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Holmes, J. A.

Paper Title Page
TUOBKI01 Experimental Characterization of the Spallation Neutron Source Accumulator Ring Collimation System 703
 
  • S. M. Cousineau, S. Assadi, J. A. Holmes, M. A. Plum
    ORNL, Oak Ridge, Tennessee
 
  Funding: ORNL/SNS is managed by UT-Battelle, LLC, for the U. S. Department of Energy under contract DE-AC05-00OR22725.

The SNS ring and associated transport lines, commissioned in January 2006, are designed to accumulate and deliver up to 1.5·1014, 1 GeV protons at 60 Hz to a liquid mercury target for neutron production. In order to control activation and to allow for routine hands-on maintenance of accelerator components, beam loss in most of the ring must remain below 1 W/m . For the full 1.4 MW beam, this translates to a fractional beam loss limit of 0.01%. Accomplishing this loss limit at full beam power will require successful utilization of the ring's two-stage betatron collimation system. In this paper we present the results of initial collimation experiments. We characterize the collimation-induced beam-loss pattern and compare our results with simulations. In addition, we discuss other existing beam-loss-related challenges in the ring.

 
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WEPMS081 Simulation and Initial Test Result of the SNS Ring RF System 2520
 
  • Y. Zhang, M. S. Champion, P. Chu, S. M. Cousineau, V. V. Danilov, T. W. Hardek, J. A. Holmes, H. Ma, M. F. Piller, M. A. Plum
    ORNL, Oak Ridge, Tennessee
 
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U. S. Department of Energy

A simulation code has been developed for the study of the Spallation Neutron Source (SNS) ring RF control. The code uses the time-domain solvers to compute beam-cavity interactions, and FFT methods to simulate time responses of the linear RF system. The important ingredients of the system are considered in the simulation model, which include the beam loading, dynamic cavity detuning, circuit bandwidth, loop delay, proportional-integral (P-I) controller for feedback and adaptive feed forward, stochastic noise, with-in-turn RF parameter change, beam current fluctuation and beam bunch leakage, etc. The beam loss in the accumulation ring goes up as the beam power increases, and thus a precise control of bunching voltage phase and amplitude is required to limit beam loss. This simulation tool will help the development a correct RF control and to achieve the goal of minimizing the beam loss.

 
THYKI02 Laser Stripping of H- beams: Theory and Experiments 2582
 
  • V. V. Danilov, A. V. Aleksandrov, S. Assadi, W. Blokland, S. M. Cousineau, C. Deibele, W. P. Grice, S. Henderson, J. A. Holmes, Y. Liu, M. A. Plum, A. P. Shishlo, A. Webster
    ORNL, Oak Ridge, Tennessee
  • I. Nesterenko
    BINP SB RAS, Novosibirsk
  • L. Waxer
    LJW, Saint Louis
 
  Funding: Research sponsored by LDRD Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy under Contract No. DE-AC05-00OR22725.

Thin carbon foils are used as strippers for charge exchange injection into high intensity proton rings. However, the stripping foils become radioactive and produce uncontrolled beam loss, which is one of the main factors limiting beam power in high intensity proton rings. Recently, we presented a scheme for laser stripping an H- beam for the Spallation Neutron Source ring. First, H- atoms are converted to H0 by a magnetic field, then H0 atoms are excited from the ground state to the upper levels by a laser, and the excited states are converted to protons by a magnetic field. In this paper we report on the first successful proof-of-principle demonstration of this scheme to give high efficiency (around 90%) conversion of H- beam into protons at SNS in Oak Ridge. The experimental setup is described, and comparison of the experimental data with simulations is presented. In addition, future plans on building a practical laser stripping device are discussed.

 
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THPAS013 Electron Cloud Simulations to Cold PSR Proton Bunches 3540
 
  • Y. Sato, S.-Y. Lee
    IUCF, Bloomington, Indiana
  • J. A. Holmes
    ORNL, Oak Ridge, Tennessee
  • R. J. Macek
    LANL, Los Alamos, New Mexico
 
  Funding: SNS through UT-Battelle, LLC, DE-AC05-00OR22725 for the U. S. DOE. Indiana University Bloomington, PHY-0552389 for NSF and DE-FG02-92ER40747 for DOE. LANL, W-7405-ENG-36.

We present ORBIT code simulations to examine the sensitivity of electron cloud properties to different proton beam profiles and to reproduce experimental results from the proton storage ring at Los Alamos National Laboratory. We study the recovery of electron clouds after sweeping, and also the characteristics of two types of electrons signals (prompt and swept) as functions of beam charge. The prompt signal means the peak height of electron sweeper signal before high voltage pulse applied on its electrode and after beam accumulation, and the swept signal means the spike height of electron sweeper signal during the high voltage pulse. To concentrate on the electron cloud dynamics, we use a cold proton bunch to generate primary electrons and electromagnetic field for electron dynamics. However, the protons receive no feedback from the electron cloud. Our simulations indicate that the proton loss rate in the field-free straight section might be an exponential function of proton beam charge and may also be lower than the averaged proton loss rate in a whole ring.

 
THPAS076 ORBIT Injection Dump Simulations of the H0 and H- Beams 3657
 
  • J. A. Holmes, M. A. Plum, J.-G. Wang, Y. Zhang
    ORNL, Oak Ridge, Tennessee
  • M. R. Perkett
    Denison University, Granville, Ohio
 
  Funding: ORNL/SNS is managed by UT-Battelle, LLC, for the U. S. Department of Energy under contract DE-AC05-00OR22725.

Simulations of the transport of H0 and H- beams to the SNS ring injection dump are carried out using the ORBIT code. During commissioning and early operations, beam losses in this region have been the highest in the accelerator and presented the most obvious hurdle to cross in achieving high intensity operation. Two tracking models are employed:

  1. a piecewise continuous symplectic representation of the lattice elements in the injection chicane and dump line, and
  2. particle tracking in full 3D magnetic fields, as obtained from OPERA code evaluations.
The physics models also include estimations of scattering from both the primary and secondary stripper foils, and beam losses due to apertures throughout the beam line.