M. Doleans

Oak Ridge National Laboratory, Oak Ridge, Florida, United States

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Publications (58)12.76 Total impact

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    ABSTRACT: A new in-situ plasma processing technique is being developed at the Spallation Neutron Source (SNS) to improve the performance of the cavities in operation. The technique utilizes a low-density reactive oxygen plasma at room temperature to remove top surface hydrocarbons. The plasma processing technique increases the work function of the cavity surface and reduces the overall amount of vacuum and electron activity during cavity operation; in particular it increases the field emission onset, which enables cavity operation at higher accelerating gradients. Experimental evidence also suggests that the SEY of the Nb surface decreases after plasma processing which helps mitigating multipacting issues. In this article, the main developments and results from the plasma processing R&D are presented and experimental results for in-situ plasma processing of dressed cavities in the SNS horizontal test apparatus are discussed.
    No preview · Article · Mar 2016
  • B DeGraff · M Doleans · B Hannah · M Howell · S Kim · T Neustadt · J Saunders
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    ABSTRACT: The Spallation Neutron Source (SNS) at Oak Ridge National Lab (ORNL) has built, commissioned and operated a Horizontal Test Apparatus (HTA) vessel in the Radiofrequency Test Facility (RFTF) test cave. It can be operated at 4.5 K using the independent Cryogenic Test Facility (CTF). The HTA is designed to be a single cavity version of an SNS cryomodule with the ability to demount and replace the cavity. It provides the functionality for testing a single dressed SNS medium or high beta Superconducting Radiofrequency (SRF) cavity. The HTA is currently being used in support of R&D for in-situ plasma processing of the cavity's inner niobium surface. The design and commissioning of the HTA at 4.5 K will be presented as well as results from operating the HTA including cool-down, warm-up and steady state operations. Results from plasma processing a warm SCRF cavity in-between cold HTA tests will also be reported.
    No preview · Article · Dec 2015
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    ABSTRACT: The Spallation Neutron Source (SNS) was designed and constructed by a collaboration of six U.S. Department of Energy national laboratories. The SNS accelerator system consists of a 1 GeV linear accelerator and an accumulator ring providing 1.4 MW of proton beam power in microsecond-long beam pulses to a liquid mercury target for neutron production. The accelerator complex consists of a front-end negative hydrogen-ion injector system, an 87 MeV drift tube linear accelerator, a 186 MeV side-coupled linear accelerator, a 1 GeV superconducting linear accelerator, a 248-m circumference accumulator ring and associated beam transport lines. The accelerator complex is supported by ~ 100 high-power RF power systems, a 2 K cryogenic plant, ~ 400 DC and pulsed power supply systems, ~ 400 beam diagnostic devices and a distributed control system handling ~ 100,000 I/O signals. The beam dynamics design of the SNS accelerator is presented, as is the engineering design of the major accelerator subsystems.
    Full-text · Article · Nov 2014 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: At the NSCL a reaccelerator with design end energy of 3MeV/u for U-238, called ReA3, is approaching the end of construction. ReA3 will be coupled to a gas stopper at the NSCL fragmentation facility to provide rare-isotope beams of nuclides not available at ISOL facilities in this energy range. An Electron Beam Ion Trap (EBIT) will be used to provide highly charged ions at an energy of about 12 keV/u. The charge breeder is followed by a room-temperature radiofrequency quadrupole (RFQ) and a series of superconducting linear accelerator structures. Initial commissioning results from the EBIT and its charge-over-mass separator are presented.
    No preview · Article · Jul 2011 · Hyperfine Interactions
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    S Assadi · M Doleans · W Hartung · M J Johnson · L Mann · F Marti · E Pozdeyev · E Tanke · X Wu · R York · Q Zhao
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    ABSTRACT: The Facility for Rare Isotope Beams (FRIB) at Michigan State University will utilize a high power, heavy-ion linear accelerator to produce rare isotopes in support of a rich program of fundamental research. The linac will consist of a room temperature-based front-end system producing beams of approximately 0.3MeV per nucleon. Three additional superconducting linac segments will produce beams of >200 MeV/u with a beam power of up to 400 kW. Because of the heavy-ion beam intensities, the required diagnostics will be largely based on non-interceptive approaches. The diagnostics suites that will support commissioning and operation are divided into lower energy <0.3 MeV/u front-end, and higher energy <200 MeV/u driver linac systems. The instruments in the driver linac include strip-line beam position and phase monitors (BPM), toroid beam current monitors (BCM), and 3-D electron scanners to measure rms beam size and emittance to match different linac segments.
    Full-text · Article · Jan 2011
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    ABSTRACT: The SNS SCL is reliably operating at 0.93 GeV output energy with an energy reserve of 10MeV with high availability. Most of the cavities exhibit field emission, which directly or indirectly (through heating of end groups) limits the gradients achievable in the high beta cavities in normal operation with the beam. One of the field emission sources would be surface contaminations during surface processing for which mild surface cleaning, if any, will help in reducing field emission. An R&D effort is in progress to develop in-situ surface processing for the cryomodules in the tunnel without disassembly. As the first attempt, in-situ plasma processing has been applied to the CM12 in the SNS SRF facility after the repair work with a promising result. This paper will report the R&D status of plasma processing in the SNS.
    Full-text · Article · Jan 2011
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    ABSTRACT: The National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU) is constructing ReA3 to reaccelerate rare-isotope beams available from gas stopping of fast radio-nuclides produced by projectile fragmentation to energies of similar to 0.3-3 MeV/nucleon. Such beams are unavailable worldwide, but are in demand for Coulomb excitation and transfer reaction studies as well as for the study of astrophysical reactions. ReA3 consists of four main components: an electron-beam ion trap (EBIT), an achromatic mass separator, a radio-frequency quadrupole (RFQ) pre-accelerator, and a superconducting radio-frequency linear accelerator (SRF-LINAC). By increasing the charge of ions injected into the RFQ and SRF-LINAC, the EBIT charge breeder is a key component to provide a compact and cost-efficient reaccelerator for short-lived isotopes. The MSU EBIT will be equipped with an electron-gun cathode yielding a few amperes. A unique EBIS-EBIT hybrid magnet configuration, composed of Helmholtz coils and a solenoid, will provide a maximum magnetic field strength of 6 T. The combination of a high-current cathode and strong magnetic field will allow the MSU EBIT to reach high electron-beam current densities of 104 A/cm(2). This will make it well suited to rapidly increase the charge state of short-lived isotopes within tens of milliseconds or less. The unique extended magnet configuration will guarantee high-beam acceptance. This publication will present an overview and status of the MSU EBIT.
    Full-text · Article · Jul 2010 · Journal of Instrumentation
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    R C York · X Wu · Q Zhao · M Doleans · F Marti · E Pozdeyev
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    ABSTRACT: The Facility for Rare Isotope Beams (FRIB), a Department of Energy (DOE) national user facility to provide intense beams of rare isotopes for nuclear science researchers, is currently being established on the campus of Michigan State University (MSU). A superconducting driver linac will deliver cw beams of stable isotopes with an energy of >200 MeV/u at a beam power of 400 kW. Highly charged ions will be produced from an Electron Cyclotron Resonance Ion Source (ECRIS) with a total extraction current of several mA. Multiple charge states of heavier ions will be accelerated simultaneously to meet the final beam power requirement. The FRIB driver linac lattice design has been developed and end-to-end beam simulations have been performed to evaluate the machine performance. An overview of the beam dynamics is presented.
    Full-text · Article · Jan 2010
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    ABSTRACT: The primary purpose of the Facility for Rare Isotope Beams (FRIB) is to produce and to perform fundamental research with rare isotopes. The rare isotope production will be accomplished using a heavy ion cw linac to provide a stable isotope beam (protons through uranium) at high power (up to 400 kW) and high energy (>200 MeV/u) on a particle fragmentation production target. The rare isotopes will be produced in quantities sufficient to support world-leading research by using particle fragmentation of stable beams. This will include research pertaining to the properties of nuclei (nuclear structure), the nuclear processes in the universe and tests of fundamental symmetries. Societal applications and benefits may include bio-medicine, energy, material sciences and national security. The overall facility status and plans will be discussed with a focus on the accelerator system.
    Full-text · Article · Jan 2010
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    S Assadi · M Doleans · W Hartung · M J Johnson · L Mann · F Marti · E Pozdeyev · E Tanke · X Wu · R York · Q Zhao
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    ABSTRACT: The Facility for Rare Isotope Beams (FRIB) at Michigan State University will utilize a high power, heavy-ion linear accelerator to produce rare isotopes in support of a rich program of fundamental research. The linac will consist of a room temperature-based front-end system producing beams of approximately 0.3MeV per nucleon. Three additional superconducting linac segments will produce beams of >200 MeV/u with a beam power of up to 400 kW. Therefore in the event of operating failures, it is extremely important to shut off the beam in a prompt manner to control the beam losses that may damage the accelerator components such as superconducting cavities. Another duty of the Machine Protection System (MPS) is to protect the accelerator against beam losses set by administrative limits to allow hands-on maintenance. FRIB has adapted the residual beam loss activation limit at 30 cm to be equivalent to 1W/m of operating beam losses. We are designing FRIB MPS to be flexible but redundant in safety to accommodate both commissioning and operations. A Machine Protection System protects the accelerator against failure and excessive beam losses; it is also dependent upon the operational mode of the accelerator and the beam dump in use. The operational mode is distributed via a finite state machine to all critical devices that have multiple hardware checkpoints and comparators. It is important to note that FRIB is a cw machine and MPS status is continuously being monitored by "device mode change" and real time data link. In case of a beam abort, the FRIB Machine Protection System will originate a stop-bit to all relevant data acquisition devices to dump the circular buffer data for post mortem analysis. In this paper, we present FRIB Machine Protection architecture, plans and implementation.
    Full-text · Article · Jan 2010
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    ABSTRACT: Rare isotope beam (RIB) accelerator facilities provide rich research opportunities in nuclear physics in particular for nuclear structure physics, nuclear astrophysics and applied physics. The National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU) is constructing a RIB facility, called 'ReA3'. The facility will provide unique low-energy rare isotope beams by stopping RIBs produced in-flight and reaccelerating them in a compact linac. ReA3 comprises gas stopper systems, an Electron Beam Ion Trap (EBIT) charge state booster, a room temperature radio frequency quadrupole (RFQ), a linac using superconducting quarter wave resonators (QWRs) and an achromatic beam transport and distribution line to the new experimental area. Beams from ReA3 will range from 3 MeV/u for heavy ions to about 6 MeV/u for light ions, as the charge state of the ions can be adjusted by the EBIT. ReA3 will initially use beams from NSCL's Coupled Cyclotron Facility (CCF). Later ReA3 will provide reacceleration capability for the Facility for Rare Isotope Beams (FRIB), a new national user facility funded by the Department of Energy (DOE) that will be hosted at MSU. The ReA3 concept and status of ReA3 will be presented, with emphasis on the commissioning of the facility, which is underway.
    Full-text · Article · Jan 2010
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    ABSTRACT: Rare-isotope beams in the energy range of a few 100 keV/u to up to several MeV/u allow for experiments such as low-energy Coulomb excitation and transfer reaction studies and for the precise study of astrophysical reactions. NSCL is currently constructing the so-called ReA3 expansion, a reaccelerator with design end energy of 3 MeV/u for ^238U. The reaccelerator will be coupled to a gas stopper at the NSCL fragmentation facility to provide rare isotope beams of nuclides not available at ISOL facilities in this energy range. An Electron Beam Ion Source/Trap (EBIS/T) will be used to boost the acceleration process by providing highly charged ions at an energy of ˜12keV/u. The charge breeder is followed by a room-temperature radiofrequency quadrupole (RFQ) and a series of superconducting linear accelerator structures housed in three cryo modules. The status of the re-accelerator project and the planned layout will be presented.
    No preview · Article · Oct 2009
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    ABSTRACT: A new device has been designed and built at NSCL which provides additional filtering of radioactive beams produced via projectile fragmentation. The Radio Frequency Fragment Separator (RFFS) uses the time micro structure of the beams accelerated by the cyclotrons to deflect particles according to their time-of-flight, in effect producing a phase filtering. The transverse RF (Radio Frequency) electric field of the RFFS has superior filtering performance compared to other electrostatic devices, such as Wien filters. Such filtering is critical for radioactive beams produced on the neutron-deficient side of the valley of stability, where strong contamination occurs at intermediate energies from 50 to 200 MeV/u.
    No preview · Article · Jul 2009 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: Solenoids are widely used to provide initial focusing of beams extracted from an ion source. However, in the case of an electron cyclotron resonance (ECR) ion source, the extracted beam will usually include different ion species and for each of them a wide distribution of charge states. When such a multicomponent beam is focused by a solenoid, the ions with a Q/A larger than the beam of interest are overfocused and usually go through a waist before reaching the analyzing magnet. If the beam currents obtained for these ions are sufficient, the resulting space charge forces can significantly degrade the emittance of the beam components with a lower Q/A and result for those in a hollow beam. Using a beam viewer and an emittance-measuring device, this paper reports on experimental findings that confirm the existence of such an effect for low charge states of argon. Moreover, by changing the experimental conditions of the ECR plasma in order to modify the charge state distribution of the extracted ion beam, it is shown that the threshold where this space charge effect starts to be significant can be changed.
    No preview · Article · Mar 2008 · Review of Scientific Instruments
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    ABSTRACT: The increased requirements towards the use of higher ion beam intensities motivated us to initiate the project to improve the overall transmission of the K130 cyclotron facility. With the facility the transport efficiency decreases rapidly as a function of total beam intensity extracted from the JYFL ECR ion sources. According to statistics, the total transmission efficiency is of the order of 10% for low beam intensities (I(total)< or =0.7 mA) and only about 2% for high beam intensities (I(total)>1.5 mA). Requirements towards the use of new metal ion beams for the nuclear physics experiments have also increased. The miniature oven used for the production of metal ion beams at the JYFL is not able to reach the temperature needed for the requested metal ion beams. In order to fulfill these requirements intensive development work has been performed. An inductively and a resistively heated oven has successfully been developed and both are capable of reaching temperatures of about 2000 degrees C. In addition, sputtering technique has been tested. GEANT4 simulations have been started in order to better understand the processes involved with the bremsstrahlung, which gives an extra heat load to cryostat in the case of superconducting ECR ion source. Parallel with this work, a new advanced ECR heating simulation program has been developed. In this article we present the latest results of the above-mentioned projects.
    No preview · Article · Mar 2008 · Review of Scientific Instruments
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    ABSTRACT: A new electron cyclotron resonance ion source (ECRIS) was constructed at the NSCL/MSU to replace the existing SC-ECRIS. This ECRIS operates at 18+14.5 GHz microwave frequencies with a planned upgrade to 24-28 GHz in the second phase of commissioning. A superconducting hexapole coil system produce the radial magnetic field; the axial trapping is produced with six superconducting solenoid coils enclosed in an iron yoke to allow the optimization of the distance between the plasma electrode and the resonant zone in the plasma. We report the details of the design, construction, and initial commissioning results of this new ECRIS.
    No preview · Article · Mar 2008 · Review of Scientific Instruments
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    ABSTRACT: The Re-accelerator ReA3 [1] being developed at the Michigan State University is a major component of a novel system proposed to first stop the high energy Rare Isotope Beams (RIBs) created using Coupled Cyclotron Facility (CCF) by the in-flight particle fragmentation method in a helium filled gas system, then increase their charge state with an Electron Beam Ion Trap (EBIT) charge breeder, and finally re-accelerate them to 3 MeV/u to provide opportunities for an experimental program ranging from low-energy Coulomb excitation to transfer reaction studies of astrophysical reactions. The accelerator system consists of a Low Energy Beam Transport (LEBT) with an external multi-harmonic buncher, a radio frequency quadrupole (RFQ), a superconducting linac, and a High Energy Beam Transport (HEBT). The superconducting linac will use quarter-wave resonators with βopt of 0.041 and 0.085 for acceleration and superconducting solenoid magnets for transverse focusing. The paper will discuss the recent progress of R&D and beam dynamics studies for ReA3.
    No preview · Conference Paper · Jan 2008
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    ABSTRACT: The rapid proton capture process has been proposed as the mechanism that powers the observed type I X-ray bursts in the universe. The time scale for the rp-process is governed by the beta-decay half-lives of several even-even N = Z waiting point nuclei, in particular, ^96Cd is the only one with an unknown beta decay half-life between ^56Ni and ^100Sn. The recently built Radio Frequency Fragment Separator (RFFS) at the NSCL filters out unwanted particles in rare proton rich beams according to their velocities, thus improving the beam purity by several orders of magnitude. The RFFS was successfully commissioned in May 2007 and used to identify ^96Cd nuclei for the first time. Preliminary results on the production rate of ^96Cd will be presented.
    No preview · Article · Oct 2007
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    ABSTRACT: The Fortran 90 RIAPMTQ/IMPACT code package is a pair of linked beam-dynamics simulation codes that have been developed for end-to-end computer simulations of multiple-charge state heavy-ion linacs for future exotic-beam facilities. The simulations can extend from the low-energy beam-transport line after the ECR ion source to the end of the linac. The work has been performed by a collaboration including LANL, LBNL, ANL, and MSU. The code RIAPMTQ simulates the linac front end including the LEBT, RFQ, and MEBT, and the code IMPACT simulates the main superconducting linac. The codes have been benchmarked for rms beam properties against previously existing codes at ANL and MSU. The codes allow high-statistics runs on parallel supercomputing platforms, such as NERSC at LBNL for studies of beam losses. The codes also run on desktop PC computers for low-statistics design work. We show results from 10-million-particle simulations at NERSC of designs by ANL and MSU for the Rare-Isotope Accelerator.
    Full-text · Conference Paper · Jul 2007
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    ABSTRACT: The Radio Frequency Fragment Separator (RFFS) proposed in [1] is now operational at the National Superconducting Cyclotron Laboratory (NSCL). The RFFS is an additional purification system for secondary beams at the NSCL after the existing A1900 fragment separator and will primarily be used to purify beams of rare neutron deficient isotopes. A similar device is already in use at RIKEN [2]. The RFFS uses an rf kicker to angularly separate unwanted particles from the desired ion beam, a pi/2 phase advance cell to rotate the beam in phase space before the beam reaches a collimating aperture for purification, and a final pi phase advance cell to transport the desired beam to the experiment. The final design for the rf kicker and the focusing system is presented and a status report on the building and commissioning effort is given.
    Full-text · Conference Paper · Jul 2007

Publication Stats

191 Citations
12.76 Total Impact Points

Institutions

  • 2002-2014
    • Oak Ridge National Laboratory
      • Spallation Neutron Source
      Oak Ridge, Florida, United States
  • 2005-2011
    • Michigan State University
      • Department of Physics and Astronomy
      East Lansing, Michigan, United States
  • 2001
    • Thomas Jefferson National Accelerator Facility
      Newport News, Virginia, United States