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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 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

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

Bunch-to-bucket injection of linac beam into the Brookhaven AGS

Description: A new fast beam chopper has been used to study injection and capture in the AGS. The chopper is a fast beam switch with 10 ns rise and fall times that can be programmed on a bunch-by-bunch basis and is synchronized to the net accelerating voltage of the synchrotron, thus allowing bunch-to-bucket injection of the 200 MeV H{sup {minus}} linac beam. The studies so far have concentrated on simple injection scenarios, at reduced intensity, where longitudinal effects are well separated from transverse. The evolution of the pre-bunched beam during the transition from injection to acceleration has been examined. Results have shown the importance of the detailed linac beam energy distribution. The ability to control the longitudinal emittance of the beam with the fast chopper has been used in other machine studies. This report includes a description of a measurement of the longitudinal coupling impedance of the AGS by the beam transfer function technique which utilized the control of longitudinal emittance provided by bunch-to-bucket injection. Plans for improvements to the chopper equipment are also describe. 6 refs., 4 figs.
Date: January 1, 1990
Creator: Brennan, J.M.; Ahrens, L. & Kats, J.
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

Effects of enhanced chromatic nonlinearity during the AGS {gamma}{sub t}-jump

Description: The {gamma}{sub t}-jump de-signed to reduce the bunch self-field mismatch and intensity loss during the AGS transition crossing can cause significant orbit and lattice distortions and dramatically enhance chromatic nonlinear effects. Employing a low-intensity, small emittance proton bunch crossing transition with the {gamma}{sub t}-jump quadrupoles excited, we found that the nonlinear momentum-compaction factor {alpha}{sub 1} increases from 2.2 to about 90 in the presence of the {gamma}{sub t}-jump. On the other hand, this enhancement can be effectively suppressed by properly exciting the chromaticity sextupoles, reducing {alpha}{sub 1} from 90 to 16. The experimental measurement agrees well with computer simulations using MAD and TIBETAN.
Date: May 1, 1995
Creator: Wei, J.; Brennan, J.M. & Ahrens, L.A.
Partner: UNT Libraries Government Documents Department

Bunched beam echos in the AGS

Description: Beam echos have been measured at FNAL and CERN in coasting beams. A coherent oscillation introduced by a short RF burst decoheres quickly, but a coherent echo of this oscillation can be observed if the decohered oscillation is bounced off a second RF burst. In this report the authors describe first longitudinal echo measurements of bunched beam in the AGS accelerator. They applied a method proposed by Stupakov for transverse beam echos, where the initial oscillation is produced by a dipole kick and is bounced off a quadrupole kick. In the longitudinal case the dipole and quadrupole kicks are produced by cavities operating at a 90 and 0{degree} phase shift, respectively.
Date: August 1, 1998
Creator: Kewisch, J. & Brennan, J.M.
Partner: UNT Libraries Government Documents Department

The RHIC accelerating cavity prototype tuner

Description: The RHIC Accelerating System runs at 26.7 MHz and is required to have an operating range of 85 kHz during the acceleration cycle. Since it also must provide sufficient range to cover manufacturing errors and temperature variation, a requirement of 300 kHz has been specified. A mechanical approach acting on the cavity accelerating gap has been chosen for financial reasons over a ferrite approach. A prototype has been constructed and fully tested on the existing test cavity, using the tuning loop feedback circuitry developed for this task. Results from both the loop response and the power tests of the prototype indicate that this design will successfully meet the performance requirements for the RHIC Accelerating Cavity.
Date: May 1, 1995
Creator: Ratti, A.; Brennan, J.M.; Brodowski, J.; Onillon, E. & Rose, J.
Partner: UNT Libraries Government Documents Department

A STATE VARIABLE DESCRIPTION OF THE RHIC RF CONTROL LOOPS.

Description: The beam transfer function changes during the RHIC ramp. The response of the RF control loops changes as a result. A state-variable description of the beam and the RF control loops was developed. This description was used to generate a set of feedback matrices that keeps the response of the RF control loops constant during the ramp. This paper describes the state-variable description and its use in determining the K matrices.
Date: June 2, 2002
Creator: SCHULTHEISS,C. & BRENNAN,J.M.
Partner: UNT Libraries Government Documents Department