Dr. Anil Kakodkar Chairman




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GOVERNING COUNCIL


Dr. Anil Kakodkar Chairman


Prof. V.S.Ramamurthy Member


Dr. S. S. Kapoor Member


Dr. Bikash C Sinha Member


Shri P. D. Karandikar Member


Ms. Sudha Bhave Member


Prof. G. S. Agarwal Member


Shri.Arvind N. Lalbhai Member


Shri V. M. Vora Member


Prof.P.K.Kaw Member


Shri M. A. Shah Non-Member Secretary


COVER STORY


INSTITUTE FOR PLASMA RESEARCH


On the west bank of the river Sabarmati, a few kilometers upstream from the Gandhi Ashram, a small number of low buildings are grouped together on a little hillock rising among the ravines and low grazing land. The pastoral setting and the quiet surroundings belie the high tech character of the place where a group of scientists are engaged in one of the most exciting and challenging tasks of this century - controlling nuclear fusion. The idea that energy can be obtained by fusing nuclei of light

elements to produce heavier elements has been known for a long time. It is also a process that continually occurs in the Sun where the fusion of hydrogen is the principle source of its energy. But the real challenge lies in trying to create this form of energy on earth by recreating the conditions of the Sun in the laboratory. The pursuit of this goal has been a worldwide effort over the last forty years. The Institute for Plasma Research, located in village Bhat - a few kilometers outside Ahmedabad, is a recent entrant in this endeavour and is the prime expression of India's commitment to this futuristic energy source.


The Institute has a broad charter of objectives to carry out experimental and theoretical research in plasma sciences with emphasis on the physics of magnetically confined plasmas and certain aspects of nonlinear phenomena. The Institute also has a mandate to stimulate plasma research and development activities in the Universities and the industrial sector. It is also expected to contribute in the training of plasma physicists and technologists in the country. Since its inception the Institute has pursued these goals in an active manner and made some effective contributions. The Institute in its second phase of experimental activity has embarked on an ambitious project of building the first Indian Steady State Superconducting (SST1) Tokamak.


EXECUTIVE SUMMARY


The Institute is pursuing several facets of plasma research and technology development. Work on fusion plasmas is being conducted on tokamak ADITYA. Some novel features of tokamak edge turbulence relevant to transport of matter and heat across field lines were studied during the year; it was shown that for short scales, turbulence exhibits features of scale invariant Levy statistics. This may have relevance to observations of bursty transport from tokamaks. Experiments with many new diagnostics and RF heating systems have also been initiated on ADITYA during the year. Many of these are preparing the ground work for SST 1 experiments. Fabrication of SST-1 subsystems is now approaching conclusion. The prototype for the 1/8th sector of vessel and cryostat has been completed by BHEL, Trichy. It has been delivered to IPR and is being used for a number of in-house tests. The liquid Helium plant has been fabricated, tested and delivered. It is getting ready for erection, commissioning and testing. The subsystem for AC power distribution systems is in an advanced state of completion. Many of the superconducting coils for SST- 1 have been wound and delivered to IPR. The coming 2 years should see the completion of all SST subsystems, their erection and early commissioning tests of the device. Fundamental plasma experiments with dusty plasmas have led to exciting new results on the first demonstration of transverse shear modes in 3-d fluid like dusty plasmas. Novel methods of current drive in a basic toroidal experiment using whistler modes have also led to unexpectedly efficient current generation.


P.K. KAW

DIRECTOR


ANNUAL REPORT


April 1, 2000 to March 31, 2001


The institute was established as an autonomous institution in 1986. The major objectives of the institute have been to carry out experimental and theoretical research in plasma physics with emphasis on the physics of magnetically confined hot plasmas and non-linear plasma phenomena.


1 SCIENTIFIC AND TECHNICAL PROGRAMMES


Scientific programme of the institute is aimed at generating expertise in high temperature magnetically confined plasma experiments. High temperature plasma environment is mandatory to achieve fusion reaction. Activities in the institute, therefore, relates to study of equilibrium and stability of high temperature plasmas and upgradation of their parameters. At the same time basic experiments and experiments related to immediate plasma technology dissemination to industry forms an integral part of the programme.

The programme can broadly be categorised in to three activities: a) studies on high temperature magnetically confined plasmas, b) basic experiments in plasma physics including Free electron laser, dusty plasmas and other nonlinear phenomena, c) industrial plasma processing and application.


The major experimental work on high temperature magnetically confined plasmas is being conducted in tokamak ADITYA. Main aim of this activity is to reliably operate a tokamak at high temperature and high plasma current. The plasma is formed by an electrical breakdown in an ultra high vacuum toroidal vessel and a current is inductively driven in the plasma. As the plasma temperature rises the efficiency to heat the plasma drops. To further raise the temperature of the plasma to fusion grade, one has to use auxiliary heating schemes. During experimentation at high temperatures, it is also required to diagnose the plasma with various sophisticated diagnostic tools. Work on these areas is being perused in these areas.


During the course of the year few new diagnostics, namely, Thomson scattering for temperature measurement, ECE diagnostic for temperature profile measurement, soft X-ray camera and laser blow-off diagnostic systems have been commissioned on ADITYA. At the same time a high power electron cyclotron resonance frequency system at 28 GHz has been successfully commissioned on ADITYA. The will be used during initial break down of the plasma as well heating at a later date.


A new experiment (SST-1) in the field of steady state operation of tokamaks is the other main experimental effort in the institute. This project is focussed to address physics and technology issues related to steady state tokamaks and so called advanced tokamak configurations. In this experiments many conventional questions in tokamak physics will be addressed in the steady state scenario. Some of these questions will be in the areas of energy, particle and impurity confinement during steady state operation. Plasma disruptions and vertical displacement episodes will also be studied. Non-inductive current drive would sustain the plasma current during steady state. Different aspects of current drive will also be studied. Since we will have long duration plasma, lot of heat will be removed by components near the edge of the plasma. Various aspects of these problems are being studied during the fabrication and integration of SST-1.


Proto type fabrication for most of the subsystems have been concluded and based on the results final fabrication of many components of the subsystems for SST-1 have concluded. They are being tested before integration. The proto-type of the vacuum vessl – cryostat has been installed at the laboratory. All invessel components would be qualified for their vacuum compatibility in it. Some of the magnetic field coils have been received at site after successful predespatch tests. Liquid helium plant is being erected and commissioned at site. Many of the components for the RF heating and NBI systems have been received at site. Final tests are being performed before integration and commissioning. Diagnostic systems, control and data acquisition systems are being prepared.


Basic experiments have always formed a major part of our research efforts. Various new and ongoing basic experiments are being carried out in the institute. Plasmas in these experiments are relatively cooler, rarer and less complicated. Hence, they can be easily and thoroughly diagnosed. They relate to understanding of various facets of plasma which is otherwise difficult to study in bigger experiments. Stability and equilibrium of toroidal plasma in presence of radio frequency waves and new current drive mechanism with these waves are being continued. Issues related to excitation, propagation and linear, nonlinear interaction of whistler and helicon waves are being studied in a large volume plasma device. Free electron laser experiment is being continued. Many aspects of dusty plasma are being experimentally studied.


Equilibrium and non-equilibrium plasma properties can be exploited for commercial uses. In the areas of plasma processing and application, the engineering and technological experties of the institute are exploited to generate advanced material processing technologies. Development programmes are selected on the basis of the need expressed by industries. A multi-disciplinary team of physicists, engineers and material scientists has been nucleated. They cover activities like liasion with industries, consultancy and technology transfer to industries. Commercial prototype of medical waste plasma pyrolysis system, plasma nitriding system installation at IGCAR, experimentation on plasma nitriding of titanium and SiOx like coating using constricted anode plasma source, supply of PSII system to IIT Kharagpur are some of the major activities concluded by this group.


Activities performed during the year in these areas are described in some detail in the following sections of this report.


1.1 ADITYA TOKAMAK


      1. THE DEVICE


ADITYA, a medium size Tokamak, is being operated for over a decade. It is regularly being operated with the transformer-converter power system. ~100 msec 80 - 100 kA plasma discharges at toroidal field of 8.0 kG are being regularly studied. During this period experiments on edge plasma fluctuations, turbulence and other related works have been conducted. Standard diagnostics have been employed during these measurements. The accompanying figure gives a view of ADITYA with the auxiliary heating systems attached to it.





Present View of ADITYA Tokamak


ADITYA has been upgraded. Upgradation has been in different fronts. Vacuum system has been upgraded interms of more cleaning facilities. Some more diagnostics have been integrated and made on-line. Some are in the design/fabrication phase. To increase the plasma energy content during the discharge, auxiliary heating systems have been integrated. A 20 – 40 MHz, 200 KW Ion Cyclotron Resonance Heating (ICRH) system has been integrated to ADITYA vacuum vessel. A 28 GHz, 200 KW gyrotron based electron cyclotron resonance heating (ECRH) system has been successfully commissioned on ADITYA tokamak.


Vacuum System


Main objective is to maintain good vacuum and wall conditioning and reduce impurity level in ADITYA Tokamak.


Lithium Surface Conditioning and Limiter Biasing Experiments have been conducted. An experiment on Molecular Beam Injection in ADITYA has also been proposed and would be carried out in future. Following other experiments have been initiated in ADITYA, edge profile measurement, lithium oven diagnostics, etc., in which ADITYA vacuum group has been involved. Efforts have been made to have pre ionisation to assist plasma break down.


During the year, complex installations of mirror box of ECRH system, movable limiter, Langmuir probes etc. have been carried out.


A new power supply with controls for Electron Cyclotron Resonance (ECR) discharge cleaning has been designed, procured, tested and installed. ECR and/or PDC discharge cleaning is routinely carried out for few hours to 24 hours in shifts, as and when required. Experiments have been carried out to optimise ECR parameters.


Molecular beam injection system has been installed on ADITYA for efficient gas feeding. Experiments would be performed using this system to study its efficiency on ADITYA.


To improve performance of ADITYA vacuum system, a control system has been designed. Experiments have been carried out to study contamination due to exposure to atmosphere. While leak testing, the gate valve on Laser blow off system was found to be leaking. It was opened and repaired in situ.


Surface analysis of coatings on various samples has been carried out at FCIPT. Aditya poloidal limiter has been exposed to more than 10,000 discharges. Therefore the tiles will be replaced with new graphite tiles which have been baked upto 1000o C for 24 hours in the vacuum oven, commissioned recently and have been kept ready for replacement during the next opening.


Like earlier times, leak testing  of various diagnostics systems  with  helium  leak detector and Ultra High Vacuum testing with UHV test-stand  have been carried out as and when required.


EXPERIMENTAL RESULTS


Lithium Surface Conditioning Experiment

An experiment in ADITYA with in-situ lithium conditioning to study effect of lithium conditioning on ADITYA discharges has been performed. The aim of lithium conditioning is to reduce hydrogen recycling, impurity influx and to improve plasma parameters viz.. plasma density, temperature, confinement time and MHD activities. Lithium conditioning has been done by evaporation of lithium in ADITYA vacuum vessel during discharge cleaning. Partial pressures of lithium and oxygen are monitored with Quadrupole Mass Analyser. An increase in partial pressure of lithium (100 %) has been observed whereas for oxygen, it is reduced to 50 %. The density achieved is 1 x 1013 /cc. It had a flat top for 30 millisecond. Sawtooth activity is suppressed. Presence of lithium is also monitored by spectroscopy. It observed an increase in H-alpha (instead of reduction) and reduction in hard X - rays. The plasma parameters thus are improved.


Experiments to study lithium coating on vacuum vessel wall have been initiated. Solid lithium target probes have been prepared. These probes are introduced in a UHV system and lithium coating experiments have been performed successfully. More experiments would be performed to study the effect of lithium coating. Lithium coating on limiter is also proposed in ADITYA.


Limiter Biasing Experiment


The ADITYA limiter consists of 16 segments of graphite tiles and thus provides an opportunity to study the role of biasing with a set of biasing in different configuration. One of the limiter tiles is biased up to –500 V with respect to the vessel. When the limiter current drawn exceeds 300 A various diagnostic signals indicate an improvement of particle/energy confinement. H radiation as well as floating potential fluctuation (monitored by Langmuir probes) shows significant reduction. The amplitude of floating potential reduced by 80 % at all frequencies. Before biasing the limiter frequency spectrum of the fluctuation shows a peak at 10-15 KHz, which disappeares during biasing. Signals from the central detector of the soft X-ray camera indicate a rise in temperature by 50-100 eV within 3-4 ms of the application of the bias. A sharp decrease up to 50 % in H radiation has been observed.


Turbulence Studies


The understanding of fluctuation driven anomalous transport of particle and heat is still of paramount interest in modern fusion devices. The apparent lack of any characteristic time and length scales in the edge plasma fluctuations has prompted a search for scale invariant properties. To that end, the floating potential fluctuations in the Scrape-off layer plasma of ohmically heated ADITYA tokamak have been analyzed. It is observed that the probability distribution function of a sum of n random fluctuations converge to a Lévy distribution for n < 40 whereas for larger n, the distribution converges to a Gaussian. The Lévy and the Gaussian processes are paradigms of super diffusive and diffusive transport processes respectively. Thus our observation indicates that the transport of small scale fluctuations takes place by convection, whereas large scales follow the diffusive law.


1.1.2 DIAGNOSTICS


New diagnostic systems include Thomson scattering, Lithium beam, ECE, Bolometer, Soft X-ray etc. Polarimetry is being designed and fabricated to be tested on ADITYA and finally used in SST-1. Some of these systems are described below.

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