摘要:

Two-exposure holographic interferometry has been employed to obtain the first quantitative measurements of the plasma densities in an intense electron beam diode. Several diode configurations which produce an intense pinch of the electron beam at the anode plane have been investigated. Holograms indicating the temporal and spatial evolution of the plasmas in these diodes are presented. Two types of plasmas are observed in these diodes: a lower density plasma( 1018/cm3)with a velocity of about 2 cm/μsec. Preliminary analysis indicates that the lower density plasma plays a dominant role in determining the primary beam dynamics.

ISSN:0022-5355    

DOI:10.1116/1.1318523

出版商:American Vacuum Society    

年代:1973

数据来源: AIP

摘要:

Program DISIC, a new diode simulation code, has been developed to study the behavior of high ν/γ diodes. The code is based on a two-dimensional finite-size particle simulation model, and is designed to provide good resolution of small anode-cathode gaps. Results are shown which (i) compare with earlier calculations, (ii) compute electron trajectories in strongly self-pinched diodes, and (iii) compute electron trajectories for a diode having a conical cross section.

ISSN:0022-5355    

DOI:10.1116/1.1318524

出版商:American Vacuum Society    

年代:1973

数据来源: AIP

摘要:

Intense electron beams are of increasing interest in controlled fusion research. Such beams exhibit several phenomena which suggest strong coupling between the beam and the background plasma via beam-generated electromagnetic fields. Observations of beam compressibility and distortion in inhomogeneous fields are reported.

ISSN:0022-5355    

DOI:10.1116/1.1318525

出版商:American Vacuum Society    

年代:1973

数据来源: AIP

摘要:

The Gamble I pulsed electron beam generator at NRL recently has undergone several major modifications. The modified generator has a nominal output into a matched 1.5-Ω load of 500 kA at 750 keV, with an 70-nsec (FWHM) pulse length and a 20-nsec (10%–90%) voltage risetime. The distinguishing characteristics of low prepulse (<1%) and high reproducibility in output voltage and current (± 3%) result primarily from conversion from operation with self-breakdown water switches to operation with triggered high-pressure gas switches. Fast pulse risetime was maintained by using a low-inductance multichannel triggered output switch in conjunction with a new low-inductance vacuum diode with a radial insulator.

ISSN:0022-5355    

DOI:10.1116/1.1318526

出版商:American Vacuum Society    

年代:1973

数据来源: AIP

摘要:

We have modified the design of our commercial “Electrocurtain” electron-beam accelerators to provide for pulsed, medium current-density beams(10–30 mA/cm2)with a total output beam-area in the range of1000–1500 cm2. Two different approaches to the design of such systems are presented. In the first approach, a cylindrically symmetric geometry is employed, with the cathode extending along the symmetry axis (typically 1-m long). Beam expansion to the desired output area is dominated by the electric fields in the coaxial accelerating gap. For the second approach, several short cathodes span the short dimension of the output window and are evenly spaced along the long dimension of the window. Beam expansion is achieved in a field-free region. In both cases, the beam current is provided by cylindrically divergent Pierce-type diodes fitted with barium-dispenser cathodes. This design allows for grid control of the output current independent of the main accelerating voltage. Computer simulations of the beam flow will be discussed.

ISSN:0022-5355    

DOI:10.1116/1.1318527

出版商:American Vacuum Society    

年代:1973

数据来源: AIP

摘要:

A family of electron accelerators is described which derives its relatively small dimensions from the dielectric strength advantages of a pulsed voltage mode and from advanced concepts of electron beam transport.

ISSN:0022-5355    

DOI:10.1116/1.1318528

出版商:American Vacuum Society    

年代:1973

数据来源: AIP

摘要:

The optimization of the performance of a high-brightness electron gun requires the correct choice of material, andLaB6has been shown to have advantages over pure metal emitters. The finely pointed tip must be accurately positioned in the grid aperture to achieve maximum brightness and the electrode positions must be maintained if the benefits of improved stability are to be realized. The brightness is measured using two apertures to define the beam and a Faraday cage to collect the current. The increased brightness is confirmed by the improved performance of the scanning electron microscope. However emission peaks have been detected under certain conditions of operation and appear to depend strongly on the position of the tip with respect to the Wehnelt. The design of this electrode has been considerably modified to a conical shape to try and achieve high brightness while suppressing some of the emission peaks. For a range of gun geometries and electrode potentials, the potential distribution near the tip and Wehnelt aperture has been computed using the finite element method. This computes the potential at points on a two-dimensional mesh, whose shape can be varied at will, which permits analysis of complex electrode configurations. Very small tip radii can be allowed for with an accurate determination of the tip field. From the tip field the electron trajectory can be computed using a “model” field near the tip and solving the paraxial ray equation from there onwards. It is observed that under certain conditions of operation a virtual crossover is obtained with pointed tip electron guns. The conditions under which Schottky enhanced emission may be present are also obtained and the emitting area of the cathode can be estimated.

ISSN:0022-5355    

DOI:10.1116/1.1318529

出版商:American Vacuum Society    

年代:1973

数据来源: AIP

摘要:

For field-emitter tip currents in the range of 100 μA, field-emission guns can compete favorably with thermionicLaB6guns for microfabrication with 2000 Å working beam diameters. The stable operation of tip currents between 10 and 1000 μA, for periods totalling hundreds of hours, requires an understanding of the steady-state and transient adsorbed gas layer on the emitter surface. This has been accomplished in a simple gun-lens. Furthermore, Boersch effect energy broadening appears to be significantly operative at emission intensities on the order of10−2 A/sr. The staircase-like current fluctuations indicate quantum events on the emitter surface. In fact, intense emission lobes have been spatially separated by spherical aberration in a large aperture configuration.

ISSN:0022-5355    

DOI:10.1116/1.1318530

出版商:American Vacuum Society    

年代:1973

数据来源: AIP

摘要:

A new high-resolution electron probe has been built for scanning microscopy studies. The probe has a final lens with a focal length of 0.8 mm, a spherical aberration coefficient; of 0.4 mm, and a chromatic aberration coefficient of 0.5 mm. A lanthanum hexaboride cathode is employed with a maximum brightness of1.5×107 A/cm2 srat 75 kV. The cathode operates satisfactorily at a pressure of10−6 mm Hg. The theoretical minimum beam size for the instrument is 5 Å. Transmission scanning electron micrographs with a beam current of1×10−12–3×1012A indicates that close to this value is obtained in practice.

ISSN:0022-5355    

DOI:10.1116/1.1318531

出版商:American Vacuum Society    

年代:1973

数据来源: AIP

摘要:

The scanned field performance of probe forming systems has been investigated leading to various methods for increasing the current that may be delivered into an electron probe scanning a square field of104lines. Programs for evaluating the third-order aberrations of both lenses and single and double deflection systems have been developed. These have been used to evaluate the performance of a typical pre-lens double deflection probe forming system. It is shown that it is possible to produce much better performance using post-lens deflection coils. Distortion, field curvature and astigmatism can be eliminated, using suitable electronics for dynamic correction, and the remaining third-order aberrations may be reduced by careful design of the deflection coils.

ISSN:0022-5355    

DOI:10.1116/1.1318532

出版商:American Vacuum Society    

年代:1973

数据来源: AIP