Filament Cathode Research Articles

High-energy electron gun with gas amplification of the filament current

A high-energy electron beam is generated using gas-ionizing collisions to amplify a small cathode filament current. The technique makes use of a crossed magnetic and electric field to reduce the effective mean free path of electrons at the cathode. At a pressure of 5×10−5 Torr helium, for example, a filament current of 0.4 mA will produce a uniform beam of 100 mA. Accelerating voltages up to 100 kV are used.

Emissionless power cathode

The combination of a weak rf discharge and a plasma current multiplier constitutes an effective dc power cathode which operates without electron emission, elevated materials temperature, or wall bombardment, etc. Such power cathodes may find application wherever filament cathode operation poses difficulties, as with reactive gases, or where filament replacement is undesirable.

A demountable variable focus X-ray tube

A demountable variable focus X-ray tube is described which permits a wide range of operation in terms of X-ray source size and hence maximum continuous tube power. By altering the position of the filament, source sizes measured on the anode face ranging from 0.25 mm*8 mm to 10 mm*8 mm can easily be obtained. The maximum continuous tube power with the present system is 2.2 kW. The X-ray tube is completely demountable and all the components can be interchanged easily. Consequently a wide range of filament sizes and cathode structures can be used with the one system.

Method of determining the reliability of a directly-heated cathode or heating filament of an electronic valve

Method of determining the reliability of a directly-heated cathode or heating filament of an electronic valve

494. Method of determining the reliability of a directly-heated cathode or heating filament of an electronic valve

494. Method of determining the reliability of a directly-heated cathode or heating filament of an electronic valve

Suppression of Oscillations in a Low-pressure Arc Discharge with Hot Filament Cathode

Suppression of Oscillations in a Low-pressure Arc Discharge with Hot Filament Cathode

Test of langmuir's three halves power law, deviations due to β2-factor and secondary emission

According to theory a small correction (the so called β2-factor) should be applied to Langmuir's law for the electron current in a cylindrical high vacuum diode. To test this, a method was developed for eliminating the potential drop along the hot cathode filament. The accuracy thus obtained disclosed an unexpectedly large deviation of the coefficient in Langmuir's formula from its theoretical value. This discrepancy is most probably due to the influence of secondary emission of the anode. It is possible to correct for this influence in a simple way by introducing an “effective reflection coefficient” of the anode. For anode voltages in the range of 1–30 V, values of this coefficient of 14% for tantalum and of 5.5% for aquadag give a good description of the experimental results. In a similar way the well known (ζ, η)-tables of Langmuir should be corrected if they are to represent the real situation.

The Study on the Presumption of the Life of the Fluorescent Lamp

There are many factors affecting the life of the fluorescent lamp, and the consumption of the oxide coated upon the electrode filament is most closely related with its absolute life., Connecting the voltmeter to the terminals of a filament, some voltage appears between them. As it seems that the filament voltage has trelation to the consumption of the oxide, the author researched its phenomena at D. C. and A. C. lighting of the fluorescent lamp. As the result of the qualitative and quantitacive investigation, it was confir-med that the filament voltage was the voltage drop which yeas produced at the filament owing to the current flowing through it. From this result, it was found that by the measurement f the cathode filament voltage, we could know the degree of the consumption of the electrode and also presume the life in a extremely short time.

A Filament Changing Device for Continuously Evacuated X-ray Tubes

In continuously evacuated dismountable X-ray tubes the cathode filament is usually renewed by removing the filament conductor assembly from the tube and replacing the filament holder with a spare holder in which a new filament has already been mounted. This necessitates the breaking of the vacuum and subsequent re-evacuation of the X-ray tube, a process which may take an hour or so to complete in the case of the 200–250 K.V. tubes used for deep X-ray therapy. Very large continuously evacuated X-ray tubes such as, for example, the 1,000 K.V. tube installed in the Mozelle Sassoon High Voltage X-ray Therapy Department at St. Bartholomew's Hospital, in London, are not so easily re-filamented as the smaller tubes, first because of the greater difficulty in removing the filament conductor assembly from the tube and secondly because of the longer time taken to break the vacuum and afterwards re-evacuate the tube. In order to reduce, as far as possible, the number of occasions on which the large X-ray tube would ...

XLIII.Experiments with inverted diodes having various filament cathodes

XLIII.<i>Experiments with inverted diodes having various filament cathodes</i>

The Emission of X Rays by Rectifying Valves

Some letters which have appeared recently in the British Journal of Radiology suggest that there is some anxiety among users of X-ray equipment regarding the dangers of X rays given off by rectifying valves. This danger undoubtedly exists, but fortunately it is singularly easy to avoid, and the object of this note is to try to set out simply the physical conditions obtaining in valves with special reference to conditions which cause the emission of X rays. It must be obvious to all that there is no essential physical difference between valves and hot cathode X-ray tubes. In each case we have a cathode in the form of a hot filament and a cool metal anode, and in each case the electrons emitted by the hot cathode serve to carry the current. The fundamental difference between the two lies in the way they are used. In order to understand this difference clearly it is necessary to examine the behaviour of “diodes” (as two-electrode tubes are collectively called). Suppose the cathode filament is heated to a certain definite temperature (determined by filament current and filament voltage) and a difference potential is applied between anode and cathode. If we construct a curve showing the relation between the current through the tube and the potential difference between its electrodes, we find that it is always of the general nature shown as A B C D E in Fig. 1. Varying the geometric conditions, etc., changes the constants of the curve, but not its general form.

Precision Measurements of the Glancing-Angle of Reflection from Calcite for Silver (Kα1) X-Rays by the "Method of Displacement."

Part I. Method of displacement.---This method permits the determination of glancing-angles in terms of linear measurements only. It consists in letting a properly limited beam of x-rays, after reflection, fall on a photographic plate placed successively in two parallel positions which differ in distance from the crystal by a known amount. The theory of the method and its practical application to the present case are briefly discussed with references to Uhler's paper.Part II. Apparatus and Adjustments.---A new high precision spectrometer, including a specially designed bearing on which the crystal rotates and a unique form of plate holder using air pressure to ensure the flatness of the photographic plate, is fully described. A special form of hot filament cathode which gives an approximately linear source of x-rays has been originated. Precision methods for adjusting and testing the reliability of the instrument are discussed at length. It is believed that the instrument is free from any defects that might cause a constant error of as much as 0.04\ensuremath{''} in the glancing-angle.Part III. Experimental prodedure.---The cleavage planes of a nearly perfect specimen of Iceland spar were used as grating. The bearing of its perfection on the widths of the spectral images is discussed. The coefficient of expansion of calcite normal to the cleavage planes was computed from the most reliable data obtainable. A mean value which is sufficiently precise, over a sixteen degree range, to reduce values of glancing-angles to 18\ifmmode^\circ\else\textdegree\fi{}C within 0.008\ensuremath{''} is ${1.02}_{3}$${(10)}^{\ensuremath{-}5}$ per \ifmmode^\circ\else\textdegree\fi{}C. Attention is called to the fact that the commonly used value ${1.04(10)}^{\ensuremath{-}5}$ is not a sufficient approximation.Distances between spectral images on each negative were measured on a Gaertner measuring engine, the errors of which were carefully investigated. The "displacements" of the photographic plate were equal to fixed intervals marked on a measuring bar and calibrated against the screw of the same measuring engine. The accuracy of these measurements and the effect of their errors on the glancing-angle are discussed.The experimental procedure and precautions used in taking and measuring spectrograms are fully described. A complete protocol of observations is given for one plate. Evidence for the accuracy of the measurements is presented and discussed.Part IV. Results.---The weighted mean value of the glancing-angle for the $K{\ensuremath{\alpha}}_{1}$-line of silver from the cleavage planes of calcite at 18\ifmmode^\circ\else\textdegree\fi{}C is 5\ifmmode^\circ\else\textdegree\fi{}17\ensuremath{'} 13.81\ensuremath{''} \ifmmode\pm\else\textpm\fi{} 0.06\ensuremath{''} giving a wave-length, if $log 2{d}_{18}=0.7823350$, of 0.558238A. This result is compared with those of other observers. It differs from Kellstr\"om's value quoted by the Int. Crit. Tables by more than ten times the combined probable errors. The only probable source of an adequate constant error in either result seems to lie in the crystal. Compton's measurements of the density of calcite are invoked to prove that different specimens of Iceland spar do differ enough in density to account for more than the discrepancy, if changes in density and grating space are interdependent.

Electronic Discharge from Cold Wires in Intense Electric Fields

Measurements were obtained for cold electronic currents at a pressure of ${10}^{\ensuremath{-}8}$mm, using thoroughly outgassed electrodes made of a minimum amount of metal. A silver plated glass cylinder served as an anode, with a coaxial tungsten filament cathode. Pure tungsten was used to avoid the changing surface conditions incident to outgassing thoriated tungsten. The gradient necessary for a given current was increased more than three fold by heating the filament for three hours at 2700\ifmmode^\circ\else\textdegree\fi{}K, the approximate period necessary for maximum gradient. The type of current-gradient curve at room temperature verifies the observations of Millikan and Eyring.Effect of temperature on the discharge of electrons from wires in intense electric fields has been extended by a study of the current-gradient relationship at liquid air temperature. These results show an intrinsic cold electronic phenomenon, possesing a type of current-gradient curve which has characteristics independent of temperature from 90\ifmmode^\circ\else\textdegree\fi{}K to 1000\ifmmode^\circ\else\textdegree\fi{}K.

Low Voltage Discharges in Helium

Discharge through helium,.01 to 2.9 mm pressure.\char22{}A hot filament cathode and disk anode were mounted in a glass frame 10 to 12 cm apart, the frame being so arranged that it could be moved magnetically inside a glass tube of diameter about 4 cm, with reference to a fixed exploring electrode. Measurements of potential distribution and of mean energy and concentration of electrons were made at three pressures,.095, 0.5 and 2.9 mm. Although precautions were taken to secure pure He, striations were obtained because of a trace of neon. The results are similar to those obtained by Bramley for ${\mathrm{hydrogen}.}^{1}$ The mean electron energy decreases to a minimum beyond the negative glow, then rises to a maximum beyond the face of the first striation. The electron concentration falls from a maximum in the negative glow to a minimum near the cathode side of the first striation; within the limits of accuracy of the work, it increases in a given region of the discharge with an increase of pressure and is proportional to the current density of the discharge at a given pressure. Calculations of the positive ion concentrations by Langmuir's formula and also by one developed by McCurdy, give results which seem to be equal to the electron concentrations, but as both methods are merely approximations, this result is not very reliable.

Absorption and Emission Spectra of the Geissler Discharge in Mercury Vapor and in Mixtures of Mercury and Hydrogen

In a quartz tube 4 cm in diameter, mercury vapor was maintained at about 3 cm pressure and a current of.5 amp. was sent from a tungsten filament cathode to a nickel anode 18 cm away. The absorption of light from a quartz Hg arc lamp on passing transversely through the discharge tube was determined with a small Hilger quartz spectrograph. (1) Absorption by the continuous positive column. Several lines of the diffuse and subordinate triplet series were absorbed by atoms in the $2p$ states, $2p\ensuremath{-}2s$ lines very strongly, $2p\ensuremath{-}3s$ lines less strongly, $2p\ensuremath{-}3d$ lines strongly, $2p\ensuremath{-}5d$ lines less strongly, $2p\ensuremath{-}5d$ lines weakly. No trace of absorption of combination lines by $2p$ atoms or of absorption by other excited atoms was observed. An unidentified faint line 4279 showed absorption. These results confirm and extend those reported by Metcalfe and Venkatesachar. The absorption by atoms in the $2{p}_{1}$ state is greatest but of the same order of magnitude as that by atoms in the $2{p}_{2}$ and $2{p}_{3}$ states. This is hard to reconcile with the extremely short life of the $2{p}_{2}$ state. (2) Absorption by the striated positive column, obtained by adding hydrogen. The bright region of the striation showed greater absorption of the $2p\ensuremath{-}2s$ lines than did the dark regions. (3) Emission spectra of various parts of the discharge. The negative glow emitted the arc spectrum and the spark line 2848. All these lines appeared with diminishing intensity through the Faraday dark space. The continuous positive column emitted the arc spectrum. The striated positive column emitted the arc spectrum and HgH bands. The intensity of emission attained its maximum for different lines at different regions in the striations in a manner apparently connected with the excitation energies for the lines.

The Diffusion of Electrons Against an Electric Field in the Non-Oscillatory Abnormal Low Voltage Arc

Oscillatory abnormal low voltage arc in pure helium.---Experiments with a tube provided with an anode and a hot filament cathode, built and used with elaborate precautions for excluding mercury vapor, disproved the suggestion that traces of mercury vapor as an impurity play an essential role in permitting arcs in helium to operate at abnormally low voltages.Non-oscillatory low voltage arc.---It has been found that, under certain conditions, arcs may be maintained at abnormally low voltages (below the lowest critical potential) and without oscillations, in helium, mercury vapor and argon, this type of arc being particularly striking and easy to obtain in argon. An arc tube, provided with a movable exploring electrode which was used according to Langmuir's method, enabled measurements of potential, of ion concentration, and of average energy to be made in all parts of the arc. With arcs operating on about 6 volts, the cathode drop was invariably very near to 11.5 volts (the minimum radiating potential of argon), so that there was a reverse field of about 5 volts existing throughout the greater part of the arc. The fact that the arc current of almost an ampere flows against this field is due to the effect of diffusion arising from the large concentration gradient. The electron concentration varied from the order of ${10}^{12}$ per cc just outside the cathode to about ${10}^{10}$ near the anode. The reverse field is due to the difference between the mobilities of electrons and of positive ions and is therefore most pronounced in the case of argon, in which electron free paths are abnormally long. The most interesting single feature of this research is the proof of the importance of ion diffusion in low voltage arcs.

On the Motions of Electrons in Gases

Motion of electrons through gases when electric field and pressure are such that collisions are elastic.---For electron speeds below a critical value characteristic of each gas, the collisions with molecules are probably as between elastic spheres, since neither ionization nor radiation is produced. The average fraction of its energy lost in elastic collision with a molecule of mass $M$, by an electron of mass $m$, is $f=2(\frac{m}{M})(1\ensuremath{-}\frac{\ensuremath{\Omega}}{U})$, where $\ensuremath{\Omega}$ and $U$ are the average kinetic energies of molecules and electrons. But while, if $Ug\ensuremath{\Omega}$, the electrons lose energy at collisions, they gain energy from the field between collisions, so the kinetic energy tends to increase or decrease to a terminal energy. Assuming Langevin's equation for mobility, we find ${U}_{t} (\mathrm{in}\mathrm{volts})=.66 \frac{\mathrm{El}}{\ensuremath{\surd}f}$ where $\mathrm{El}$ is the product of field strength and mean free path. In the case of plane parallel electrodes the number of collisions per cm and also the ratio of the speed at any point to the terminal speed, are both found to be independent of the field strength. In the case of a straight filament cathode surrounded by a coaxial cylindrical anode, the electrons may acquire their maximum speed near the cathode and subsequently lose speed while approaching the anode, their speed being greater than the terminal speed for this region. Curves are given for various cases. Substituting the value of terminal speed in Langevin's equation leads to the following expression for electron mobility: $\ensuremath{\mu}=\frac{0.815l\ensuremath{\surd}(\frac{\frac{1}{2}e}{m})}{{[\frac{1}{2}\ensuremath{\Omega}+{(\frac{{\ensuremath{\Omega}}^{2}}{4}+{W}^{2})}^{\frac{1}{2}}]}^{\frac{1}{2}}}$ where the energy due to the field is $eW=\frac{\mathrm{leE}}{1.506\ensuremath{\surd}f}$. This expression is somewhat similar to that given by Loeb (corrected for numerical error) but leads to values 0 to 10 per cent higher. When the collisions are inelastic the mobility is shown to be greater.

Low Voltage Arcs in Diatomic Gases. I. Hydrogen, Nitrogen, and Iodine

Low-voltage Arcs in Hydrogen, Nitrogen, and Iodine Vapor.---After a general review of the previous experimental results and theoretical suggestions, (1) current-voltage curves obtained with a simple two-electrode tube are described. Precautions were taken to insure pure gases. The breaking potential was always the ionizing potential of the gas, 16.3, 16.2, and 14.6 volts, respectively, for the three gases. The striking potential was greater than the breaking one by an amount which increased with the pressure and with increasing cathode filament temperature. In dissociated hydrogen, maintained at a high temperature within a thin tungsten cylinder heated electrically, an arc was readily maintained at the ionizing potential of the atom, 13.7 volts, and under very favorable conditions, at the radiating potential, 10.0 volts. In dissociated iodine vapor, the arc was maintained at 12.1 volts and under certain conditions at the ionizing potential, 10.2 volts. Nitrogen was not appreciably dissociated in the furnace. The critical potentials given above agree with the best previous results within \ifmmode\pm\else\textpm\fi{} 0.2 volt as a rule. Those associated with the atom are experimentally distinguished from those associated with the molecule.Electric Furnace Spectra of Hydrogen, Nitrogen and Iodine to 2500\ifmmode^\circ\else\textdegree\fi{} C.---In hydrogen, the series lines flashed in when the arc was struck, even as low as 10.6 volts, but the bands did not appear. Evidently the series lines are due to the atom and the bands to the molecule. In nitrogen, a brilliant flare was produced at potentials which decreased from 70 to 40 volts as the temperature was increased. This flare shows both the positive and negative bands along with the spectrum of tungsten; it is probably due to the formation of active nitrogen. At 70 volts the first lines, 5006 and 5003 \AA{}., appeared, and at 90 volts only two more, 5680 and 5667 \AA{}. Reasons are given for assigning the positive bands to the neutral molecule, the negative bands to the ionized molecule and the lines to the atom. In iodine, the arc lines, particularly 4860 \AA{}., flashed in when the arc struck, the enhanced lines coming in at higher voltages. No band spectrum appeared.New negative bands of nitrogen were found at 5075, 5018 and 4961 \AA{}.