An investigation on the interaction of high energy muons, associated with EAS and having energies greater than several hundred GeV, has been carried out at Kolar Gold Fields. A visual detector consisting of neon flash tube hodoscope has been used together with a scintillator detector to observe the muons and accompanying showers at the underground level.

It has been found that nearly 90% of the showers observed at the underground level are generated in course of pure electromagnetic interactions of the muons with the matter traversed by them. The observed number of the showers is found to be consistent with the expected number calculated using the cross-sections for knock-on, bremsstrahlung and direct pair production processes.

Rest of the observed showers do not appear to fit in the pure electromagnetic interaction scheme. Various possible production processes for these events have been discussed. Considering these events to be due to photonuclear interaction of muons in the rock, the observed number leads to a production cross-sectionσ_μ(≳25 GeV) ⋍(1.6±0.75)10⁻²⁹ cm²/nucl.

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.K-spectra for density and potential fluctuations follow power law with indices (−3·7 ± 0·5) and (−5·6 ± 0·6) respectively.

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 amplitudem = 2 mode displays strong sidebands indicating particle trapping by the non-linear waves. Non-linear wave-wave and wave particle interactions, thus, appear to play at important role in the saturation of the cross field instability.

An experiment has been carried out at a vertical depth of 580 m.w.e. at Kolar Gold Fields, to investigate various characteristics of energetic muons (E_mln ⋍ 150 GeV) associated with extensive air showers (EAS). Double parallel penetrating particles with narrow separations (<1m) have an exponential decoherence distribution withe-folding separation of ⋍ 25 cm.

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.

The double layer like potential jumps have been observed in a double plasma device. They do not correspond to a switching of plasma potential from one metastable state to another but are caused by the ionisation of a very minute amount of the gas that inevitably leaks into the system during the probe movement.

Results of the investigation on the formation of double layers in double plasma device are presented. By appropriate modifications in the biasing conditions, we have been able to obtain both weak (eΔφ<10KT_e) and strong double layers (eΔφ>10kT_e) in the device. Unlike previous experiments, we have not been limited to potential jumps equal to ionisation potential of the neutral gas. A detailed investigation has been carried out to find out why earlier experiments in similar devices were limited to only weak double layers.

We have also investigated the phenomenon of the so-called psuedo-double layers and have shown that they are potential jumps over the thickness of the order of Debye length and precede plasma expanding with velocity many times the ion-acoustic velocity. They do not represent metastable states of the plasma as suggested by earlier investigators.

The spatial and temporal structures of magnetic signal in the tokamak ADITYA is analysed using recently developed singular value decomposition (SVD) technique. The analysis technique is first tested with simulated data and then applied to the ADITYA Mirnov coil data to determine the structure of current peturbation as the discharge progresses. It is observed that during the current rise phase, current perturbation undergoes transition from m=5 poloidal structure to m=4 and then to m=3. At the time of current termination, m=2 perturbation is observed. It is observed that the mode frequency remains nearly constant (≈10 kHz) when poloidal mode structure changes from m=4 to m=2. This may be either an indication of mode coupling or a consequences of changes in the plasma electron temperature and density scale length.

A typical device for carrying out sophisticated and complex dusty plasma experiments is designed, fabricated and made operational at the Institute for Plasma Research, India. The device is named as complex plasma experimental device (CPED). The main aim of this multipurpose machine is to study the formation and behaviour of dust vortices in the absence of external magnetic field under the effect of various plasma parameters. Further, the device is equipped with advanced imaging diagnostics for studying many other interesting phenomena such as dust oscillations, three-dimensional crystalline structures, dust rotation, etc. The device is quite flexible to accommodate many innovative experiments. Detailed design of the device, its diagnostics capabilities and theadvanced image analysis techniques are presented in this paper.