Showing papers on "Perveance published in 1982"

Ion beamlet vectoring by grid translation

Abstract: Ion beamlet vectoring is investigated by collecting deflection and divergence angle data for two-grid systems as a function of the relative displacement of these grids. Results show that at large displacements, accelerator grid impingement becomes a limiting factor and this determines the useful range of beamlet deflection. Beamlet deflection was shown to vary linearly with grid offset angle over this range. Values of deflection-to-offset angle ratio and useful range of deflection are presented as functions of grid-hole geometries, perveance levels, and accelerating voltages. It is found that the divergence of the beamlets is unaffected by deflection over the useful range of beamlet deflection. The grids of a typical dished-grid ion thruster are examined to determine where over the grid surface the grid offsets exceed the useful range, which indicates the regions on the surface where high accelerator grid impingment is probably occurring.

Ion extraction capabilities of closely spaced grids

Abstract: The ion extraction capabilities of accelerator systems with small screen hole diameters (less than 2.0 mm) are investigated at net-accelerating voltages of 100, 300, and 500 V. Results show that the impingement-limited perveance is not dramatically affected by reductions in screen hole diameter to 1.0 mm, but impingement-limited performance was found to be dependent on the grid separation distance, the discharge-to-total accelerating voltage ratio, and the net-to-total accelerating voltage ratio. Results obtained using small hole diameters and closely spaced grids indicate a new mode of grid operation where high current density operation can be achieved with a specified net acceleration voltage by operating the grids at a high rather than low net-to-total acceleration voltage. Beam current densities as high as 25 mA/sq cm were obtained using grids with 1.0 mm diameter holes operating at a net accelerating voltage of 500 V.

A study of cathode edge emission

Abstract: A great deal of experimental evidence shows that the perveance of high‐power klystrons is much higher than normal at low voltage. Thus the three‐halves power law is violated in that range. It is hypothesized that this is caused by edge emission. A detailed analysis is given. The calculated magnitude is reasonably coincident with experimental results. The analysis is also valid for other thermionic tubes.

Simulation of a klystron gun

Abstract: A two-dimensional, fully relativistic particle-in-cell code was used to present time-dependent and fully electromagnetic simulations of the operational characteristics of the XK-5 klystron gun used at the Stanford Linear Accelerator Center The beam current density and perveance were consistent with experimental and numerical results The beam current density exhibited time-dependent noise, but no significant electromagnetic gun oscillations were observed A particle-in-cell simulation of the full klystron, including all cavities, is feasible but expensive

Assembly method for electron gun

Abstract: PURPOSE:To economically obtain an electron gun whose change of perveance caused by the dimensional ununiformity in the assembly process is small by combining a cathode and a focussing electrode, then correcting the relative position between the cathode and an anode, and fixing the anode. CONSTITUTION:A cathode cylinder 1 is fixed to a focussing electrode 3 through a cathode support body 2 and a cathode frame is assembled. An anode support plate 11, cathode frame support body 6, heater electrode plate 7, electron gun support body 8, and vacuum enclosure ceramics 9a-9d are laminated alternately. Then a vacuum container 10 is assembled by brazing every part on their contact surface. Subsequently, L2 is determined by the L1 value measured when the cathode frame was assembled in such that the variation of perveance due to DELTAL1 which is a deviation of design value L1 is corrected in its characteristics and the support plate 11 of an anode 12 is fixed to the L2 position by welding. As a result, the dimensional ununiformity in the assembly process is absorbed by the post process and the change of perveance can be reduced.

Optimisation of low-perveance electron gun by experimental and numerical methods

Abstract: The paper presents a proposed method for improving the electron gun used for microscopes or similar electron beam devices. The electron gun has been divided into two zones: the high perveance cathode zone and the low perveance lens zone. The final virtual crossover of the gun is thus the image of the exit pupil of the cathode zone. This image is produced by the action of the lens zone. The basic assumption of this approach is that the electron brightness does not depend significantly on the lens zone electron-optical parameters. Based on this assumption the optimisation of the electrodes has been carried out. This has been done experimentally in the cathode zone and by means of numerical calculations in the lens zone. Results obtained for the scanning electron microscope gun are presented as an example of this approach.