Role of pinch in Argon impurity transport in ohmic discharges of Aditya-U Tokamak.

We present experimental results of the trace argon impurity puffing in the ohmic plasmas of Aditya-U tokamak performed to study the argon transport behaviour. Argon line emissions in visible and Vacuum Ultra Violet (VUV) spectral ranges arising from the plasma edge and core respectively are measured simultaneously. During the experiments, space resolved brightness profile of Ar1+ line emissions at 472.69 nm (3p44s 2P3/2-3p44p 2D3/2), 473.59 nm (3p44s 4P5/2-3p44p 4P3/2), 476.49 nm (3p44s 2P1/2-3p44p 2P3/2), 480.60 nm (3p44s 4P5/2-3p44p 4P5/2) are recorded using a high resolution visible spectrometer. Also, a VUV spectrometer has been used to simultaneously observe Ar13+ line emission at 18.79 nm (2s22p 2P3/2-2s2p2 2P3/2) and Ar14+ line emission at 22.11 nm (2s2 1S0-2s2p 1P1). The diffusivity and convective velocity of Ar are obtained by comparing the measured radial emissivity profile of Ar1+ emission and the line intensity ratio of Ar13+ and Ar14+ ions, with those simulated using the impurity transport code, STRAHL. Argon diffusivities ~ 12 m2/s and ~ 0.3 m2/s have been observed in the edge (ρ > 0.85) and core region of the Aditya-U, respectively. The diffusivity values both in the edge and core region are found to be higher than the neo-classical values suggesting that the argon impurity transport is mainly anomalous in the Aditya-U tokamak. Also, an inward pinch of ~ 10 m/s mainly driven by Ware pinch is required to match the measured and simulated data. The measured peaked profile of Ar density suggests impurity accumulation in these discharges.

Impurity toroidal rotation profile measurement using upgraded high-resolution visible spectroscopic diagnostic on ADITYA-U tokamak.

A high-resolution spectroscopic diagnostic for the measurement of spatial profiles of impurity ion toroidal rotation velocities on the ADITYA-U tokamak has been upgraded to cover the complete plasma minor radius. Earlier, the coverage of diagnostics toward the plasma edge was restricted due to the placement of collection optics on the tangential port outside the vacuum vessel. The coverage of the full plasma minor radius, from 0 to 24 cm, has been achieved using the newly designed and developed collection optics that have seven lines of sight to view the tokamak plasma mounted inside a customized re-entrant view port which is installed in the shadow of the limiter inside the vacuum vessel. The upgraded diagnostic also includes a faster charged coupled device detector with a smaller pixel size for the detection of a small wavelength shift. The complete spatial profile has been measured using the Doppler shifted passive change exchange spectral line at 529.0 nm from the C5+ ion. In this article, we present the collection optics' design, installation, calibration, and results obtained using the upgraded diagnostic.

Observations of visible argon line emissions and its spatial profile from Aditya-U tokamak plasma.

The spectroscopic studies of medium and high Z impurities have been the subject of interest in fusion research due to their role in mitigating plasma disruption and reducing heat load on the plasma facing components. Line emissions from these impurities provide the rotation velocity and ion temperature measurements along with the understanding of the overall impurity behavior in plasma. In the Aditya-U tokamak, the spatially resolved Ar II line emissions have been observed using a high resolution multi-track spectroscopic diagnostic consisting of a 1 m Czerny-Turner spectrometer coupled with a charge coupled device (CCD) detector using seven lines of sight viewing plasma tangentially along the toroidal direction. The spatially resolved Ar II lines at 458.96 nm have been observed. The singly ionized Ar emission peaks at the radial location of ρ = 0.8 of the plasma having a minor radius of 25 cm. Moreover, a 0.5 m UV-visible spectrometer coupled with a CCD detector and having a line of sight passing through the plasma midplane from the radial port was used to record visible Ar survey spectra within the 670-810 nm wavelength range, and all these lines have been identified for further analysis.

Characterizing breast cancer tissues through the spectral correlation properties of polarized fluorescence.

We study the spectral correlation properties of the polarized fluorescence spectra of normal and cancerous human breast tissues, corresponding to patients belonging to diverse age groups and socioeconomic backgrounds. The emission range in the visible wavelength regime of 500 to 700 nm is analyzed, with the excitation wavelength at 488 nm, where flavin is one of the active fluorophores. The correlation matrices for parallel and perpendicularly polarized fluorescence spectra reveal correlated domains, differing significantly in normal and cancerous tissues. These domains can be ascribed to different fluorophores and absorbers in the tissue medium. The spectral fluctuations in the perpendicular component of the cancerous tissue clearly reveal randomization not present in the normal channel. Random matrix-based predictions for the spectral correlations match quite well with the observed behavior. The eigenvectors of the correlation matrices corresponding to large eigenvalues clearly separate out different tissue types and identify the dominant wavelengths, which are active in cancerous tissues.

Plasma rotation measurement using UV and visible spectroscopy on Aditya-U tokamak.

A high resolution spectroscopic diagnostic for the measurement of the spatial profile of toroidal rotation velocity (vt) and temperature (Ti) of carbon ions has been developed and implemented on the Aditya-U tokamak. The diagnostic consists of a high resolution 1 m (f/8.7) spectrometer having an 1800 grooves/mm grating coupled with a charged couple device. The setup allows measurements from 5 toroidal lines-of-sights passing through different minor radii in the horizontal mid-plane of the Aditya-U tokamak. The carbon line emissions at 529 nm in visible and 229.6 and 227.09 nm in the ultra violet spectral range are recorded using the setup. Initial results show that typical Aditya-U plasmas have a maximum carbon ion temperature (Ti) of ∼120 eV and a rotation velocity (vt) of ∼-14 km/s in the counter plasma-current direction.

Design of tangential x-ray crystal spectrometer for Aditya-U tokamak.

A tangential soft x-ray crystal spectrometer has been designed to measure the x-ray spectrum of He-like argon for the Aditya-U tokamak plasma. The system enables to measure electron temperature using the intensity ratio of the resonance line to the satellite line. For this purpose, an x-ray spectral line at 3.9494 Å from He-like argon, Ar16+, is considered. The spectrometer consists of a cylindrically bent silicon (111) crystal and a CCD detector to measure the resonance spectral line and its satellite lines in the wavelength region of 3.94-4.0 Å, viewing the plasma tangentially at an angle of 26° with respect to the toroidal direction in the magnetic axis. Considering Aditya-U tokamak plasma parameters and its geometrical constraints, plasma to crystal and crystal to detector distances have been kept at 1.47 m and 0.5 m, respectively, to detect a sufficient signal. The engineering design has been optimized after adequately addressing the issues related to port geometry and machine accessibility. Details on the design of the crystal spectrometer are presented in this paper.