Author: Ruan, J.
Paper Title Page
MOPWA063 Proposed Coherent Diffraction Radiation Measurements of Bunch Length at ASTA 822
  • A.H. Lumpkin, J. Ruan, R.M. Thurman-Keup
    Fermilab, Batavia, USA
  Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
The feasibility of using the autocorrelation of coherent diffraction radiation (CDR) as a non-intercepting diagnostics technique for bunch length and indirectly rf phase measurements is evaluated and proposed for the Advanced Superconducting Test Accelerator (ASTA) facility under construction at Fermilab. Previous experiments on an rf thermionic cathode gun beam at 50 MeV provide a proof-of-principle reference for the ASTA injector. The ASTA injector is based on an L-band rf photocathode (PC) gun with UV pulse drive laser, two L-band superconducting accelerator structures, a chicane bunch compressor, and an electron spectrometer. The injector energy of 40-50 MeV is expected. The 3-MHz micropulse repetition rate with micropulse charges up to to 3.2 nC and 1-ps bunch lengths should generate sufficient CDR signal for standard pyroelectric detectors to be used. The CDR signals will also be evaluated as a bunch compression signal for beam-based feedback for rf phase. The technique would also be applicable at high energy in straight transport lines after the cryomodules.
MOPWA064 Microwave Resonator Diagnostics of Electron Cloud Density Profile in High Intensity Proton Beam 825
  • Y.-M. Shin, J. Ruan, C.-Y. Tan, J.C.T. Thangaraj, R.M. Zwaska
    Fermilab, Batavia, USA
  We have developed an novel technique to accurately estimate the density of dilute electron clouds emitted from high intensity proton beams. The strong phase shift enhancement from multiple reflections of standing microwaves in a resonating beam pipe cavity has been demonstrated with numerical modeling using dielectric approximation and e S-parameter measurements. The equivalent dielectric simulation showed a ~ 10 times phase shift enhancement (Pi-mode, 1.516 GHz) with the cavity beam pipe compared to the waveguide model. The position-dependence of the technique is investigated by overlapping the field distributions of harmonic resonances. The simulation with various positions of dielectric insertions confirmed that resonance peaks in phase-shift spectra corresponding to the relative distance between field-nodes and electron cloud position, which allows for one-dimensional mapping. Preliminary experimental studies based on a bench-top setup confirm the results of the simulation showing that thicker reflectors enhance the phase-shift measurement of the electron cloud density.  
WEPME057 Commission of the Drive Laser System for Advanced Superconducting Test Accelerator 3061
  • J. Ruan, M.D. Church, D.R. Edstrom, Jr, T.R. Johnson, J.K. Santucci
    Fermilab, Batavia, USA
  Currently an advanced superconducting test accelerator (ASTA) is being built at Fermilab. The accelerator will consist of a photo electron gun, injector, ILC-type cryomodules, multiple downstream beam lines for testing cryomodules and carrying advanced accelerator researches. In this paper we will report the commissioning and the drive laser system for this facility. It consists of a fiber laser system properly locked to the master frequency, a regen-amplifier, several power amplifier and final wavelength conversion stage. We will also report the characterization of the whole laser system and the performance of the laser system.  
WEPME058 Integrated System Modeling Analysis of a Multi-cell Deflecting-mode Cavity in Cryogenic Operation 3064
  • Y.-M. Shin, M.D. Church, J. Ruan
    Fermilab, Batavia, USA
  Over the past decade, multi-cell deflecting (TM110) mode cavities have been employed for experiments on six-dimensional phase-space beam manipulation *,**,***,****,****** at the A0 Photo-Injector Lab (16 MeV) in Fermilab and their extended applications with vacuum cryomodules are currently scheduled at the Advanced Superconducting Test Accelerator (ASTA) user facility (> 50 MeV). Despite the successful test results, the cavity, however, demonstrated limited RF performance during liquid nitrogen (LN2) ambient operation that was inferior to theoretic prediction. We thus fully inspected the cavity design with theoretical calculation (based on Panofsky-Wenzel theorem) combined with RF simulations. Also, we are extensively developing an integrated computational tool with comprehensive system analysis capacity to solve complex thermodynamics and mechanical stresses of a high-Q deflecting-mode cryomodule. We will benchmark simulation analysis result with experimental data from high power RF tests in Fermilab. Successfully developed modeling tool will be potentially used for prompt assessment on RF performance of vacuum-cryomodules.
* D. A. Edwards, LINAC 2002
** Y.-E Sun, PRTAB 2004
*** P. Piot, PRSTAB2006
**** J. Ruand et al., PRL 2011
***** Y.-E. Sun, et al., PRL 2010