1. D.E. Johnson, T.R. Johnson, K.L. Duel, M. Gardner, V. Scarpine, R.J. Tesarek Motivation Notching process in the Booster creates about 30-35% of the total loss on a cycle by cycle basis. This is a major source of activation for tunnel components Move process to 750 keV where component activation does not occur. Figure 1: Booster Losses. When Booster becomes operational at 15 Hz* notching losses at 700 MeV projected to 300W. *Goal of PIP 700 kW upgrade program. Optical Cavity 3DCADmodel of Optical cavity and flange between RFQ and Quad. Laser Notcher Optical cavity flange attached to RFQ showing laser path in to and out of cavity. Flange removed to reveal cavity mirrors an laser path within cavity. (mirror holders removed) Enlarged cavity geometry showing laser and H- ion path. (mirror substrate removed) H-H- Location Concept Removal of outer electron of H- by photoionization with laser -> create H0 ( to be lost) Fraction neutralized (not dependent on H- intensity) Reduction of laser pulse energy Select  LAB = 1064 nm form Yb doped substrate Increase interaction time with multiple interactions Reduce laser pulse width to match bunch length 97% Neutralization assuming: 21 interactions 2 mJ laser pulse energy 0.6 mm H by 10mm V laser profile 2 ns laser pulse length Goals Remove losses due to the notching process from the Booster tunnel  Move the process to 750 keV line Develop a laser system / optical cavity that:  will fit into the highly constrained space in the 750 keV MEBT  will generate an arbitrary number of notches within a linac pulse  will generate an arbitrary notch length for each notch  will be capable of neutralization of 99% of the H- ions in each H- bunch Linac Pulse structure with notches. Beam Stacker Half-wave plates rotate polarizations to +/-45 degrees, allowing BBO crystals to Equally split the beam Merging beamlets by increasing Input Gaussian beam size to form roof-top profile BBO crystal geometry and Impact on a polarized beam (figure from Pmoptics.com white paper) (a technique for Gaussian to roof-top spatial profile) Demonstration Experiment Wall Current Monitor Laser profile used in Experiment Experimental layout using installed Optical Cavity We would like to thank the following who contributed to the success of the Demonstration Experiment. Comparison with measurement Demonstration Experiment used Quantel 100 mJ Q-switched Nd:YAG laser Profile from Quanel vs Diode & fiber amplifier Laser System 450 kHz burst 200 MHz pulses in each burst Single 200 MHz pulses to match bunch temporal structure Laser IN Laser OUT MIRROR Laser IN Laser OUT A “Notch” is a segment of the circumference of an accelerator void of beam to allow for the extraction kicker rise time. (In Booster ~60ns out of 2.2  s.) ~2.5” --- Mirrors ~ 25 mm square R=99.95% --- H- bunch frequency 201.25 MHz -- bunch length ~1.5-2 ns Andrea Saewert Mike Kucera Jamie Santucci Fred Mach High Rise & PPD Machine shops Matt Quinn Dave Baird Ray Lewis Fernanda Garcia, Bob Zwaska, Bill Pellico