A. Qayyum
Abstract
A newly developed diagnostic system based on linear photodiode array and triple Langmuir probe for spatial and temporal characterization of hydrogen plasma in Glass Spherical Tokamak (GLAST-III) has been reported. The spectral range of each silicon photodiode is from 300 nm to 1100 nm with response time of 10 ns and active area of 5 mm2(circular).The light from the plasma is collected through narrow opening along 4 lines of sight channels with spatial resolution of about 5 cm. The photodiode's signals located at position of 10 and 14 cm from inboard side show fluctuating behaviour of the central plasma region. Moreover, the sequence of plasma lighting shows that plasma instigates from the central resonant field region and then expands outwards. At lower pressure, outboard movement of the plasma is slower suggesting better plasma confinement. In addition to photodiode array, an Ocean spectrometer (HR2000+) has been used to record the visible spectrum over the selected range (597–703 nm) with a spectral resolution of 0.15 nm. The studies have been conducted during initial phase of plasma formation for two different hydrogen gas fill pressures. Triple Langmuir probe (TLP) is used to obtain time-resolved information on plasma parameters in the edge region. The time evolution of whole discharge including microwave pre-ionization phase and current formation phase has been well seen by temporal profiles of light emission and plasma floating potential.
