Study of magnetic annular plasma accelerator Summary report, 15 Apr. 1964 - 14 Jan. 1966

Magnetic annular arc for achieving high propulsive efficiencie

Contactless measurement of electric current using magnetic sensors

We review recent advances in magnetic sensors for DC/AC current transducers, especially novel AMR sensors and integrated fluxgates, and we make critical comparison of their properties. Most contactless electric current transducers use magnetic cores to concentrate the flux generated by the measured current and to shield the sensor against external magnetic fields. In order to achieve this, the magnetic core should be massive. We present coreless current transducers which are lightweight, linear and free of hysteresis and remanence. We also show how to suppress their weak point: crosstalk from external currents and magnetic fields

Local magnetic measurements in magnetic circuits with highly nonuniform electromagnetic fields

In this paper, local magnetic measurements are carried out in magnetic circuits with highly non uniform electromagnetic field patterns, including excitation winding and/or air gaps, as in the case of rotating electrical machines. The effect of sensor choice, sensor noise sensitivity, electromagnetic field nonlinearity, and magnetic shielding are investigated. Moreover, the validity of the local magnetic measurements is confirmed by numerical models

EFFECT OF LITHIUM COATING ON THE IMPURITIES AND SHIELDING EFFECT OF PLASMA ON THE RESONANT MAGNETIC PERTURBATIONS FIELD IN THE STOR-M TOKAMAK PLASMA

Effects of lithium coating of the chamber wall on the impurities in the STOR-M tokamak plasma were studied in this thesis work. Impurities have been identified as one of the major concerns since the beginning of tokamak plasma research, as they enhance the radiation losses and prevent plasma from being heated to a desired high temperature. The radiation losses are primarily due to line radiation from incomplete stripped impurity ions. Impurities are introduced into the plasma from the walls of the tokamak due to plasma-wall interactions, and the type of impurities observed in a tokamak is partially determined by the kind of material used for the tokamak chamber wall and the gases absorbed in the wall. In the STOR-M tokamak, inner surface walls are made of bare stainless steel, and the major impurities observed are from carbon and oxygen. The emission lines from these impurities are in the visible range of the electromagnetic spectrum. They are CIII which is observable at 464.74 nm, CVI at 529.05 nm, and OV at 650.02 nm. Before the chamber was coated with lithium, the intensities of the impurity lines were measured and then compared to the intensities after the lithiumization of the chamber wall. The intensities of the impurity lines were recorded during the stable period of plasma before and after the lithium coating using a spectrometer and an intensified charge-coupled device (ICCD) camera. It was observed that the intensities of the impurities reduced during the discharges immediately after the lithium coating. Further experimental analysis revealed that the freshly coated lithium caused plasma density to decrease, and increase after 300 plasma discharge shots. It was also found that after 600 and 900 plasma discharge shots, lithium coating does not appear to play any role in the reduction of the impurity intensities, but repetitive plasma discharge cleaning may be responsible for the decrease in the impurity intensities. In another experiment, an internal radial magnetic probe array was used to investigate effects of plasma and tokamak chamber wall on resonant magnetic perturbation (RMP) field applied externally to plasma. An internal magnetic probe array was used to measure the magnetic field at four radial locations at plasma edge after the application of RMP current. The plasma response magnetic field measured was subtracted from the vacuum field measured when RMP current was fired without plasma. The time delay caused by the plasma and tokamak chamber wall to the RMP field was also studied by calculating the difference between the RMP current waveform peak time and the magnetic field waveforms peak times in plasma. It was observed that RMP field in vacuum was 50% larger than the RMP field in plasma, and the penetration time of the RMP fields decreased as they penetrate through the vacuum wall into the plasma. The RMP field was found to travel faster in plasma than in vacuum

Development of non-conventional instrument transformers (NCIT) using smart materials

In this paper is presented a novel approach for current measurement using smart materials, magnetic shape memory (MSM) alloys. Their shape change can be controlled by the application of magnetic field or mechanical stress. This gives the possibility to measure currents by correlating the magnetic field produced by the current, shape change in an MSM- based sensor and the voltage output of a Linear Variable Differential Transducer (LVDT) actuated by this shape change. In the first part of the paper is presented a review of existing current measurement sensors by comparing their properties and highlighting their advantages and disadvantages

Analysis and possible improvements of a Rogowski transducer for current measurements in a lightning laboratory for aerospace applications

Problems related to the measurement of high current lightning pulse in a noisy environment are investigated, to improve the Data Acquisition System of Morgan Botti Lightning Laboratory. A transducer based on Rogowski coil and passive RC integrator is tested. Solutions are proposed to enhance SNR, including numerical and electronic filtering. Results show that measurements are affected by type of coil used, its position in the circuit and by an initial disturb. Hypothesis on its origin are mad

Design and construction of a new coaxial high voltage fast impulse current transducer

Since the introduction of zinc-oxide material in 1968 much research has been directed towards the characterisation of the electrical behaviour of the material under various stress conditions. An aim of some of these investigations is to achieve an equivalent circuit representation, which adequately simulates the observed test results. An adequate equivalent circuit representation will aid the reliable and efficient design of the overvoltage protection and help to improve the optimisation of the protective devices. A significant impediment to the accurate characterisation of zinc oxide has been the lack of reliable test data especially for fast-rate-of-rise impulses in the microsecond and sub-microsecond range. The measurement of current impulses in this range is highly influenced by the circuit arrangement and measurement transducer characteristics. In this work, a non-inductive coaxial current shunt was designed and constructed. The fast impulse tubular current shunt was based on the nickel chromium resistive material with a designed value of 5mΩ and 10kA current capability. The current shunt was successfully constructed except the nickel chromium material, which could not be successfully soldered to the aluminium casings. It is recommended that the work is to be completed in future projects