• 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.

• M.P. Stockli, S. Assadi, W. Blokland, T.V. Gorlov, B. Han, C.D. Long, T.R. Pennisi
  ORNL, Oak Ridge, Tennessee

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

The new SNS Allison emittance scanner measures emittances of 65 kV ion beams over a range of ± 116 mrad. Its versatile control system allows for time-dependent emittance measurements synchronized by an external trigger, and therefore is suited for studying pulsed systems. After a programmable delay the system acquires a variable array of beam current measurements, each averaged over a changeable time span. The baseline of the current measurements are determined by averaging a fraction of 1 ms shortly before the start of the ion beam pulse. This paper presents the time evolution of emittance ellipses during the 1 ms H^- beam pulses emerging from the SNS test LEBT, which is important for loss considerations. In addition it presents the time evolution of emittance ellipses during the 3 week active lifetime of an SNS H^- source, which is an operational issue. Additional emittance data characterize the dependence on the electron-dump voltage, the extractor voltage, and the LEBT lens voltages, all of which were critical for reaching the 38 mA baseline H^- beam current. Emittance data for the dependence on the beam current highlight the challenges for the SNS power upgrade.