Taro Sometani

Electrostatic separation of plastics by friction mixer with rotary blades

A mixture of plastic pellets or waste plastic pieces is electrostatically separated. The mixture is charged by friction in a mixer and falls through a horizontal electric field of 4 kV/cm into three zones under the field. A mixture of two kinds of plastic pellets is separated with a purity of not less than 90%. A mixture of three kinds of pellets is separated to some extent in the zones at the extreme ends in the first separation, according to the locations of the different kinds of pellets in the triboelectric charging sequence. This mixture will be separated in successive separations following the first one into the respective pellet types. A mixer made of suitable plastic material and adapted to enhance the friction between different kinds of pellets assures easy and reliable separation. Proper mixing time, a high rotational speed of the mixer, and low humidity increase the purity of the separated pellets. Since the effect of blended additives of pellets on charging characteristics appears with good reproducibility, pellets and waste plastic pieces with such additives may likewise be successively separated into the respective plastics.

Eddy Current Measurement on a Noncircular Model Shell

Toroidal eddy current density is measured on a 1/7 model of the aluminum shell (vacuum vessel) of the R-tokamak in order to confirm experimentally the computation done by eddy current analysis computer code EDDYTOR 6. Parallel and perpendicular components of magnetic induction measured with four sets of magnetic probes near the internal and external surfaces of the model shell are expanded in Fourier series of the poloidal angle of the shell. The eddy current density is determined from the measured components based on Amperes law. Acceptable agreement is found between measurement and computation.

Analysis of the Magnetic Field Penetrating through a Cylindrical Resistive Shell of a Tokamak

An analysis is described which gives the magnetic field produced by sinusoidal currents in then axial conductors arranged outside a cylindrical resistive shell. The frequency characteristics of the amplitude and the phase angle of the field are obtained. The result of several numerical computations agrees with the result of the corresponding model experiment. The time constant for the rise of the field, at the center of the shell, due to the shell current agrees completely with that of a thin casing.

Method for solving electrostatic problems having a simple dielectric boundary

Electrostatic problems having a simple dielectric boundary are solved using the concept of polarization charge. Using elementary mathematics, it is shown that the electrostatic field due to the total polarization charge distributed on a boundary surface between two homogeneous and isotropic dielectrics, is equivalent to that due to the lumped image charge used conventionally in teaching these problems. The demonstration of the equivalence of the surface polarization charge to the image charge will help students to understand the physical base of the image charge. Two problems are treated: a plane dielectric boundary, and a dielectric sphere immersed in a uniform field.

Feedback position control apparatus of tokamak plasma horizontal position with a digital drive

A plasma horizontal position feedback control system (PHPFCS) and a digital current drive (DCD) for controlling vertical magnetic field are made on an experimental base, and the horizontal position of a plasma in a small tokamak (HAMANA-T) is controlled by PID operations from the initial phase of plasma generation. The DCD consists of constant-current discharge units for multiple condensers and drives a digital current analogous as a whole to the control signal of PHPFCS in the range of ±90 A. The maximum value of the digital current increases in proportion to the number of units. This PHPFCS elongates plasma duration from 1.3 ms to 2.1 ms, smooths the waveform of plasma current, and reduces the plasma loop voltage from 25 V to 20 V. Furthermore, PHPFCS reduces the range of variation in plasma horizontal displacement from 3.5 cm to within 0.5 cm and makes it possible to set accurately the horizontal position from the initial phase in the inner region of a vacuum chamber.

Magnetic field of a current ring

An expression for a magnetic field of a current ring is presented. The current distribution in the cross section of a thin current ring is expressed as a two‐dimensional delta function and is substituted in Poisson’s equation for vector potential. The expression, derived from the solution of the equation, is given in the form of an integral with respect to a parameter. The expression is applied to the problem of the magnetization current on the surface of an iron core and to the problem of the self‐inductance of an air‐core coil.

An Arrangement of Current Conductors for the Min. \barB Field

An arrangement of current conductors producing the min. \barB field of the periodic multipole type is given. If the current conductors are suitably arranged on some cylindrical surfaces with radii small compared with an axial pitch, the deviation of field lines from the axis can be kept so small that the by-axial calculation of the field components is allowed.

Drive to generate digital current for control vertical field in a small Tokamak

The horizontal position of a small Tokamak plasma has been controlled by a circuit to generate the control vertical field. The circuit must respond quickly to the position signal from a feedback circuit and feed a large current in a short time. We have assembled the circuit to generate a digital current called a drive. The drive includes several units, and each unit is made up of a capacitor, a transistor, a protective resistor and a comparator. We have installed the drive on a small Tokamak, the Hamana-T and obtained satisfactory results. The performance of the drive is described.

Evaluation of Error Poloidal Field in an Iron-Cored Tokamak

The error field (magnetic induction) conjectured to originate from the connecting conductors and the turnback coil of toroidal field coils and the poloidal field, which is applied to compensate the error field and the electron toroidal drift, are computed with semianalytic expressions. The vertical component of the computed error field agrees roughly with the error vertical field which is evaluated indirectly by determining the optimum value of the applied poloidal field from the standpoint of the tokamak gas breakdown. The computed value of the applied poloidal field produced by simple circular coils agrees satisfactorily with the directly measured one.

Poloidal Magnetic Field of an Iron-Cored Tokamak

The poloidal magnetic field is measured on the remodelled JFT-2 apparatus. The measured field agrees well with the field calculated by a relatively simple method proposed by one of the authors. A combination of poloidal field coils is discussed which can effectively produce the vertical field required to maintain a plasma current.