D. Gassner

Brookhaven National Laboratory, New York City, New York, United States

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Publications (98)

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    [Show abstract] [Hide abstract] ABSTRACT: A new system used for monitoring energetic coulomb-scattered electrons as the main diagnostic for accurately aligning the electron and ion beams in the new Relativistic Heavy Ion Collider electron lenses is described in detail. Other possible applications of such energetic electrons are also discussed, such as similar systems for aligning electron beams for long-range beam-beam compensation and hollow electron beams for halo collimation and halo monitoring. A new type of "electron wire" beam profile monitor is described as well. Use of atomic electrons from the residual gas accelerated to high energies by the relativistic ions could lead to yet another type of non-destructive beam diagnostics, in this case not requiring an electron beam.
    Full-text Article · Jan 2016
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    [Show abstract] [Hide abstract] ABSTRACT: This document presents BNL's plan for an electron-ion collider, eRHIC, a major new research tool that builds on the existing RHIC facility to advance the long-term vision for Nuclear Physics to discover and understand the emergent phenomena of Quantum Chromodynamics (QCD), the fundamental theory of the strong interaction that binds the atomic nucleus. We describe the scientific requirements for such a facility, following up on the community wide 2012 white paper, "Electron-Ion Collider: the Next QCD Frontier", and present a design concept that incorporates new, innovative accelerator techniques to provide a cost-effective upgrade of RHIC with polarized electron beams colliding with the full array of RHIC hadron beams. The new facility will deliver electron-nucleon luminosity of $\sim10^{33} cm^{-2}sec^{-1}$ for collisions of 15.9 GeV polarized electrons on either 250 GeV polarized protons or 100 GeV/u heavy ion beams. The facility will also be capable of providing an electron beam energy of 21.2 GeV, at reduced luminosity. We discuss the on-going R\&D effort to realize the project, and present key detector requirements and design ideas for an experimental program capable of making the "golden measurements" called for in the EIC-White Paper.
    Full-text Article · Sep 2014
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    [Show abstract] [Hide abstract] ABSTRACT: Heavy ion cross sections totaling several hundred barns have been calculated previously for the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). These total cross sections are more than an order of mag-nitude larger than the geometric ion-ion cross sections, and are primarily due to Bound-Free Pair Production (BFPP) and Electro-Magnetic Dissociation (EMD). Apart from a general interest in verifying the calculations experimen-tally, an accurate prediction of the losses created in the heavy ion collisions is of practical interest for the LHC, where some collision products are lost in cryogenically cooled magnets and have the potential to quench these magnets. In the 2012 RHIC run uranium ions collided with each other at a center-of-mass energy of 192.8 GeV per nucleon-pair with nearly all beam losses due to collisions. This allows for the measurement of the total cross section and a comparison with calculations.
    Full-text Dataset · Jan 2014
  • [Show abstract] [Hide abstract] ABSTRACT: The Relativistic Heavy Ion (RHIC) electron lenses being commissioned to attain higher polarized proton luminosities by partially compensating the beam-beam effect require good alignment of the electron and proton beams. These beams propagating in opposite directions in a 6 T solenoid have an rms width as small as 300 microns and need to overlap each other over an interaction length of about 2 m with relative deviations of less than ∼50 microns. A new beam diagnostic tool to achieve and maintain this alignment is based on detecting electrons that are backscattered in close electron-proton encounters. Maximizing the production of these electrons ensures optimum beam overlap. The successful commissioning of these electron backscattering detectors (eBSDs) using 100 GeV/nucleon gold and 3He beams is described. Future developments are discussed that could further improve the sensitivity to small angular deviations.
    Article · Jan 2014
  • [Show abstract] [Hide abstract] ABSTRACT: Brookhaven National Laboratory's BLIP facility produces radioisotopes for the nuclear medicine community and industry, and performs research to develop new radioisotopes desired by nuclear medicine investigators. A raster scanning system is being installed to provide a better distribution of the H- beam on the targets, allow higher beam intensities to be used, and ultimately increase production yield of the isotopes. The upgrade consists of horizontal and vertical dipole magnets sinusoidally driven at 5 kHz with 90 deg phase separation to produce a circular raster pattern, and a suite of new instrumentation devices to measure beam characteristics and allow adequate machine protection. The instrumentation systems include multi-wire profile monitors, a laser profile monitor, beam current transformers, and a beam position monitor. An overview of the upgrade and project status will be presented.
    Article · Jan 2014
  • [Show abstract] [Hide abstract] ABSTRACT: RHIC polarized proton operation requires fast and reliable proton polarimeter for polarization monitoring during stores. Polarimeters based on p-Carbon elastic scattering in the Coulomb Nuclear Interference(CNI) region has been used. Two polarimeters are installed in each of the two collider rings and they are capable to provide important polarization profile information. The polarimeter also provides valuable information for polarization loss on the energy ramp. As the intensity increases over years, the carbon target lifetime is getting shorter and target replacement during operation is necessary. Simulations and experiment tests have been done to address the target lifetime issue. This paper summarizes the recent operation and the target test results.
    Article · Jan 2014
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    [Show abstract] [Hide abstract] ABSTRACT: Heavy ion cross sections totaling several hundred barns have been calculated previously for the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). These total cross sections are more than an order of magnitude larger than the geometric ion-ion cross sections primarily due to Bound-Free Pair Production (BFPP) and Electro-Magnetic Dissociation (EMD). Apart from a general interest in verifying the calculations experimentally, an accurate prediction of the losses created in the heavy ion collisions is of practical interest for the LHC, where some collision products are lost in cryogenically cooled magnets and have the potential to quench these magnets. In the 2012 RHIC run uranium ions collided with each other at $\sqrt{s_{NN}} = 192.8$ GeV with nearly all beam losses due to collisions. This allows for the measurement of the total cross section, which agrees with the calculated cross section within the experimental error.
    Full-text Article · Dec 2013 · Physical Review C
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    T. Tsang · D. Gassner · M. Minty
    [Show abstract] [Hide abstract] ABSTRACT: A residual gas fluorescence beam profile monitor at the Relativistic Heavy Ion Collider (RHIC) has successfully recorded beam images of various species of relativistic heavy ions during FY2012 operations. These fully striped ions include gold, copper, and uranium at 100, 99.9, and 96.4 GeV/n, respectively. Their beam profiles give an independent measurement of the RHIC beam size and emittance. We estimated their corresponding fluorescence cross sections to be 2.1×10^{-16}, 1.8×10^{-17}, and 2.6×10^{-16} cm^{2}, and obtained their rms transverse beam sizes of 0.36, 0.37, 0.24 mm for gold, copper, and uranium ions, respectively. They are the smallest ion beam width, thus lowest beam emittance, ever produced at RHIC or any other high-energy heavy ion colliders. These extremely small beam sizes may have reached a fundamental limit to residual gas fluorescence based beam profile monitor. Nevertheless, this beam diagnostic technique, utilizing the beam-induced fluorescence from residual gas where hydrogen is still the dominant constituent in nearly all vacuum systems, represents a passive, robust, truly noninvasive, monitor for high-energy ion beams.
    Full-text Article · Oct 2013 · Physical Review Special Topics - Accelerators and Beams
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    [Show abstract] [Hide abstract] ABSTRACT: The R&D ERL project at BNL aims to demonstrate a high charge, high current Energy Recovery Linac (ERL). One of the key ERL systems is the 704 MHz half-cell Superconducting RF (SRF) photoemission gun. The SRF gun is designed to deliver up to 0.5 ampere beam at 2 MeV with 1 MW of CW RF power. The gun commissioning in the ERL block house started in November of 2012. After high power RF conditioning, the cavity is now able to operate at 2 MV in CW mode. This paper briefly addresses the SRF gun system design, then describes the cold emission tests and discusses the results. Copyright © 2013 by JACoW- cc Creative Commons Attribution 3.0 (CC-BY-3.0).
    Full-text Article · Jan 2013
  • [Show abstract] [Hide abstract] ABSTRACT: Heavy ion cross sections totaling several hundred barns have been calculated previously for the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). These total cross sections are more than an order of magnitude larger than the geometric ion-ion cross sections, and are primarily due to Bound-Free Pair Production (BFPP) and Electro-Magnetic Dissociation (EMD). Apart from a general interest in verifying the calculations experimentally, an accurate prediction of the losses created in the heavy ion collisions is of practical interest for the LHC, where some collision products are lost in cryogenically cooled magnets and have the potential to quench these magnets. In the 2012 RHIC run uranium ions collided with each other at a center-of-mass energy of 192.8 GeV per nucleon-pair with nearly all beam losses due to collisions. This allows for the measurement of the total cross section and a comparison with calculations.
    Article · Jan 2013
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    C Liu · D Gassner · M Minty · P Thieberger
    [Show abstract] [Hide abstract] ABSTRACT: A code for determining the beam emittance from a multi-slit image has been developed. To verify its validity, we simulated a beam distribution in 4D phase space at the multi-slit position and the resulting image at a downstream profile measurement device. We applied the algorithm to this image pattern to recover the beam emittance at the slit position. The dependence of the relative difference of the inferred emittance and the input emittance on the slit width and drift length are studied in detail and presented in this report.
    Full-text Dataset · Dec 2012
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    Full-text Conference Paper · Sep 2012
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    [Show abstract] [Hide abstract] ABSTRACT: A half-cell superconducting rf electron gun is designed to provide 0.5 A, 2 MeV beam for the Brookhaven National Laboratory R&D Energy Recovery Linac. Total rf power of 1 MW must be delivered to beam to meet the beam current and energy specifications, resulting in very strong coupling. Two opposing fundamental power couplers (FPCs) are employed to minimize the transverse kick to beam traversing the structure and to halve the power through the coupler. A single-window coaxial coupler has been designed to meet the average power and rf coupling requirements. The coupler features a planar beryllia rf window for better handling high thermal stresses and a “pringle”-shaped tip of the antenna for enhancing rf coupling. Two FPCs have been fabricated and tested in preparation for the gun cryomodule assembly. A room-temperature test stand was used for conditioning couplers in full reflection regime with variable phase of the reflecting wave. The couplers were tested up to 250 kW in pulse mode and 125 kW in cw mode at different settings of the reflecting wave phase to expose all rf surfaces along the couplers to high fields. Several multipacting barriers were encountered and successfully processed away. The rf power levels, at which multipacting was found, match well those found in computer simulations.
    Full-text Article · Jul 2012 · Review of Modern Physics
  • [Show abstract] [Hide abstract] ABSTRACT: The 704 MHz SRF gun for the BNL Energy Recovery Linac (ERL) prototype uses twofundamental power couplers (FPCs) to deliver up to 1 MW of CW RF power to the half-cellcavity. To prepare the couplers for highpower RF service and process multipacting, the FPCsshould be conditioned prior to installation into the gun cryomodule. A room-temperaturetest stand was configured for conditioning FPCs in full reflection regime with varied phaseof the reflecting wave. The FPCs have been conditioned up to 250 kW in pulse mode and 125kW in CW mode. The multipacting simulations were carried out with Track3P code developed atSLAC. The simulations matched the experimental results very well. This paper presents theFPC RF and thermal design, multipacting simulations and conditioning of the BNL gun FPCs.
    Article · Jan 2012
  • [Show abstract] [Hide abstract] ABSTRACT: A stepper motor controlled wire scanner system has recently been modified to support testing of the Brookhaven National Laboratory (BNL) Collider-Accelerator department's Energy Recovery Linac (ERL) beam position monitor (BPM) system. The ERL BPM consists of four 9.33 mm diameter buttons mounted at 90 degree spacing in a cube with 1.875 inch inside diameter. The buttons were designed by BNL and fabricated by Times Microwave Systems. Libera brilliance single pass BPM electronic modules with 700 MHz bandpass filter, manufactured by Instrumentation Technologies, will be used to measure the transverse beam positions at 14 locations around the ERL. The wire scanner assembly provides the ability to measure the BPM button response to a pulsed wire, and evaluate and calibrate the Libera position measurement electronics. A description of the wire scanner system and test result data will be presented.
    Article · Jan 2012
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    [Show abstract] [Hide abstract] ABSTRACT: The Relativistic Heavy Ions Collider (RHIC) would benefit from improved beam position measurements near the interaction points that see both beams, especially as the tolerances become tighter when reducing the beam sizes to obtain increased luminosity. Two limitations of the present beam position monitors (BPMs) would be mitigated if the proposed approach is successful. The small but unavoidable cross-talk between signals from bunches traveling in opposite directions when using conventional BPMs will be reduced by adopting directional BPMs. Further improvements will be achieved by cancelling residual cross-talk using pairs of such BPMs. Appropriately delayed addition and integration of the signals will also provide pulses with relatively flat maxima that will be easier to digitize by relaxing the presently very stringent timing requirements.
    Full-text Article · Jan 2012
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    Full-text Article · Jan 2012
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    D. Boer · M. Diehl · R. Milner · [...] · P. Zurita
    [Show abstract] [Hide abstract] ABSTRACT: This report is based on a ten-week program on "Gluons and the quark sea at high-energies", which took place at the Institute for Nuclear Theory in Seattle in Fall 2010. The principal aim of the program was to develop and sharpen the science case for an Electron-Ion Collider (EIC), a facility that will be able to collide electrons and positrons with polarized protons and with light to heavy nuclei at high energies, offering unprecedented possibilities for in-depth studies of quantum chromodynamics. This report is organized around four major themes: i) the spin and flavor structure of the proton, ii) three-dimensional structure of nucleons and nuclei in momentum and configuration space, iii) QCD matter in nuclei, and iv) Electroweak physics and the search for physics beyond the Standard Model. Beginning with an executive summary, the report contains tables of key measurements, chapter overviews for each of the major scientific themes, and detailed individual contributions on various aspects of the scientific opportunities presented by an EIC.
    Full-text Article · Aug 2011
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    D. Boer · M. Diehl · R. Milner · [...] · P. Zurita
    [Show abstract] [Hide abstract] ABSTRACT: This report is based on a ten-week program on "Gluons and the quark sea at high-energies", which took place at the Institute for Nuclear Theory in Seattle in Fall 2010. The principal aim of the program was to develop and sharpen the science case for an Electron-Ion Collider (EIC), a facility that will be able to collide electrons and positrons with polarized protons and with light to heavy nuclei at high energies, offering unprecedented possibilities for in-depth studies of quantum chromodynamics. This report is organized around four major themes: i) the spin and flavor structure of the proton, ii) three-dimensional structure of nucleons and nuclei in momentum and configuration space, iii) QCD matter in nuclei, and iv) Electroweak physics and the search for physics beyond the Standard Model. Beginning with an executive summary, the report contains tables of key measurements, chapter overviews for each of the major scientific themes, and detailed individual contributions on various aspects of the scientific opportunities presented by an EIC.
    Full-text Article · Jul 2011
  • [Show abstract] [Hide abstract] ABSTRACT: As part of the search for a phase transition or critical point on the QCD phase diagram, an energy scan including 5 different energy settings was performed during the 2010 RHIC heavy ion run. While the top beam energy for heavy ions is at 100 GeV/n and the lowest achieved energy setpoint was significantly below RHICs injection energy of approximately 10 GeV/n, we also provided beams for data taking in a medium energy range above injection energy and below top beam energy. This paper reviews RHIC experience and challenges for RHIC medium energy operations that produced full experimental data sets at beam energies of 31.2 GeV/n and 19.5 GeV/n. The medium energy AuAu run covered two beam energies, both above the RHIC injection energy of 9.8 GeV but well below the standard store energy of 100 GeV (see table 1). The low energy and full energy runs with heavy ions in FY10 are summarized in [1] and [2]. Stochastic Cooling ([3]) was only used for 100 GeV beams and not used in the medium energy run. The efficiency of the transition from 100 GeV operation to 31.2 GeV and then to 19.5 GeV was remarkable. Setup took 32 h and 19 h respectively for the two energy settings. The time in store, defined to be the percentage of time RHIC provides beams in physics conditions versus calendar time, was approximately 52% for the entire FY10 heavy ion run. In both medium energy runs it was well above this average, 68% for 31.5 GeV and 82% for 19.5 GeV. For both energies RHIC was filled with 111 bunches with 1.2 10{sup 9} and 1.3 10{sup 9} ions per bunch respectively.
    Conference Paper · Mar 2011