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[en] A corona model is used in analyzing the Doppler shifted spectroscopy (DSS) data for estimating the ion species mix and beam species fractions in positive ion based neutral beam injectors. In this model the excited neutral atom is assumed to decay solely by a spontaneous radiative process. However, at the beam energies of 20-60 keV/amu, collisional quenching of the excited neutrals affects these estimations when background pressure exceeds 1 mTorr. We present here a modified corona model that takes into account the effects of collisional quenching. We also describe the results of application of the present model to a typical DSS data obtained in the first phase of operation of the SST-1 neutral beam injector.
[en] A positive ion neutral injector (PINI) capable in delivering 5MW (55kV, 90A) ion beam power is being operated for SST-1 neutral beam injection (NBI). The production and neutralization of the ion beams in the injector requires a gas throughput of 20 torr I/s in the plasma box and 50-100 torr I/s in the neutralizer section. It is necessary to maintain operating pressure of vessel at 10-5 torr to reduce the re-ionization loss of beam within tolerable limits. Conventional Turbo molecular pumps cannot maintain this vacuum level at required gas feed rate so two cryo condensation pumps are being operated to achieve require vacuum in vessel. In order to monitor and optimize the performance of cryopumps, it is necessary to measure the temperature at various locations in LN2 and LHe path. It is also required to monitor the level of LHe and LN2 in cryopumps. Several temperature and level sensors are mounted at various places in cryopumps and integrated with PLC and SCADA based control system. This paper presents the details of sensor mounting, signals conditioning, scheme of their integration with PLC and SCADA and results in detail. (author)
[en] The temporal profiles of the spectral lines Li I and Li II emitted by a laser blow off of LiF-C film were analyzed. Fast neutrals having energies of ∼310 eV were observed. It was found that these fast neutrals have kinetic energies similar to that of the ablated ions. Photon production rates at 670.8 nm were estimated for the recombination and charge exchange processes. We attempted to qualitatively understand the role of electron-ion recombination (two and three body recombinations) and charge exchange processes in producing observed fast neutrals. Our analysis indicates that charge exchange is the dominant process in the production of fast neutrals
[en] We have pointed out that in the race to develop negative ion source plasma physical and technical issues related to the plasma production and its transport, negative ion production and its extraction, effects of Cs and its recycling inside the source etc. have remained poorly understood. For any further improvement in the performance of the source, it is necessary to unravel different physical mechanisms leading to the formation of H- ions and its extraction and transport. For understanding these studies, we present here a conceptual design of an inductively coupled radio frequency (RF; ∼ 150 kW, 1 MHz) negative hydrogen ion source for the neutral beam injector (NBI). The source shall deliver 1.5 MW of hydrogen beam at 150 keV. A transverse magnetic filter field with ∫B.dl ∼2000 Gauss-cm, helps to separate the driver region (Te ∼ 20 eV, ne ∼ 1013 cm-3) from the extractor region (Te ∼ 1 eV, 1012 cm-3). Injection of Cs in the extractor region helps to enhance the negative ion production. During the extraction of the negative ions, the electrons are also co-extracted. Permanent magnets embedded in the extraction grid system help to filter out these electrons. (author)
[en] The evolution features of lithium ions and neutrals generated by two different schemes viz. the laser-blow-off (LBO) of multicomponent LiF-C thin film and conventional laser ablation (referred here as LPP) from solid lithium have been studied using optical emission spectroscopic technique. The optical signal emitted by Li I (at 670.8 nm) and Li II (548.4 nm) was monitored as a function of laser fluence, ambient gas pressure, and distance ''z'' from the target. Apart from their similarities, some interesting differences were noticed in temporal profiles of the plumes generated by LPP and LBO both in vacuum as well as in the presence of the ambient gas. A comparative analysis of experimental results indicates that the ablation mechanism and subsequent laser-plume interaction were responsible for the observed differences in LPP and LBO plumes. Expansion features of the plume are discussed in the light of two different models
[en] Asymmetric broadening of Hα line from cathode glow region has been studied. In the cathode glow, mean energy and fractional population of very fast hydrogen atoms were found to be ∼130 eV and ∼55%, respectively. These values reduced to ∼90 eV and ∼20% when measured at negative glow region. The observed asymmetry was attributed to the presence of the fast hydrogen atoms near the cathode surface. The mean energy and number density of excited fast hydrogen atoms were estimated from the velocity distribution of H+, H2+, and H3+ considering collisions inside the cathode sheath. The reduction in the mean energy and number density of the excited fast hydrogen atoms, at the other locations of the discharge, was explained by energy relaxation and thermalization of the neutrals with the background gas.
[en] Neutral beam injectors (NBI) find applications in the field of plasma heating current drive and diagnostics of tokamak plasma. The neutral beams are generated by neutralization of the ion beams (H+ of energy 30-100 keV) produced from high current ion sources. The ion sources used in application of plasma heating have a characteristic beam divergence of ∼1°. Whereas, ion sources used as a diagnostic tool requires divergence less than 1°. Divergence is dependent on the configuration of ion beam extraction/acceleration grid system. In general, the grid system is made up of a set of circular apertures. Recent investigation indicates that slit shaped apertures yield lower divergence thus, making them suitable for application to the plasma diagnostics. We present here a design study of slit type apertures for the extraction/acceleration system in the development of H+ ion source. In IPR, these studies are being carried by means of ion trajectory simulation (OPERA-3D). We include here the salient features of the design. (author)
[en] High resolution spectral analysis of lithium plasma formed by single and double laser ablation has been undertaken to understand the plume-laser interaction, especially at the early stages of the plasma plume. In order to identify different atomic processes in evolving plasma, time resolved spectral emission studies at different inter-pulse delays have been performed for ionic and neutral lithium lines emitting from different levels. Along with the enhancement in emission intensity, a large line broadening and spectral shift, especially in the case of excited state transition Li I 610.3 nm have been observed in the presence of the second pulse. This broadening and shift gradually decrease with increasing time delay. Another interesting feature is the appearance of a multi-component structure in the ionic line at 548.4 nm and these components change conversely into a single structure at the later stages of the plasma. The multi-component structures are correlated with the presence of different velocity (temperature) distributions in non-LTE conditions. Atomic analyses by computing photon emissivity coefficients with an ADAS code have been used to identify the above processes.
[en] Steady state Superconducting Tokamak (SST-1) machine is equipped with a Neutral Beam Injector (NBI) to raise the plasma ion temperature ∼ 1 keV. This injector has a capability of injecting hydrogen beam with power of 0.5 MW at 30 keV. To fulfill this requirements NBI need to extract 1 MW at 30 kV from ion source. NBI sub-systems are Neutralizer, Magnet Coil (MC), Magnet Liner (ML), Ion Dump (ID), V-Target (VT), Pre Duct Scraper (PDS), Beam Transmission Duct (BTD), Shine Through (ST). In addition to this auxiliary systems are Power Supply, Data Acquisition and Control System (DACS), Cooling Water System (CWS), Cryogenic System and Vacuum System. During operation neutral beam has to travel 7 m from exit plane of ion source to Tokamak plasma center. All the above mentioned subsystems shall receive various heat load from 50 kW – 500 kW and to remove the same active cooling is provided to each subsystem for safe operation. This paper shall describe in details about NBI water cooling system from concept to engineering design. After study of heat load to each subsystem, we have finalized required water flow rate and pressure drop in each line of cooling network. Engineering design has been done and Piping Instrumentation and Design (PID) drawing also completed. Presently NBI CWS is in fabrication stage and shall be commissioned at the end of this year. (author)
[en] Atomic analysis of the emission from laser-produced plasma from bulk lithium (Li) block has been made. The observed changes in the emission from lithium neutral and ionic species have been explained by considering various atomic processes. We demonstrate that the excitation process in case of neutral lithium Li (I) is electron impact excitation whereas for singly ionized lithium Li (II), radiative recombination is the dominant mechanism. We also show that the ionized species are dominant in the LPP plume.