Diagnostics

Tokamak ISTTOK Diagram

Magnetic diagnostics:

• Rogowski coil: There are two coils of this type, with 500 spires each and 3.25 mm in diameter, measuring both the internal (plasma) and the external (total) toroidal currents.
• Sin and Cos coils: Each of these coils, 3.2 mm in diameter, has 300 spires. Together they are used for the determination of the position of the plasma current axis.
• Mirnov coils: There are twelve Mirnov coils distributed along the poloidal direction, in a single transverse plane. They measure the MHD activity and may be used for the determination of the position of the plasma column.
• Toroidal loop: This diagnostic is constituted by a single loop and measures the loop voltage.

Electric probes: Four different electric probe systems are routinely used: (i) a radial array of probes (rake probe); (ii) a turbulent transport probe; (iii) a Gundestrup probe; and (iv) an array of emissive probe.

• Rake probe: The rake probe consists of a boron-nitride head carrying nine tungsten tips with a spatial resolution down to 4 mm, given information of the edge floating potential and ion saturation current radial profiles with high temporal and spatial resolution.
• Gundestrup probe: Information on the plasma flow patterns in the edge plasma is obtained using a Gunderstrup probe, which consists of eight conducting segments mounted around an insulating cylindrical housing in order to measure the polar diagram of the ion saturation current.
• Turbulent transport probe: The turbulent transport probe consists in radially and poloidally separated pins measuring the floating potential and the ion saturation current and allows the determination of the turbulent particle flux.
• Emissive probes: The array of emissive probes has been specifically designed to investigate the difference between emissive and Langmuir probes for turbulence studies;

Interferometer: A single channel interferometer, at 100 GHz, with heterodynic detection used to determine the line-averaged density;

Bolometer tomography: The bolometer tomographic diagnostic is based on 3 linear 10-pixel detectors. The reconstruction of the plasma emissivity profile is performed using overdetermined analytical methods (Cormack based);

Heavy-ion beam diagnostic: A 10 μA, 22 keV, Cesium primary beam is used to probe the plasma. Secondary ions are collected by a surface array detector with a maximum of 16 x 4 copper cells, sampling cylindrical plasma volumes with the primary beam cross section and a length of about 10 mm. This diagnostic allows the determination of the density, temperature and poloidal magnetic field radial profiles. The heavy-ion beam diagnostic has been recently upgraded to allow the determination of the plasma potential profile using the time-of-flight technique;

Line radiation monitors: Photodiodes with interference filters of narrow bandwidth centered in the Hα line or in impurities lines (e.g. CIII);

Visible and VUV spectroscopy: Visible and UV radiation emission comes mainly from impurity lines. A high resolution spectrometer is used for ion temperature and ion rotation measurements (Doppler spectroscopy). Another diagnostic based on a spectrometer, a multi-channel (x7) fiber to collect the light and a CCD camera for radiation detection is used to measure radial density profile of different impurity lines at the plasma edge;

Residual gas analyzer: The residual vacuum of ISTTOK is analyzed by means of a quadrupolar RGA (Spectramass DATAQUAD);

Emissive electrode: A movable emissive electrode has been developed for the biasing experiments in ISTTOK. The emissive electrode consists of a LaB6 (Lanthanum Hexaboride) disk with a diameter of 16 mm and covered by a Tantalum cylinder, which is protected by Boron Nitride cup as insulating material to be exposed to the plasma. When heated the electrode emits up to 30 A of steady state curren

Data Acquisition

The Control and Data Acquisition System (CODAS) of ISTTOK has served not only to support and operate the tokamak but also to test new ideas and developments specific of fusion devices. From the beginning of the ISTTOK project, state of the art equipment has been used in this area. ISTTOK has served as a test bed for new hardware and software developments that later ware exported to other fusion devices. As a consequence of this approach, the ISTTOK CODAS has evolved continuously, starting from the early VME buses, through PCI and nowadays ATCA. Recently, a strong afford has been placed in real time control and remote participation. As an example, an ISTTOK “virtual control room” has been developed and it is available at the moment over the Internet.

Remote Data Access

A common software layer between end-users and laboratories has been developed at CFN in order to allow an easy and unified data access to any of the participating associations data. Detailed information on the access to the ISTTOK database may be found here (Link).

Education and Training

ISTTOK has been used to support the experimental part of post-graduation programmes on plasma physics and engineering. During the past eight years about twenty Master and five PhD thesis have been written based on work performed on this tokamak. Visits to our laboratories are often organized for high school and undergraduate students. Furthermore, in the past 3 years a one week summer course has been organized for typically 10 high school students. This programme of education and training has allowed CFN to create a research team with the adequate number of qualified professionals.