Hideo Akimune

ENERGY LOSS OF LOW-ENERGY PROTONS AND DEUTERONS IN EVAPORATED METALLIC FILMS.

The energy losses, the energy stragglings, and the charge-exchanges of protons and deuterons in the evaporated metallic films Be, Al, Cu, Ag, and Au were measured in the energy range of the incident particles from 7 to 40 keV. The experimental stopping cross-sections of Be, Al, Cu, Ag, and Au for protons are approximately proportional to V 0.8 and are also approximately proportional to square roots of the atomic numbers of the stopping substances. The electronic stopping cross-section of Cu for protons shows a good agreement, in the velocity scale, with that for deuterons measured with the same foil within the experimental error. The experimental energy straggling \(\varOmega^{2}/\varDelta E\) is proportional to E 0.8 and to the 0.68-th power of the atomic number of the stopping substance. The experimental stopping cross-sections and energy stragglings are compared with the Lindhards theoretical calculations. The measured population ratios of hydrogen atoms to protons in the emergent beam were found to a...

Dynamic Stabilization of Flute Instability

The problem on dynamic stabilization of plasma has been treated. The stability is considered under the condition that the plasma is divided to two regions. The destabilizing force is gravitational force and E × B rotation and the stability is sought by the ponderomotive force by rf electric field of ω rf ≃ω ci perpendicular to magnetic field. It is found that the low frequency electro-static waves are stabilized by rf field in case that the rf electric field can penetrate only in the peripheral region. The effect of the dynamic stabilization is experimentally investigated and discussed.

Stabilization of Flute Instability by Means of High Frequency Field

Flute instability is studied theoretically from the point of view of the non-linear interaction of charged particles with an inhomogeneous high frequency field whose electric field component is parallel to the confining magnetic field. The reciprocal action between the high frequency field and the instability is supposed to occur as a result of the particle motions induced by the field parallel to the wave number vector of the instability wave. The two effects of the field are found out; one is attributed to the electron drifts motivated by a quasi-potential derived from the high frequency field and the other is owing to the induced periodic displacement of ions or electrons. The instability is stabilized by the electron drifts whose velocities are nearly equal to or larger than those of ions driving the instability and moreover may be effectively stabilized by the above additional periodic displacements of ions or electrons oscillating with their cyclotron frequencies. These displacements are excited by ...

Secondary Electron Emission Type Neutral Particle Detector

Experimental studies have been made on the secondary electron emission yields from metal surfaces bombarded by H10, H1+, and H20 with energies ranging by 10 to 40 KeV. The yields increase with the incident beam energy. The yield from H10 is smaller than that by H1+ and is proportional to the cosecant of the incidence angle. The yield by H20 is larger by a factor of two than that by H10 with the same velocity. The mechanism of the secondary electron emission is discussed by comparing the yield by H10 with that by H1+ and by considering the observed angular dependence. The observed difference in the yields by H10 and H1+ is considered to originate essentially from the difference between the ionization cross-sections of the two particles within the shallow layer below the surface. A neutral particle detector has been made on the basis of the angular dependence results.

Stabilization of Flute Instability by High Frequency Field

The effects of external inhomogeneous high-frequency field on the flute instability is studied theoretically from a point of view of non-linear particle interaction instead of an approach using a time averaged quasi-static potential or the Mathieu stability diagram. In this paper, it is assumed that the electric field component of the high-frequency field is perpendicular to the steady state confining magnetic field. It turns out that the h f field can compensate the perturbation of the flute instability with the aid of the ion drift induced by the field. The results appear to show that this field has the stabilizing effect in case that ω 0 >ω c i and has the exciting effect in case that ω 0 <ω c i , provided that the h f intensity increases with distance outwardly from the plasma, where ω 0 is the h f field frequency and ω c i is the ion cyclotron frequency.

Plasma Density and Depolarization Current in Mirror-Torus-System-1 with Divertor Magnetic Field

Mirror-Torus-System-1 (racetrack form) consists of two straight mirrors connected by U -bend with four divertors in order to obtain the equilibrium plasma.The plasma in a U -bend is detouched from the wall for the divertor configuration and concentrates on the magnetic axis. A depolarization current reducing the electric field by the toroidal drift is experimentally measured. The depolarization current flowing along the azimuthal direction is considered to be composed of two kinds of motions of electrons in a field free area in the divertor. One is the non-adiabatic motion and the other is B ×\bar V B drift motion. The measured value in U -bend, 8.7 µA/mm 2 , for the current flowing along the line of force passing the neutral line agrees with the calculated one based on the single particle model.

NON-LINEAR PHENOMENA IN BEAM-PLASMA INTERACTION.

A modulated weak electron beam is injected into a low-density diffused plasma and growth rates of convective instabilities are observed. The growth rates obtained experimentally are in pretty good agreement with those calculated from the dispersion relation including only the collisional damping effect if the beam density is relatively low. However, if the beam density is high, the experimental results conspicuously deviate from the calculated values. These results suggest that it becomes difficult for the amplified wave to maintain its coherence as the amplitude increases, and that such non-linear effect would cause breakdown of the amplified waves. The ratio I 1 / I 0 is adopted as a measure of the threshold over which the non-linear effect becomes remarkable, where I 0 and I 1 are the zero-order and first order electron currents in the beam-plasma system respectively. As I 1 / I 0 approaches unity breaking of the wave becomes observable.

Plasma Production by Molecular Ion Injection into a Magnetic Mirror Supplemented with a Radio Frequency Electric Field

Observations with a 27‐keV molecular ion injection experiment are described. In the experiment, an rf electric field is applied transversely to a containing magnetic mirror field in the mid‐region. The rf‐field intensity is proportional to r4, and the frequency relation is ω = 2.5ωci = 5ωcm, where r is the radius, and ωci and ωcm are the cyclotron frequencies of protons and hydrogen molecular ions, respectively. Accumulation of plasma greatly increases with an rf potential of about 1.4 kV, and a density of 7×107 particles/cm3 is obtained with an injection current of 2 mA. Perpendicular proton velocity distribution is well spread with an rf potential of about 1.4 kV. The spreading is caused during the process of deceleration of the injected molecular ions. Emissions at the second harmonic and the fourth harmonic of the proton cyclotron frequency are observed. Intensity of the fourth harmonic is reduced with a rise in strength of the rf field. As the rf field is switched off, there are plasma loss processes...

Suppression of Precessional Drift Wave by External Inhomogeneous High Frequency Field

The effect of a high frequency field on a flute like mode is investigated. The experiment has been made on a plasma produced by means of the molecular ion injection into a simple mirror. The flute like mode arises from the plasma rotation due to a static electric field, which is controlable by means of potential applied to the end plates. the strength of the high frequency field increases with radius and the frequency is near to the ion cyclotron frequency. It is confirmed from the relation between the h f field strength needed to suppress the wave and the plasma potential giving a rise in the wave that the h f electric field parallel to a confining steady state magnetic field reveals major effect on the suppression of the flute like mode and that the perpendicular one has minor effect.

Microinstability of Mirror Confined Energetic Plasma in an R.F. Electric Field

Microinstability of the mirror confined plasma (mean ion energy is 5∼10 keV and maximum density is 7×10 7 cm -3 under an r f electric field, ω 0 =2.5ω c i is investigated experimentally and theoretically, where ω 0 is the frequency of the r f field and ω c i is the ion cyclotron frequency. The frequency of the observed oscillation, which is satisfactorily explained as a temporal growing loss cone instability, is above or nearly equal to 4ω c i . It seems, as predicted by the calculation, to shift slightly from 4ω c i by the effect of the r f field. This instability oscillation is damped with the r f field. The stabilization is owing to the energy spreading of ions and owing to the electron drifts induced by the r f field whose frequency is off-resonant from ion cyclotron frequency and its harmonics.