SUPLS —  Student Poster Session-Lake Superior   (01-Sep-19   14:00—16:00)
Paper Title Page
High Dynamic Voltage Range Studies of Piezoelectric Multilayer Actuators at Low Temperatures  
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  • C. Contreras-Martinez
    FRIB, East Lansing, Michigan, USA
  • Y.M. Pischalnikov, J.C. Yun
    Fermilab, Batavia, Illinois, USA
  Piezo actuators are used for resonance control in superconducting linacs. In high accelerating gradients linacs, such as those operated in a pulsed mode, the piezos require a large operating voltage. This is due to the Lorentz forced detuning which causes a large frequency shift and is compensated with an active piezo-tuning system. In this high dynamic voltage range the piezo is expected to warm up drastically due to it being in an insulated vacuum. This study characterizes the dielectric properties (capacitance, dielectric losses), the piezo stroke (from geophone), and thermal properties such as heating. Results obtained in the temperature range of 20K to 300K will be presented and discussed.  
A Pulsed, Current Regulated Magnet Power Supply for Small Magnets  
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  • G.D. Wyche, B.L. Beaudoin, L. Dovlatyan, D.F. Sutter
    UMD, College Park, Maryland, USA
  Funding: Work supported by U. S. Department of Energy grant number DESC00010301
The University of Maryland Electron Ring (UMER) has two pulsed quadrupoles in the injection section that must be current regulated to the same precision as the other DC quadrupoles in the ring, as well as accurately synchro-nized to the ring operating cycle. To meet this need, a practical pulsed current, regulated power supply has been designed and built using a commercial power operational amplifier for output, standard operational amplifiers for feedback control and monitoring, and matched resistor pairs to produce the desired transfer function of 10 Volts to 6 Amperes. For other applications the circuit can be modified to produce a range of transfer functions by varying the appropriate resistor pair ratios. Output pulse width and timing are generated by a standardized TTL pulse from the control system that gates the output of the amplifier. Installed safety circuitry detects the absence of a proper control pulse, an open circuit or shorted output, and measures and returns to the control system the actual operating amplitude of the current pulse. In this paper we present the design, implementation, and operational results of the prototyped pulsed current source.
Analysis of High Field Q-Slope (HFQS) Causes and Development of New Chemical Polishing Acid  
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  • D. Luo, E.S. Metzgar, L. Popielarski, K. Saito, S.M. Shanab, G.V. Simpson
    FRIB, East Lansing, Michigan, USA
  • T. Nakajima, I. Nasu, J. Taguchi
    Nomura Plating Co, Ltd., Osaka, Japan
  Funding: U.S. National Science Foundation under Grant PHY-1565546.
In our previous studies of High Field Q-slope (HFQS) we have concluded that nitrogen contamination from the nitric acid is the main cause of the degradation of the Q in buffered chemical polished cavities. Our conclusion is made based on previously unresolved phenomena which are found from huge amount of published cavity test data, include fine grain, large grain and single crystal cavities treated with EP and BCP. According to this analysis, we have started developing new nitrogen-free chemical polishing acid. Hydrogen peroxide with HF mixture was reported able to react with Nb, and there’s no extra element contamination in it, so we replace the conventional BCP with this mixture to start our study. In this paper, some Nb coupon sample results with new acid will be reported. We complete the first step of developing the new acid and we got the Nb finish roughness no worse than conventional BCP.
Recent Developments of Nb3Sn at Jefferson Lab for SRF Accelerator Application  
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  • U. Pudasaini, M.J. Kelley
    The College of William and Mary, Williamsburg, Virginia, USA
  • G.V. Eremeev, M.J. Kelley, C.E. Reece
    JLab, Newport News, Virginia, USA
  Funding: U.S. Department of Energy, Office of Science, Office of Nuclear Physics.
The desire to reduce the construction and operating costs of future SRF accelerators motivates the search for alternative, higher-performing materials. Nb3Sn (Tc ~ 18.3 K and Hsh ~ 425 mT) is the front runner. However, tests of early Nb3Sn-coated cavities encountered strong Q-slopes limiting the performance. Learnings from studies of coated materials related to cavity performance prompted significant changes to the coating process. It is now possible to routinely produce slope-free single-cell cavities having Q0 ≥ 2×1010 at 4 K and > 4×1010 at 2 K up to the accelerating gradient in excess of 15 MV/m at its best. Obtaining similar results in five-cell cavities is a current goal to test them under an accelerator environment. This contribution discusses recent developments at Jefferson Lab.
DC Field Dependence Studies for High-Q Niobium SRF Cavities  
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  • J.T. Maniscalco, M. Liepe
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  We present studies of the dependence of the microwave surface resistance on applied DC surface magnetic fields, investigating clean and nitrogen-doped niobium at 550 MHz, 1.3 GHz, and 2.1 GHz. These studies are performed with a new apparatus which uses calorimetric techniques to measure changes in the surface resistance. The results provide insight into the mechanism of positive Q-slope in nitrogen-doped niobium SRF cavities, an observed increase in cavity quality factor with increasing RF field strength. This mechanism has been key to recent advances in high-efficiency SRF accelerators such as LCLS-II; understanding the underlying physics is essential for further progress.  
First Cold Test Results of a Medium-Beta 644 MHz Superconducting 5-Cell Elliptical Cavity for the FRIB Energy Upgrade  
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  • K.E. McGee, B.W. Barker, K. Elliott, A. Ganshyn, W. Hartung, S.H. Kim, P.N. Ostroumov, J.T. Popielarski, A. Taylor, C. Zhang
    FRIB, East Lansing, Michigan, USA
  • M.P. Kelly, T. Reid
    ANL, Lemont, Illinois, USA
  Funding: Work supported by Michigan State University.
The superconducting linac for the Facility for Rare Isotope Beams (FRIB) will accelerate ions to 200 MeV per nucleon, with the possibility of a future energy upgrade to 400 MeV per nucleon via additional cavities. A 5-cell superconducting β = 0.65 elliptical cavity was designed for this purpose. Two unjacketed 5-cell niobium cavities were fabricated; the first of these was Dewar tested in February 2019. The surface preparation was bulk electropolishing (EP, 150 um), hydrogen degassing (600 degrees C, 10 hours), light EP (20 um), clean-room high-pressure water rinsing, and in-situ baking (120 degrees C, 48 hours). We achieved Q0 = 2·1010, equivalent to Rs = 10 nΩ, at the design gradient of 17.5 MV/m. The cavity was tested in a newly refurbished FRIB test Dewar, equipped with a variable input coupler.
Progress in Nb3Sn SRF Cavities at Cornell University  
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  • R.D. Porter, H. Hu, M. Liepe, N.A. Stilin, Z. Sun, M.J. Tao
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  Niobium-3 Tin (NbSn) is the most promising alternative material for next-generation SRF cavities. The material can obtain high quality factors (> 1010) at 4.2 K and could theoretically support ~ 96 MV/m operation of a TESLA elliptical style cavity. Current Nb3Sn cavities made at Cornell University achieve high quality factors but are limited to about 17 MV/m in CW operation due to the presence of a surface defect. Here we examine recent results on studying the quench mechanism and propose that surface roughness is a major limiter for accelerating gradients. Furthermore, we discuss recent work on reducing the surface roughness including chemical polishing, modification of material growth, and tin electroplating.  
Development of a Secondary Sn Source for Nb3Sn Coating of Half-Wave Coaxial Resonator  
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  • J.K. Tiskumara, J.R. Delayen, H. Park
    ODU, Norfolk, Virginia, USA
  • G.V. Eremeev
    JLab, Newport News, Virginia, USA
  • U. Pudasaini
    The College of William and Mary, Williamsburg, Virginia, USA
  Superconducting thin films have the potential of reducing the cost of particle accelerators. Among the potential materials, Nb3Sn has a higher critical temperature and higher critical field compared to niobium. Sn vapor diffusion method is the preferred technique to coat niobium cavities. Although there are several thin-film-coated basic cavity models that are tested at their specific frequencies, the Half-wave resonator could provide us data across frequencies of interest for particle accelerators. With its advanced geometry, increased area, increased number of ports and hard to reach areas, the half-wave resonator needs a different coating approach, in particular, a development of a secondary Sn source. We are commissioning a secondary Sn source in the coating system and expand the current coating system at JLab to coat complex cavity models.  
Design and Analysis of a Halo-Measurement Diagnostics  
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  • C.J. Marshall, P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
  • S.V. Benson, J. Gubeli
    JLab, Newport News, Virginia, USA
  • P. Piot, J. Ruan
    Fermilab, Batavia, Illinois, USA
  Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear physics under contract DE-AC05-06OR23177 and DE-AC02-07CH11359.
A large dynamical-range diagnostics (LDRD) design at Jefferson Lab will be used at the FAST-IOTA injector to measure the transverse distribution of halo associated with a high-charge electron beam. One important aspect of this work is to explore the halo distribution when the beam has significant angular momentum (i.e. is magnetized). The beam distribution is measured by recording radiation produced as the beam impinges a YAG:Ce screen. The optical radiation is split with a fraction directed to a charged-couple device (CCD) camera. The other part of the radiation is reflected by a digital micromirror device (DMD) that masks the core of the beam distribution. Combining the images recorded by the two cameras provides a measurement of the transverse distribution with over a large dynamical range. The design and analysis of the optical system will be discussed including optical simulation using SRW and the result of a mockup experiment to test the performances of the system will be presented.
slides icon Slides SUPLS10 [2.290 MB]