Abstract
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 Ar
1+
line emissions at 472.69 nm (3p
4
4s
2
P
3/2
–3p
4
4p
2
D
3/2
), 473.59 nm (3p
4
4s
4
P
5/2
–3p
4
4p
4
P
3/2
), 476.49 nm (3p
4
4s
2
P
1/2
–3p
4
4p
2
P
3/2
), 480.60 nm (3p
4
4s
4
P
5/2
–3p
4
4p
4
P
5/2
) are recorded using a high resolution visible spectrometer. Also, a VUV spectrometer has been used to simultaneously observe Ar
13+
line emission at 18.79 nm (2s
2
2p
2
P
3/2
–2s2p
2
2
P
3/2
) and Ar
14+
line emission at 22.11 nm (2s
2
1
S
0
–2s2p
1
P
1
). The diffusivity and convective velocity of Ar are obtained by comparing the measured radial emissivity profile of Ar
1+
emission and the line intensity ratio of Ar
13+
and Ar
14+
ions, with those simulated using the impurity transport code, STRAHL. Argon diffusivities ~ 12 m
2
/s and ~ 0.3 m
2
/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.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Abstract We have carried out atomic structure calculations using systematically enlarged multiconfiguration Dirac-Fock wavefunctions of Li-like ions of the most prominent plasma impurities (Ar, Ti, ...Fe, Ni, Kr and W) found in presently working tokamaks. Relativistic Breit interaction and quantum electrodynamic (QED) corrections such as vacuum polarization and self-energy corrections are also included in the calculations prior to the evaluation of low lying energy levels, transition probabilities, oscillator strengths and line strengths. Selective radiative data for electric dipole and magnetic quadrupole transitions are also reported. Special emphasis is given in the computations of fundamental quantities such as oscillator strengths as they are widely used in atomic data and analysis structure (ADAS) databases to evaluate quantities such as effective collision strengths. Present computed values are compared with existing available results on NIST database and few similar earlier computations and a good agreement has been found. We believe that the detailed atomic data with the relativistic and QED corrections will assist in spectroscopic studies such as accurate line identification and plasma modelling work in tokamak plasma, laser induced breakdown spectroscopy (LIBS), highly charged ions clocks and astrophysical observations.
The effective charge, Zeff, of the plasmas of the Aditya tokamak has been analyzed to understand its behavior. It has been measured through the monitoring of the visible bremsstruhlang continuum ...emission around 523.4 nm from the plasma using an optical fiber, interference filter and photo multiplier tube based visible spectroscopic system. It has been found that the values of Zeff fall in the range of 1.7-4.0 and decrease with increasing plasma electron density, ne and the incremental value of Zeff is inversely proportional to ne2. The value of Zeff reduces in the range of 1.7-2.5 in the discharges produced after the Li coating compare to the values of 2.0-3.5 range in the discharges before the Li coating in the Aditya tokamak. Details analysis on the contribution to Zeff from various impurities suggests that reduction of Zeff after Li coating is not only due to decrease of oxygen concentration, but also other impurities, such as iron, inside the plasma.
The present study details the generalization of a stability condition for the semi-implicit formulation of the one-dimensional impurity transport equation for tokamak plasmas in terms of the magnetic ...flux surface coordinate system (ρ). The radial impurity transport equation for tokamak plasmas is a set of non-linear, parabolic, partial differential equations, solving which generates the radial distributions of all impurity charge states (Z) within the plasma. The present study illustrates the application of a semi-implicit method over the ρ-based impurity transport equation, generated by applying a transformation of the coordinate for the poloidal cross-section of the torus-shaped plasma confinement system, from its geometric radius (r) to the magnetic flux surface coordinate system (ρ). The study further discusses the von Neumann stability analysis of the numerical scheme applied to this transformed (ρ-based) impurity transport equation. The von Neumann stability analysis of the semi-implicit formulation of the radial impurity transport equation has been reported earlier. The stability condition derived in this study is, therefore, a generalization to the earlier reported stability condition now applicable to all ρ(r) including the specific case ρ = r considered in the earlier study. The effects of the impurity transport coefficient (D and v) profiles and the plasma and impurity parameter profiles on the derived ρ-based stability condition are analysed in this study. The impurity element considered is oxygen (1 ≤ Z ≤ 8) and the geometry and plasma parameters of the ADITYA tokamak are applied to the cases studied for consistency.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
On ADITYA-U tokamak, a spectroscopic diagnostic has been developed to measure the radial profile of visible continuum radiation for determining the plasma effective charge, Zeff, to study the ...impurity transport and MHD driven instabilities. It consists of the collimating lenses, optical fibers, a multi-channel wavelength selection system, and photo multiplier tubes. The optical system allowing continuum radiation measurements around 536 nm (the wavelength selection system) consists of set of lenses, optical fibers and an interference filter with diameter of 5 cm and bandwidth of 3 nm. The spatial profile of radiation with a spatial resolution of ∼ 3 cm has been recorded from eight lines of sight viewing the plasma using an UHV compatible rectangular view port placed on the bottom port of the ADITYA-U tokamak. The centrally peaked spatial profile of visible continuum radiation has been recorded from the ADITYA-U tokamak plasmas. The chord averaged Zeff values estimated from the brightness measured along the central chord fall within 2.5 to 4.1 for the electron densities of 1.0 - 2.2 × 1019 m−3.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The first Indian tokamak, ADITYA, operated for over two decades with a circular poloidal limiter, has been upgraded to a tokamak named ADITYA Upgrade (ADITYA-U) to attain shaped-plasma operations ...with an open divertor in single and double-null configurations. Experimental research using ADITYA-U has made significant progress since the last FEC in 2016. After installation of a plasma facing component and standard tokamak diagnostics in ADITYA-U, the Phase-I plasma operations were initiated in December 2016 with a graphite toroidal belt limiter. Ohmically heated circular plasmas supported by filament pre-ionization with plasma parameters Ip ~ 80-95 kA, duration ~80-180 ms, with a maximum toroidal field ~1 T and chord averaged electron density ~2.5 × 1019 m−3, have been obtained. The runaway electron (RE) generation, transport and mitigation experiments, along with magneto hydrodynamic (MHD) activities and density enhancement with H2 gas puffing experiments were carried out in Phase-I, which was completed in March 2017. Preparation for the Phase-II operation in ADITYA-U includes calibration of magnetic diagnostics followed by commissioning of major diagnostics and installation of a baking system. After repeated cycles of baking the vacuum vessel up to ~135 °C, the Phase-II operations resumed in February 2018 and are continuing to achieve plasma parameters close to the design parameters of circular limiter plasmas, using real-time plasma position control. The plasma current has been raised to ~135 kA in Phase-II, with a maximum chord averaged electron density of ~4 × 1019 m−3. Hydrogen gas breakdown has been observed in more than 2000 discharges, including Phase-I and Phase-II operations, without a single failure. Several experiments have been carried out, including the control of REs with the fuelling of supersonic molecular beam injection as well as sonic H2 gas puffing during current flat-top, MHD mode studies using multiple periodic gas puffs, and radiative improved modes using neon gas puffs. The experimental results from Phase-I and Phase-II operations of the ADITYA-U tokamak are discussed in this paper.
Dust events are recorded in the SST-1 tokamak with fast visible imaging and infrared imaging systems. The events are analyzed from the image sequences with an in-house developed dust tracking routine ...in MATLAB called FINDUST. Specific operating scenarios for dust observation and their deleterious effects on discharge evolution are identified. A clear correlation of the dust events frequency and strength with the successful start-up and discharge evolution is observed over eight consecutive experimental campaigns in SST-1. It has been seen that the electron cyclotron resonance heating (ECRH) generated pre-ionization slab annular-plasma around the fundamental layer is most likely to generate dust, while the strongest effect of the ECRH fundamental layer on the plasma facing components is seen when the confined plasma column disrupts by some means while the ECRH pulse is still ON.
The radial impurity transport equation for tokamak plasma is a form of diffusion–convection–reaction equation. The impurity transport equation is solved to determine the distribution of impurity ...(non-fuel) ion species with different ionization states perpendicular to magnetic surfaces of tokamak plasma. The equation for each charge (ionization) state Z is a non-linear, second-order in space, first-order in time, parabolic partial differential equation coupled to the previous Z − 1 and the next Z + 1 charge states of the impurity species through its reaction term. The number of differential equations to be solved simultaneously is hence determined by the number of ionization states of the impurity species studied. The solution to the set of these coupled equations can be obtained using a semi-implicit numerical method applied on it. The present study describes the application of von Neumann stability analysis over the semi-implicit numerical method applied over the radial impurity transport equation and determines a generic stability criterion for the method. The stability analysis is further illustrated using the geometry of Aditya tokamak installed at the Institute for Plasma Research Gandhinagar, India as an example. The impurity species considered is oxygen (Atomic number = 8). This leads to a set of eight coupled equations for charge states Z = 1 to 8 over which von Neumann analysis is illustrated in present study.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In the ADITYA Upgrade tokamak, glow discharge wall conditioning (GDC) is performed regularly during the high-temperature plasma operation cycle using hydrogen (H) and helium (He) gases. H GDC is ...carried out after long durations (few hours) of plasma operations on every plasma operation day in automatic mode to control oxygen (O) and carbon (C) containing impurities. This leads to high retention of H gas on graphite limiter plates and stainless steel (SS) vessel walls. Subsequently, the high outgassing of H requires a prolonged pumping time and high H recycling during plasma discharges affects the plasma performance in respect to H fueling control of the plasma. To overcome the above-mentioned issues with continuous H GDC for longer durations, a new approach involving pulsed glow discharge wall conditioning (P-GDC) has been introduced in the ADITYA-U tokamak to reduce the residual H and He concentration in SS vessel walls and graphite limiter plates. To facilitate the fast initiation of a discharge in the case of P-GDC, a source of free electrons from a hot filament has been introduced in the vessel. A fast feedback controlled pulsed-gas-fueling system has been developed to initiate a glow discharge in each gas-feed pulse at various operating pressures from 1 × 10−4 Torr to 10−3 Torr in the presence of an applied DC voltage. The different P-GDC experiments have been carried out with H, He and argon as the working gases and the results are compared with traditional continuous GDC. The P-GDC experiments have been optimized to provide beneficial wall conditioning for plasma operations. In this paper, the design, development and operation of P-GDC has been described along with the preliminary studies of its effect on the measured impurity line radiation during a plasma discharge.
