M. Liepe

Cornell University, Ithaca, New York, United States

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Publications (73)36.15 Total impact

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    ABSTRACT: The dependence of the Q-value on the RF field (Q-slope) is actively studied in various accelerator laboratories. Although remedies against this dependence have been found, the physical cause still remains obscure. A rather straightforward two-fluid model description of the Q-slope in the low and high field domains is presented with emphasis on the recently experimentally identified improvement of the Q-value by so-called "N-doping".
    07/2014;
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    ABSTRACT: Future particle accelerators will require continuous wave operation of SRF cavities capable of supporting high beam currents. An example of this is the Energy Recovery Linac (ERL) at Cornell University, a next generation light source designed to run high currents (100 mA) with a high bunch repetition rate (1.3 GHz). Obtaining the beam emittance necessary to meet design specification requires strong damping of higher-order modes that can lead to beam breakup. We discuss the optimization and verification of the accelerating cavity. Next we show that an ERL constructed from the optimized cavity geometry - including realistic shape errors - can support beam currents in excess of 300 mA while still maintaining beam stability. A niobium prototype 7-cell cavity was fabricated and tested in a horizontal cryomodule. We show that the prototype cavity exceeds quality factor and gradient specifications of 2×1010 at 16.2 MV/m at 1.8 K by 50%, reaching Q=(3.0±0.3)×1010. The prototype cavity also satisfies all design constraints and has a higher order mode spectrum consistent with the optimized shape geometry. At 1.6 K, the cavity set a record for quality factor of a multicell cavity installed in a horizontal cryomodule reaching Q=(6.1±0.6)×1010.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2014; · 1.14 Impact Factor
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    ABSTRACT: Cornell University has been designing and building superconducting accelerators for various applications for more than 50 years. Currently, an energy-recovery linac (ERL) based synchrotron-light facility is proposed making use of the existing CESR facility. As part of the phase 1 R&D; program funded by the NSF, critical challenges in the design were addressed, one of them being a full linac cryo-module. It houses 6 superconducting cavities- operated at 1.8 K in continuous wave (CW) mode - with individual HOM absorbers and one magnet/ BPM section. Pushing the limits, a high quality factor of the cavities (2⋅1010) and high beam currents (100 mA accelerated plus 100 mA decelerated) are targeted. We will present the design of the main linac cryo-module (MLC) being finalized recently, its cryogenic features and report on the status of the fabrication which started in late 2012.
    12/2013; 1573(1).
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    ABSTRACT: High-power, high-brightness electron beams are of interest for many applications, especially as drivers for free electron lasers and energy recovery linac light sources. For these particular applications, photoemission injectors are used in most cases, and the initial beam brightness from the injector sets a limit on the quality of the light generated at the end of the accelerator. At Cornell University, we have built such a high-power injector using a DC photoemission gun followed by a superconducting accelerating module. Recent results will be presented demonstrating record setting performance up to 65 mA average current with beam energies of 4–5 MeV.
    Applied Physics Letters 01/2013; 102(3). · 3.79 Impact Factor
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    ABSTRACT: Beam-breakup calculation algorithms have been devel-oped in the general framework of the Cornell X-ray ERL design software, enabling their extension to multi-pass op-tics design for ERLs. A status report of this work is pre-sented, together with initial results comparing the insta-bility thresholds calculated for single-and two-turn optics with recently developed RF cavity designs.
    01/2009;
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    ABSTRACT: Several of the typical RF absorbing materials utilized in particle accelerator environments have DC electrical conductivities that decrease significantly when cooled to cryogenic temperatures. If such RF absorbers are in close proximity to a beamline, they are prone to collecting static charge and may deflect the particle beam. The DC electrical conductivities of two types of ferrite and a ceramic are measured at various temperatures, showing that the electrical conductivities indeed decrease, often to unacceptably low levels in regard to static charge accumulation.
    01/2009;
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    ABSTRACT: Cornell University has developed and fabricated a SRF injector cryomodule for the acceleration of the high current (100 mA), low emittance beam in the Cornell ERL injec- tor prototype. This cryomodule is based on superconduct- ing rf technology with five 2-cell rf cavities operated in the cw mode. To support the acceleration of a low energy, ul- tra low emittance, high current beam, the beam tubes on one side of the cavities have been enlarged to propagate Higher-Order-Mode power from the cavities to broadband RF absorbers located at 80 K between the cavities. Each cavity is surrounded by a LHe vessel and equipped with a frequency tuner including piezo-driven tuners for fast fre- quency control. The cryomodule provides the support and precise alignment for the cavity string, the 80 K cooling of the HOM loads, and the 2 K LHe cryogenic system for the high cw heat load of the cavities. In this paper results of the commissioning phase of this cryomodule will be reported.
    01/2009;
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    01/2008;
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    ABSTRACT: A single-cavity horizontal test cryomodule (HTC) has been designed and fabricated recently at Cornell University for ERL project. This cryomodule is a shortened version of the full injector cryomodule, housing five superconducting cavities. It serves as a test bench for new design features and for testing fully dressed two-cell ERL injector cavities. The cryostat design has been optimized for precise cavity alignment, good magnetic shielding, and high cryogenic loads from the RF cavities, input couplers, and HOM loads. The HTC was made long enough so in the future it can accommodate longer, multicell cavities of the ERL main linac. In this paper we report on results from the first full test of the HTC, including RF system and superconducting cavity performance, cryomodule studies and operation of a new 2 K cryogenic system.
    01/2008;
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    ABSTRACT: Two high power 1300 MHz RF systems have been developed for the Cornell University ERL Injector. The first system, based on a 16 kWCW IOT transmitter, is to provide RF power to a buncher cavity. The second system employs five 120 kWCW klystrons to feed 2-cell superconducting cavities of the injector cryomodule. The sixth, spare klystron is used to power a deflecting cavity in a pulsed mode for beam diagnostics. A digital LLRF control stem was designed and implemented for precise regulation of the cavities' field amplitudes and phases. All components of these systems have been recently installed and commissioned. The first operational experience with the systems is discussed.
    01/2008;
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    ABSTRACT: Six 1300 MHz superconducting niobium 2-cell cavities are manufactured in-house for the prototype of the Cornell ERL injector to boost the energy of a high current, low emittance beam produced by a DC gun. Designed for high current beam acceleration, these cavities have new characteristics as compared to previously developed low-current cavities such as those for TTF Precision manufacture is emphasized for a better straightness of the cavity axis so as to avoid unwanted emittance dilution. We present the manufacturing, processing and vertical test performance of these cavities. We also present the impact of new cavity characteristics to the cavity performance as learnt from vertical tests.
    Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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    ABSTRACT: The status of plans for an energy-recovery linac (ERL) X-ray facility at Cornell University are described. Cornell currently operates the Cornell high energy synchrotron source (CHESS) at the CESR ring. The ERL is planned to be an extension to that ring by a 5-GeV superconducting c.w. linac. The very small electron-beam emittances would produce an X-ray source that is considerably better than any existing storage-ring light source. The ERL design that is presented has to allow for non-destructive transport of these small emittances. It includes up to 18 X-ray beamlines for specific areas of research that are currently being defined by an international community. Special attention is given to reuse of many of the existing ring components. Here it is described which subjects are being investigated or will have to be studied at Cornell to prepare for the construction of this new hard X-ray source; references to other contributions to this conference (PAC07) demonstrate this effort. This project illustrates how existing storage rings could be upgraded as ERL light sources with vastly improved beam qualities and with limited dark time for X-ray users. The presented list of research topics shows R&D issues for any such upgrade project.
    Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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    ABSTRACT: Cornell is building a 1.3 GHz Injector Cryomodule for an ERL prototype. The cryomodule consists of five two-cell niobium cavities, each cavity having two coaxial input couplers. Cavity and coupler pairs require acceptance testing at high power prior to assembly in the injector cryomodule. A liquid nitrogen cryostat for testing the couplers at high power has been built and the first input coupler test is complete. In addition, a Horizontal Test Cryostat (HTC) is being built to test input coupler pairs and cavities as a set. The first HTC test is scheduled for summer 2007. Details for instrumentation of the Coupler Test Cryostat (CTC) and HTC are presented.
    Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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    ABSTRACT: Cornell University is developing and fabricating a SRF injector cryomodule for the acceleration of the high current (100 iriA) beam in the Cornell ERL prototype and ERL light source. Major challenges include emittance preservation of the low energy, ultra low emittance beam, cw cavity operation, and strong HOM damping with efficient HOM power extraction. Prototypes have been completed for the 2-cell niobium cavity with helium vessel, coaxial blade tuner with piezo fine tuners, twin high power input couplers, and beam line HOM absorbers loaded with fer- rites and ceramics. Axial symmetry of HOM absorbers, together with two symmetrically placed input couplers per cavity, avoids transverse on-axis fields, which would cause emittance growth. A one-cavity cryostat has been designed following concepts of the TTF cryostat, and is presently under fabrication and assembly. The cryostat design has been optimized for precise cavity alignment, good magnetic shielding, and high dynamic cryogenic loads from the RF cavities, input couplers, and HOM loads. In this paper we report on the status of the assembly and first test of the one-cavity test cryostat.
    Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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    ABSTRACT: For Energy Recovery applications, the requirement for high-Q accelerating structures, operating in CW mode, at large beam currents, with precise phase & amplitude stability and modest accelerating gradients are all fundamental in achieving intense photon fluxes from the synchronised FEL insertion devices. Both Daresbury Laboratory and Cornell University are developing designs for advanced Energy Recovery Linac (ERL) facilities which require accelerating Linacs which meet such demanding criteria. The specification for the main ERL accelerator for both facilities dictates a modest accelerating gradient of 20 MV/m, at a Q o of better than 10 10 , with a Q ext of up to 10 8 . A collaborative R&D program has been set-up to design and fabricate a 'proof-of-principle' cryomodule (which is well underway) that can be tested on ERLP at Daresbury and also on the Cornell ERL injector. This paper details the new cryomodule design, provides an insight to the design solutions employed and reports on the present status of the project.
    01/2007;
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    ABSTRACT: Cornell University is developing and fabricating a SRF injector cryomodule for the acceleration of the high cur- rent (100mA) beam in the Cornell ERL prototypeandERL light source. Major challenges include emittance preserva- tion of the low energy, ultra low emittance beam, cw cavity operation, and strong HOM damping with efficient HOM power extraction. Axial symmetry of HOM absorbers, to- gether with two symmetrically placed input couplers per cavity, avoid transverse on-axis fields, which would cause emittance growth. Fabrication of five 2-cell niobium cav- ities and coaxial blade tuners, ten twin high power input couplers, and six beam line HOM absorbers has finished. The injector cryomodule is presently under assembly at Cornell University with beam test planned for early 2008. In this paper we report on the cryomodule fabrication and assembly status.
    01/2007;
  • Valery Shemelin, Matthias Liepe, Hasan Padamsee
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    ABSTRACT: Complex values of dielectric permittivity and magnetic permeability of 10 different materials, ferrites and ceramics, are measured in a frequency range from 1 to 40 GHz at room temperature and at 80 K. Recommendations are done for material usage in a cryogenic load for higher-order modes in the superconducting RF cavities of the Energy Recovery Linac.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 02/2006; 557(1):268–271. · 1.14 Impact Factor
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    M. Liepe, J. Knobloch
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    ABSTRACT: Since superconducting RF for particle accelerators made its first appearance in the 1970s, it has found highly successful application in a variety of machines. Recent progress in this technology has made so-called Energy-Recovery Linacs (ERLs)—originally proposed in 1965—feasible, and interest in this type of machine has increased enormously. A superconducting linac is the driving heart of ERLs, and emittance preservation and cost efficiency is of utmost importance. The resulting challenges for the superconducting cavity technology and RF field control are manifold. In March 2005 the first international workshop on ERLs was held at Newport News, VA, to explore the potential of ERLs and to discuss machine-physics and technology challenges and their solutions. This paper reviews the state-of-the-art in superconducting RF and RF control for ERLs, and summarizes the discussions of the SRF working group on this technology during the ERL2005 workshop.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2006; · 1.14 Impact Factor
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    Georg H. Hoffstaetter, Matthias Liepe
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    ABSTRACT: The rest-gas in the beam-pipe of a particle accelerator is readily ionized by effects like collisions, synchrotron radiation and field emission. Positive ions are attracted to electron beams and create a nonlinear potential in the vicinity of the beam which can lead to beam halo, particle loss, optical errors or transverse and longitudinal instabilities. In an energy recovery linac (ERL) where beam-loss has to be minimal, and where beam positions and emittances have to be very stable in time, these ion effects have to be avoided. Here we investigate three measures of avoiding ion accumulation: (a) A long gap between linac bunch trains that allows ions to drift out of the beam region, a measure regularly applied in linacs; (b) a short ion clearing gap in the beam that leads to a time varying beam potential and produces large excited oscillations of ions around the electron beam, a measure regularly applied in storage rings; (c) Clearing electrodes that create a sufficient voltage to draw ions out of the beam potential, a measure used for DC electron beams and for antiproton beams.For the parameters of the X-ray ERL planned at Cornell University we show that method (a) cannot be applied, method (b) is technically cumbersome, and (c) should be most easily applicable.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2006; 557(1):205-212. · 1.14 Impact Factor

Publication Stats

522 Citations
36.15 Total Impact Points

Institutions

  • 2004–2013
    • Cornell University
      • • Cornell Laboratory for Accelerator-based ScienceS and Education (CLASSE)
      • • Laboratory for Elementary Particle Physics
      Ithaca, New York, United States
  • 2007
    • Ithaca College
      Ithaca, New York, United States
  • 2001–2003
    • Deutsches Elektronen-Synchrotron
      Hamburg, Hamburg, Germany
  • 2002
    • Warsaw University of Technology
      Warszawa, Masovian Voivodeship, Poland
    • Universität Hamburg
      • Institut für Experimentalphysik
      Hamburg, Hamburg, Germany