[en] An upgrade program is being carried out at Los Alamos to increase the peak beam current from the present H^- injector to provide 200 μA average current for the proton storage ring at LANSCE. In order to meet this objective, the injector must provide at least 30% more current than presently available. More optimal operation however, requires a factor of two higher peak current in order to reduce circulating losses in the ring. At these higher currents, a lower beam emittance is needed to limit beam losses in the linac. Beam simulations have been carried out to model the operation of the present injector and to determine what changes will be required to operate with these higher beam currents. A collaboration with the Lawrence Berkeley National Laboratory (LBNL) is now in progress to modify the present converter ion source to produce 40-mA peak of H^- beam current with reduced beam emittance. Beam simulations show that a new 80-kV accelerating column will be needed to accelerate and transport these higher current beams with acceptable beam size and divergence. Experimental results for the initial phase of this program are presented together with a comparison to these beam simulations

[en] The Ion Beam Facility operated for 6000 machine hours last year, ranging in energy from 300 Kev to 24 Mev. Improvements include cryopumps replacing diffusion pumps, a rebuilding of the tandem chopper electronics and the vertical's corona charging system. Methane molecules were successfully accelerated by the vertical in quantities of hundreds of nanoamperes. Two replacement magnet power supplies on the tandem and a completely new capacitor shell regulator on the vertical are soon to be installed

[en] A 100-mA, 2.07-MeV Radio-Frequency Quadrupole (RFQ III) has been commissioned and operated routinely on the Accelerator Test Stand (ATS) at Los Alamos National Laboratory. To characterize the RFQ output beam dynamics, measurements were made of the beam transmission and of the transverse and longitudinal phase-space distributions. Data were taken for different RFQ III operating conditions and compared to simulations

[en] We report the first observation of nonresonant excess photon absorption (for ionization as well as detachment) in competition with the single photon process. A 35keV negative hydrogen ion beam is irradiated with focused Nd:YAG laser pulses; the 1.165eV photon energy exceeds the electron binding energy by 0.41eV. The time of flight spectrum of detached electrons exhibits the absorption of one and two photons. The detached electrons exit with a P wave angular distribution for the one-photon detachment and primarily a D wave for the two photon excess photon detachment. copyright 1997 The American Physical Society

[en] One-photon detachment and two-photon nonresonant excess photon detachment of electrons from the H^- ion (outer-electron binding energy = 0.7542 eV) are observed with 1.165 eV laser pulses from a Nd:YAG laser (where YAG denotes yttrium aluminum garnet). A Penning ion source produces a pulsed 8 μA, 35 keV H^- beam that intersects a laser beam cylindrically focused down to a 17 μm full width at half maximum waist in the ion beam direction, creating a high-intensity interaction region with peak intensities of up to 10¹¹ W/cm². The interaction time is 7 ps. The detached electrons are detected by a time-of-flight apparatus enabling us to detect a very small two-photon signal in the presence of a very large signal from single photon detachments. By rotating the linear polarization angle, we study the angular distribution of the electrons for both one- and two-photon detachments. The spectra are modeled to determine the asymmetry parameters and one- and two-photon cross sections. We find β₂ to be 2.54+0.44/-0.60 and β₄ to be 2.29+0.07/-0.31, corresponding to a D state of 89+3/-12% of the S wave and D wave detachments for the two-photon results. The relative phase angle between the S and D amplitudes is measured to be less than 59 degree sign . The measured cross sections are found to be consistent with theoretical predictions. The one-photon photodetachment cross section is measured to be (3.6±1.7)x10^-17 cm². The two-photon photodetachment generalized cross section is (1.3±0.5)x10^-48 cm⁴ sec, consistent with theoretical calculations of the cross section. The three-photon generalized cross section is less than 4.4x10^-79 cm⁶ sec². (c) 1999 The American Physical Society