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This paper presents a scheme for three-step laser-based stripping of an H ÿ beam for charge exchange injection into a high-intensity proton ring. First, H ÿ atoms are converted to H 0 by Lorentz stripping in a strong magnetic field, then neutral hydrogen atoms are excited from the ground state to upper levels by a laser, and the remaining electron, now more weakly bound, is stripped in a strong magnetic field. The energy spread of the beam particles gives rise to a Doppler broadened absorption linewidth, which makes for an inefficient population of the upper state by a narrow-band laser. We propose to overcome this limitation with a ''frequency sweeping'' arrangement, which populates the upper state with almost 100% efficiency. We present estimates of peak laser power and describe a method to reduce the power by tailoring the dispersion function at the laser-particle beam interaction point. We present a scheme for reducing the average power requirements by using an optical ring resonator. Finally, we discuss an experimental setup to demonstrate this approach in a proof-of-principle experiment.

This Letter presents the first complete six dimensional phase space measurement of a beam in an accelerator. The measurement was made on the Spallation Neutron Source Beam Test Facility. The data reveal previously unknown correlations in the six dimensional phase space distribution that are not visible in lower dimensionality measurements. The correlations are shown to be intensity dependent.

We report on an experiment in which a negative hydrogen ion beam in the Spallation Neutron Source (SNS) linear accelerator was replaced with a beam of protons with similar size and dynamics. Fractional beam loss in the superconducting part of the SNS accelerator was measured to be at least 2×10(-5) for the H(-) beam, and it was an order of magnitude lower for the protons. Also beam loss has a stronger dependence on intensity with H(-) than with proton beams. These measurements verify a recent theoretical explanation of unexpected beam losses in the SNS superconducting linear accelerator based on an intrabeam stripping mechanism for negative hydrogen ions. This previously unidentified mechanism for beam loss is important for the design of new high current linear ion accelerators and the performance improvement of existing machines.

Thin carbon foils are used as strippers for charge exchange injection into high intensity proton rings. However, the stripping foils become radioactive and produce uncontrolled beam loss, which is one of the main factors limiting beam power in high intensity proton rings. Recently, we presented a scheme for laser stripping an H ÿ beam for the Spallation Neutron Source (SNS) ring. First, H ÿ atoms are converted to H 0 by a magnetic field, then H 0 atoms are excited from the ground state to the upper levels by a laser, and the excited states are converted to protons by a magnetic field. In this paper we report on the proof-ofprinciple demonstration of this scheme to give high efficiency (around 90%) conversion of H ÿ beam into protons at SNS in Oak Ridge. The experimental setup is described, and comparison of the experimental data with simulations is presented.

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