First Demonstration of Laser-Assisted Charge Exchange for Microsecond Duration ${\mathrm{H}}^{-}$ Beams

This Letter reports on the first demonstration of laser-assisted ${\mathrm{H}}^{-}$ charge exchange for microsecond duration ${\mathrm{H}}^{-}$ beam pulses. Laser-assisted charge exchange injection is a breakthrough technology that overcomes long-standing limitations associated with the traditional method of producing high intensity, time structured beams of protons in accelerators via the use of carbon foils for charge exchange injection. The central theme of this experiment is the demonstration of novel techniques that reduce the laser power requirement to allow high efficiency stripping of microsecond duration beams with commercial laser technology.

Figure 1

Schematic of the laser stripping concept in this experiment, showing Lorentz stripping of the first electron by a dipole magnet in the first step (the far right), resonant excitation of the second electron by the laser in the second step (the middle), and, finally, stripping of the excited electron by the second dipole magnet (the left).

Figure 2

The macropulse (top), minipulse (middle), and micropulse (bottom) structure of the ${\mathrm{H}}^{-}$ beam (blue), the laser in this $10\mu \mathrm{s}$ experiment (light purple), and the laser in the POP experiment (green).

Figure 3

Schematic of the experimental layout, and photo of the as-installed experimental vessel (top left) and the stripper magnet ensemble (bottom right).

Figure 4

The experimental results. The average beam current for a $11\mu \mathrm{s}$ ${\mathrm{H}}^{-}$ beam measured by the beam current monitor at the interaction point before stripping (blue), and eight separately measured stripped proton beam pulses on the same beam current monitor during stripping (red).