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An accurate and reliable measurement of poloidal β is essential to assess the performances of Joint European Torus (JET). The diamagnetic loop can measure β values as low as 0.1 in JET discharges with a plasma current larger than 2 × 10[sup 6] A. The instrumentation used includes a flux loop rigidly fitted on a toroidal field (TF) coil, a large Rogowski coil measuring the TF busbar current, and a displacement gauge measuring the TF coil expansion. The fluxes to be compensated originate, in order of importance, from the TF current, the eddy current in the vessel, the TF coil expansion, and the stray coupling with the poloidal fields. The TF and eddy currents must be particularly well compensated on JET since the plasma current starts before the toroidal field has reached its plateau value. Comparison between the diamagnetic and other evaluations of β shows a good agreement. [ABSTRACT FROM AUTHOR]

Measurement of the plasma generated diamagnetic flux on tokamak à configuration variable (TCV) is used to derive the plasma pressure, as on other magnetic confinement experiments. However, specificities of the device make the measurement more difficult: for passive stabilization of the vertical position of highly elongated plasmas, the vessel has a low electrical resistivity, leading to large image currents in the vessel. For the same reason the plasma must also be kept close to the conducting wall, so that the in-vessel double loop method usually used to compensate for these currents cannot be applied. In order to achieve proper compensation, the diamagnetic measurement diagnostic on TCV uses the signal from a single loop wound outside the vessel in combination with appropriate signal processing that accurately matches the fast component of the induced vessel current. This allows extraction of the plasma diamagnetic flux with a remarkable bandwidth, of ∼10 kHz, and with the required accurate compensation of 0.05 mWb out of 2 Wb. As a result, rapid changes in plasma pressure can be studied, for example during additional heating power modulation or fast plasma instabilities. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: The ITER high-frequency (HF) magnetic diagnostic system has to provide essential measurements of MHD instabilities with |δB MEAS/B POL|∼10−4 (∼1G) for frequencies up to 2MHz to resolve toroidal mode numbers (n) in the range |n|=10 to |n|=50. A review of the measurement requirements for HF MHD instabilities in ITER was initiated during the TW4 work-program and led to significant interest for physics and real-time control issues in measuring modes with |δB MEAS| as low as ∼10−3 G at the position of the sensors, with |n|≤30 and poloidal mode numbers |m|∼2|n| up to |n|∼15, for a frequency range extending up to ∼500kHz. We have examined the ability of the current ITER design for the individual sensors and the diagnostic system as a whole to meet these needs, and have explored what adjustments to the design (of the individual sensors and/or of the system as a whole) or to the requirements would be needed to meet them when considering different hypothesis for the financial costs and risk management over the ITER life-time. First, we find that the proposed diagnostic layout, with 168 sensors in total, does not meet the more stringent measurement requirements and risk management criteria: these can only be met by a revision of the design requiring 350–500 sensors, depending on different costing and risk management options. Second, we find that the current design for the ITER HF Mirnov-type pick-up coil could be usefully revised. [Copyright &y& Elsevier]

This paper presents the multiple set of requirements for the ITER magnetic diagnostic systems and the current status of the various R&D activities performed by the EU partners. [ABSTRACT FROM AUTHOR]

Examines the design of tokamak configuration variable to create plasma shapes. Requirement of plasma flexibility; Description of the magnetic sensor geometry, fabrication, calibration, associated electronics and diagnostic operation in sensor position and monitoring; Method for deriving corrections in sensor position and calibration.