P I John
Articles written in Pramana – Journal of Physics
Volume 8 Issue 2 February 1977 pp 123-132 Plasma Physics
Results on dispersion and spectral characteristics of crossfield instability in a collisional magnetoplasma are presented for different values of externally applied radial electric field. The dispersion relation obtained experimentally differs significantly from predictions of linear theory for strong electric fields.
At large values of applied electric fields, the main crossfield modes appear to give rise to a number of other modes possibly through non-linear wave-wave interactions. Large amplitude
Volume 14 Issue 3 March 1980 pp 175-183 Plasma Physics
Experimental investigations of the phenomena occurring when low density electron and plasma beams are injected into a nonadiabatic magnetic mirror are presented. Effects of nonadiabaticity and mirror ratio on the reflectivity of the magnetic mirror are measured. Transition of the mirror from adiabatic to strongly nonadiabatic results in setting up of a potential barrier which enhances the reflectivity.
Volume 17 Issue 3 September 1981 pp 279-285 Plasma Physics
A technique for improving the transmission of intense electron beams through cusp magnetic field in vacuum using dielectric drift tubes has been demonstrated. The plasma produced by the material of the dielectric tube increases the transmission efficiency by a factor of four over vacuum values.
Volume 23 Issue 1 July 1984 pp 1-16 Plasma Physics
Experimental results on interaction of a rotating relativistic electron beam with plasma and neutral gas are presented. The rotating relativistic electron beam has been propagated up to a distance of 150 cm in a plasma. The response of the plasma to the rotating electron beam is found to be of magnetic diffusion type over a plasma density range 1011–1013 cm−3. Excitation of the axial and azimuthal return currents by the rotating beam and subsequent trapping of the azimuthal return current layer by the magnetic mirror field are observed. A field-reversed configuration has been formed by the rotating relativistic electron beam when injected into neutral hydrogen gas. We have observed field reversal up to three times the initial field in an axial length of 100 cm.
Volume 44 Issue 1 January 1995 pp 55-66
Experiments on collisional ion sheaths are carried out by applying a pulsed negative bias on a disc electrode immersed in a collisional plasma. The pulse is characterized by a linear rise, followed by a constant voltage phase and then exponential decay. The measured currents to the electrode are compared to predictions from a dynamic collisional ion sheath model which is developed from the basic two fluid equations. The parameter determining the degree of collisionality is also defined. The agreement between the two in the rising and the flat top phases of the pulse is found to be good. Some residual discrepancies as well as the disagreement in the decay phase are discussed.
Volume 44 Issue 3 March 1995 pp 263-270
Experimental results on the measurement of current collected by an electrode immersed in a plasma for a pulsed negative bias are presented. The measured current is compared with a model based on the concept of an expanding capacitor. The scaling laws predicted by the model are verified for the measured current which agree each other. The paper emphasizes the role of displacement current in an expanding ion sheath.
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