MOYBB —  Monday Parallel Session 2   (02-Sep-19   10:30—12:30)
Chair: P.N. Ostroumov, ANL, Lemont, Illinois, USA
Paper Title Page
Recent Advance in SRF Cavity Technologies  
  • M. Martinello
    Fermilab, Batavia, Illinois, USA
  FNAL has been making great accomplishments in SRF technology recent years under her leadership. Notably the nitrogen doping technique to significantly increase the quality factor of SRF cavities has been made use of all over the world nowadays, being exemplified by LCLS II. In addition, the theoretical understanding of the effect is progressing well. Systematic, extensive study/analysis is ongoing on the basis of the joint effort of experiment and theory. Deeper understanding of RF superconductivity obtained through these efforts is benefitting world-wide accelerator institutes using SRF technology.  
slides icon Slides MOYBB1 [34.170 MB]  
Recent Advance in ECR Heavy Ion Sources  
  • G. Machicoane, N.K. Bultman, P. Morrison, M. Omelayenko, X. Rao
    FRIB, East Lansing, Michigan, USA
  • D. Arbelaez, R.R. Hafalia, P. Pan, S. Prestemon
    LBNL, Berkeley, California, USA
  Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661, the State of Michigan and Michigan State University.
High continuous wave (cw) current of highly charged ion beams are required for several heavy ion accelerator facilities including the Facility for Rare Isotope Beams (FRIB). In most cases, Electron-Cyclotron-Resonance (ECR) ion sources remain the only ion source capable to meet the beam intensity requirement for these facilities. Performances of ECR ion source have increased by several order of magnitude since their inception in the 1970s mostly driven by increasing the resonance frequency with today current state of the art ECR ion source operating from 24 to 28 GHz. This paper provides an overview of recent advance in the design and operation of ECR ion source including plans to develop the next generation of ion source capable of operating above 40 GHz. A detailed account of the design and status of the new superconducting ECR ion source in construction for FRIB will also be reported.
slides icon Slides MOYBB2 [9.475 MB]  
MOYBB3 Progress in Nb3Sn SRF Cavities at Cornell University -1
SUPLS08   use link to see paper's listing under its alternate paper code  
  • 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.  
MOYBB4 Large-Scale Dewar Testing of FRIB Production Cavities: Statistical Analysis -1
MOPLO16   use link to see paper's listing under its alternate paper code  
  • C. Zhang, W. Chang, W. Hartung, S.H. Kim, J.T. Popielarski, K. Saito, J.F. Schwartz, T. Xu
    FRIB, East Lansing, Michigan, USA
  The Facility for Rare Isotope Beams (FRIB) requires a driver linac with 324 superconducting cavities to deliver ion beams at 200 MeV per nucleon. About 1/3 of the cavities are quarter-wave resonators (QWRs, 805. MHz); the rest are half-wave resonators (HWRs, 322 MHz). FRIB cavity production is nearly complete, with more than 90% of the required cavities certified for installation into cryomodules (as of May 2019). We have accumulated a large data set on performance of production QWRs and HWRs during Dewar certificating testing of jacketed cavities. In this paper, we will report on the data analysis, including statistics on the BCS resistance, residual resistance, energy gap, and Q-slope. Additionally, we will discuss performance limitations and conditioning (multipacting, field emission).  
slides icon Slides MOYBB4 [1.185 MB]  
MOYBB5 Characterization and Performance of Plasma Window for Gas Flow Restriction in Different Geometries -1
SUPLE17   use link to see paper's listing under its alternate paper code  
WEPLH05   use link to see paper's listing under its alternate paper code  
  • A. Lajoie
    NSCL, East Lansing, Michigan, USA
  • J. Gao, F. Marti
    FRIB, East Lansing, Michigan, USA
  Funding: This work is supported by NSF Award PHY-1565546.
The plasma window is a DC cascaded arc whose function is to restrict gas flow from a high pressure region to a low pressure region without the use of any solid separation*. As a result, the plasma window allows a greater pressure to be maintained than otherwise possible. This is a beneficial characteristic for gas charge strippers for ion accelerators, since the higher pressures enable the stripper to be shorter and allow the same amount of stripping interactions**. The flow rate reduction is established by the increase in gas temperature from the power deposited into the plasma via the cathodes, resulting in a dramatically increased viscosity. The flow rate reduction, depends on the properties of the plasma, including the electron density and temperature, pressure, and electrical conductivity. Understanding these properties in multiple arc geometries - in this work having either 6 mm or 10 mm channel diameter - provides a means optimizing the plasma window for a given design. Determinations of the properties for different conditions are shown, and results are compared with a PLASIMO simulation, which has been shown to yield comparable properties to measurements in an argon arc***.
*A. Hershcovitch, Phys. Plasma 5, 2130 (1998).
**J. A. Nolen and F. Marti, Rev. Accel. Sci. Tech. 6, 221 (2013).
***G. M. W. Kroesen et al., Plas. Chem. and Plas. Proc. 10, 531 (1990).
slides icon Slides MOYBB5 [4.252 MB]  
MOYBB6 X-Ray Detector Array for Spatial and Temporal Diagnostic at the LANSCE Linac -1
  • M. Sanchez Barrueta, G.O. Bolme, J.T.M. Lyles, J.E. Zane
    LANL, Los Alamos, New Mexico, USA
  • R.Z. Pinsky
    NERS-UM, Ann Arbor, Michigan, USA
  Funding: Work supported by the United States Department of Energy, National Nuclear Security Agency, under contract 89233218CNA000001
A recent industrial development has made possible the use of chip-scale radiation detectors by combining a Cerium-doped Lutetium based scintillator crystal optically coupled with a Silicon Photomultiplier (SiPM) as a detector. At the Los Alamos Neutron Science Center (LANSCE), there has been an ongoing effort to determine the location of high voltage breakdowns of the accelerating radio-frequency field inside of an evacuated resonant cavity. Tests were conducted with an array of 8 X-ray detectors with each detector observing a cell of the Drift Tube Linac (DTL) cavity. The array can be moved along the DTL cavity and record X-ray emissions from a section of the cavity and their timing with respect to the RF field quench using a fast 8 channel mixed-signal oscilloscope. This new diagnostic allowed us to map the most energetic emissions along the cavity and reduce the area to investigate. A thorough visual inspection revealed that one of the ion pump grating welds in the suspected area was exposing a small gap and melting copper on both sides. Sparking across this discontinuity is believed to be a source of electrons that drive the high voltage breakdowns in the drift tube cells.
slides icon Slides MOYBB6 [39.306 MB]