scholarly journals The effect of small traces of water vapour on the velocities of ions produced by Röntgen rays in air

1910 ◽  
Vol 84 (569) ◽  
pp. 173-181 ◽  
Keyword(s):  
Electric Field ◽  
Water Vapour ◽  
Lateral Diffusion ◽  
Negative Ions ◽  
Complete Removal ◽  
The Other ◽  
Electric Force ◽  
Dry Air ◽  
Positive Ions ◽  
Low Pressures

Some experiments by Prof. J. S. Townsend on the lateral diffusion of a narrow stream of ions moving in an electric field led to the conclusion that negative ions in perfectly dry air are much smaller than those in air containing a small quantity of moisture. It was consequently to be expected that the complete removal of water vapour would cause an increase in the velocity with which negative ions move under the influence of an electric field of force. At his suggestion the following investigation of the velocities of ions in air at low pressures was undertaken, and it was found that, while the complete removal of water vapour had only a small effect on the velocities of positive ions, yet the same cause increased the velocities of the negative ions by a factor varying between 2 and 30 for the range of pressures and electric forces used in the experiments. The method adopted was to let the ions travel between two gauzes under a known electric force for a time t and then to reverse the field. If v is the velocity of the ions and d is the distance between the gauzes, then ions starting from one gauze will reach the other if t ≮ d / v . If t is gradually decreased, it is possible to find, by means of an electrometer, when ions cease to reach the second gauze; when this happens v = d / t .

scholarly journals Effect of a magnetic force on the motion of negative ions in a gas

1912 ◽  
Vol 87 (596) ◽  
pp. 357-365 ◽  
Keyword(s):  
Charged Particle ◽  
Atmospheric Pressure ◽  
Magnetic Force ◽  
Large Range ◽  
Negative Ions ◽  
Negative Ion ◽  
Electric Force ◽  
Dry Air ◽  
Low Pressures ◽  
Made In

1. When the velocity of a charged particle in a gas is proportional to the electric force and inversely proportional to the pressure, the size of the particle is unaltered either by changes in the pressure or in the force. For a large range of pressures and forces the mass of an ion is thus shown to be constant, since the velocity is proportional to the ratio X / P. At low pressures when the ratio X / P exceeds a certain value the velocity of the negative ions undergoes large changes when small variations are made in the force or in the pressure. The increase in the mobility may be explained on the hypothesis that the mass associated with the negative ion diminishes. Thus in dry air at a pressure of 29 mm. the velocity of the negative ions is 926 cm. per second, under a force of 2·3 volts per centimetre, whereas if the ion travelled with the same mass that it has at atmospheric pressure the velocity would be about 114 cm. per second.

scholarly journals The motion of electrons in gases

1913 ◽  
Vol 88 (604) ◽  
pp. 336-347 ◽  
Keyword(s):  
Electric Field ◽  
Lateral Diffusion ◽  
Ultra Violet ◽  
Negative Ions ◽  
Central Line ◽  
Transverse Magnetic ◽  
Uniform Electric Field ◽  
Internal Diameter ◽  
Narrow Slit ◽  
Electric Force

1. The methods of investigating the motion of negative ions in gases at low pressure that have been explained in some previous papers may be extended to cases in which larger variations are made in the electric force and pressure. In order to find the kinetic energy of the motion of agitation of the ions, the velocity in the direction of an electric force, and the value of e / m for different forces and pressures, it is necessary to investigate experimentally two properties which are characteristic of the motion of electrons. These are the abnormal lateral diffusion of a stream of ions moving in a uniform electric field, and the deflection of the stream produced by a small transverse magnetic force. In the previous experiments the two phenomena were investigated separately and in each case with apparatus which gave satisfactory results when small electric forces were used and the pressures were limited to a certain range. In order to investigate the motion under larger forces an apparatus of more suitable dimensions was constructed, by means of which both the required sets of experiments may be made. 2. The negative ions were generated by the action of ultra-violet light on the plate A, fig. 1, and after traversing the distance from A to B some of the ions passed through a narrow slit S, 2 mm. wide and 15 mm. long, in the centre of the metal sheet B. The electric force was in the same direction on the two sides of B, so that the ions, after passing through the slit, continue their motion towards the plane electrodes C, which were parallel to the plane of B. The electrodes C were 4 cm. from B, and three flat rings, R 1 , R 2 , R 3 , 7 cm. internal diameter, were fixed at distances of 1, 2, and 3 cm. respectively from the plane of the electrode C. A separate connection for each ring and for the plates A and B was brought out through a large ebonite plug fitted in the brass cover of the apparatus, and was maintained at a potential proportional to the distance of the corresponding ring, or plate, from the electrodes C. The stream of ions that came through the slit moved in a uniform electric field and was received by the three insulated electrodes c 1 , c 2 , c 3 . These were portions of a disc 7 cm. in diameter, the central section c 2 being 4.5 mm. wide and separated from the two equal side plates c 1 and c 3 by air gaps 0.5 mm, wide. The narrow gaps between the electrodes were parallel to the direction of the slit in B. In the calculations it will be supposed that the electrode c 2 is 5 mm. wide, and that the side plates c 1 and c 3 come within 2.5 mm. of the central line.

scholarly journals The diffusion of ions into gases at low pressure

1912 ◽  
Vol 87 (596) ◽  
pp. 350-357 ◽  
Keyword(s):  
Water Vapour ◽  
Royal Society ◽  
Ultra Violet ◽  
Negative Ions ◽  
Large Change ◽  
Electric Force ◽  
Aluminium Foil ◽  
Ultra Violet Light ◽  
Violet Light ◽  
Low Pressures

1. In papers published in the ‘Proceedings’ of the Royal Society, the charges on ions produced by the action of Rontgen rays and radium on air were determined by a method depending on the diffusion of the ions, and in the course of the investigations it was observed that the removal of water- vapour from the gas produced a large change in the motion of negative ions. In this paper the results are given of some accurate experiments on the ions produced by radium, and experiments at low pressures on the motion of the ions produced by ultra-violet light are described. In the latter case, effects similar to those observed by Prof. Townsend when the gas was ionised by Rontgen rays have been found, and some interesting results at pressures lower than those previously employed have been obtained. 2. The arrangement of the apparatus is here reproduced (fig. 1). The ions are generated in the field A by radium placed in shallow horizontal grooves f , covered with aluminium foil, in brass blocks F. They pass under the action of the electric force through the grating g and the aperture h into the field B, which was kept constant by means of the brass rings G maintained at definite potentials. Here they diffuse and the ratio R of the charge received by the disc D to the charge received by the disc and the ring S together is measured. This ratio is a known function of c = N e Z/P, where e is the charge on an ion, N the number of molecules in a cubic centimetre of air at pressure P at the temperature of the laboratory, and Z the electric force in the field B.

Numerical Simulation of Leakage Current on Conductive Insulator Surface

2019 ◽  
Vol 8 (4) ◽  
pp. 9487-9492
Keyword(s):  
Numerical Simulation ◽  
Electric Field ◽  
Leakage Current ◽  
Method Of Lines ◽  
Electron Attachment ◽  
Negative Ions ◽  
Conduction Current ◽  
Insulator Surface ◽  
Finite Difference Approximations ◽  
Positive Ions

The outdoor insulator is commonly exposed to environmental pollution. The presence of water like raindrops and dew on the contaminant surface can lead to surface degradation due to leakage current. However, the physical process of this phenomenon is not well understood. Hence, in this study we develop a mathematical model of leakage current on the outdoor insulator surface using the Nernst Planck theory which accounts for the charge transport between the electrodes (negative and positive electrode) and charge generation mechanism. Meanwhile the electric field obeys Poisson’s equation. Method of Lines technique is used to solve the model numerically in which it converts the PDE into a system of ODEs by Finite Difference Approximations. The numerical simulation compares reasonably well with the experimental conduction current. The findings from the simulation shows that the conduction current is affected by the electric field distribution and charge concentration. The rise of the conduction current is due to the distribution of positive ion while the dominancy of electron attachment with neutral molecule and recombination with positive ions has caused a significant reduction of electron and increment of negative ions.

scholarly journals Electrical Breakdown in Air and in SF6

1995 ◽  
Vol 48 (3) ◽  
pp. 453 ◽  
Author(s):  
R Morrow ◽  
JJ Lowke
Keyword(s):  
Electric Field ◽  
Electric Field Distribution ◽  
Electrical Breakdown ◽  
Negative Ions ◽  
Continuity Equations ◽  
Positive Ions ◽  
Positive Space Charge ◽  
Attachment Coefficient ◽  
Positive Space ◽  
Positive Point

A theory is presented for the development of streamers from a positive point in atmospheric air. The continuity equations for electrons, positive ions, and negative ions are solved simultaneously with Poisson's equation. For an applied voltage of 20 kV across a 20 mm gap, streamers are predicted to cross the gap in 26 ns, and the calculated streamer velocities are in fair agreement with experiment. When the gap is increased to 50 mm for the same voltage, the streamer is predicted not to reach the cathode. In this case an intense electric field front rapidly propagates about 35 mm into the gap in 200 ns. For a further 9�5 �s the streamer slowly moves into the gap, until the electric field at the head of the streamer collapses, and the streamer front stops moving. Finally, only positive space-charge remains; this moves away from the point, allowing the field near the point to recover, giving rise to a secondary discharge near the anode. The electric field distribution is shown to be quite different from that found previously for SF6; this is explained by the much lower attachment coefficient in air compared with that in SF6. These results show that streamers in air have a far greater range than streamers in SF6. This greater range cannot be explained by comparison of the values of E*, the electric field at which ionisation equals attachment.

The Boltzmann relation in electronegative plasmas: When is it permissible to use it?

2000 ◽  
Vol 64 (2) ◽  
pp. 131-153 ◽  
Author(s):  
R. N. FRANKLIN ◽  
J. SNELL
Keyword(s):  
Fluid Model ◽  
Negative Ions ◽  
Ionization Rate ◽  
Negative Ion ◽  
Simple Relationship ◽  
Ion Temperature ◽  
Ion Density ◽  
Positive Ions ◽  
Electronegative Plasmas ◽  
Low Pressures

This paper reports the results of computations to obtain the spatial distributions of the charged particles in a bounded active plasma dominated by negative ions. Using the fluid model with a constant collision frequency for electrons, positive ions and negative ions the cases of both detachment-dominated gases (such as oxygen) and recombination-dominated gases (such as chlorine) are examined. It is concluded that it is valid to use a Boltzmann relation ne = ne0exp(eV/kT) for the electrons of density ne, where the temperature T is approximately the electron temperature Te, and that the density nn of the negative ions at low pressures obeys nn = nn0exp(eV/kTn), where Tn is the negative-ion temperature. However, at high pressure in detachment-dominated gases where the ratio of negative-ion density to electron density is constant and greater than unity, and when the attachment rate is larger than the ionization rate, the negative ions are distributed with the same effective temperature as the electrons. In all other cases there is no simple relationship. Thus to put nn/ne = const, nn = ne0exp(eV/kTe) and nn = nn0exp(eV/kTn) simultaneously is mathematically inconsistent and physically unsound. Accordingly, expressions deduced for ambipolar diffusion coefficients based on these assumptions have no validity. The correct expressions for the situation where nn/ne = const are obtained without invoking a Boltzmann relation for the negative ions.

scholarly journals The diffusion of electrons through a slit

1914 ◽  
Vol 90 (615) ◽  
pp. 69-72 ◽  
Keyword(s):  
Differential Equation ◽  
Electric Field ◽  
Simple Form ◽  
Lateral Diffusion ◽  
Metal Plate ◽  
Electric Force ◽  
Narrow Strip ◽  
Air Gaps ◽  
Uniform Rate

In a paper on “The Motion of Electrons in Gases,” by Prof. Townsend and Mr. Tizard* it was shown how, by measuring the lateral diffusion of a stream of electrons in an electric field, it is possible to find k the factor by which the energy of agitation of the electrons exceeds that of the surrounding molecules. The ions come at a uniform rate through a slit S of width 2 a in a large metal plate A, and traverse a distance c in the direction of an electric force Z. The plane of the plate A may be taken as that of xy , the origin of co-ordinates being the centre of the slit which latter is taken parallel to the axis of y . The ions are received on three insulated electrodes, c 1 c 2 , C 3 , which were portions of a disc of diameter 7 cm., c 2 being a narrow strip 5 mm. wide, cut from the centre of the disc and insulated by narrow air gaps from the two electrodes, c 1 c 3 , on each side of it. The electric field between A and the electrodes C was maintained constant by a series of rings of diameter 7 cm., kept at uniformly decreasing potentials. In this case the differential equation giving the distribution n of electrons in the electric field is ∇ 2 n = 41 Z/ k . ∂ n /∂ z . If q is defined to be ∫ ndy , this equation becomes ∂ 2 q /∂ x 2 + ∂ 2 q /∂ z 2 = 41 Z/ k . ∂ q /∂ z . If n 1 n 2 , n 3 are the charges received by the electrodes c 1 , c 2 , c 3 , it is shown that the values of Z/ k can be found by determining the ratio R = n 2 /( n 1 + n 2 + n 3 ), i . e . the value of k corresponding to any Z can be found. Experiments had previously been performed in which a circular stream of ions was collected on concentric circular electrodes, and from the results it appeared that the term ∂ 2 n /∂ z 2 was small compared with the others. By neglecting this term, Prof. Townsend obtained a solution of the differential equation in a simple form and plotted a curve with co-ordinates R and Z/ k .

scholarly journals Dissociation, recombination and attachment processes in the upper atmosphere II. The rate of recombination

1939 ◽  
Vol 170 (942) ◽  
pp. 322-340 ◽  
Keyword(s):  
Negative Ions ◽  
Neutral Molecule ◽  
Upper Atmosphere ◽  
The Other ◽  
Negative Ion ◽  
Neutral Atoms ◽  
Attachment Rate ◽  
Additional Advantage ◽  
Positive Ions ◽  
Positive Ion

The ionized regions of the upper atmosphere include, not only neutral atoms and molecules, electrons and positive ions, but also negative ions. Of these, electrons are alone effective in producing reflexion of wireless waves; so that an electron attached to a neutral molecule to form a negative ion is as effectively removed from active participation in these phenomena as one recombined with a positive ion to form a neutral molecule. The decay of electron density at night has been attributed by some authors to recombination with positive.ions and by others to attachment by neutral molecules. The first process is in agreement with the observed law of decay and has the additional advantage of making it easily possible to understand the formation of layers of concentrated ionization; on the other hand, the chance of attachment to a molecule per impact would have to be extremely small for the attachment rate to be negligible, since the number of collisions per second with neutral atoms is very much greater than with positive ions.

scholarly journals Mobility of the positive and negative ions in gases at high pressure

1912 ◽  
Vol 86 (584) ◽  
pp. 154-162 ◽  
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Mathematical Expression ◽  
Negative Ions ◽  
Negative Ion ◽  
Positive Ions ◽  
Low Pressures ◽  
Positive Ion ◽  
Reduced Pressures

The velocity of ions in gases at reduced pressures was first investigated by Rutherford and by Langevin. Recently the author and others have carried out similar investigations. The results of these investigations show that for the negative ions in air the product of the mobility and the pressure is constant for pressures ranging from 760 mm. to 200 mm. of mercury, but with further reduction the product increases with the reduction of pressure, this increase becoming very great at low pressures. For the positive ions in air the product of the mobility and pressure is constant for pressures investigated between 760 mm. and 3 mm. of mercury. Similar results were obtained for the mobilities of the ions in other gases. The results show that if the ion is an aggregation of molecules, this aggregation becomes, at low pressures, less complex in the ease of the negative ion, while in the ease of the positive ion it persists down to 3 mm. of mercury. The purpose of the present research was the study of the mobilities of both kinds of ions in gases at high pressures. The method of investigation is based on the mathematical expression, developed by Prof. Rutherford, for the current between two plates, assuming that a very intense ionisation exists near the surface of one of the electrodes.

scholarly journals The mobility of ions in air

1930 ◽  
Vol 127 (805) ◽  
pp. 298-314 ◽  
Keyword(s):  
Experimental Method ◽  
Water Vapour ◽  
Negative Ions ◽  
Resolving Power ◽  
General Shape ◽  
Dry Air ◽  
Upper Limit ◽  
Mobility Of Ions ◽  
Lower Limits ◽  
Peak Value

In a previous paper I have described an experimental method of measuring ion mobilities in a gas, which yields accurate values for both upper and lower limits of a distribution range, and from which one can also derive a curve showing the general shape of the distribution band, with a calculable resolving power. It was found that negative ions in dry air at normal pressures had mobilities ranging from 2∙15 to 1∙45 cm. per second per volt per centimetre, while the distribution band showed a peak value about 1∙8 and a sharp upper limit at 2∙15. There was also some reason to believe that in the presence of water vapour the band was narrowed, the faster ions being eliminated in the manner found by other observers, and the slower ions remaining comparatively unaffected. In the experiments here described, an improved form of the apparatus is used to study in greater detail the effect of water and other vapours on the mobility distribution, for positive and negative ions in air.

Sign in / Sign up

Export Citation Format

Share Document