Suppressor Grid Research Articles

Cylindrical hot cathode ionisation gauge – The concept and simulations

A novel design of an ionisation vacuum gauge is presented, aiming to achieve predictable sensitivity and high accuracy in high and the ultra-high vacuum range. The proposed design features a belt-like electron beam emitted from a linear filament, following a circular trajectory between two cylindrical electrodes, resembling a cylindrical analyser. The proposed design offers several key upsides: a precisely defined electron beam trajectory with reduced susceptibility to path variations, effective electron collection in a Faraday cup able to contain secondary emissions and backscattered electrons, and the inclusion of a suppressor grid in front of the ion collector to eliminate ion-induced secondary electron emission. These features are expected to secure high stability of the gauge and the low pressure limit. An in-depth description of the design is presented, along with the discussions on simulations of the key components that provide the improved performance.

Analysis of the Effect of Beam Divergence Angle on Back-Streaming Electron Region in Ion Source for EAST-Neutral Beam Injection

During the process of beam extraction in positive ion source under high voltage region, a large number of electrons are produced in the gaps of grids. After back-streaming acceleration, these electrons go back to arc chamber or impinge grids and then heat back plate or grids, which are harmful for the safety of ion source. Under the situation of poor beam extraction optics, a large part of the primary beam ions bombard the surface of suppressor grid (SG). And this process produces a large number of electrons. Due to the huge extracted voltage, the secondary electron emission coefficient of the SG surface is also high. As a result, the grids' current grows. According to the measurement of the current of SG and the calculation of the perveance of the corresponding shoot, the effect of ion beam divergence angle on back-streaming electrons can be analyzed. When the beam divergence angle increases, the number of back-streaming electrons increases rapidly, and grids' current changes significantly, especially the current of gradient grid and SG. The results can guide the parameters operating on the ion source for Experimental Advanced Superconducting Tokamak-neutral beam injection (EAST-NBI) and find the reasonable operation interval of perveance and to ensure the safety and stable running of the ion source, which has great significance on the development of long pulse, high power ion source.

Characteristics of low-energy intense ion beam formation and transport

MEVVA-ion sources with a modified three-electrode ion optical system for the formation of wide aperture low-energy (100–400 V) ion beams were used to produce ion beams of different elements with a current up to 40 mA and energy up to 400 V. The peculiarities of such beam formation and transport by a wide-aperture plasma lens (PL) are investigated. Beam transport in the transport channel is shown to be improved by the PL. PL operation in the magnetic regime shows that the suppressor grid secondary electron emission beam accompanying the ion beam has a current of 30% of the total ion beam current. These electrons contribute to the charge-compensation plasma medium in the beam transport channel and in the PL. The main contribution to the compensating secondary electron production (60%–70%) is due to the ion beam but experimentally observed values of the beam floating potential appear high enough (25–50 V), and this does not exclude an influence of dynamical decompensation.

Direct Energy Recovery from Helium Ion Beams by a Beam Direct Converter with Secondary Electron Suppressors

A 5-yr study of beam direct energy conversion was performed at the Kyoto University Institute of Atomic Energy to clarify the essential features of direct energy recovery from monoenergetic ion beams so that the performance characteristics of energy recovery can be predicted reasonably well by numerical calculations. The study used an improved version of an electrostatically electron-suppressed beam direct converter originally proposed by Lawrence Livermore National Laboratory. Secondary electron suppressor grids were added, and a helium ion beam was used with typical parameters of 15.4 keV, 90 mA, and 100 ms.By adopting negatively biased secondary electron suppressor grids, the energy recovery efficiency increased from 72 ± 4 to 87 ± 6% even at relatively high pressures of 10−2 Pa, based on three independent measurements of the incident ion current, including a newly developed “in situ” measurement by a Rogowski coil sensor. The operational region could also be extended to more high-pressure regions.A comparison of experimental results with numerical results by the two-dimensional Kyoto University Advanced DART (KUAD) code, including evaluation of atomic processes, shows excellent agreement. Adoption of the mesh-type electron suppressor instead of the solid suppressor results in further improvements in the beam direct energy recovery.

Energy distributions of oxygen and argon ions generated in a special glow-discharge source

The energy distributions of ions generated in a special glow-discharge source were measured by the suppressor grids method and calculated according to the Davis model. The suppressor grids method was used in order to eliminate the influence of ion beam divergence on the distribution shape. Space potential distribution, necessary in the Davis model, was determined with an electrostatic probe. The theoretical and experimental ion distributions obtained were very similar and closer than those of corresponding distributions described in a previous report [Z Wroński, Vacuum, 36, 329 (1986)], where distributions were measured by mass spectrometry.

Simple spot photometer for LEED intensity measurements

Abstract

Geometrically focused neutral beam accelerators

A more reliable 40 kV, 65 A power supply drain at 0.4 A/cm2, neutral-beam accelerator was developed for the Tandem Mirror Experiment (TMX). Multiple slotted aperture grids of 60% transparency are fabricated from refractory metal wires mounted to form a spherical surface. This geometrically focuses the beam by aiming individual beamlets at the center of curvature of the spherical grid (r = 3.2 m). We attain greater reliability and faster conditioning with geometrical focusing than with the previous technique of electrostatically steering beamlets to a common point. Electrostatic steering, accomplished by offsetting grid wires, is satisfactory if the offset of a beamlet is much less than the distance from the beamlet to the grids. It was found that Pierce Angle entrance grids performed better if sharper edged. A redesigned accelerator grid support structure reduced the number of ceramic-to-metal vacuum joints, and eliminated O rings between precisely aligned parts. The suppressor grid feedthrough is required to withstand a maximum voltage of 15 kV occurring during breakdown, greatly exceeding the operating voltage of 1.5 kV. Convenient fabrication and assembly techniques have been developed. Assembly of accelerators and plasma sources in a clean room appears to reduce the conditioning time. Following the successful testing of the prototype, eight 40 kV accelerators were built for TMX. Furthermore, ten 20 kV versions were built that are modifiable to 40 kV by exchanging the entrance grid.

Design study of a 120-keV,3He neutral beam injector

We describe a design for a 120-keV, 2.3-MW,3He neutral beam injector for use on a D-3He fusion reactor. The constraint that limits operating life when injecting He is its high sputtering rate. The sputtering is partly controlled by using an extra grid to prevent ion flow from the neutralizer duct to the electron suppressor grid, but a tradeoff between beam current and operating life is still required. Hollow grid wires functioning as mercury heat pipes cool the grid and enable steady state operation. Voltage holding and radiation effects on the acceleration grid structure are discussed. We also briefly describe the vacuum system and analyze use of a direct energy converter to recapture energy from unneutralized ions exiting the neutralizer. Of crucial importance to the technical feasibility of the3He-burning reactor are the injector efficiency and cost; these are 53% and $5.5 million, respectively, when power supplies are included.

Effect of RPA transparency dependence on ion masses upon ion temperature and density determination with direct space measurements

The impact on the total transparency of field inhomogeneity around the grid wires of a plane retarding potential analyser (RPA) is taken into consideration at normal incidence of the ion flux. The RPA transparency is determined mainly by the suppressor grid's geometry and attractive potential and not so much by the analysing grid's repulsive potential. Whereas in a floating potential regime the suppressor grid transparency differs for different ion species, in a retarding ion regime it is the same for all. However, at all swept voltage values of the analysing grid the total RPA transparency remains dependent on the ion masses and the grid potentials.

Experimental study of ion beamlet steering by aperture displacement in two-stage accelerator

The steering of ion beamlets in a two-stage accelerator has been measured as functions of both aperture displacement and field intensity ratio between extraction and acceleration regions. Three different types of displacement have been investigated; i.e., displacement of (1) plasma grid, (2) gradient grid, or (3) suppressor grid with respect to the other three grids. In each case, the steering angle is found to be linear with the aperture displacement, and independent of final beam energy and beam current. The variation of steering angle with displacement distance is compared with the value predicted by linear theory using thin lens approximation. It is confirmed that they agree well in the case of (3), while they show appreciable differences in the cases of (1) and (2). This is because the lens effect of the gradient grid is weaker than is predicted by the linear theory. The deterioration of beam optics due to steering has not been observed.

Study of Low Pressure Application of the Orbitron Ion Gauge

Three experimental orbitron gauges have been fabricated: a standard split cathode design, a reduced area cathode (ion collector) design, and a suppressor grid (three concentric electrodes) design. The low pressure response characteristics and operating parameters of each gauge are discussed. Each gauge has displayed a linear ion-current-to-pressure response.

A CS 2 Lyman-alpha photon counter

A high counting rate Lyman-alpha photon proportional counter with a sensitivity of 20–25% is described which uses a photo-electron suppressor grid. The filling gas is CS 2.

A General Equation for the Suppressor Controlled Transconductance of a Pentode

ABSTRACT The pentode valve is a well-known vacuum tube device which has wide applications. In some of the applications the suppressor grid of a pentode, instead of being connected to the cathode, is given a negative bias. Under these conditions the transconductance of the pentode becomes a function of both suppressor and control grid voltages. A general equation For this transconductance is obtained which is useful for analysis of circuits employing this configuration.

A novel approach to a low cost, high-gain television intermediate frequency amplifier

A new tube, consisting of a dual control and a sharp cut-off pentode in the same envelope has been developed. Development of the tube, the Y-1187, makes possible a one-tube, two-stage, IF amplifier that attains the same performance level as most three-stage IF amplifiers that are used in black and white television receivers at considerably less cost. The input section of the Y-1187 is similar to the 6GK7, while the output section is similar to the 6DK6. The problem of interelectrode capacitances that results from placing two such high performance tubes in the same envelope is minimized by applying special shielding techniques within the tube. Experimental results indicate that the Y-1187 when operated as a two-stage IF amplifier, yields excellent gain, response, and AGC characteristics. Some of the primary features of the tube are: 1. Low-cost construction. 2. High-transconductance and low-capacitanee in each section 3. AGC applied to suppressor grid of the input section, which allows control grid bias to remain reasonably constant. 4. Additional gain obtained by the elimination of the need for unbypassed cathode resistors, and by the use of a quadrature-boost circuit. 5. Circuit costs and space requirements reduced by the elimination of one tube socket and a portion of the associated circuitry and circuit components. The writers wish to acknowledge the assistance of W.F. Cullen of the Tube Department, and W.P. Kimker, formerly of the Tube Department, without whom this paper could not have been prepared.

Novel tube and circuit designs for automatic gain controlled broad band intermediate frequency amplifiers

A special pentode tube for broad band intermediate frequency amplifier application is designed with the purpose of eliminating cathode degeneration while maintaining the capability to control the gain. The amplification of the stage is further increased by utilizing the space charge coupling between the plate current and suppressor grid. The circuits are developed to move the poles of the amplifier and vary the bandwidth in a predetermined manner. The new tube, which can be used either as a sharp cut off or remote cut off pentode, is completely free of run away effects due to gas or grid emission, and because of its inherent characteristics, the clipping of the modulation from the signal cannot occur. As a result of this development, it is now possible to eliminate one of the three stages of video intermediate frequency amplifiers presently used in black and white television sets without loss of performance.

A STUDY ON THE MEASUREMENT OF ELECTROSTATIC CHARGE IN THE TEXTILE INDUSTRY

The circular condenser which contains variable electric resisting plates made of dielectric matter, having large enough electric capacity, is inserted between the cathode and suppressor grid in an electron tube and a stable circuit is equipped, having one edge of an interpole connected to the edge of the suppressor grid and another edge suffering the action of electric field of change body, thereupon some displacement current is made to cause by transition-phenomena at the electrostatic influence period, and the electron tube is given some minus power which is not relative to the plus or the minus of the charge body but is in proportion to its quantity. Thus investigation is aimed to make it clear that the relation between the quantities of electricity and the electric denisity of the field which will vary with time by the strength of plate current.

An all-electric clock

The synchronous motor usually employed for obtaining seconds' intervals from a 1 kc./sec. source controlled by a high-frequency crystal oscillator is replaced by three multi-vibrators whose controlled periods are 10, 100, and 1000 times that of the source respectively. On account of the extremely sharp rise of current in the multivibrator circuits, the intervals provided by the seconds multi-vibrator are equal to within 10 micro-seconds. Each multi-vibrator consists of a single triode-pentode valve, injection from one stage to the next being effected on the suppressor grid of the pentode section, a method of injection which has proved superior to anode-circuit or grid-circuit injection. A check that the multi-vibrators are in step is obtained by using their outputs to charge a condenser through the coils of a cathode-ray oscillograph whose time base is synchronized by the 1 kc./sec. input.

A Power Amplifier for Ultra-High Frequencies*

A consideration of the special problems encountered at ultra-high frequencies has led to the design of a push-pull power pentode, useful as an amplifier, frequency multiplier, and modulator at frequencies of 300 megacycles per second and below. Unusual construction features include the mounting of two pentodes in the same envelope with interconnected screen and suppressor grids, complete shielding between the input and output circuits with no common leads, and provision for cooling all grids while maintaining extremely small inter-electrode spacings. The electrical characteristics depart from the conventional mainly in the low value of lead inductances and the high value of the grid input resistance at ultra-high frequencies. The second part of the paper describes a single stage amplifier unit built for testing the tube at frequencies between eighty and 300 megacycles, and the associated apparatus for measuring input impedance, gain, and harmonic distortion. The results given indicate that by using this new tube it is possible to construct stable amplifiers at ultra-high frequencies up to 300 megacycles, having gains of twelve to twenty-five decibels per stage and delivering several watts of useful power. Stability and distortion compare favorably with those obtained from conventional tubes at much lower frequencies.

A Power Amplifier for Ultra-High Frequencies

A consideration of the special problems encountered at ultra-high frequencies has led to the design of a push-pull power pentode, useful as an amplifier, frequency multiplier, and modulator at frequencies of 300 megacycles per second and below. Unusual construction features include the mounting of two pentodes in the same envelope with interconnected screen and suppressor grids, complete shielding between the input and output circuits with no common leads, and provision for cooling all grids while maintaining extremely small interelectrode spacings. The electrical characteristics depart from the conventional mainly in the low value of lead inductances and the high value of the grid input resistance at ultra-high frequencies. The second part of the paper describes a single stage amplifier unit built for testing the tube at frequencies between eighty and 300 megacycles, and the associated apparatus for measuring input impedance, gain, and harmonic distortion. The results given indicate that by using this new tube it is possible to construct stable amplifiers at ultra-high frequencies up to 300 megacycles, having gains of twelve to twenty-five decibels per stage and delivering several watts of useful power. Stability and distortion compare favorably with those obtained from conventional tubes at much lower frequencies.

Recent Trends in Receiving Tube Design

This paper gives a brief summary of the important steps in receiving tube design over the past ten years. The significance of new forms of grids and in particular the suppressor grid are discussed. Characteristics of new radio-frequency tubes containing suppressor grids are shown. Improvements in cathode and grid designs are illustrated by the characteristics of a new triode as well as two triple-grid tubes. A new tube for class B audio amplification is described together with a mercury vapor rectifier for supplying power to the class B amplifier.