Compact Electron Gun Based on Secondary Emission Through Ionic Bombardment
We present a new compact electron gun based on the secondary emission through ionic bombardment principle. The driving parameters to develop such a gun are to obtain a quite small electron gun for an in-flight instrument performing Electron Beam Fluorescence measurements (EBF) on board of a reentry vehicle in the upper atmosphere. These measurements are useful to characterize the gas flow around the vehicle in terms of gas chemical composition, temperatures and velocity of the flow which usually presents thermo-chemical non-equilibrium. Such an instrument can also be employed to characterize the upper atmosphere if placed on another carrier like a balloon. In ground facilities, it appears as a more practical tool to characterize flows in wind tunnel studies or as an alternative to complex electron guns in industrial processes requiring an electron beam. We describe in this paper the gun which has been developed as well as its different features which have been characterized in the laboratory.
Design & Simulation of High Energy Thermionic Electron Beam Gun Accelerators Applications
. Introduction Emission current density and emittance of beam are the charcteristics parameters that determine quality of the source in use. igh emission current density is responsible for producing high eam current. Low emittance is very essential for minimum energy pread and loss of the beam particles, therefore, is a governing arameter for the emission current density in any electron gun 1]. Point source emitters usually serve as temperature limited (the perator controls the heater current with a knob until he gets the urrent he needs, or the hairpin burns out). The point source elecron beam guns provide intense heating and deep penetration to ery small area, which make them useful for welding of thick and hin as well as of dissimilar metals [2–4]. Such types of guns provide igh current density and low emittance [4] which makes them easible for the use in electron optical devices [5,6] and electron ccelerators [7]. Sabchevski et al. [2], reported the current denity and normalized emittance of 50 A/cm2 and 0.5 mm-mrad espectively at an acceleration potential of 25 kV. Jansky et al. 4], calculated current density of 50 A/cm2 and emittance around .5 mm-mrad at 50 kV of acceleration potential. These emission arameters were worked out by using the Whenelt electrode in the uns. ∗ Corresponding author at: Centre for High Energy Physics, University of the Punab, Lahore 54590, Pakistan. Tel.: +923335210952. E-mail address: muniqbal.chep@pu.edu.pk (M. Iqbal). ttp://dx.doi.org/10.1016/j.ijleo.2015.11.132 030-4026/© 2015 Elsevier GmbH. All rights reserved. In this work, we have simulated a hairpin source electron beam gun for maximum emission density and low emittance of the beam through optimization process using electromagnetic focusing and then compared the results with test of the assembly at 10 kV acceleration potential. We have also worked out the emission characteristics of the gun at 100 kV of acceleration potential. Simulations were performed using SLAC electron beam trajectory program (EGUN) [8]. EGUN computes electrons trajectories in electromagnetic fields including the space charge effects. Poisson’s equation is solved using finite difference method with appropriate boundary conditions (Neumann and Dirichilet boundaries). Electric fields are calculated by the differentiation of potential distribution. In first step, input file is made and boundary conditions are set up using the boundary definition program POLYGON that converts polygonal boundary input to the required form of mesh oriented input for EGN2W. It also reads and adds the input parameter list in NAMELIST format, including magnetic field data. There are several ways to add the magnetic field; we used coils input by defining the radius, current and position of the coils to include the magnetic field. EGN2W produces an output file; plot of electron beam trajectories and equipotential lines. Then in the post processing (CPLCOMP & PPPROF); the quality of the beam is analyzed by computing emission current density and emittance of the ensemble of particles [8–11]. 2. Gun design and description The gun shown in Fig. 1a and b has a thermionic hairpin cathode as an emitter. The emitter was fabricated from Tungsten wire 1906 G.u. Islam et al. / Optik 127 (2016) 1905–1908 Fig. 1. (a) 2-D side view and (b) 3-D view of the gun. o m o n t a e T a t f a M a 3
Optical rotatory dispersion and absolute configuration—III
Abstract Optical rotatory dispersion measurements on pyrrolidine, piperidine, and tetrahydro-isoquinoline alkaloids indicate that the absolute configuration of the α-asymmetric center may be assigned directly from the dispersion curve, provided either that the nitrogen atom is not protonated, or that the compound contains a chromophore absorbing above 200 mμ.