J. Golden

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.

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.

Compact, high‐current accelerators and their prospective applications

This paper briefly surveys the three compact, high‐current accelerators that are presently under development in the United States in support of a national program. In addition, it reports recent experimental results from the Naval Research Laboratory (NRL) modified betatron [Phys. Rev. Lett. 64, 2374 (1990)] with emphasis on the electron‐cyclotron resonance that presently limits the energy of the beam to approximately 18 MeV. Finally, it briefly addresses selective existing and prospective applications of accelerators.

Internal Injection into the NRL Modified Betatron

We are reporting preliminary experimental results on the injection and trapping in the NRL Modified Betatron. In internal injection, the beam is produced by a diode located within the chamber. Using one half of the 1 m toroidal vacuum chamber, the propagated beam current and displacement are monitored as functions of the applied magnetic fields (BZ, and the toroidal field, B¿). Our preliminary results are in agreement with theoretical predictions.

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.

STUDIES OF SYNCHROTRON RADIATION EMISSION FROM THE MODIFIED BETATRON ACCELERATOR

Numerical calculations of synchrotron radiation emitted from the modified betatron accelerator show that, for relativistic electron energies up to approximately 2 MeV, the single‐particle intensity spectrum is characterized by a peak at the Doppler‐shifted cyclotron frequency associated with the applied toroidal field. As the electron energy is increased above a few MeV, the calculated spectrum becomes comparable to that of an electron in purely circular motion. Measurements of the radiation using fixed‐frequency heterodyne receivers indicate that the polarization, amplitude, and the temporal evolution of radiated power during the first few hundred microseconds of acceleration are in good agreement with the predicted single‐particle spectrum. These observations have been used to confirm the energy evolution and provide information about the magnitude of the transverse velocity of the beam electrons. Late‐time signal decay suggests that electrons are moving off the minor axis in a manner that is consistent...

Computer simulation studies of strong proton rings

Results are reported from a numerical simulation study on the propagation of a rotating proton pulse and the formation and trapping of the resulting strong proton ring. It is observed that the self‐magnetic field has a very pronounced effect on the dynamics of such systems. In addition, it is observed that rings trapped in a magnetic mirror field are r, z stable for the entire confinement time tested of 550 nsec and suffer neither axial nor radial particle losses.