ORNL, Oak Ridge, Tennessee, USA
This paper describes a longitudinal H− beam profile scanner that utilizes laser light to detach convoy electrons and an MCP to collect and measure these electrons. The scanner is located in MEBT with H− energy of 2.5MeV and an RF frequency 402.5MHz. The picosecond pulsed laser runs at 80.5MHz in sync with the accelerator RF. The laser beam is delivered to the beam line through a 30m optical fiber. The pulse width after the fiber transmission measures about 10ps. Scanning the laser phase effectively allows measurements to move along ion bunch longitudinal position. We are able to reliably measure production beam bunch length with this method. The biggest problem we have encountered is background signal from electrons being stripped by vacuum. Several techniques of signal detection are discussed.
