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Switch over to the high frequency rf systems near transition

Description: The purpose of this note is to point out that since bunch narrowing naturally occurs in the acceleration process in the vicinity of transition, it should be possible to switch over to the high frequency system close to transition when the bunch has narrowed enough to fit directly into the high frequency bucket. The advantage of this approach is the simplicity, no extra components or gymnastics are required of the low frequency system. The disadvantage, of course, is for protons which do not go through transition. But on the other hand, there is no shortage of intensity for protons and so it should be possible to keep the phase space area low for protons, and then matching to the high frequency bucket should be easily accomplished by adiabatic compression. 3 refs., 7 figs.
Date: January 1, 1988
Creator: Brennan, J. M. & Wei, J.
Partner: UNT Libraries Government Documents Department

The upgraded rf system for the AGS and high intensity proton beams

Description: The AGS has been upgraded over the past three years to produce a record beam intensity of 6 {times} 10{sup 13} protons per pulse for the fixed-target physics program. The major elements of the upgrade are: the new 1.5 GeV Booster synchrotron, the main magnet power supply, a high frequency longitudinal dilution cavity, a feedback damper for transverse instabilities, a fast gamma transition jump system, and a new high-power rf system. The new rf system and its role in achieving the high intensity goal are the subjects of this report. The rf system is heavily beam loaded, with 7 Amps of rf current in the beam and a peak power of 0.75 MW delivered to the beam by ten cavities. As an example of the scale of beam loading, at one point in the acceleration cycle the cavities are operated at 1.5 kV/gap; whereas, were it not for the new power amplifiers, the beam-induced voltage on the cavities would be over 25 kV/gap. The upgraded rf system, comprising: new power amplifiers, wide band rf feedback, improved cavities, and new low-level beam control electronics, is described. Results of measurements with beam, which characterize the system`s performance, are presented. A typical high intensity acceleration cycle is described with emphasis on the key challenges of beam loading.
Date: May 1, 1995
Creator: Brennan, J.M.
Partner: UNT Libraries Government Documents Department

The RF beam control system for the Brookhaven AGS synchrotron

Description: The new 1.5 GeV Booster synchrotron completes the injector chain for the Relativistic Heavy Ion Collider, RHIC. It enables the AGS to accelerate all heavy ions to 14 GeV/c for collider operation and also in the intensity of the AGS for fixed-target experiments by a factor of four. The ultra-high vacuum enables acceleration of partially stripped ions from the Tandem Van de Graaff to energies sufficient for complete stripping. For high intensities, it accelerates the 200 MeV linac beam in four batches of three bunches per AGS cycle. At 1.5 {times} 10{sup 13} protons per batch, it has the same space charge tune spread as the AGS at 200 MeV. This variety of applications means the Booster must accommodate a very wide range of particle masses and intensities. Since it operates in a Pulse-by-Pulse Modulation mode at 7.5 Hz, the computer controlled functions of time and magnetic field, and the 64 timing triggers of the beam control system take on unique values for each of four PPM users. Beams of {sup 197}Au{sup +33} ions and protons have been accelerated in the same PPM cycle.
Date: September 1, 1992
Creator: Brennan, J. M.
Partner: UNT Libraries Government Documents Department

Rf beam control for the AGS Booster

Description: RF beam control systems for hadron synchrotrons have evolved over the past three decades into an essentially standard design. The key difference between hadron and lepton machines is the absence of radiation damping and existence of significant frequency variation in the case of hadrons. Although the motion of the hadron in the potential well of the rf wave is inherently stable it is not strongly damped. Damping must be provided by electronic feedback through the accelerating system. This feedback is typically called the phase loop. The technology of the rf beam control system for the AGS Booster synchrotron is described. First, the overall philosophy of the design is explained in terms of a conventional servo system that regulates the beam horizontal position in the vacuum chamber. The concept of beam transfer functions is fundamental to the mathematics of the design process and is reviewed. The beam transfer functions required for this design are derived from first principles. An overview of the beam signal pick-ups and high level rf equipment is given. The major subsystems, the frequency program, the heterodyne system, and beam feedback loops, are described in detail. Beyond accelerating the beam, the rf system must also synchronize the bunches in the Booster to the buckets in the AGS before transfer. The technical challenge in this process is heightened by the need to accomplish synchronization while the frequency is still changing. Details of the synchronization system are given. This report is intended to serve two purposes. One is to document the hardware and performance of the systems that have been built. The other is to serve as a tutorial vehicle from which the non-expert can not only learn the details of this system but also learn the principles of beam control that have led to the particular design choices made.
Date: September 26, 1994
Creator: Brennan, J. M.
Partner: UNT Libraries Government Documents Department

The new BNL AGS phase, radial and synchronization loops

Description: The AGS and the RHIC must be synchronized before bunch-to-bucket transfer of the beam. A feedback loop has been designed and an improvement has been made to the AGS phase and radial loops. In both cases, the design uses a state variable representation to achieve greater stability and smaller errors. The state variables are beam phase, frequency and radius , the integral of the difference between the radius and its reference and the phase deviation of the bunch from the synchronous phase. Furthermore, the feedback gains are programmed as a function of the beam parameters to keep the same loop performances through the acceleration cycle.
Date: July 1, 1996
Creator: Onillon, E. & Brennan, J.M.
Partner: UNT Libraries Government Documents Department

High intensity performance of the Brookhaven AGS

Description: Experience and results from recent high intensity proton running periods of the Brookhaven AGS, during which a record intensity for a proton synchrotron of 6.3 x 10{sup 13} protons/pulse was reached, is presented. This high beam intensity allowed for the simultaneous operation of three high precision rare kaon decay experiments. The record beam intensities were achieved after the 1.5 GeV Booster was commissioned and a transition jump system, a powerful transverse damper, and an rf upgrade in the AGS were completed. Recently even higher intensity proton synchrotrons are studied for neutron spallation sources or proton driver for a muon collider. Implications of the experiences from the AGS to these proposals and also possible future upgrades for the AGS are discussed.
Date: July 1, 1996
Creator: Brennan, J.M. & Roser, T.
Partner: UNT Libraries Government Documents Department

A barrier bucket experiment for accumulating de-bunched beam in the GAS

Description: The AGS accumulates four batches of two bunches from the 1.5GeV Booster at 7.5Hz. At an intensity of 6 x 10{sup 13} protons per AGS cycle, slow beam loss during the 400ms accumulation time is important. The experiment demonstrated the principle of accumulating beam and storing it in an essentially debunched state by using barrier cavities. When the beam is de-bunched the peak-to-average current ratio drops by an order of magnitude. By using two barriers with time varying relative phase, any number of injections is possible, limited only by the momentum acceptance of the ring. In a test with beam, six injections of one bunch yielded 3 x 10{sup 13} protons in the AGS. The benefits of reduced space charge tune shift from lower peak current suggest that barrier cavities may be a path to higher AGS intensities.
Date: July 1, 1996
Creator: Blaskiewicz, M. & Brennan, J.M.
Partner: UNT Libraries Government Documents Department

Spallation neutron source/proposed rf system

Description: The rf system for the synchrotrons of the spallation neutron source is designed to accelerate 1.4 {times} 10{sup 14} protons/pulse to an energy of 3.6 GeV. Injection energy is 600 MeV. The synchrotron repetition frequency is 30 Hz, with a 50% duty factor. The choice of operating frequency is somewhat arbitrary. The authors propose a low frequency of 1.3 to 1.6 MHz, which is the second harmonic of the revolution frequency. The advantages of such a low frequency system are: (1) There will be two bunches in the machines and the time between bunches will be sufficiently long to allow for the rise time of the extraction kicker. No missing bunches will be necessary, which simplifies injection, and transient beam loading problems are avoided. (2) With only two bunches there are no unstable coupled-bunch modes of longitudinal instability. (3) In multi-gap low frequency cavities the transient time factor is essentially unity because the rf wavelength is much longer than the cavity dimensions. (4) Cavities in this low frequency range are basically lumped-element type structures, where the sources of the inductance and capacitance are clearly identified. This allows effective control of higher order mode impedances in such cavities. (5) Ferrite-loaded low-frequency cavities are necessarily low impedance structures; ferrites are lossy. This low impedance makes it possible to achieve system stability without large amounts of feedback in a heavily beam loaded system. (6) BNL has a good deal of experience in building rf systems in this range of frequency, voltage, and power level. This report outlines the essential parameters of a practical rf system for the synchrotrons of the Spallation Neutron Source. The design uses materials, ferrites and vacuum tubes, that are commercially available and with which the laboratory has recent experience.
Date: September 30, 1993
Creator: Meth, M. & Brennan, J. M.
Partner: UNT Libraries Government Documents Department

The RF beam control system for the Brookhaven AGS synchrotron

Description: The new 1.5 GeV Booster synchrotron completes the injector chain for the Relativistic Heavy Ion Collider, RHIC. It enables the AGS to accelerate all heavy ions to 14 GeV/c for collider operation and also in the intensity of the AGS for fixed-target experiments by a factor of four. The ultra-high vacuum enables acceleration of partially stripped ions from the Tandem Van de Graaff to energies sufficient for complete stripping. For high intensities, it accelerates the 200 MeV linac beam in four batches of three bunches per AGS cycle. At 1.5 {times} 10{sup 13} protons per batch, it has the same space charge tune spread as the AGS at 200 MeV. This variety of applications means the Booster must accommodate a very wide range of particle masses and intensities. Since it operates in a Pulse-by-Pulse Modulation mode at 7.5 Hz, the computer controlled functions of time and magnetic field, and the 64 timing triggers of the beam control system take on unique values for each of four PPM users. Beams of {sup 197}Au{sup +33} ions and protons have been accelerated in the same PPM cycle.
Date: January 1, 1992
Creator: Brennan, J. M.
Partner: UNT Libraries Government Documents Department

BUNCHED BEAM STOCHASTIC COOLING PROJECT FOR RHIC.

Description: The main performance limitation for RHIC is emittance growth caused by IntraBeam Scattering during the store. We have developed a longitudinal bunched-beam stochastic cooling system in the 5-8 GHz band which will be used to counteract IBS longitudinal emittance growth and prevent de-bunching during the store. Solutions to the technical problems of achieving sufficient kicker voltage and overcoming the electronic saturation effects caused by coherent components within the Schottky spectrum are described. Results from tests with copper ions in RHIC during the FY05 physics run, including the observation of signal suppression, are presented.
Date: September 18, 2005
Creator: BRENNAN, J. M. & BASKIEWICZ, M. M.
Partner: UNT Libraries Government Documents Department

H/sup -/ source and beam transport experiments for a new RFQ

Description: A new RFQ preinjector is being built for the 200 MeV Linac at the AGS. For injection into this RFQ, a symmetric emittance has been obtained from a circular aperture magnetron H/sup -/ source. Transport studies are beginning to address possible problems with space charge or instabilities in the 35 keV line. A volume H/sup -/ source is being tested as an eventual replacement for the magnetron.
Date: January 1, 1987
Creator: Alessi, J.G.; Brennan, J.M.; Kponou, A. & Prelec, K.
Partner: UNT Libraries Government Documents Department

Stochastic cooling of a high energy collider

Description: Gold beams in RHIC revolve more than a billion times over the course of a data acquisition session or store. During operations with these heavy ions the event rates in the detectors decay as the beams diffuse. A primary cause for this beam diffusion is small angle Coloumb scattering of the particles within the bunches. This intra-beam scattering (IBS) is particularly problematic at high energy because the negative mass effect removes the possibility of even approximate thermal equilibrium. Stochastic cooling can combat IBS. A theory of bunched beam cooling was developed in the early eighties and stochastic cooling systems for the SPS and the Tevatron were explored. Cooling for heavy ions in RHIC was also considered.
Date: September 4, 2011
Creator: Blaskiewicz, M.; Brennan, J.M.; Lee, R.C. & Mernick, K.
Partner: UNT Libraries Government Documents Department

STOCHASTIC COOLING OF HIGH-ENERGY BUNCHED BEAMS

Description: Stochastic cooling of 100 GeV/nucleon bunched beams has been achieved in the Relativistic Heavy Ion Collider (RHIC). The physics and technology of the longitudinal cooling system are discussed, and plans for a transverse cooling system are outlined.
Date: June 25, 2007
Creator: BLASKIEWICZ,M. & BRENNAN, J.M.
Partner: UNT Libraries Government Documents Department

BUNCHED BEAM STOCHASTIC COOLING SIMULAITONS AND COMPARISON WITH DATA

Description: With the experimental success of longitudinal, bunched beam stochastic cooling in RHIC it is natural to ask whether the system works as well as it might and whether upgrades or new systems are warranted. A computer code, very similar to those used for multi-particle coherent instability simulations, has been written and is being used to address these questions.
Date: September 10, 2007
Creator: BLASKIEWICZ,M. & BRENNAN, J.M.
Partner: UNT Libraries Government Documents Department

Feedback damper system for quadrupole oscillations after transition at RHIC.

Description: The heavy ion beam at RHIC undergoes strong quadrupole oscillations just after it crosses transition, which leads to an increase in bunch length making rebucketing less effective. A feedback system was built to damp these quadrupole oscillations and in this paper the characteristics of the system and the results obtained are presented and discussed.
Date: June 23, 2008
Creator: Abreu,N.; Blaskiewicz, M.; Brennan, J.M. & Schultheiss, C.
Partner: UNT Libraries Government Documents Department

SUCCESSFUL BUNCHED BEAM STOCHASTIC COOLING IN RHIC.

Description: We report on a successful test of bunch-beam stochastic cooling in RHIC at 100 GeV. The cooling system is designed for heavy ions but was tested in the recent RHIC run which operated only with polarized protons. To make an analog of the ion beam a special bunch was prepared with very low intensity. This bunch had {approx}1.5 x 10{sup 9} protons, while the other 100 bunches contained {approx}1.2 x 10{sup 11} protons each. With this bunch a cooling time on the order 1 hour was observed through shortening of the bunch length and increase in the peak bunch current, together with a narrowing of the spectral line width of the Scottky power at 4 GHz. The low level signal processing electronics and the isolated-frequency kicker cavities are described.
Date: June 23, 2006
Creator: BRENNAN, J.M.; BLASKIEWICZ, M. & SEVERINO, F.
Partner: UNT Libraries Government Documents Department

Stochastic cooling in RHIC

Description: After the success of longitudinal stochastic cooling of bunched heavy ion beam in RHIC, transverse stochastic cooling in the vertical plane of Yellow ring was installed and is being commissioned with proton beam. This report presents the status of the effort and gives an estimate, based on simulation, of the RHIC luminosity with stochastic cooling in all planes.
Date: May 4, 2009
Creator: Brennan,J.M.; Blaskiewicz, M. M. & Severino, F.
Partner: UNT Libraries Government Documents Department

Experience with split transition lattices at RHIC

Description: During the acceleration process, heavy ion beams in RHIC cross the transition energy. When RHIC was colliding deuterons and gold ions during Run-8, lattices with different integer tunes were used for the two rings. This resulted in the two rings crossing transition at different times, which proved beneficial for the 'Yellow' ring, the RF system of which is slaved to the 'Blue' ring. For the symmetric gold-gold run in FY2010, lattices with different transition energies but equal tunes were implemented. We report the optics design concept as well as operational experience with this configuration.
Date: May 23, 2010
Creator: Montag, C.; Tepikian, S.; Blaskiewicz, M. & Brennan, J.M.
Partner: UNT Libraries Government Documents Department

LONGITUDINAL IMPEDANCE MEASUREMENT IN RHIC.

Description: The very clean Schottky spectra of gold beams in RHIC allow an accurate measurement of potential well distortion. By observing the variation in the small amplitude, incoherent synchrotron tune with intensity and bunch length, the intensity dependent longitudinal force can be measured. Dynamical effects associated with coherent motion are not important though some new dynamical effects appear. Measurements were carried out both at injection energy and store, which allowed the space charge and wall contributions to be individually determined.
Date: June 2, 2002
Creator: BLASKIEWICZ,M.; BRENNAN,J.M.; CAMERON,P. & FISCHER,W.
Partner: UNT Libraries Government Documents Department