Robert V. Pyle

Intense, mixed-energy hydrogen beams for CTR injection

Present high-current ion sources for neutral injection experiments accelerate a mixture of atomic and molecular hydrogen species that are converted into neutral particles with different energies and neutralization efficiencies. Beam composition can have important effects on injection system efficiency, vacuum design, and first-wall loading. Beam composition measurements of the 20-keV LBL high-current sources are used to calculate the relative power in the various hydrogen and deuterium beam components expected at higher energies.

MACROSCOPIC INSTABILITY OF THE POSITIVE COLUMN IN A MAGNETIC FIELD

The positive column of a glow discharge has previously been shown to become unstable when immersed in a longitudinal magnetic field of the order of 1 kgauss, the instability transforming the azimuthally symmetric column into a constricted rotating helical stage. The measurements have been extended, with emphasis on the properties and growth of the instability, to permit a quantitative comparison between experiment and the theory of Kadomtsev and Nedospasov. The properties of the helical state have been measured in H2, D2, He, and Ne as functions of gas pressure and tube radius. The dependence of the critical magnetic field, and the frequency and wavelength of the oscillation on the kind of gas, pressure, and the tube radius are in fairly good agreement with the predictions made by the perturbation theory of Kadomtsev and Nedospasov. It is interesting that the onset of the instability is also fairly well predicted by the simple sheath‐instability theory of Hoh, but the agreement is not as good as in the previous case, nor is the nature or appearance of the instability specified.

Optimization of H− production in a magnetically filtered multicusp source

Different techniques to increase the H− yield in a multicusp source have been investigated. It is shown that the extracted H− current can be enhanced by optimizing the discharge voltage, the neutral gas pressure, or by employing a magnetoelectrostatic containment scheme. A factor of 6 increase in H− output has been achieved by placing the extractor very close to the magnetic filter. It is also found that the extracted electron current is much reduced at this optimum geometry.

Nuclear fission induced by radiationless transitions in the MU-mesonic atoms Th232, U235 and U238

Abstract The time distribution of fissions in Th232, U235, and U238 indueed by μ− mesons was measured with a multiplate gas-scintillation fission chamber. A significant number of prompt fissions not associated with μ− nuclear capture was observed. The results are: Nucleus Ratio of Promp fissions to fissions from nuclear capture Th232 0.064±0.022 U238 0.072±0.014 U235 0.111± The work of Mukhin et al. shows that the intensities of μ-mesic K x-rays for these elements relative to Pb are 0.85±0.0 (Th), 0.77±0.04 (U238), and 0.71±0.05 (U235). This intensity reduction is qualitatively consistent with earlier predictions that, for these elements, a direct excitation of the nucleus competes with electromagnetic radiation in the transition to the ground state of the mesic atom. Our results indicate such direct nuclear excitation. The number of fissions observed may be consistent with the results of Mukhin et al. and with photofission data, if allowance is made for the effect on the fission barrier of the μ meson in the 1S state of the mesic atom.

MULTIPLE APERTURE EXTRACTOR DESIGN FOR PRODUCING INTENSE ION AND NEUTRAL BEAMS.

A calculational and experiITlental prograITl to optiITlize the extractor design of high-current ITlultiple-aperture ion sources is in progress. In general, the cOITlputed and ITleasured properties of extractors with circular apertures agree well. Very preliITlinary tests with a ITlultiple slot extractor are encouraging.

Two Electron Models of a Constant‐Frequency Relativistic Cyclotron

Two model constant‐frequency cyclotrons based on the principle of L. H. Thomas, as extended by David L. Judd, are described. Both accelerated electrons to speeds of half that of light in magnetic fields of three‐fold azimuthal periodicity. Three 60°‐wide wedge‐shaped electrodes, driven 120° out of phase, provided an energy gain per revolution of 3 eV0, where V0 is the peak electrode‐to‐ground voltage. Electrons were accelerated to 75 kv with V0=23 v, implying a minimum of one thousand revolutions in the cyclotron. The beam reached full energy without axial loss and it was demonstrated that essentially all of the circulating current will emerge from this type of accelerator without the use of additional deflecting systems. The success of this development program has shown the feasibility of a high‐current, high‐energy cyclotron based on the Thomas principle.

EFFECT OF GAS MIXING ON H- PRODUCTION IN A MULTICUSP SOURCE

The effect of gas mixing on volume H− production in a magnetically filtered multicusp source has been investigated. By applying the proper bias voltage on the plasma electrode, the addition of xenon or argon gases to a hydrogen discharge can enhance the H− yield. This increase in H− output is closely related to the increase in plasma electron density in the filter and extraction chamber regions.

Development of the plasma generator for a long pulse 10×40 neutral beam

Users of fusion devices have identified heating requirements for positive ion based neutral beams to include energies of 80 or 120 kV with pulse length up to 30 s. Additional requirements are low beam divergence (0.3°×1.0°; 1/e half angles), low impurity (less than 1%), high species (over 80% atomic), and cathode lifetime exceeding 5 h of beam operation. Accelerator design remains as an engineering problem, whereas most of the performance goals have required development of the plasma generator. Problems of concern which relate to the performance goals are the heat dissipation, magnetic field configuration, and cathode placement. The plasma generator was tested on TS IIA (the plasma generator testing facility) which does not have beam extraction capability but is used to evaluate efficiency, operating conditions, arc notching characteristics, species, plasma uniformity, and cathode conditioning. The source, consisting of the plasma generator mounted on the long pulse accelerator was mounted on NBETF (Neutr...

Cross-sections for electron capture by 0.3- to 70-keV deuterons in H2, H2O, CO, CH4 and C8F16 gases

Electron-capture cross-section measurements are reported for 0.3- to 70-keV deuterons in H2, H2O, CO, CH4, and C8F16 gases. The experimental apparatus and the method employed – slow-ion collection – are described. The results are discussed, particularly the low-energy behaviour in molecular hydrogen.

Volume production of negative hydrogen and deuterium ions in a reflex-type ion source☆

The extraction of negative and positive hydrogen and deuterium ions from a reflex-type negative ion source has been investigated. Extracted positive and negative ion currents were measured as functions of the gas flow rate, the axial magnetic field, and the bias potential of the cylindrical wall of the arc-chamber. By biasing the cylindrical wall several volts negative relative to the anode, a maximum H− current of 9.7 mA (J− ⋍ 100 mA/cm2) and D− current of 4.1 mA (J− ⋍ 42 mA/cm2) were obtained in steady state operation. This result shows a factor of two improvement over previous data. The total impurity negative ion content was less than 1%. When the source was arranged for positive ion extraction, a high proton ratio (90%) was observed. The extracted negative ion current was approximately as large as the positive ion current.