A. Malaquias

Engineering aspects of the tokamak ISTTOK

AbstractThe first Portuguese magnetic confinement experiment, the tokamak ISTTOK, has been in operation since 1993. This tokamak device is described and the main technological features, as well as the novel techniques of its diagnostics and control and data acquisition system, are reported. A synopsis of the experimental activity is also presented.

The heavy ion beam diagnostic for the tokamak ISTTOK

In this paper we describe the heavy ion beam diagnostic for the tokamak ISTTOK, which has been designed to determine the temporal evolution of the plasma density, poloidal magnetic field and plasma potential profiles. This diagnostic makes use of a new type of high density caesium plasma source, a multiple cell detector and a fast data acquisition system. We describe the numerical code for trajectory and beam attenuation simulations, a method for the experimental determination of the poloidal field profile, the ion gun and the detection, control and data acquisition systems. Calibration tests and the first experimental results are presented. >

Integration of in-vessel diagnostic sensors in ITER

Integration of diagnostic electrical sensors and their signal transmission in ITER is a combination of the process of physical location within a limited space and complex topology, while accounting for effects on the transmitted signals from the particular local nuclear environment [1]. All components of the signal transmission chain are important. Diagnostic sensors are seen in all parts of the ITER vacuum vessel and transmission lines must cross many functional zones, notably the blanket and the vacuum/pressure boundaries. Effects on the signal emanate from conductor variations (radiation and thermally induced conductivity drift, thermo-electric effects, e-m loading, contact resistance), insulator variations (reduction of voltage stand-off, resistivity degradation, material deposition) and interference (e-m noise, microphony, current and voltage leakage). The particular nuclear aspects to be addressed are the high first wall photon flux, the high fast neutron and gamma fluxes, and high neutron fluence. Designs have been developed for the integration of sensors and their connecting wiring within the vacuum vessel, shielding blanket, divertor cassettes and port structures. These are presented here, considering first the radiation effects, then the integration of the diagnostic sensors, the transmission routes and finally the transmission hardware.

Measurements of the plasma potential by HIBP using a TOF method

A heavy ion beam diagnostic is being developed for the tokamak ISTTOK (R=0.46 m, a=0.085 m, Bt≅0.5 T, Ip=6–9 kA), based on multiple cell array detectors, aimed at the study of the time variation of the plasma density, electron temperature, poloidal magnetic field, and plasma potential radial profiles. In this article we describe an alternative method to the traditional electrostatic energy analyzers for measurements of the plasma potential based on the time-of-flight technique. The initial results of the measurements of the changes on the average plasma potential during tokamak discharges with minor disruptions are also presented. These results have been obtained measuring the time-of-flight of the ions of a pulsed primary beam from the electrostatic plates of the ion gun to the primary detector.

Development of a new type of Cs plasma ion gun for application in a heavy ion beam tokamak diagnostic

A new type of high-density caesium plasma ion source is described, which is capable of producing Cs+ beam currents of up to 300 mu A. The ion emitting surface in the caesium plasma conforms automatically to the accelerator geometry to give perveance match, providing that the ion density is correctly adjusted with respect to the required beam energy. Ready operation of the source at different energies with constant perveance is facilitated in this way. Consequently, the beam divergence is practically independent of the beam energy. The plasma density is maintained at the required level by controlling the temperature of the source chamber walls on which atomic caesium is deposited. The ion source and the beam transport line have been developed at Culham and deliver a low-divergence 1.5 mu A Cs+ beam at the gun output, with an energy of up to 25 keV. The apparatus now serves as the injection part of the heavy ion beam deflection analyser of the ISTTOK tokamak in Lisbon.

ITER diagnostics: Integration and engineering aspects

ITER diagnostic equipment is integrated in six equatorial and 12 upper ports, five lower ports, and the 16 divertor cassettes directly in front of them, and at many locations in the vacuum vessel. The integration has to satisfy multiple requirements and constraints and at the same time must deliver the required diagnostic performance. Design work has been carried out in problematical and interfacing areas for most diagnostics. The main diagnostic support components, the port plugs and divertor port racks, comprise common structural elements with dedicated modules from several diagnostics. The scope of the engineering task is summarized and an overview of the integration of the diagnostic equipment is given. The engineering work to date represents the input to the port engineering tasks of the construction phase with common or repeated elements being assessed for feasibility, resolving issues, and identifying show stoppers. It has been dominated by allocation and spatial integration in the tokamak. The work that follows will be more oriented towards the acceptability for operation, suitability for function, and conformity for licensing.

New detection system and signal processing for the tokamak ISTTOK heavy ion beam diagnostic

The tokamak ISTTOK havy ion beam diagnostic (HIBD) operates with a multiple cell array detector (MCAD) that allows for the plasma density and the plasma density fluctuations measurements simultaneously at different sampling volumes across the plasma. To improve the capability of the plasma density fluctuations investigations, a new detection system and new signal conditioning amplifier have been designed and tested. The improvements in MCAD design are presented which allow for nearly complete suppression of the spurious plasma background signal by applying a biasing potential onto special electrodes incorporated into MCAD. The new low cost and small size transimpedance amplifiers are described with the parameters of 400 kHz, 10(7) V/A, 0.4 nA of RMS noise, adequate for the plasma density fluctuations measurements.

Evolution of the poloidal magnetic field profile of the ISTTOK plasma followed by heavy ion beam probing

Abstract The evolution of the poloidal magnetic field profile during the initial current ramp-up in the ISTTOK tokamak plasma has been followed with a heavy ion beam diagnostic. The experimental results are compared with numerical simulations. The validity of the retrieved poloidal field profiles is discussed.

Radial profile measurements of plasma pressure-like fluctuations with the heavy ion beam diagnostic on the tokamak ISTTOKa)

The Heavy Ion Beam Diagnostic (HIBD) on the tokamak ISTTOK (Instituto Superior Técnico TOKamak) has been modified, in terms of signal conditioning, to measure the local fluctuations of the neσ1,2(Te) product (plasma density times the effective ionization cross-section) along the tokamak minor diameter, in 12 sample volumes in the range of -0.7a < r < 0.7a, with a maximum delay time of 1 μs. The corresponding signals show high correlation with the magnetic Mirnov coils in the characteristic MHD frequency range of ISTTOK plasmas and enable the identification of tearing modes. This paper describes the HIBD signal conditioning system and presents a preliminary analysis of the radial profile measurements of local neσ1,2(Te) fluctuations.

Comparative study design of a heavy ion and neutral beam diagnostic for the International Tokamak Experiment Reactor

In this article, we address the major physics principles and the engineering issues associated with the implementation of a heavy ion beam diagnostic for the International Tokamak Experiment Reactor (ITER) for the edge measurements of the plasma electric and poloidal magnetic fields. Two different diagnostic configurations are discussed. The ions’ trajectories and attenuations were calculated by dedicated simulation codes using the relevant ITER equilibrium parameters. Estimations of measurement accuracy are presented for a chosen configuration.