摘要:

Measurements have been made of the relative light intensity distribution in an rf glow discharge (exhibiting the characteristics of a rapidly alternating dc glow discharge) maintained between copper electrodes in air at atmospheric pressure. Both the spatial distribution and the dependence on time of the light intensity were examined. The face diameter of each electrode was 3 mm and the electrode separation was 0.5 mm± 0.025 mm. All data were taken with a discharge frequency of 0.2 MHz and a discharge current of 0.6 A. Image converter data are presented as well as photomultiplier tube data. The experimental data presented verify that the cathode glow does definitely shift position from one electrode to the other in alternating half‐cycles and that essentially a total light turn‐off occurs prior to reignition in the next half‐cycle.

ISSN:0021-8979    

DOI:10.1063/1.1659063

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

rf glow discharges at high pressure are quenched after every half‐cycle and must be reignited in the following half‐cycle. The reignition voltageViwas investigated experimentally in the frequency range 0.15–1 MHz. It was found thatVigrows with electrode distancedup to a certain valuedmax. Atdmax,Videcreases distinctly and stays low for a further increase ofd. The explanation given for this effect is that at relatively small electrode distances all charge carriers can be removed from the discharge gap before reignition and breakdown must take place without support from space charges. For larged, however, the charge carriers cannot travel through the whole gap in the given time. Some remain in the gap and facilitate breakdown. Therefore a smaller value ofVican reignite a long gap. The measured frequency response ofVisupports this explanation. A theoretical estimate of values ofdmaxis within a factor of 1.6 of experimental values.

ISSN:0021-8979    

DOI:10.1063/1.1659064

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The application of an electric voltage to two electrodes between which a quasineutral plasma is contained results in charge transport and charge separation in the plasma. In this paper, the charge distribution, field distribution, and current density in the plasma resulting from the application of a monotonously increasing voltage are computed. The solution is derived under the assumption that the current in the plasma is essentially ion and electron current, and that displacement current can be neglected.

ISSN:0021-8979    

DOI:10.1063/1.1659065

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Experimentation involving the transients of the starting behavior of gas discharges reveals that this proceeds, in general, in three distinct stages: (1) a time lag for breakdown, termed plateau A, (2) a period of transition due to interaction between discharge and cathode, termed plateau B, and (3) the establishment of a final steady state for both discharge and cathode, termed plateau C. The initial state of plateau B is identified as a state of cathode and discharge that would constitute a steady state if the effects of ionic bombardment and Joule heating were absent. This state is found to obey the following relation, which is analogous to the Schottky equation for cathodes in vacuum:lnI=lnI&thgr;+[d(lnI)/d(V1/2)](V1/2−V&thgr;1/2),whereI&thgr;=AT2exp (−∈&phgr;/kT), the Richardson‐Dushman thermionic emission;V&thgr;is constant with a value near the ionization potential of the gas in the diode, and the voltage at which occurs a readily determined rearrangement of the cathodic sheath; the sloped(lnI)/d(V1/2) is a constant dependent on cathode material and the atomic number of the gas in the diode. It is shown that the extrapolated linear dependence of Eq. (1) intersects the ordinate (V=0) at a singular pointIR, independent of the atmosphere of the diode (vacuum, gas or type of gas) and identical with the zero‐field current of the cathode in vacuum. All experimental observations appear consistent with a theoretical model postulating a Schottky effect at the cathode. A consequence of these results is a firm correlation of cathode behavior in vacuum and in gas discharges.

ISSN:0021-8979    

DOI:10.1063/1.1659066

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The energy balance equation is applied to induction plasmas in thermal equilibrium. Approximate, iteration‐type, solutions are obtained for cases where heat losses by radiation, axial conduction, and convection can be disregarded. It is assumed that the electric conductivity rises in proportion to the heat conduction potential and that the radial distribution of the induced electric field can be represented by a power law. Under these conditions, the equation can be transformed into Bessel's equation and solved for the heat conduction potential. With a uniform field, the solution reduces to that for a dc arc. The condition of vanishing temperature at the enclosing wall establishes an eigenvalue for the induced electric field at the circumference. Absolute temperature distributions can be calculated as a function of gas properties and applied conditions. It is shown that the latter are given by the time rate of change of primary magnetic flux through the discharge section. The method is applied to argon plasmas at atmospheric pressure. For these plasmas, optimum conversion of magnetic energy into heat should occur at a primary flux rate of 48 V. This value is lowered by the secondary current in the plasma to an actual burning voltage of 32 V. Both values are independent of driving frequency and plasma radius. Skin depth ratio and conversion efficiency at the optimum point agree closely with the values known from induction heating of metals. Experimental data indicate that the discharge has a tendency to operate near this point. Comparison of temperature distributions obtained by this method with exact computer solutions show that the axis temperature is over‐estimated by about 15&percent;, but the general shape of the profile is well approximated.

ISSN:0021-8979    

DOI:10.1063/1.1659067

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Approximate solutions have been obtained of the Elenbaas‐Heller equation for a two‐zone model of thermal induction plasmas. Most of the heat production takes place in the external zone, where it is kept in balance by conduction losses. The major portion is lost to the wall, the minor transferred to the internal zone. This heat supply accounts for most of the radiation losses, which are confined to the internal zone. A small fraction of radiation is balanced by direct dissipation. Under these conditions, the distribution of the heat conduction potential assumes a parabolic shape for the inner zone, whereas it is described by Bessel functions in the external zone. A coordinate transformation in this zone accounts for the nonuniformity of the induced electric field and explicitly shows the effect of skin depth upon the profile shape. Matching of the zonewise solutions yields temperature distributions that are continuous to the first derivative and display the characteristic minimum at the axis known from experimental work. Generalized charts are presented by which a particular profile can be calculated from the gas transport properties and the time rate of change of primary magnetic flux. The method is applied to argon plasmas at atmospheric pressure with radiation properties calculated from atomic theory. Simple expressions are derived for the total radiated power and the radiation efficiency of the discharge by a further idealization of the model. They indicate that, at most, 50&percent; of the input power can be converted into radiation as long as the discharge remains attached to the tube wall. It is also shown that large field penetration depth improves the efficiency. The results are in qualitative agreement with available experimental data. A quantitative check will require more complete experiments.

ISSN:0021-8979    

DOI:10.1063/1.1659068

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A general solution is presented for the end‐region stress in a composite cylindrical rod where differential thermal expansion or contraction occurs between the core and cladding. Results describe local conditions set up in the ends of clad laser rods during manufacture and permit an analytical assessment of the optical path distortion which can arise in this geometry from residual strain. The formulations are obtained by superposition of the infinite rod solution and a solution to the boundary value problem posed by an axial force distribution, of equal but opposite magnitude to the infinite rod stress, applied to the surface of a stress‐free cylinder. Expressing the applied tractions as a Fourier‐Dini expansion at the axial boundary and the radial stress as a Fourier expansion at the radial boundary leads to a double infinite series form for the principal stresses. Implementation of Fejer's theorem was helpful in smoothing the numerical results; however, summing as many as 100 series terms with the computer was necessary to gain satisfactory convergence. Principal stress‐strain distributions are presented for a typical glass rod with a core‐cladding diameter ratio of 0.7 to 1 and contraction ratio below the transformation temperature of 0.95 to 1. Results show the end‐region domian extends less than 1 rod diameter. Optical pathlength variation across the core aperture for radial and tangential beam polarizations was computed to be 0.58 and 0.51 &mgr;, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1659069

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A mechanism has been proposed to explain the undamped spiking of the output power occurring in some multilevel maser oscillators. The phenomenon is explained in terms of the coupling between the signal frequency energy storage and the circuit properties at the pump frequency induced by the dependence of the pump level populations on the former. Approximate numerical calculations have shown that the coupling may be strong enough to render the operation of the oscillator unstable. Theoretical results obtained are in qualitative agreement with some of the observed properties of the spiking phenomenon.

ISSN:0021-8979    

DOI:10.1063/1.1659070

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

General design considerations for internal laser acousto‐optic modulators are given. Calculations are carried out for the time dependence of the power within the cavity and of the external pulsed power. Based on these calculations, acousto‐optic quartz modulators were designed to be inserted inside He&sngbnd;Ne and argon folded cavities. Light pulses, with duration continuously variable from 15 nsec to cw and with repetition rate variable from single pulses to a few MHz have been extracted from the cavities. After dumping out most of the cavity energy, the time required for the internal power to rise from 10&percent; to 90&percent; of its steady‐state value is of the order of 3 &mgr;sec. With a pulse repetition rate of 1 MHz, the average light power was essentially the same as of the cw power capability of the lasers. The peak power intensity of the scattered light could reach the value of more than 50 times the cw power which was about 5 W for a 100mW He&sngbnd;Ne laser and 100 W for a 2‐W argon laser. The ability to pulse modulate the laser power at high repetition rates with negligible sacrifice in average power is important in many applications, including optical memories and laser machining.

ISSN:0021-8979    

DOI:10.1063/1.1659071

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The intensity correlation function of the light from a non‐Q‐switched Nd:glass laser has been measured, using an optical gate (OG) to produce second‐harmonic light. The resolution time of this optical gate depends on the differences of the group velocities involved and the crystal length of the optical gate; in the described experimental arrangement a time resolution of about 10−13sec is achieved. The effect of thick crystals on the time dependence of the second‐harmonic light intensity is discussed for some special cases. The experimental results are in agreement with the freerunning laser model, namely that a non‐Q‐switched Nd:glass laser has intensity fluctuations similar to thermal light. These results confirm some earlier results which have been achieved by a different technique.

ISSN:0021-8979    

DOI:10.1063/1.1659072

出版商:AIP    

年代:1970

数据来源: AIP