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| MOPA004 | Status of Slip Stacking at Fermilab Main Injector | target, injection, booster, emittance | 347 | ||
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Funding: Operated by Universities Research Association, Inc. for the U.S. Department of Energy under contract DE-AC02-76CH03000. |
In order to increase proton intensity on anti proton production cycle of the Main Injector we are going to use the technique of 'slip stacking' and doing machine studies. In slip stacking, one bunch train is injected at slightly lower energy and second train is at slightly higher energy. Afterwards they are aligned longitudinally and captured with one rf bucket. This longitudinal stacking process is expected to double the bunch intensity. The required intensity for anti proton production is 8·1012 protons in 84 bunches. Beam studies of the slip stacking process have started and we have already established that the stacking procedure works as expected for a low beam intensity. In order to make this stacking process usable for higher intensity beam in standard mode of operation, we are working on high intensity beam and the development of the feedback and feed forward system is under way. |
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| MPPE073 | Effects of the Passive Harmonic Cavity on the Beam Bunch | radiation, synchrotron, impedance, electron | 3904 | ||
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In this paper, we present a computer tracking code, which can investigate the bunch length, energy spread and the critical current of Robinson instability under the influence of the passive harmonic cavity. The effects of the radiation damping, quantum excitation and the beam loading of the harmonic cavity are included in the computation. The calculated result shows that the beam has a constant energy spread and blows up as the beam current increases from below to over the threshold current of the Robinson instability. It also indicates that the shunt impedance of the harmonic cavity is critical for whether the harmonic cavity can reach the designed goal, a stable and lengthening beam at the design beam current.
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| MPPP016 | Adaptive Feed Forward Beam Loading Compensation Experience at the Spallation Neutron Source Linac | SNS, Spallation-Neutron-Source, linac, klystron | 1467 | ||
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Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. |
When initial beam studies at the Spallation Neutron Source (SNS) indicated a need for better compensation of the effects of beam loading, a succession of rapid-prototyping and experimentation lead to the development of a simple yet successful adaptive feed forward technique within a few weeks. We describe the process and first results. |
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| MPPP020 | RF Phase Modulation at the LNLS Electron Storage Ring | simulation, synchrotron, single-bunch, resonance | 1686 | ||
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Funding: FAPESP |
In the Brazilian Electron Storage Ring, we observed that modulating the phase of accelerating fields at twice the synchrotron frequency suppressed remarkably well a longitudinal coupled-bunch mode of the beam driven by one of the RF cavities. We present results of a set of systematic measurements, in single and multi-bunch mode, aimed at characterizing the effects of the modulation on the beam. We also compare those experiments with the results of tracking simulations. |
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| MPPP033 | Beam Transfer Functions and Beam Stabilisation in a Double RF System | synchrotron, damping, injection, space-charge | 2300 | ||
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The high intensity proton beam for LHC accelerated in the CERN SPS is stabilised against coupled-bunch instabilities by a 4th harmonic RF system in bunch-shortening mode. Bunch-lengthening mode, which could also be useful to reduce peak line density and alleviate problems from e-cloud and kicker heating does not give desirable results for beam stability. In this paper an analysis of the limitations of these two different modes of operation is presented together with measurements of the Beam Transfer Function for the double RF system. As predicted by theory, for sufficiently long bunches with the same noise excitation, the measured amplitude of the beam response in bunch-lengthening mode is an order of magnitude higher than that for bunch-shortening mode or for a single RF system.
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| TOAC002 | Beam Loading Compensation for Super B-Factories | feedback, impedance, synchrotron, storage-ring | 154 | ||
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Funding: Work supported by U.S. Department of Energy contract DE-AC02-76SF00515. |
Super B-factory designs under consideration expect to reach luminosities in the 1035 - 1036 range. The dramatic luminosity increase relative to the existing B-factories is achieved, in part, by raising the beam currents stored in the electron and positron rings. For such machines to succeed it is necessary to consider in the RF system design not only the gap voltage and beam power, but also the beam loading effects. The main effects are the synchronous phase transients due to the uneven ring filling patterns and the longitudinal coupled-bunch instabilities driven by the fundamental impedance of the RF cavities. A systematic approach to predicting such effects and for optimizing the RF system design will be presented. Existing as well as promising new techniques for reducing the effects of heavy beam loading will be described and illustrated with examples from the existing storage rings including PEP-II, KEKB, and DAFNE. |
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| TPAP031 | Simulations of an Acceleration Scheme for Producing High Intensity and Low Emittance Antiproton Beam for Fermilab Collider Operation | emittance, acceleration, simulation, antiproton | 2164 | ||
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Funding: Operated by Universities Research Association, Inc. for the U.S. Department of Energy under contract DE-AC02-76CH03000. |
During Fermilab collider operation, the Main Injector (MI) provides high intensity and low emittance proton and antiproton beams for the Tevatron. The present coalescing scheme for antiprotons in the Main Injector yields about a factor of two increase in the longitudinal emittance and a factor of 5% to 20% decrease in intensity before injection to the Tevatron. In order to maximize the integrated luminosity delivered to the collider experiments, it is important to minimize the emittance growth and maximize the intensity of the MI beam. To this end, a new scheme* using a combination of 2.5 MHz and 53 MHz accelerations has been developed and tested. This paper describes the full simulation of the new acceleration scheme, taking account of space charge, 2.5 MHz and 53 MHz beam loading, and the effect of residual 53 MHz rf voltage during 2.5 MHz acceleration and rf manipulations. The simulations show the longitudinal emittance growth at the 10% level with no beam loss. The experimental test of the new scheme is reported in another PAC'05 paper. *G.P. Jackson, The Fermilab Recycler Ring Technical Design Report, FERMILAB-TM-1991, November 1996. |
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| TPPT020 | 30 GHz Power Production in CTF3 | linac, beam-losses, vacuum, dipole | 1695 | ||
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One of the major objectives of CTF3 (CLIC Test Facility) is the production of 30 GHz power for the high-gradient testing of CLIC accelerating structures. To this end a dedicated beam line, power generating structure and power transfer line have been designed, installed and commissioned. 52 MW of 30 GHz power with a pulse length of 74 ns and a repetition rate of 16 Hz were delivered to the high-gradient test area. This will allow operation of test accelerating structures in the coming run of CTF3 up to the nominal CLIC accelerating gradient of 150 MV/m and beyond the nominal pulse length. The system is described and the performances of the CTF3 linac, beam line and the rf components are reviewed.
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| TPPT027 | 53 MHz Beam Loading Compensation for Slip Stacking in the Fermilab Main Injector | feedback, proton, cathode, radio-frequency | 1958 | ||
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Funding: Operated by Universities Research Association, Inc. for the U.S. Department of Energy under contract DE-AC02-76CH03000. |
Recently In-Phase and Quadrature (I&Q) was added to both the 53 MHz Feedback and Feedforward Beam Loading Compensation for Slip Stacking in the Fermilab Main Injector. With 53 MHz Feedback, we can now turn the 18 Radio Frequency (RF) Stations off down to below 100 V. In using I&Q on Feedforward, beam loading compensation to the beam on both the upper and lower frequencies of Slip Stacking can be applied as we slip the beam. I&Q theory will be discussed. |
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| TPPT054 | CW Operation of the TTF-III Input Coupler | vacuum, klystron, linac, simulation | 3292 | ||
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Many newly proposed light sources, operating in the CW regime, are based on superconducting TESLA technology. Since this was originally developed for pulsed, 1-% duty-factor operation, it is important to determine the limitations of the TESLA cryomodule and its components when operated CW. Among the critical components is the RF input coupler. Two tests have been performed to determine the average power limit of the TTF-III system. First, room temperature tests up to 4 kW were performed at the Forschungszentrum Rossendorf. These permitted the calibration of computer codes developed to calculate the temperature distribution in the coupler. The programs then were used to make predictions for the (normal) cold operation of the coupler. At BESSY, the coupler test stand was assembled inside the HoBiCaT horizontal cryostat test facility to operate the coupler in an environment close to that of a real accelerator. The results of the two tests are presented here.
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| WPAT040 | Pushing the Limits: RF Field Control at High Loaded Q | linac, resonance, klystron, feedback | 2642 | ||
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Funding: This work is supported by Cornell University. |
The superconducting cavities in an Energy-Recovery-Linac will be operated with a high loaded Q of several 1E7, possible up to 1E8. Not only has no prior control system ever stabilized the RF field in a linac cavity with such high loaded Q, but also highest field stability in amplitude and phase is required at this high loaded Q. Because of a resulting bandwidth of the cavity of only a few Hz, this presents a significant challenge: the field in the cavity extremely sensitive to any perturbation of the cavity resonance frequency due to microphonics and Lorentz force detuning. To prove that the RF field in a high loaded Q cavity can be stabilized, and that Cornell's newly developed digital control system is able to achieve this, the system was connected to a high loaded Q cavity at the JLab IR-FEL. Excellent cw field stability – about 2·10-4 rms in relative amplitude and 0.03 deg rms in phase - was achieved at a loaded Q of 2.1·107 and 1.4E8, setting a new record in high loaded Q operation of a linac cavity. Piezo tuner based cavity frequency control proved to be very effective in keeping the cavity on resonance and allowed reliable to ramp up to high gradients in less than 1 second. |
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| WPAT064 | Low Level RF Control System of J-PARC Synchrotrons | synchrotron, proton, feedback, linac | 3624 | ||
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We present the concept and the design of the low level RF (LLRF) control system of the J-PARC synchrotrons. The J-PARC synchrotrons are the rapid cycling 3-GeV synchrotron (RCS) and the 50-GeV main ring (MR) which require very precise and stable LLRF control systems to accelerate the ultra-high proton beam current. The LLRF system of the synchrotron is a full-digital system based on the direct digital synthesis (DDS). The functions of the system are (1) the multi-harmonic RF generation for the acceleration and the longitudinal bunch shaping, (2) the feedbacks for stabilizing the beam, (3) the feedforward for compensating the heavy beam loading, and (4) other miscellaneous functions such as the synchronization and chopper timing. The LLRF system of the RCS is now under construction. We present the details of the system. Also, we show preliminary results of performance tests of the control modules.
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| FPAE049 | Development and Implementation of ?T Procedure for the SNS Linac | linac, SNS, monitoring, simulation | 3064 | ||
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Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. |
The ?t procedure is a time of flight technique for setting the phases and amplitudes of accelerating fields in a multi-cavity linac. It was initially proposed and developed for the LAMPF linac in the early seventies and since then has been used in several accelerators. The SNS linac includes four CCL modules (Side Coupled Structure) operating at 805 MHz for the energy range from 86.8 MeV up to 185.6 MeV. The ?t procedure has been implemented for the SNS CCL linac and was used for its initial beam commissioning. Brief theory of the procedure, the results of the design parameter calculations and the experimental results of phase and amplitude setpoints are presented and discussed. |
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| FPAT034 | Dispersion Analysis of the Pulseline Accelerator | ion, impedance, acceleration, vacuum | 2330 | ||
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Funding: This work was perfomed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. |
We analyze the sheath helix model of the pulseline accelerator.* We find the dispersion relation for a shielded helix with a dielectric material between the shield and the helix and compare it against the results from 3-D electromagnetic simulations. Expressions for the fields near the beam axis are obtained. A scheme to taper the properties of the helix to maintain synchronism with the accelerated ions is described. An approximate circuit model of the system that includes beam loading is derived. *"Helical Pulseline Structures for Ion Acceleration," Briggs, Reginato, Waldron, this conference. |
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