R. A. Mahaffey

Intense electron‐beam pinch formation and propagation in rod pinch diodes

Intense electron‐beam pinches are formed and propagated at relatively high impedance (5–25 Ω) using rod pinch diodes. Pinch propagation of up to 20 cm with 45% efficiency and ion‐generation efficiency ≳15% has been observed.

Intense proton beam current measurement via prompt gamma rays from nuclear reactions.

The current of an intense, pulsed proton beam is experimentally determined by monitoring prompt gamma rays from nuclear reactions induced in a suitable target. Relevant data are given on the reactions employed including (7)Li(p,gamma) (8)Be, (19)F(p,alphagamma) (16)O, and (12)C(p,gamma) (13)N so that absolute currents can be determined. This method avoids the complication of target blowoff and the need for attenuating screens when applied to high current density beams.

Studies of Ion Beam Generation Efficiency with Reflex Tetrodes.

The unidirectionality of the ion current in a reflex tetrode has as a result the efficient generation of pulsed, ion beams. Experimental results are reported on the dependence of the ion generation efficiency, in a reflex tetrode, upon the applied voltage, total current, anode-anode and anode-cathode separations and applied magnetic field.

Intense proton‐beam‐pumped Ar‐N2 laser

Gas laser action using a current and space‐charge‐neutralized proton beam as a pump source has been demonstrated. Stimulated emission at 357.7 and 380.5 nm, corresponding to the v′=0→v″=1 and v′=0→v″=2 transitions of the N2 (C→B) band, has been observed in Ar/5%N2 gas mixtures. In comparison with electron beams, protons appear to be more efficient for excitation sources of high‐pressure uv and visible lasers.

High‐power ion beam generation with an inverse reflex tetrode

A new reflexing‐electron ion source is described. The device produces a unidirectional ion beam with relatively high efficiency even when the applied magnetic field exceeds the self‐field. This new source operates at a low, constant impedance during much of the applied voltage pulse and is better matched to available high‐power, low‐impedance generators than previous reflexing‐electron devices. Proton pulses with peak current ∼500 kA have been produced with the inverse reflex tetrode coupled to the Gamble II generator.

Efficient XeF laser excited by a proton beam

The efficient generation of stimulated emission from XeF at 351 and 353 nm has been achieved by pumping RG/Xe/NF3 gas mixtures (RG=argon, neon, or helium) with an intense (∼10 A cm−2) beam of ∼200‐keV protons. For an active medium (T=300 °K) consisting of Ar, Xe, and NF3 at a total pressure of 1 atm and 30% cavity output coupling, the volumetric output, efficiency, and threshold pump power for the laser were determined to be 5–10 J/liter amagat, 1.7±0.7%, and 1.5 MW cm−3, respectively. Much lower efficiencies were obtained for neon and helium diluent mixtures.

Parametric focusing of intense ion beams

Focusing of charge‐ and current‐neutralized intense ion beams is accomplished by propagating the beam along a spatially periodic axial magnetic field. This focusing results in local variations in the beam radius and density. At one location, the measured particle density is enhanced over the emitted density by at least a factor of 4. Current density enhancements in excess of an order of magnitude using this method should be obtainable.

Effects of the beamfront velocity on collective acceleration with relativistic electron beams

Observations of accelerated protons during the injection of rotating relativistic electron beams into neutral hydrogen (50–400 mTorr) indicate that ions from the beam‐formed plasma are trapped and accelerated by a potential well at the beamfront. Measurements show that the number of accelerated protons decreases as the beamfront velocity is increased. Moreover, at a given velocity, the number accelerated is relatively insensitive to the neutral gas pressure.