The dynamics of space charge neutralization at the front of an intense self-focused electron beam pulse exhibits important differences in different gas pressure regimes. At very low pressures, the beam front is in the so-called ion-focused regime (IFR) where all secondary electrons are expelled from the beam region by the radial electric field without causing significant additional ionization. We estimate the upper pressure boundary of this regime by considering the distance scale length for cascade (avalanche) ionization. Data from the FX-25 diode experiments indicate a critical transition pressure (P/sub c/) that agrees with this estimate and with its scaling among various gas types. Normal mobility-limited treatments (local conductivity models) of the secondary electrons at the beam front are not justified until the gas pressure is 10 to 50 times higher than P/sub c/, due to runaway of these secondary electrons in the strong space-charge electric field at the lower pressures. The main conclusion of this study is that a non-local phase space (Boltzmann) treatment of the secondary electrons is required to accurately describe these different beam front regimes and the transitions between them; such a code model is currently under development.

A new system of detectors (MPS II) which has been installed and operated in the Brookhaven National Laboratory Multiparticle Spectrometer (MPS), consisting of short drift distance drift chambers is briefly described. (WHK)

It is concluded that the dynamic range of a streak tube does not depend on whether it uses a fine-mesh or an open structure to provide the extraction field. An RCA C-73435 streak tube body was fitted with two extraction grid structures by replacing the conventional open grid with a steel plate containing two apertures. One aperture simulated the open grid structure; the other was a 2 x 20 mm slit covered with a fine mesh (40 wires per mm, 38% transmissive). The apertures were equal distances above and below the tube axis. Using 35-ps pulses, dynamic range curves were taken at 1.06 ..mu..m on one aperture at a time, while blocking the other aperture. As we anticipated, the tube saturated at nearly the same point for the open and mesh apertures. The noise levels for both apertures were almost equal and very close to the film fog level. Noise level was lower than for earlier measurements on other makes of tubes with a fine-mesh grid. The dynamic range for both apertures was in the order of 6000, which indicates that the lower dynamic range of other tubes must be due to something other than the use of a fine-mesh …

This report documents the technical evaluation of the proposed design modifications and Technical Specification change for protection of Class 1E equipment from grid voltage degradation for the Millstone Nuclear Power Station, Unit 1. The review criteria are based on several IEEE standards and the Code of Federal Regulations. The evaluation finds that the licensee has not provided sufficient information on the undervoltage protection system to allow a complete evaluation into the adequacy of protecting the Class 1E equipment from sustained voltage degradation.

Document issued by the Office of the Attorney General of Texas in Austin, Texas, providing an interpretation of Texas law. It provides the opinion of the Texas Attorney General, Mark White, regarding a legal question submitted for clarification; Construction of Article 3930(c), V.T.C.S.