Experimental demonstration of sequential excitation scheme for H − laser assisted charge exchange

Charge exchange injection is the standard mechanism used to accumulate short, intense pulses of proton beams from an H^{-} injector into a synchrotron. Historically, this process has relied on injection foils to remove the two electrons from the H^{-}, a technique that has been successfully employed for beam powers up to 1.4 MW. However, such foils are known to sublimate beyond a threshold beam power density, requiring the development of another stripping technology that does not have the same limitation. This work reports on the experimental development of laser assisted charge exchange (LACE) as a mechanism for replacing the foils. In the present work, a method of laser assisted charge exchange that is scalable to full duty factor operation is experimentally demonstrated. The method, termed “sequential resonance excitation,” relies on a two-step quantum excitation of the electron from the ground state to the excited state. Compared with previously reported LACE experiments that utilized a single-step excitation, this method significantly reduces the required peak laser power, allowing for scalability to millisecond-long H^{-} pulses with conventional laser technology.