Browsing by Author "M. Sakuntala"

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Acoustic wave interaction with plasma
(1978) M. Sakuntala; V.K. Jain
Experiments have been conducted to find the variation of the velocity of an acoustic wave propagating through air plasma. It is found that the velocity of sound increases with increasing charged particle density in the plasma. Also it has been observed that as the frequency of the acoustic wave through the plasma increases, the perturbed variation in charged particle density and the electron-neutral atom elastic collision frequency remain constant as long as the frequency of the sound wave is less than the ionisation frequency of the plasma. For further increase in the wave frequency, equal to, or greater than, the ionisation frequency of the plasma, the change in the number density reduces to a minimum value while the elastic collision frequency of the plasma increases.
Discharges in potassium seeded argon at elevated temperatures
(1965) M. Sakuntala
The variation of the plasma current with the voltage applied between stainless steel electrodes, 0.1 to 1 cm apart, was measured in argon at 1 atmosphere containing potassium vapour at pressures of 0.4 to 4 torr, for temperatures between 1000 and 1200°K. It was found that as the electrode voltage was gradually raised from zero, the current, originally of the order 10-6 A and below 0.1 V independent of the voltage, increased first slowly and later more rapidly with the voltage. At about 20 V, corresponding to a current of order 10 mA, a sudden transition into a hot cathode arc occurred while the current rose to several amperes. Measurements of the potential distribution in the hot plasma by means of electrostatic probes showed the presence of a relatively large cathode fall, of a smaller anode fall and of a region of constant potential gradient between the two fall regions. An analysis of the observations revealed that thermionic emission from the potassium covered electrodes, thermal ionization of potassium vapour, space charge fields and production of positive ions by electron collisions were the dominant features of this discharge plasma. A relation was derived for the transition to take place from the low to the high current mode assuming space charge neutralization to be the controlling factor.
Electronics section: The decay of the electric conductivity in a moving hydrogen plasma†
(1962) M. Sakuntala; A. Von engel
An electrically driven shock tube filled with pure hydrogen at pressures between 0·5 and 8 mm Hg was fitted with internal cold probes arranged at different positions in the expansion tube to observe oscillographieally the voltage pulse produced between the probes by the plasma shock wave passing a magnetic field up to 5000 gauss strength. The results show that the peak value of the open circuit probe voltage ( ≤ 60 v) rises strictly linearly with the field, that the flow velocity of the shock wave is proportional to the condenser voltage and inversely proportional to the square root of the ambient gas pressure and distance between probes and discharge tube. The voltage-time integral taken at different probe positions agreed with the magnetic flux linked with the plasma wave. The (ionic) plasma resistivity as a function of the pressure was found to have a minimum dependent on the probe position ; its value is lower the larger the probe distance and the higher the condenser's energy. This minimum arises from an increase in charge concentration in the gas with rising pressure which results from a conversion of flow and potential energy to ionization and compression ; beyond the minimum a rising pressure reduces the charge concentration and increases the resistivity, since, on account of the lower flow velocity, the gas temperature in the shock front is gradually reduced. © 1962 Taylor and Francis Group, LLC.
Ionic conductivity of highly ionized plasmas
(1960) M. Sakuntala; A. Von Engel; R.G. Fowler
When a cloud of highly ionized gas ejected by a plasma shock tube is made to travel across a constant magnetic field, an electromotive force is produced in the plasma in a direction normal to both the field and the plasma path. Using two probes facing one another this electromotive force has been measured with an oscillograph. Its maximum value was found to be proportional to the field and the probe separation. By taking the maximum probe potential for different values of the external resistance between the probes, the lowest value of the "resistivity of the plasma" as measured by a current entering and leaving it was obtained. The resistivity has been shown to be independent of the magnetic field, the collecting area, the separation and surface state of the probes. All experiments were made in hydrogen at a gas pressure between 0.5 and 5 mm Hg with a nearly critically damped current pulse of order 104 amperes lasting for about 6-8 μsec and fields <2000 gauss. The plasma resistivity between the probes was found to be of the order 1 ohm cm at a gas pressure of a few mm of Hg. This is about 100 times larger than the electronic resistivity of a fully ionized gas for currents circulating internally. The degree of ionization is thought to be high enough for interaction between charged particles to predominate. The measured values of the plasma resistivity agree with the results obtained from theory based on ionic conduction in the plasma which is here the necessary prerequisite for maintaining the electric neutrality of the moving plasma. From the measured probe voltage the flow velocity of the plasma was derived. Its variation with gas pressure agrees with shock wave theory. © 1960 the American Physical Society.
Microwave propagation through modulated air plasma
(Springer India, 1979) S.K. Varshney; M. Sakuntala
When a microwave propagates through a plasma in which electron density and electron collision frequency periodically vary, the propagating wave is modulated in amplitude and phase. An approximate theory is derived to suit the laboratory experimental conditions. Introducing the amplitude and phase difference, the dependence of electron density and electron collision frequency has been derived for different radio frequency modulation and frequency parameter. A scanning double probe technique is used to measure the exact time variation in the plasma parameters at any fixed position during a single cycle of the applied field. Theoretical values agree with those of experiment. © 1977 the Indian Academy of Sciences.