• Y. Liu, A.V. Aleksandrov, C.D. Long
  ORNL, Oak Ridge, Tennessee
• C.C. Peters
  ORNL RAD, Oak Ridge, Tennessee

A laser wire system* has been developed in the Spallation Neutron Source (SNS) superconducting linac (SCL). The SNS laser wire system is the world largest of its kind with a capability of measuring profiles of an operational hydrogen ion (H-) beam at each of the 23 cryomodule stations along the SCL by using a single light source. Presently 9 laser wire stations have been commissioned that measure profiles of the H^- beam at energy levels from 200 MeV to 1 GeV. The laser wire diagnostics has no moving parts inside the beam pipe and can be run parasitically on a neutron production H^- beam. This talk reports our recent study of the laser wire profile measurement performance. Parasitic profile measurements have been conducted at multiple locations of SCL on an operational one-megawatt neutron production beam that SNS recently achieved as a new world record. We will describe experimental investigations of the laser wire system performance including the stability and repeatability of the measurement and the influence of the laser parameters. We will also discuss novel beam diagnostics capabilities at the SNS SCL by using the laser wire system.

* Liu et al., "Laser wire beam profile monitor in the SNS superconducting linac," Nucl. Instr. and Meth. A, to appear.

• M.A. Plum, J. Galambos, S.-H. Kim, P. Ladd, Y. Polsky, R.W. Shaw
  ORNL, Oak Ridge, Tennessee
• C.F. Luck, C.C. Peters
  ORNL RAD, Oak Ridge, Tennessee
• R.J. Macek
  LANL, Los Alamos, New Mexico
• D. Raparia
  BNL, Upton, Long Island, New York

The diamond stripper foils in use at the Spallation Neutron Source worked successfully with no failures until May 3, 2009, when we started experiencing a rash of foil failures after increasing the beam power to ~840 kW. The main contributions to foil failure are thought to be 1) convoy electrons, stripped from the incoming H− beam, that strike the foil bracket and may also reflect back from the electron catcher, and 2) vacuum breakdown from the charge developed on the foil by secondary electron emission. In this paper we will detail these and other failure mechanisms, and describe the improvements we have made to mitigate them.