The role of multielectrode geometry in the generation of pulsedintense electron beams in preionization-controlled open-endedhollow-cathode transient discharges

High-voltage hollow-cathode glow discharges are used more and more to generate intense, pulsed electron beams. Such intense electron beams can be produced with high efficiency in preionization-controlled open-ended hollow-cathode transient discharges (PCOHC). This novel discharge is initiated by a low-current dc preionization discharge. The beam parameters are similar to those of the electron beam generated in pseudospark discharges. In this work, we present some measurements of the parameters for the electron beam generated by using a multielectrode (multigap) system instead of the single-gap device in this PCOHC configuration. This kind of multielectrode device was already used in pseudosparks to improve the intensity and collimation of the extracted beam. By using the multigap instead of the single gap, the total beam current (100-120 A) and the energetic part of the beam current (peak current 60-90 A and electron energies higher than approximately 3 keV) were substantially increased. However, the energy spectrum of the fast component has a large fraction of electrons at lower energies (4-10 keV for 26 kV breakdown voltage) when a multigap device is used instead of the single-gap configuration. A comparison between the single-gap and multigap PCOHC-produced pulsed intense electron beam is made too. The differences between the high-power pulsed electron beams produced in single-gap and multigap PCOHC configurations seem to be due to different developments of beam generation phases     

Pulsed intense electron beams generated in transient hollow cathodedischarges: fundamentals and applications

For the commercial application of pulsed power, material processing with intense pulsed particle beams is a very interesting subject. Recently, high-voltage (1-70 kV), low-pressure (1-100 Pa) transient hollow-cathode discharges turned out to be sources for pulsed intense electron beam generation suitable for this application. The remarkable parameters of these electron beams-beam currents of 50-1000 A (10-30% of the maximum discharge current) with a high energy component (mean energy of about 0.25-0.75 of maximum applied voltage) of 20-70% of the maximum beam current, power density up to 10 W/cm², beam diameters of 0.1-3 mm, beam charge efficiency of 3-5%-captured the attention not only of the scientific community in the last decade. The electron beam is emitted during the early phases of the discharge, and only weak dependence of the high energetic peak of the beam current was found on the external capacity, which determine the development of the later high-current phases. However, the beam parameters depend on the breakdown voltage, gas pressure, and discharge geometry (including self-capacity). In this paper, the characteristics of the pulsed intense electron beams generated in two configurations-multigap pseudosparks and preionization-controlled open-ended hollow-cathode transient discharges (PCOHC)-are described. Such electron beams already were used successfully in a variety of pulsed power applications in material processing, deposition of superconducting (YBaCuO) and diamond-like thin films, microlithography, electron sources for accelerators, and intense point-like X-ray sources, and some preliminary experiments revealed new potential applications such as pumping of short-wavelength laser active media. These pulsed electron beams could be used further in any kind of pulsed power applications that require high-power density, small or high electron energy, and small-beam diameters     

How Fast can a Subharmonic Function Decay Along a Ray?

Much is known about the connection between the growth and decayof subharmonic functions. The results indicate that there isa general principle: asubharmonic function cannot decay ‘toofast’ relative to its growth.Three theorems are provedwhich, together with work previously published elsewhere, givea fairly complete account of how this principle works out fora subharmonic function having extremal decay along a ray. 1991Mathematics Subject Classification: 30D20, 31A05.     

DNA vaccine containing the mycobacterial hsp65 gene prevented insulitis in MLD-STZ diabetes

Background  

Our group previously demonstrated that a DNA plasmid encoding the mycobacterial 65-kDa heat shock protein (DNA-HSP65) displayed prophylactic and therapeutic effect in a mice model for tuberculosis. This protection was attributed to induction of a strong cellular immunity against HSP65. As specific immunity to HSP60 family has been detected in arthritis, multiple sclerosis and diabetes, the vaccination procedure with DNA-HSP65 could induce a cross-reactive immune response that could trigger or worsen these autoimmune diseases.     

Qualitative properties of modified equations

Suppose that a consistent one-step numerical method of orderr is applied to a smooth system of ordinary differential equations.Given any integer m 1, the method may be shown to be of orderr + m as an approximation to a certain modified equation. Ifthe method and the system have a particular qualitative propertythen it is important to determine whether the modified equationsinherit this property. In this article, a technique is introducedfor proving that the modified equations inherit qualitativeproperties from the method and the underlying system. The techniqueuses a straightforward contradiction argument applicable toarbitrary one-step methods and does not rely on the detailedstructure of associated power series expansions. Hence the conclusionsapply, but are not restricted, to the case of Runge-Kutte methods.The new approach unifies and extends results of this type thathave been derived by other means: results are presented forintegral preservation, reversibility, inheritance of fixed points.Hamiltonian problems and volume preservation. The techniquealso applies when the system has an integral that the methodpreserves not exactly, but to order greater than r. Finally,a negative result is obtained by considering a gradient systemand gradient numerical method possessing a global property thatis not shared by the associated modified equations.     

Analogy between unconventional superconductivity and unconventional states of liquid crystals

An analogy is stressed between the order-parameter symmetries of the two-dimensional d-pairing wave superconductors and of liquid-crystal mesophases formed from achiral bent-shaped molecules. It leads to a definition of a class of liquid-crystal states which are the analogs of the unconventional superconducting states, and are characterized by a loss of discrete symmetry operations of the parent state.