required.
UMD, College Park, Maryland
Beam halo is one of the major limiting factors to the effective transport of intense beams. In this paper, we use the WARP particle-in-cell code to numerically investigate the effect of different initial particle distributions on the properties of mismatch-induced halo. In particular, we use equilibrium and non-equilibrium distributions, the latter prompted by experimental measurements of the beam distribution in the University of Maryland Electron Ring (UMER). In both cases, we observe the phase space structure expected in the case of resonances between beam envelope oscillations and single-particle trajectories.
GSI, Darmstadt
Resonant effects caused by space charge may occur in circular as well as linear accelerators for high intensity. In the present work we focus on the so-called space charge structure resonances in 2D approximation, where the driving force is induced by space charge only (emittance exchange, fourth and sixth order structure resonances) and show that they can be described by a common class of scaling laws. A distinctive feature is the presence or absence of trapping of particles, which is also reflected in the power of the scaling law. An important requirement is the fully self-consistent modeling, which describes correctly the evolution of beam core as well as halo.
IUCF, Bloomington, Indiana
Fermilab, Batavia, Illinois
Scaling laws of the emittance growth factor (EGF) for a beam crossing the 6th order systematic space-charge resonances and the random 4th order resonance driven by octupoles are obtained by numerical multi-particle simulations. These scaling laws can be used in setting the minimum acceleration rate, and the maximum tolerable resonance strength for the design of non-scaling fixed-field alternating gradient (FFAG) accelerators.
GSI, Darmstadt
In the talk we report on an extensive experimental campaign performed at GSI on the SIS18 synchrotron. We measured the evolution of beam properties over 1 second storage of several beams for several working points in the vicinity of a machine resonance. With this data we benchmark our code predictions and test the understanding of the underlying beam degradation mechanisms.
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.
STFC/RAL/ISIS, Chilton, Didcot, Oxon
ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Presently, it runs at beam powers of 0.2 MW, with upgrades in place to supply increased powers for the new Second Target Station. Studies are also underway for major upgrades in the megawatt regime. Underpinning this programme of operations and upgrades is a study of the high intensity effects that impose the limitations on beam power. This paper summarises work looking at the key topics of half integer resonance, image effects and injection painting under high space charge conditions, plus progress on overall machine modelling. A core aim of the work is to experimentally confirm simulations and theory, therefore progress on modelling the machine in both operational and specially configured modes is reported. Closely related diagnostics studies are also described, as is initial work on instabilities. Finally, future plans are summarised.
CERN, Geneva
In the CERN Proton Synchrotron (PS), a slow beam loss of few percents is still observed on the long injection flat-bottom with the nominal beam for LHC after fine tuning of the working point. The understanding of space-charge effects is therefore of paramount importance to try and alleviate this limitation. This is why controlled benchmarking space-charge experiments were performed in the last few years. The results are presented in detail with a particular emphasis on the maximum achievable space-charge tune shift with long lifetime. On the contrary, space-charge effects usually play a minor role in high-energy machines like the CERN Super Proton Synchrotron (SPS). However, they could potentially become a limitation for the heavy ion beams needed for the LHC. Therefore, experimental studies on space-charge limitations were also performed in the SPS in the last few years. The results are discussed in detail in the present paper. Furthermore, it is worth mentioning that observations similar to the ones measured in the PS in the presence of space-charge were also measured in the SPS with electron cloud.
UMD, College Park, Maryland
Space charge can significantly affect the resonant properties of rings. The University of Maryland Electron Ring is a scaled experiment in which we have circulated beams with unprecedented intensities. Here we discuss the resonance analysis performed using the electrostatic particle-in-cell code WARP, to understand the effect of space charge on the ring resonances. Beams with varying degrees of space charge in both the emittance- and space-charge-dominated regimes are attempted. The operating point is scanned to map the tune diagram under various lattice and injection errors. The results of the simulation study are compared to experimental measurements.
ORNL, Oak Ridge, Tennessee
GSI, Darmstadt
The 4ν=1 resonance of a linac is found when the depressed tune is around 90 deg. It is observed that this fourth order resonance is dominating over the better known envelope instability and practically replacing it. Simulation study shows a clear emittance growth by this resonance and its stopband. Experimental measurement of the stopband of this resonance is proposed and conducted in 2008 using the UNILAC at GSI. This study will serve as an excellent benchmarking.
SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.
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.