The starting mechanism of the first stage of the ring discharge

1965 ◽  
Vol 284 (1398) ◽  
pp. 442-454 ◽  
Keyword(s):  
Band Spectrum ◽  
Axial Component ◽  
Uniform Field ◽  
Glass Wall ◽  
Electron Collisions ◽  
Frequency Independent ◽  
Gas Ionization ◽  
Frequency Magnetic Field ◽  
Hydrogen Lines ◽  
Low Pressures

When the high frequency magnetic field of a coil surrounding a cylindrical vessel filled with hydrogen is increased above a critical value, a faint discharge starts which emits the H 2 -band spectrum. If the current in the coil is raised further, an intense ring discharge suddenly develops showing predominantly the atomic hydrogen lines. The first stage is shown to be initiated by the axial component of the electric field of the coil, even when conventional electrostatic screens are used. When the axial component is suppressed, a circumferential component of even twice the axial starting field fails to initiate the discharge. This axial uniform field is calculated for low pressures, at which the mean free electron path exceeds the size of the vessel, by assuming that electrons are multiplied by collisions with the glass wall; it is thus independent of the gas and its density. The dependence of the starting field on length, pressure and frequency is measured using a vessel of variable length and 4 cm radius. Values of 9 and 5V/cm peak at 15 an d 5 Mc/s respectively are found between 10 -4 and 10 -2 mmHg a t 20 cm length, in agreement with theory. For pressures between 0.1 and 1 mmHg the starting field is calculated by balancing the rate of gas ionization by electron collisions and the loss of charge by diffusion to the wall, field-dependent energy losses being allowed for. Its value, now depending on the nature of the gas, rises with increasing pressure and becomes frequency-independent at higher pressures. Again, theory and experiment agree quantitatively.

Comment on ‘‘Shifts of hydrogen lines from electron collisions in dense plasmas’’

1985 ◽  
Vol 32 (3) ◽  
pp. 1906-1907 ◽  
Author(s):  
C. A. Iglesias ◽  
D. B. Boercker ◽  
R. W. Lee
Keyword(s):  
Electron Collisions ◽  
Dense Plasmas ◽  
Hydrogen Lines

scholarly journals On the excitation of the band spectrum of helium

1925 ◽  
Vol 109 (750) ◽  
pp. 267-272 ◽  
Keyword(s):  
Discharge Tube ◽  
High Current Density ◽  
Band Spectrum ◽  
Essential Condition ◽  
Spark Gap ◽  
In Series ◽  
Pure Helium ◽  
Faint Band ◽  
The Individual ◽  
Low Pressures

It is now generally agreed that the band spectrum of helium, which was first observed by Curtis (‘Roy. Soc. Proc.,’ A, vol. 89, p. 146, 1913) and by Goldstein (‘Verh. d. Deutsch. Phys. Gesell.,’ vol. 15, p. 402, 1913), is to be attributed to some molecule of helium. This band spectrum is peculiar in the fact that the heads of the bands have been shown by Fowler (‘Rov. Soc. Proc.,’ A, vol. 91, p. 208, 1915) to follow the law usually associated with line spectra, though the individual lines composing the bands can be represented by the parabolic arrangement appropriate to band series. More recently, Curtis has carried out a series of investigations (‘Roy. Soc. Proc.’) on the structure of the bands in terms of the quantum theory. Attention may here be drawn to two peculiarities in the spectrum. There is one isolated band with a head at about λ = 5733 A., which is degraded to the violet, whilst all the remaining bands are degraded to the red. Also Goldstein ( loc. cit. ) observed a number of faint band lines in the region about λ = 5390 A. to λ = 5270 A., which were not recorded in Curtis’s paper ( loc. cit .). It is well known that in vacuum tubes excited by uncondensed discharges only faint traces of the principal band heads are visible in the positive column though the complete band spectrum appears in the negative glow. The band spectrum can be excited with much greater intrinsic brightness by using a discharge tube with a wide tube in place of the usual capillary, and exciting it by means of a discharge from an induction coil or transformer, with a condenser in parallel and a small spark gap in series with the discharge tube, the band spectrum under these conditions appearing throughout the tube. There appears to be an optimum length of spark gap and the spectrum tends to become weaker when the length is increased beyond a certain point. Curtis ( loc. cit .) has found that the band spectrum is not strongly developed at low pressures, and this condition appears to be independent of other conditions of excitation. In the present investigation we have found that under certain conditions the band spectrum can be greatly modified. It was observed that when a vacuum tube, containing pure helium, which had been made with the capillary in several sections of different bore, was excited with an uncondensed discharge the narrowest section, which was of the finest thermometer tubing that could be worked conveniently in the blowpipe, showed nothing but the line spectrum, but in the wider sections on either side the band spectrum was quite strongly developed. This seems to show that a high-current density is not an essential condition for the excitation of the band spectrum, but it was remarkable that with these tubes it appeared in the wider parts, where it would not have been seen if the capillaries had not been provided with a section of narrow bore.

scholarly journals The hydrogen band spectrum: new band systems in the violet

1927 ◽  
Vol 115 (772) ◽  
pp. 528-548 ◽  
Keyword(s):  
Ultra Violet ◽  
Band Spectrum ◽  
Final States ◽  
Electron Stream ◽  
King's College ◽  
Long Wave ◽  
Wave Numbers ◽  
Sufficient Intensity ◽  
Initial States ◽  
Low Pressures

The system of bands described in this paper includes much of the strength of the secondary hydrogen spectrum when this is excited by direct electron impact on the H 2 molecule and there are no additional complications. I first observed it on a photograph of the spectrum of hydrogen at a pressure below 0·01 mm. of mercury, excited by a sharply limited electron, stream, which was kindly sent to me by Mr. P. M. S. Blackett. This photograph, which was taken by Mr. Blackett, had insufficient resolution and dispersion for the identification of the lines of the secondary spectrum. Up to the present I have not been able to get sufficient intensity at low pressures to obtain this spectrum with the purity shown on Mr. Blackett’s photograph and the requisite resolution; but by work­ing at pressures of about 0·3 mm. I have, with the help of Mr. D. B. Deodhar, got some plates on the large quartz Littrow spectrograph at King’s College which show this spectrum sufficiently enhanced and the rest sufficiently reduced for the main features to be recognised with confidence. The present paper deals with but a portion of what I have been able to arrange provisionally in this spectrum, but it is a unit which seems to be complete in itself, except that I am only able to give the Q branches of the bands, whereas there are indications, still insufficiently explored, that P and R branches do exist. There are two band systems, the first very strongly developed. The nucleus (0→0 Q (1) line) of the first band is at λ 4633·95 (9) = v 21573·81. The Q branch of the 1→0 band is the series 20Q ( m ) of Richardson and Tanaka. All the bands are degraded towards the violet, i. e ., in the opposite sense to those in the systems described in Structure, Parts IV and V. Each line of the bands is accompanied by a fainter component on the long-wave side of it. The intensity of the fainter line is usually about one-fourth of that of the stronger in terms of the numbers of the usual conventional scale of intensities, and the separation of the two lines is in the neighourhood of 4 wave-numbers. The final states of the present bands appear to be the same as the initial states of the Lyman bands in the far ultra-violet.

scholarly journals A new band spectrum associated with helium.­

1913 ◽  
Vol 89 (608) ◽  
pp. 146-149 ◽  
Keyword(s):  
Principal Series ◽  
The Other ◽  
Band Spectrum ◽  
Previous Record ◽  
Hydrogen Lines

In the course of Prof. Fowler’s recent observations of the principal series of hydrogen lines in the spectra of helium tubes traces were frequently seen of a band spectrum the origin of which was unknown, and of which no previous record could be found. The most prominent features visually were bands having their heads at about λλ 6400, 5732, 4649, and 4626. The band at 5732 was degraded towards the violet end of the spectrum, the opposite being the case with the other three. Although in the first instance the new bands were always comparatively feeble, they were such a frequent and persistent feature of the spectra of the various tubes that it was thought desirable to investigate their origin, and to determine their positions. It was soon found possible, by choosing suitable conditions of pressure and discharge, to obtain the new spectrum quite brightly, when a number of other bands were observed, some visually and others by photography. These bands were evidently associated with those first noticed.

scholarly journals Ionization, excitation, and chemical reaction in uniform electric fields II-The energy balance and energy efficiencies for the principal electron processes in hydrogen

1936 ◽  
Vol 157 (890) ◽  
pp. 146-166 ◽  
Keyword(s):  
Electric Field ◽  
Random Motion ◽  
Electron Collision ◽  
Uniform Electric Field ◽  
Uniform Field ◽  
Mean Velocity ◽  
Electron Collisions ◽  
Average Electron Energy ◽  
Stationary Concentration ◽  
Gas Molecules

In a previous communication, Part I, Emeléus, Lunt, and Meek* have discussed the rate of an electron collision process, ionization, in a uniform electrical field. In this paper we elaborate their analysis and extend it to five other types of electron collision processes. The discharge conditions now postulated are those of a swarm of electrons moving through a gas under the influence of a uniform electric field so that the system is in a steady state, the current density being sufficiently low so that the stationary concentration of all products of electron collisions (ions and excited particles) is negligible compared with that of the gas molecules in the ground state. Such conditions are realized with considerable exactitude in the uniform positive column. This is of particular importance because in such a discharge the rates of the various types of electron collisions contemplated in the present theory are sufficiently large to enable comparisons to be made between experiment and the predictions of the theory. There are many experiments, notably those of Townsend* and Langmuir, relating to the conditions now postulated which show the velocities of the electrons in the swarm are distributed at random about a mean, and that the mean velocity greatly exceeds that of the gas molecules (or atoms) in which the swarm moves; in a given gas the average electron energy, V electron-volts, has been shown by Townsend and his collaborators to be a function of X p -1, the ratio of the electric field to the gas pressure. In addition to this random motion, there is a relatively small drift motion of the swarm in the direction of the uniform field X ; the drift velocity, W cm. sec.-1, in a given gas is also a function of X p -1, and its magnitude determines the rate at which electrons gain energy from the field, and also the magnitude of the (drift) current carried by the ionized gas.

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