The SLAC Quark Search Group has demonstrated successful operation of a low cost, high mass throughput Millikan apparatus designed to search for fractionally charged particles. About six million silicone oil drops were measured with no evidence of fractional charges. A second experiment is under construction with 100 times greater throughput which will utilize optimized search fluids. Invited talk presented at 1996 Meeting of the Division of Particles and Fields of the American Physical Society Minneapolis, Minnesota August 10-15, 1996 * Work supported by Department of Energy contract DE–AC03–76SF00515. AN IMPROVED SEARCH FOR ELEMENTARY PARTICLES WITH FRACTIONAL ELECTRIC CHARGE

We outline the design of a fully automated Millikan droplet apparatus that could detect a single free fractional charge in several hundred grams of matter even without the use of a prefilter. This would constitute an improvement over current limits by about three orders of magnitude. The experiment achieves high material throughput and high background rejection through on-line processing which allows for a feedback system that can concentrate the measurement effort on anomalous droplets. The task is simplified by generating a monodisperse stream of droplets which will be preprocessed to let only a very narrow range of charges enter the Millikan chamber. Because the droplets can act as carriers of finely dispersed materials it is also possible to search for fractional charge in matter that has not undergone extensive refinement that may have excluded fractionally charged atoms from the sample. In a large refinery style operation many such Millikan chambers could run concurrently to achieve extremely large material throughput.

The interaction of a stream of dielectric spheres in an electric field in a high vacuum is investigated both theoretically and experimentally. This investigation is motivated by an attempt to detect fractional electric charges which might exist in matter, namely, a search for isolated quarks in matter. The theoretical analysis is intended to pinpoint the basic interaction mechanism by which a stream of dielectric spheres becomes destabilized in an electric field. One important result of this analysis is a suggested method by which the destabilizing forces can be eliminated. The experiments performed are intended to study the behavior of a stream of uniform liquid drops in an electric field in a high vacuum. It is seen from these experiments that the deflections of any two drops in the stream with charges differing by one electronic charge is the same except for the effects of some destabilizing forces.

This is a study of the charge distribution and the forces on an electrically driven jet. A numerical solution of the charge distribution is presented, based on the measurement of the jet profile and the jet current. The influence of the charge distribution and fluid conductivity on jet length is considered. As a check on the charge distribution calculations, the electric driving forces are compared to the reaction forces.

Many inertial confinement target designs have the fuel as a frozen spherical shell of hydrogen isotopes. One method of manufacturing these targets would be to produce the spherical shell first. In this paper we report on an experimental study on the production of spherical shells of liquid and solid hydrogen. These shells are made by acoustically breaking up a jet of superheated liquid hydrogen into drops and at the same time cavitating a bubble in the center of each drop. The resulting growth of the bubbles by evaporation produces the spherical shells. The size and the aspect ratio of the spherical shells are found to be affected by several parameters. The mass of the drop depends on the diameter of the nozzle from which the jet emerges. Also, varying the frequency of the acoustic excitation gives some control of the droplet size. The aspect ratio depends most strongly on the liquid temperature and the droplet-chamber pressure. Increasing the temperature or lowering the pressure increases the aspect ratio of the shell. If the pressure is lowered below the triplet-point pressure of hydrogen, the shells freeze forming a spherical shell of solid hydrogen.

1.(a) A 45° inclined planar electric curtain is used to act on charged (1) lycopodium (2) silica (3) feldspar and (4) flyash particles. The accumulation of sample particles near the lower end of the curtain is apparent.2.(b) A force, produced by a horizontal planar electric curtain excited by a six-phase a.c. voltage, is a travelling wave in nature. This force is observed not only to support the particles weight against gravity but also to transport them in a preselected direction.3.(c) A vertical planar curtain, energized by a six-phase a.c. power supply and oriented with its plane perpendicular to the direction of air flow, covers a cross-section in the wind duct. The charged test particles carried in the air flow are forced to interact with the repulsive force generated by the vertical curtain. It is observed that the motion of some of the charged particles is confined to a plane in front of, and parallel to, the surface of the vertical curtain. Of all the tested samples, the flyash was found to be the most difficult one to stop with the vertical electric curtain. The highest air flow speed against which the flyash particles could be stopped at the curtain surface was 1.08 cm/s.

An apparatus has been constructed which produces uniform spheres of solid hydrogen for experiments testing the feasibility of using the solid hydrogen pellets for refueling fusion reactors. Two versions of the apparatus were developed, one which produced 70-μm-diam pellets at the rate of 105/sec and another which produced 210-μm pellets at the rate of 2.6×104/sec. The first step in the pellet production is to liquefy the hydrogen by flowing it through a liquid-helium-cooled heat exchanger. Then, a liquid hydrogen jet is formed by flowing the hydrogen through a nozzle. The jet is broken up into uniform drops by an acoustical excitation. The drops are frozen by evaporation in a pressure less than the triple point pressure of hydrogen. Finally, the drops are injected into vacuum for the experiments.

Electrical coalescers offer an effective means for decontaminating distillate fuels. Some of the charging mechanisms occurring in this type of coalescer are described.

An apparatus has been constructed which produces uniform hollow shells of liquid. The techniques used are to ultrasonically excite and inject a gaseous jet into a liquid jet. The physical arrangement consists of dual capillary nozzles with the gas nozzle coaxial to and inside the liquid nozzle. The gas jet is broken up into uniform bubbles by acoustical excitation. The bubbles then break up the fluid jet into uniform spheres which contain the bubbles and therefore are hollow shells. The system was tested with Freon-113 (C2Cl3F3) as the liquid and nitrogen as the gas. This system was built as a prototype to evaluate these procedures before proceeding to construct apparatus to produce solid hydrogen shells.

Research and development in diverse fields of scientific and engineering interest often require a knowledge of the electric charge on a single macroscopic particle. The methods which have been developed for the determination of particle charge include electric and magnetic field deflection techniques, current measurements, and direct sensing by induced charge effects. Several methods are discussed, and experimental results are given for two of these methods. Charge magnitudes to about 10-17 C are of interest in these studies.

Many laser fusion experiments require the use of hollow spherical shells of hydrogen (deuterium-tritium mixture) as targets. We have produced hollow particles of normal hydrogen in preparation for producing shells of the various hydrogen isotopes and controlled mixtures of these isotopes. The hollow spheres were produced by ultrasonically nucleating bubbles in superheated liquid drops of hydrogen. Evaporation into the bubble increased its size and produced the shells.

In many fields of industrial interest, particle sampling and/or control is very important. However, the calibration and testing of sampling equipment have been difficult because of the lack of sources of uniform particles. In this paper a source of uniform solid or liquid particles is described together with the characteristics of the source and the particles produced. Fractional standard deviatio...

An electrohydrodynamic ion source has been constructed and attached to a high resolution mass spectrometer. This ionization process is based on the interaction of a conducting liquid surface and an intense electrostatic field. An ion source operating on Ga–In eutectic alloy has produced in excess of 30 μA of ion current. The mass spectra obtained from the Ga–In source provided conclusive proof of the production of singly charged, monatomic ions. In addition the ion source ionized five impurities dissolved in the liquid eutectic.

A method is described for the generation of large quantities of uniform solid particles of 0.5-10 mu m radius. The particles are produced by the evaporation of the solvent content of liquid droplets of solution sprayed in air and driven down a high temperature evaporation column. The generation of the drops is accomplished by the Rayleigh method, that is, by the electromechanical excitation of unstable capillary waves on the surfaces of liquid jets issuing from capillary tubes, resulting in the breakup of the jets into uniform drops. This method allows the routine generation of droplets of 10-300 mu m radius at rates of up to 400000 droplets per second per capillary. The particles obtained from the evaporation of the drops are spherically shaped polycrystalline structures of the solute material. The sizes of the particles correspond to the initial concentration of solute in the solution droplets, implying nearly complete evaporation of the solvent constituent. A theoretical explanation is made of the evaporation process and the subsequent solute recovery.

A general theoretical analysis of the behavior of a conducting liquid drop in an electric field is presented. Numerical results are given for the quiescent distortion, resonant frequencies, and normal modes of oscillation of the drop as functions of applied field strength.