• B. Goddard, W. Bartmann
  CERN, Geneva
• V.V. Danilov
  ORNL, Oak Ridge, Tennessee
• D.E. Johnson
  Fermilab, Batavia

Laser stripping for an H^- injection system into the proposed PS2 accelerator could provide an attractive alternative to the use of a conventional stripping foil. In this paper possible concepts for a 4 GeV laser stripping system are outlined and compared, using either laser or magnetic initial stripping steps and a resonant excitation of the intermediate H0 atom, followed by a final magnetic stripping. Issues of laser power, overall efficiency and emittance growth are discussed.

• V.V. Danilov, Y. Liu
  ORNL, Oak Ridge, Tennessee
• K.B. Beard, V.G. Dudnikov, R.P. Johnson
  Muons, Inc, Batavia
• M.D. Shinn
  JLAB, Newport News, Virginia

Funding: Supported in part by USDOE Contract No. DE-AC05-84-ER-40150. Supported in part by USDOE Contract DE-AC05-00OR22725

The ORNL spallation neutron source (SNS) user facility requires a reliable, intense beams of protons. The technique of H^- charge exchange injection into a storage ring or synchrotron has the potential to provide the needed beam currents, but it will be limited by intrinsic limitations of carbon and diamond stripping foils. A laser in combination with magnetic stripping has been used to demonstrate a new technique for high intensity proton injection, but several problems need to be solved before a practical system can be realized. Technology developed for use in Free Electron Lasers is being used to address the remaining challenges to practical implementation of laser controlled H^- charge exchange injection for the SNS. These technical challenges include (1) operation in vacuum, (2) the control of the UV laser beam to synchronize with the H^- beam and to shape the proton beam, (3) the control and stabilization of the Fabry-Perot resonator, and (4) protection of the mirrors from radiation.

• T.V. Gorlov, V.V. Danilov, A.P. Shishlo
  ORNL, Oak Ridge, Tennessee

Funding: *SNS is managed by UT-Battelle, LLC, for the U. S. Department of Energy under Contract No. DE-AC05-00OR22725.

Thin carbon foils used as a charge strippers for H־ ions have a limited life time and produce uncontrolled beam loss. Thus, foil based injection is one of the factors limiting beam power in high intensity proton rings. There is a possibility to replace such foils by laser-assisted stripping of negative hydrogen ions, a method developed and demonstrated at the SNS accelerator in Oak Ridge. In this paper we present progress in the physics and computation of H־ laser stripping. We present a physical model which includes such factors as the Stark effect, the polarization of the laser field, and the spontaneous relaxation and autoionization of hydrogen atoms in a strong electro-magnetic field. The model formulates a quantum mechanical problem that can be solved numerically using a module created for the PyORBIT parallel code developed at SNS.

• V.V. Danilov
  ORNL, Oak Ridge, Tennessee

Funding: SNS is managed by UT-Battelle, LLC, for the U. S. Department of Energy under Contract No. DE-AC05-00OR22725.

The paper presents a new variety of one-dimensional nonlinear integrable accelerator lattices with periodic and exponential invariants in coordinates and momenta. Extension to two-dimensional transverse motion, based on a recently published approach*, is discussed.

*V. Danilov, “Practical Solutions for Nonlinear Accelerator Lattice with Stable Nearly Regular Motion”, Phys. Rev. ST AB 11, 114001 (2008)

• J.A. Holmes, S.M. Cousineau, V.V. Danilov
  ORNL, Oak Ridge, Tennessee
• Z. Liu
  IUCF, Bloomington, Indiana

Funding: ORNL/SNS is managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725.

During one of the high beam intensity runs in SNS, a coasting beam instability was observed in the ring when the beam was stored for 10000 turns. This instability was observed at an intensity of about 12 microcoulombs and was characterized by a frequency spectrum peaking at about 6 MHz. A likely cause of the instability is the impedance of the ring extraction kickers. We carry out here a detailed benchmark of the observed instability, uniting an analysis of the experimental data, a precise ORBIT Code tracking simulation, and a theoretical estimate of the observed beam instability.