Secondary Emission Multiplier Research Articles

Моделирование процессов электронного усиления в каналах умножителей на пористых структурах оксида алюминия

The secondary-emission multiplier of spatial-distributed flows of electrons – microchannel membrane – determines along with the photocathode, luminescent screen, electron-optical system determines the amplifying characteristics of the electron-optical transformers, photoelectronic multipliers. This, in its turn, determines the application areas and the operating range of the items. The actual task is an improvement of the microchannel membrane parameters and the search for new approaches to manufacture on alternative materials of the secondary-emission multipliers. In the paper the use of self-organizing high-ordered porous anode structures of aluminum oxide as the secondary-electronic emitters have been considered. The theoretical and practical approaches to development and the implementation of the computer models of processes of multiplying electrons in the channel of the based on aluminum oxide, have been offered. Based on the results of the calculations, performed using this model, the amplifying ability of such channels has been determined, their optimal caliber is 25, and the supply voltage is 300 V. A comparative analysis of these characteristics of secondary electron multipliers with corresponding parameters of microchannel plates based on lead silicate glass has been performed. It has been determined that that porous anodized alumina may be suitable for the manufacture of secondary electron multipliers. Its secondary emission ability is comparable to lead silicate glass.

Segmentoid Electrostatic Analyzers for Detection of Low-Energy Charged Particles

A new type of electrostatic analyzer for the detection of low-energy charged particles (denoted as a segmentoid analyzer) was developed. The field strength between the plates of the analyzer was determined. A small-size spectrometric unit was developed on the basis of the segmentoid analyzer and the ВЭУ-7 secondary-emission multiplier (particle detector). The main characteristics (energogeometric coefficient and angular and energy transmission curves) of the spectrometric unit were considered. The calculated value of the energogeometric coefficient agrees well with the experimental value obtained during calibration.

High quality flux control system for electron gun evaporation

A high-quality flux control system for electron gun evaporation has been developed and tested for the MBE (molecular beam epitaxy) growth of high-temperature superconductors. The system can be applied to any electron gun without altering the gun itself. Essential elements of the system are a high-bandwidth mass spectrometer, control electronics, and a high-voltage modulator to sweep the electron beam over the melt at high frequencies. The sweep amplitude of the electron beam is used to control the evaporation flux at high frequencies. The feedback loop of the system has a bandwidth of over 100 Hz, which makes it possible to grow superlattices and layered structures in a fast and precisely controlled manner. The drift of the total system is dominated by the temperature drift of the secondary emission multiplier in the mass spectrometer. This drift is typically 1-2%/h for copper as measured by an independent quartz-crystal thickness monitor. The system has been successfully tested with evaporation rates of 0.001 to 1 nm/s for various materials and under ozone and oxygen pressures up to 10/sup -4/ mbar. The feedback system has successfully been used for the fabrication of YBa/sub 2/Cu/sub 3/O/sub 7/ thin films.

Measurements of noise in image orthicons

Current fluctuations in the primary readout beam and fluctuations introduced by the secondary emission multiplier of several 5820 image orthicons were measured. The noise in the photocurrent leaving the photocathode was measured and found to be full shot noise. It was found that the primary beam noise is not suppressed by space charge but shows full shot noise. It was reconfirmed that the only dynode in the secondary multiplier chain contributing significantly to the noise at the multiplier output was the first.

Untersuchung der Feldelektronenemission und ihrer Temperaturabh�ngigkeit bei Stromst�rken zwischen 10?14 und 10?19 A

The field emission of a tungsten point cathode at very low emission currents was investigated by means of a secondary emission multiplier. The validity of the Fowler-Nordheim equation was experimentally confirmed within the range from 10−8 to 10−19 A. The dependence of the total emission current on temperature and electrical field strength was measured in the transition region between thermionic and field emission. A comparison is drawn with the theory ofMurphy andGood.

An Infrared Pickup Tube

The infra-red (IR) pickup tube contains a sensitive target surface in the form of a thin layer of the photoconductor on a transparent window forming one end of the tube. The photoconductor emnployed must have a very high resistance when the material is in darkness. At the other end of the tube, there is an electron gun producing a low velocity beam of electrons. Electrons returning from the target enter a secondary emission multiplier which is coaxial with the gun, and the greatly amplified return current is supplied to the signal lead. The electron beam is focused by an axial magnetic field and deflected by a system of orthogonal deflecting coils producing fields at right angles to the motion of the beam. The operation of this type of pickup tube is discussed in detail.

Design of Photomultipliers for the Sub-Millimicrosecond Region

In considering the design of a photomultiplier with good time resolution characteristics, it is convenient to divide the problem into two parts, one dealing with the photocathode-to-first dynode region, the other with the secondary emission multiplier structure. The two principal causes of poor time resolution in both of these parts are: 1) the different path lengths of electrons originating from separated points on a second, and 2) the effect of initial velocities of the emitted electrons on transit times. The electron optical approach to the alleviation of the transit time spread due to path differences is discussed for both the cathode region and the structure. The focusing spiral method of analyzing the performance of a structure is of considerable value. The effects of initial velocities can be reduced by ensuring that the electron velocities within the photomultiplier are very high. It is not practical to obtain these high velocities simply by applying a high over-all voltage to the tube because of the loss of secondary emission gain and because of internal and external insulation difficulties. However, the necessary high velocities can be obtained by the use of high voltage field electrodes between successive dynodes, so arranged that electrons are rapidly accelerated to a high velocity and then decelerated before they reach the next dynode. A photomultiplier is described whose design is based upon these two principles. A high voltage central electrode system between successive dynodes serves to give electrons the high velocity required to minimize transit time spread.

Stable Secondary Emission Multiplier with Brass Dynodes for Beam Current Measurements

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A new secondary cathode

One of the main difficulties in the use of secondary-emission multiplier stages in thermionic valves is the instability of the secondary cathode, which is usually characterized by a gradually decreasing secondary-emission ratio during its useful life. In this paper, experiments are described showing that this instability is due to the bombardment of the secondary cathode by the primary electron beam, and it is shown that this bombardment causes disintegration of the surface layer. A new type of secondary cathode, formed from a mixture of magnesium oxide and barium carbonate, has been found to have a stable life of over 1 000 hours, when operating at 400° C and with a primary bombarding current density of 20 mA/cm2. The use of this secondary cathode has made possible the development of a single-stage thermionic electron-multiplier valve, with a mutual conductance of 20 mA/volt.

The Orbital-Beam Secondary-Electron Multiplier for Ultra-High-Frequency Amplification

A developmental ultra-high-frequency receiving tube in which secondary-emission electron multiplication has been applied to a conventional high-transconductance tube structure to increase the transconductance without a corresponding increase in interelectrode capacitances and input conductance is described. It was designed primarily for wide-band amplification at a frequency of approximately 500 megacycles, as required for television radio relay systems. The tube uses conventional circuits and requires a power supply of less than 400 volts. The structure adopted permits the most efficient use of the secondary-emission multiplier consistent with satisfactory life and good high-frequency performance. The structure also permits the use of beam deflection to provide a convenient gain-control method, free from the input capacitance and conductance variations attending the usual gridbias control. A novel method of measuring interstage gain, involving the use of transmission lines, is discussed.

The Secondary Emission Multiplier-A New Electronic Device

This paper describes the construction, theory, and performance of various types of fixed field secondary emission multipliers. Detailed consideration is given of multiplier phototubes employing crossed electrostatic and magnetic fields and of electron multipliers using electrostatic focusing alone, to serve as coupling and amplifying units for cathode-ray tubes such as the Iconoscope. It is shown that while the power required for the operation of the secondary emission multiplier is about the same as that for the conventional amplifier, it is superior to the latter from the standpoint of noise. In the case of the multiplier phototube the signal-to-noise ratio is essentially determined by the shot of the photoemission, and is therefore sixty to one hundred times greater than that for a thermionic amplifier and phototube under conditions of low light intensity. Multiplier phctotubes have been built with an amplification factor of several millions and serve to replace the conventional phototube and accompanying amplifier system. Their low noise level, together with their excellent frequency response and extreme simplicity, make these electron multipliers a very satisfactory form of amplifier.