Author: Liepe, M.
Paper Title Page
MOOAA01 Performance of the Cornell High-Brightness, High-Power Electron Injector 20
  • B.M. Dunham, A.C. Bartnik, I.V. Bazarov, L. Cultrera, J. Dobbins, C.M. Gulliford, G.H. Hoffstaetter, R.P.K. Kaplan, V.O. Kostroun, Y. Li, M. Liepe, X. Liu, F. Löhl, P. Quigley, D.H. Rice, E.N. Smith, K.W. Smolenski, M. Tigner, V. Veshcherevich, Z. Zhao
    CLASSE, Ithaca, New York, USA
  • S.S. Karkare, H. Li, J.M. Maxson
    Cornell University, Ithaca, New York, USA
  Funding: NSF DMR-0807731
The last year has seen significant progress in demonstrating the feasibility of a high current, high brightness photoinjector as required for the Energy Recovery Linac driven X-ray source at Cornell University. Both low emittances (0.4 mm-mrad rms normalized for 100% of the beam at 20 pC per bunch and 0.15 mm-mrad rms core emittance with 70% of the beam, and twice these values at 80 pC per bunch) and high average currents with a good lifetime well in excess of 1000 Coulombs at 5 MeV, 20 mA have been demonstrated. If these beams can be accelerated to 5 GeV without diluting the phase space, it would already provide a beam brightness higher than any existing storage ring. Operational experience, results, and the outlook for the future will be presented.
slides icon Slides MOOAA01 [1.424 MB]  
MOPPP026 Cryogenic Distribution System for the Proposed Cornell ERL Main Linac 619
  • E.N. Smith
    Cornell University, Ithaca, New York, USA
  • Y. He, G.H. Hoffstaetter, M. Liepe, M. Tigner
    CLASSE, Ithaca, New York, USA
  Funding: This material is based upon work supported by the National Science Foundation under Grant No. DMR-0807731.
The proposed Cornell ERL main linac requires a total cooling power of nearly 8kW at 1.8K, 5kW at 5K and over 100kW at 80K. This is distributed over approximately 65 cryomodules, each containing 6 rf cavities and associated input couplers and higher order mode absorbers. situated in two underground tunnels. While the total heat load is comparable to that for each of the 8 individual LHC cryoplants, the very high ratio of dynamic heat load to static heat load, combined with the high power density at various sites produces interesting challenges for the cryogenic distribution system. A schematic view of the design choices selected, some of which are different from existing large cryogenic systems, and the basis for these decisions, is presented in this paper.
TUPPR045 Multi-cell VEP Results: High Voltage, High Q, and Localized Temperature Analysis 1918
  • F. Furuta, B. Elmore
    Cornell University, Ithaca, New York, USA
  • A.C. Crawford
    Fermilab, Batavia, USA
  • G.M. Ge, G.H. Hoffstaetter, M. Liepe
    CLASSE, Ithaca, New York, USA
  We are developing Vertical Electro Polishing (VEP) system for niobium superconducting RF cavity at Cornell University. VEP has been successfully applied on different cell shapes (TESLA and Re-entrant), and single and multi-cell cavities. VEP achieved high gradient of 39MV/m with TESLA shape single cell and of 36MV/m with TESLA shape 9-cell, respectively. Preliminary results of R&D on VEPed cavities show removal dependence on cavity performance. Temperature oscillation asymmetry was also found during the VEP process. We will report these recent results and further R&D plan of Cornell VEP.  
WEEPPB015 Temperature Dependence of the Superheating Field: DC and RF Critical Fields 2197
  • N.R.A. Valles, M. Liepe
    CLASSE, Ithaca, New York, USA
  The superheating field is a metastable state at which the Meissner state persists at fields higher than would be predicted from steady-state energy considerations. Previous work demonstrated that a phenomenological approach based on the RF superheating field scaling near the critical temperature is also consistent with low temperature results. This work expands upon the RF results by measuring the DC superheating field, and comparing it to RF results and theoretical predictions.  
WEPPC070 Automated Cavity Test Suite for Cornell's ERL Program 2372
  • D. Gonnella, M. Liepe, N.R.A. Valles
    CLASSE, Ithaca, New York, USA
  As of 2011, fabrication and testing of main linac 7-cell cavities has begun for Cornell's Energy Recovery Linac prototype project. To standardize the testing process, minimize errors and allow for quick and precise measurements of these cavities, a suite of MatLab programs has been written to automate cavity tests. The programs allow measuring the quality factor versus temperature, and quality factor vs. accelerating gradient, and allow extracting material properties such as RRR and residual resistance. They are compatible with EPICS input/output controllers or standalone computers. Finally, the program can measure continuous Q vs E curves from a single high field decay curve, and can perform temperature mapping and quench localization from oscillating superleak transducer data.  
WEPPC071 Quench Studies of a Superconducting RF Cavity 2375
  • D. Gonnella, M. Liepe, S. Posen
    CLASSE, Ithaca, New York, USA
  In tests of superconducting RF cavities, it is important to understand the cause of high field quenches. Quenches at high field above 25 MV/m are a limiting factor in the performance of high accelerating field cavities but their causes are currently not well understood. An ILC shaped single cell cavity with quench field near 40 MV/m was tested with temperature mapping to determine the cause of its hard quench. Prior to quench, heating on the order of 25 mK was concentrated in two hot spots. After a quench, these two hot spots remain and a new one appears with much higher heating (about 40 mK). The quench location was found by the temperature mapping system to be centered at the new hot spot, not at the two hot spot locations before that dominated quench. By studying the quench location and heating on the surface of the cavity, some hints were gained as to the cause of this quench.  
WEPPC072 High Current Operation of the Cornell ERL Superconducting RF Injector Cryomodule 2378
  • M. Liepe, G.H. Hoffstaetter, S. Posen, P. Quigley, V. Veshcherevich
    CLASSE, Ithaca, New York, USA
  Cornell University has developed a SCRF injector cryomodule for the acceleration of high current, low emittance beams in continuous wave operation. This cryomodule is based on superconducting RF technology, and is currently under extensive testing in the Cornell ERL injector prototype with CW beam currents exceeding 25 mA. Strong damping of Higher-Order-Modes in the cavities is essential for high beam current operation, and is achieved by beamline RF absorber located at cryogenic temperatures in the beam pipe sections between the cavities. This paper gives an overview of the experience gained during the high beam current operation of the cryomodule.  
WEPPC073 Progress on Superconducting RF Work for the Cornell ERL 2381
  • M. Liepe, F. Furuta, G.M. Ge, Y. He, G.H. Hoffstaetter, T.I. O'Connell, S. Posen, J. Sears, M. Tigner, N.R.A. Valles, V. Veshcherevich
    CLASSE, Ithaca, New York, USA
  Cornell University is developing the superconducting RF technology required for the construction of a 100 mA hard X-ray light source driven by an Energy-Recovery Linac. Prototypes of all beam line components of the 5 GeV cw SRF main linac cryomodule have been fabricated and tested in detail. This work includes an optimized 7-cell SRF cavity, a broadband HOM beamline absorber, a cold frequency tuner, and a 5 kW CW RF input coupler. A one-cavity test cryomodule has been assembled for a first full cryomodule test of the main linac cavity, and is currently under testing. In this paper we give an overview of these extensive R&D activities at Cornell.  
WEPPC074 HOM Studies on the Cornell ERL Prototype Cavity in a Horizontal Test Cryomodule 2384
  • N.R.A. Valles, M.G. Billing, G.H. Hoffstaetter, M. Liepe, C.E. Mayes
    CLASSE, Ithaca, New York, USA
  The main linac 7-cell cavity for Cornell's Energy Recovery Linac was optimized to maximize threshold current through the ERL. This was achieved by designing center and end cells that reduce the strength of dipole higher-order modes. A prototype cavity was fabricated based on the optimized RF design and found to meet fundamental mode specifications in a vertical test. The higher-order-mode spectrum was measured when the cavity was installed in a horizontal test cryomodule and is compared to 2D and 3D EM simulations.  
WEPPC075 Testing of the Main-Linac Prototype Cavity in a Horizontal Test Cryomodule for the Cornell ERL 2387
  • N.R.A. Valles, F. Furuta, G.M. Ge, Y. He, K.M.V. Ho, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, S. Posen, P. Quigley, J. Sears, M. Tigner, V. Veshcherevich
    CLASSE, Ithaca, New York, USA
  Cornell has recently finished producing and testing the first prototype 7-cell main linac cavity for the Cornell Energy Recovery Linac (ERL). The cavity construction met all necessary fabrication constraints. After a bulk BCP, 650C outgassing, final BCP, and 120C bake the cavity was vertically tested. The cavity met quality factor and gradient specifications (2·1010 at 16.2 MV/m) in the vertical test. Progressing with the ERL linac development, the cavity was installed in a horizontal test cryomodule and the quality factor versus accelerating gradient was again measured. This baseline measurement is the first test in a sequence of tests of the main linac cavity in the test cryomodule. Subsequent tests will be with increased complexity of the beam line, e.g. with HOM beamline loads installed, to study potential sources of reducing the cavity’s quality factor.  
WEPPC078 Recent Developments in the Cornell Nb3Sn Initiative 2390
  • S. Posen, G.H. Hoffstaetter, M. Liepe, Y. Xie
    CLASSE, Ithaca, New York, USA
  Superconducting accelerator cavities coated with Nb3Sn have already demonstrated significantly higher unloaded quality factors than standard niobium cavities at surface magnetic fields <30 mT. Theoretical predictions suggest that the maximum critical field of such cavities could be twice that of niobium cavities. Significant facilities have been developed at Cornell University to fabricate Nb3Sn using the vapor diffusion technique. In this paper, recent progress is presented from our Nb3Sn program. The first RF results from a test of a Nb3Sn sample in a TE pillbox sample cavity are presented as well as first images of the newly constructed apparatus for coating full 1.3 GHz single cell cavities.  
WEPPC079 Residual Resistance Studies at Cornell 2393
  • S. Posen, D. Gonnella, G.H. Hoffstaetter, M. Liepe
    CLASSE, Ithaca, New York, USA
  • J. Oh
    Cornell University, Ithaca, New York, USA
  The Cornell single-cell temperature mapping system has been adapted for use with ILC and Cornell ERL-shape superconducting accelerator cavities. The system was optimized for low-noise, high-precision measurements with the goal of measuring resistances as low as 1 nohms. Using this system, a T-map of an ILC single cell was obtained at accelerating fields below the onset of Q-slope and at temperatures at which BCS resistance is small, producing a measurement of the distribution of residual resistance over the surface of the cavity. Standard procedures were used in preparing the cavity to avoid Q-disease and trapped flux caused by cooling the cavity through its transition in the presence of magnetic fields. Studying the T-map gives clues to the source of residual resistance, so that steps can be taken to reduce it, thereby lowering losses and increasing Q0. The temperature map noise-reduction studies as well as the residual resistance results are presented in this paper.  
WEPPC080 Minimizing Helium Pressure Sensitivity in Elliptical SRF Cavities 2396
  • S. Posen, M. Liepe
    CLASSE, Ithaca, New York, USA
  Superconducting cavities in CW operation with small beam loading can operate at high QL to significantly reduce power requirements. However, the resulting small bandwidth makes them vulnerable to microphonics from helium pressure fluctuations, which can detune the cavity and cause it to trip. In this paper, we present a mechanical optimization of elliptical cavities for minimization of df/dp, the sensitivity to helium pressure changes. Using the Cornell ERL main linac cavity as an example, an analytical model is developed to illustrate the factors that contribute to df/dp. Methods to reduce df/dp are presented. In addition, df/dp measurements made at the Cornell Horizontal Test Cryostat are presented and corrections to the model are made to account for the thickness of the welds in the helium vessel.  
WEPPC081 Measurement of the Mechanical Properties of Superconducting Cavities During Operation 2399
  • S. Posen, M. Liepe
    CLASSE, Ithaca, New York, USA
  The Horizontal Test Cryostat (HTC) contains the first prototype 7-cell 1.3 GHz superconducting cavity for the Cornell ERL main linac. In this paper, experimental measurements of the cavity's mechanical properties are presented. The mechanical resonances were studied using a Dynamic Signal Analyzer, which measured the transfer function from the fast piezo tuner to itself and the cavity frequency. The microphonics detuning of the cavity was measured, and found to satisfy the specification that the maximum detuning be below 20 Hz, even without feedback from the piezos. Correlations were studied between the microphonics detuning and the helium pressure, piezo sense signal, and the ground vibrations. The Lorentz force detuning (LFD) coefficient was also measured. The frequencies of the mechanical resonances were compared to simulation. In addition, the performance of the frequency tuners was evaluated. Both the mechanical tuner and the piezo were found to be highly linear with very little hysteresis even on small scales.  
WEPPC082 First Results on Cornell TE-type Sample Host Cavities 2402
  • Y. Xie, M. Liepe
    CLASSE, Ithaca, New York, USA
  Funding: Work supported by NSF and Alfred P. Sloan Foundation.
In order to measure surface resistance of new materials other than niobium such as Nb3Sn and MgB2, two sample host niobium cavities operating at TE modes have been developed at Cornell University. The first one is a 6GHz pillbox TE011 cavity modified from an older vision enabling testing 2.75'' diameter flat sample plates. The second one is an optimized mushroom-shape niobium cavity operating at both 5GHz TE012 and 6GHz TE013 modes for 3.75'' diameter flat sample plates . First results from the commissioning of the two TE cavities will be reported.
WEPPC031 Completed Assembly of the Daresbury International ERL Cryomodule and its Implementation on ALICE 2272
  • P.A. McIntosh, M.A. Cordwell, P.A. Corlett, P. Davies, E. Frangleton, P. Goudket, K.J. Middleman, S.M. Pattalwar, A.E. Wheelhouse
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • S.A. Belomestnykh
    BNL, Upton, Long Island, New York, USA
  • A. Büchner, F.G. Gabriel, P. Michel
    HZDR, Dresden, Germany
  • J.N. Corlett, D. Li, S.M. Lidia
    LBNL, Berkeley, California, USA
  • G.H. Hoffstaetter, M. Liepe, H. Padamsee, P. Quigley, J. Sears, V.D. Shemelin, V. Veshcherevich
    CLASSE, Ithaca, New York, USA
  • T.J. Jones, J. Strachan
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
  • R.E. Laxdal
    TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
  • D. Proch, J.K. Sekutowicz
    DESY, Hamburg, Germany
  • T.I. Smith
    Stanford University, Stanford, California, USA
  The completion of an optimised SRF cryomodule for application on ERL accelerators has now culminated with the successful assembly of an integrated cryomodule, following an intensive 5 years of development evolution. The cryomodule, which incorporates 2 x 7-cell 1.3 GHz accelerating structures, 3 separate layers of magnetic shielding, fully adjustable & high power input couplers and fast piezo tuners, has been installed on the ALICE ERL facility at Daresbury Laboratory. It is intended that this will permit operational optimisation for maximised efficiency demonstration, through increased Qext adjustment whilst retaining both effective energy recovery and IR-FEL lasing. The collaborative design processes employed in completing this new cryomodule development are explained, along with the assembly and implementation procedures used to facilitate its successful installation on the ALICE ERL facility.