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.
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.
BNL, Upton, Long Island, New York
Operational experience on crossing RHIC transition as well as observed beam dynamics effects are described. The techniques to provide the successful transition crossing without beam losses and deterioration of the beam quality in both transverse and longitudinal plane are reviewed. Presently the ion beam intensity is limited by the transverse instability happenning at the transition region. It was observed that the threshold of the instability was significantly affected by the presence of the electron cloud. The results of recent studies of the intensity limiting instability are presented.
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.
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.
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.
Fermilab, Batavia, Illinois
Understanding the behavior of high-intensity beams in the Fermilab Main Injector is crucial for the future physics program at the lab. Simulations of the Main Injector including collective effects are a crucial part of this understanding. We are building up a set of integrated simulations of collective effects using the Synergia accelerator simulation framework. As a step in this work we present simulations of space-charge effects combined with impedance effect in the Main Injector.
Fermilab, Batavia, Illinois
BNL, Upton, Long Island, New York
Beam-beam interaction is one of the dominant sources of emittance growth and luminosity lifetime deterioration. A current carrying wire has been proposed to compensate long-range beam-beam effects in the LHC and the principle is now being experimentally investigated at RHIC. Tune shift, beam transfer function, and beam loss rate are measured in dedicated experiments. In this paper, we do simulations to study the effect of wire compensator based on diffusive apertures, beam loss rates, and beam transfer function using a parallel weak-strong beam simulation code (bbsimc) without parasitic collisions. The simulation results are compared with measurements.
BNL, Upton, Long Island, New York
A strong interest in running RHIC at low energies in a range of 2.5-25 GeV/nucleon total energy of a single beam has emerged recently. Providing collisions in this energy range, which in RHIC case is termed “low-energy” operation, will help to answer one of the key questions in the field of QCD about existence and location of critical point on the QCD phase diagram. To evaluate the challenges of RHIC operation at such low energies there have been several short test runs during RHIC operations in 2006, 2007 and 2008. The beam lifetime observed during the test runs was clearly limited by machine nonlinearities. This performance can be improved provided sufficient time is given for machine development at these low energies. After the lifetime caused by nonlinearities is improved the strongest limitation comes from transverse and longitudinal Intra-beam Scattering (IBS), and ultimately by the space-charge limit. A significant luminosity improvement can be provided with electron cooling applied directly in RHIC at low energies. This report summarizes various beam dynamics limiting effects and possible improvement with electron cooling.
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.
Tech-X, Boulder, Colorado
BNL, Upton, Long Island, New York
Jefferson Lab, Newport News, Virginia
Novel electron-hadron collider concepts are a long-term priority for the international nuclear physics community. Effective beam cooling for intense, relativistic hadron beams will be necessary to obtain the orders-of-magnitude higher luminosities being proposed. Coherent electron cooling (CEC) [1] combines the best features of electron cooling and stochastic cooling, via free-electron laser technology [2], to offer the possibility of cooling high-energy hadron beams much faster. Many technical difficulties must be resolved via full-scale 3D simulations, before the CEC concept can be validated experimentally. The parallel VORPAL framework [3] is the ideal code for simulating the modulator and kicker regions, where the electron and hadron beams will co-propagate as in a conventional electron cooling section. We present initial VORPAL simulations of the electron density wake driven by single ions in the modulator section. Also, we present a plan for simulating the full modulator-amplifier-kicker dynamics, by through use of a loosely-coupled code suite including VORPAL, an FEL code and a beam dynamics code.
[1] Y.S. Derbenev, Proc. COOL07, 149 (2007).
[2] V.N. Litvinenko & Y.S. Derbenev, Proc. FEL07, 268 (2007).
[3] G.I. Bell et. al., J. Comp. Phys. (2008), in press.
Fermilab, Batavia, Illinois
Obit Response Matrix (ORM) Fit method has been successfully used to calibrate linear optics at Recycler Ring at Fermilab. The linear model of the Recycler optics ring has been significantly improved. Based on the build-up model, lattice measurement of the Recycler ring has been done several times, each after some magnets move and the tunes change. Large beta-wave(~20%) has been found in horizontal plane after the working point was moved from (0.424,0.434) to (0.456, 0.467) for the reason of lowering the beam instabilities. The source of the beta-wave, and the correction will be presented in this paper. In addition, we found an easy way to extend the tuning range in the recycler lattice. A new application program for adjusting the tunes operationally was introduced and the measured results will be presented.
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.
ORNL, Oak Ridge, Tennessee
The 248 meter Spallation Neutron Source accumulator ring is designed to operate with a beam intensity of 1.5·1014 ppp. A major concern for high intensity operation is the possibility of beam instabilities. Recently a series of experiments have been performed to systematically map out the instability parameter space. Beam instabilities have been measured versus betatron tune, ring RF voltage, lattice chromaticity, and beam intensity. The results of these studies are presented here
LBNL, Berkeley, California
We present electron-cloud build-up simulations for the FNAL Main Injector at the location of the RFA electron detector. By comparing our simulated results against measurements for various bunch intensities and beam fill patterns, we determine the likely value of the peak secondary emission yield. We then extrapolate our results to higher intensities, within the range contemplated by the proposed MI upgrade program. We predict a substantial increase of the electron cloud density relative to its present value. We consider two values of the RF frequency, namely 53 and 212 MHz, and compare the electron cloud density for these two frequencies at fixed total beam intensity. We contrast the MI results against those from a similar simulation for the PS2, the first storage ring in the proposed future upgrade of the LHC injector complex. Time permitting, we will briefly comment on effects from the electron cloud on the beam dynamics.
LANL, Los Alamos, New Mexico
TechSource, Santa Fe, New Mexico
Recent beam studies have focused on understanding the main sources and locations of electron clouds (EC) which drive the observed e-p instability at the PSR. New results using a recently developed electron diagnostic will be reported which demonstrate the important role of EC activity in quadrupole magnets, including definitive evidence that ~80% or more of the drift space EC signal is “seeded” by electrons ejected by ExB drifts from adjacent quadrupole magnets*. Other observations include distinctive brown colored tracking in various dipole and quadrupole vacuum chambers, which we hypothesize is caused by energetic electrons striking the wall during beam-induced multipacting. The tracking observations point to a simple and useful signature for regions of EC activity. Modeling of EC observations using a modified version of the POSINST** code shows general agreement on many features of the observations, given the large uncertainties in the distribution of seed electrons from beam loss which is a key input into the simulations. Progress will be reported on resolving the features not in agreement.
* R. Macek et al, PRSTAB, 11, 010101 (2008).
** M. T. F. Pivi and M. A. Furman, PRSTAB, 6, 034201 (2003).
The University of Texas at Austin, Austin, Texas
The Fermilab Main Injector is a rapid-cycling synchrotron designed to produce high-flux, high-energy protons beams for fixed-target applications, including antiproton and neutrino production. The present Main Injector produced about 400 kW of 120 GeV protons, but proposed upgrades are designed to produce in excess of 2 MW. One instability of concern is the electron cloud. We have observed the formation of the electron cloud at the Main Injector. At presents intensities it produces no instabilities. We will present measurements made at the Main Injector, including: a threshold for cloud formation, bunch length dependence, conditioning with exposure. In addition, we will describe the evolving program for making measurements at the Main Injector, in anticipation of beam charge upgrades.
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.
CERN, Geneva
Recent developments relative to the injection and storage of the 160 MeV Linac4 high brightness beam for LHC into the CERN PS Booster are reviewed. This talk reports simulations made with the Orbit code. Focus is on H- charge exchange injection and following beam emittance evolution at 160 MeV. Injection is done via a painting scheme for optimal shaping of the initial particle distribution. Next, benchmarking of Orbit and Accsim simulations with measurements performed in the PS Booster on a stored beam at 160 MeV are discussed.
ORNL, Oak Ridge, Tennessee
Operating at 0.5 MW beam power on target, the Spallation Neutron Source (SNS) is already the world's most powerful pulsed neutron source. However, we are only one third of the way to full power. As we ramp toward full power, the control of the beam and beam loss in the ring will be critical. In addition to practical considerations, such as choice of operating point, painting scheme, and rf bunching, it may be necessary to understand and mitigate collective effects due to space charge, impedances, and electron clouds. In dedicated high intensity beam study shifts, we have already observed resistive wall, impedance driven, and electron cloud activity. The analysis and simulation of this data are important ongoing activities at SNS. This talk will discuss the status of this work, as well as other considerations necessary to the successful full power operation of SNS.
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.
BNL, Upton, Long Island, New York
Intra-beam scattering (IBS) is the limiting factor of the luminosity lifetime for RHIC operation with heavy ions. Over the last few years the process of IBS was carefully studied in RHIC with dedicated IBS measurements and their comparison with the theoretical models. Recently, in order to suppress transverse IBS growth, a new lattice was designed and implemented in RHIC, which lowered the average arc dispersion by 30%. This lattice became operational during RHIC Run-8. We review the IBS suppression mechanism, IBS measurements before and after the lattice change, and comparisons with predictions.
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.
BNL, Upton, Long Island, New York
NSCL, East Lansing, Michigan
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.
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.
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.
CIAE, Beijing
PSI, Villigen
Abstract: Space charge effects play an important role in high intensity cyclotrons, as the most important collective effects. For cyclotrons with small turn separation, single bunch space charge effects are not the only contribution. The interaction of radially neighboring bunches are also present but their effect has, in greater detail, not yet been investigated. In this paper, for the first time, a new PIC based self-consistent numerical simulation model is presented, which covers neighboring bunch effects and is implemented in a three-dimensional object-oriented parallel code OPAL-cycl, a flavor of the OPAL framework. Apart from the full 3D tracking mode with space charge, the code is also capable to do single particle tracking and betatron tune calculation for ordinary cyclotron machine design. We present simulation results from the PSI 590 MeV Ring cyclotron in the light of the ongoing high intensity upgrade program, with the goal of 1.8 MW CW on target. We will also compare calculations with measurements from the Ring cyclotron.
Tech-X, Boulder, Colorado
KEK, Ibaraki
At low current, accelerators are dominated by their independent, separated-function magnets, and hence essentially all accelerator simulation codes have used not time but longitudinal distance, s, as the independent variable. The simulation of space-charge effects within this approach has been at best ad hoc, as it requires a (thoroughly approximate) transformation between a pancake of space charge at fixed s to a particle bunch at fixed t. We shall describe recent modifications to the accelerator simulation code PTC [1] that make it possible to, in effect, perform time-based particle tracking in a code that correctly handles the full geometry and wide dynamic range of current designs for FFAGs. In addition, we shall describe the associated space-charge computation and present initial results from simulations that cover a large energy gain in a model non-scaling FFAG.
[1] E. Forest, Y. Nogiwa, F. Schmidt, "The FPP and PTC Libraries", Proceedings of ICAP 2006.