• S K Varshney

      Articles written in Pramana – Journal of Physics

    • Microwave propagation through modulated air plasma

      S K Varshney M Sakuntala

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      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.

    • Electron temperature (Te) measurements by Thomson scattering system

      R Rajesh B Ramesh Kumar S K Varshney Manoj Kumar Chhaya Chavda Aruna Thakkar N C Patel Ajai Kumar Aditya Team

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      Thomson scattering technique based on high power laser has already proved its superoirity in measuring the electron temperature (Te and density (ne) in fusion plasma devices like tokamaks. The method is a direct and unambiguous one, widely used for the localised and simultaneous measurements of the above parameters. In Thomson scattering experiment, the light scattered by the plasma electrons is used for the measurements. The plasma electron temperature is measured from the Doppler shifted scattered spectrum and density from the total scattered intensity. A single point Thomson scattering system involving a Q-switched ruby laser and PMTs as the detector is deployed in ADITYA tokamak to give the plasma electron parameters. The system is capable of providing the parameters Te from 30 eV to 1 keV and ne from 5 × 1012cm−3−5 × 1013cm−3. The system is also able to give the parameter profile from the plasma center (Z=0 cm) to a vertical position of Z=+22 cm to Z=−14 cm, with a spatial resolution of 1 cm on shot to shot basis. This paper discusses the initial measurements of the plasma temperature from ADITYA.

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