Abstract
A new scheme with sequential resonant excitation for laser assisted charge exchange injection of ${\mathrm{H}}^{\ensuremath{-}}$ beams is proposed. In contrast with the one step excitation scheme, the proposed scheme requires significantly less laser power for high efficiency stripping. It also provides greater flexibility in the choice of laser wavelength for a given beam energy and extends the range of energies where laser stripping can be effectively applied. Calculations and experimental plans for 1.0 GeV and 1.3 GeV ${\mathrm{H}}^{\ensuremath{-}}$ beams at the Spallation Neutron Source are presented. Results indicate that the sequential excitation scheme allows the use of more convenient green laser with much smaller power in place of the UV laser previously used.
Highlights
The laser assisted charge exchange method is being developed as an alternative option to the foil-based scheme, which suffers from limiting complications associated with foil lifetime and induced residual radiation from particle scattering in the foil [1]
The experimental evolution of the concept began in 2006 at the Spallation Neutron Source accelerator with a proof of principle demonstration [3] followed by a proof of practicality demonstration [4,5], both resulting in stripping efficiencies > 90%
Where Ib is the ion beam current; k is the efficiency of excitation from the ground level to the n 1⁄4 2 level; g1 is number of fluorescence photons emitted per unit of length, from the Table I; l is the distance from the interaction point to the magnet entrance; g2 is the fraction of photons per radian at the detection angle as show in Fig. 9(b); d is the photomultiplier tube (PMT) photocathode diameter; R is the distance from the photons emission points to the PMT; g3 is the PMT photocathode efficiency; G is the PMT gain
Summary
The laser assisted charge exchange method is being developed as an alternative option to the foil-based scheme, which suffers from limiting complications associated with foil lifetime and induced residual radiation from particle scattering in the foil [1]. The laser assisted charge exchange scheme developed for stripping 1 GeV H− beams at the Spallation Neutron Source accelerator (SNS) consists of a three step process whereby the first electron is Lorentz stripped in a magnet field (H− to H0), the second electron is excited by a. (1) and (2) result in approximately an order of magnitude in laser power savings by using the double excitation scheme This savings can be used to simplify the laser system using a low power laser to achieve the same stripping efficiency, or to use the laser power with an optical cavity for stripping H− beams with larger emittance or energy spread. The preliminary design of an experimental implementation of the scheme, utilizing the UV laser configuration already in place at the SNS is discussed
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