TCV – Specific diagnostics

 

Langmuir probes

AXUV diagnostic

Fast framing visible camera

Infrared cameras

Charge exchange spectroscopy

Hard-X rays tomography spectrometer

Tangential phase contrast imaging

 

Langmuir probes

 

  • Measures currents or potential
  • Plasma temperature, density and potential can be inferred
  • Graphite tips embedded in the wall tiles
  • 26 probes on the machine floor, 37 on the inner wall, 19 (+17 soon) on the outer wall.

 

Reference: R. A. Pitts, R. Chavan and J.-M. Moret, The Design of Central Column Tiles for the TCV Tokamak
Nuclear Fusion 39 (1999) 1433  

 

 

 

Already installed (blue) and forthcoming (green) Langmuir probes position in the TCV walls.

 

 

Contact person: Benoit Labit

 

The AXUV diagnostic:

  • Measures the total radiated power emitted by the plasma
  • 7 pinhole cameras with 20 lines-of-sight each.
  • Photodiodes with a high temporal response (5 mus)
  • Tomographic reconstruction possible.

 

References:

I. Furno et. al., RSI 1999 Fast bolometric meas. on the TCV tokamak

A. W. Degeling RSI 2004 AXUV bolometer & Lyman-alpha cameras on the TCV

G. Veres JNM 2007 Radiation distributions in TCV

 

Contact person: Basil P. Duval

 

 2D time resolved radiated power emitted by the plasma over an ELM cycle. From left to right, the plasma shape changes from a single-null divertor to the snowflake divertor

 

 

 

Fast framing visible camera

 

A fast imaging system, comprising a fast framing camera and telescope optics monitors the visible light fluctuations, up to 250kframes/s. Such system allows a fully non-perturbative reconstruction of plasma dynamics at different scales, with a spatial resolution as high as a few mm.

 

 

Visible light emitted by the plasma during an ELMy H-mode in TCV. Camera parameters: 1024 x 1024 pixels, 3000 frames/s

 

Contact person: Ivo Furno

 

 

 

 

Infrared cameras

 

State-of-the-art of fast infrared camera

Measures the heat deposition around the divertor targets

Fast time-scale (up to 25 kHz): ELM- and disruption-related studies,

Combined with Langmuir Probe data

Detector: Thermosensorik CMT256M HS, a camera using a 256×256 pixel semiconductor detector with CMT (Cadmium Mercury Telluride) technology.

Photons are digitized on 14 bits.

 

Left Figure: Experimentimental setup for the vertical Infrared camera on TCV.

 

 

 

 

 

 

 

 Contact person: Holger Reimerdes

 

 

 

 

Charge exchange spectroscopy (CXRS)

Provides local measurements of ion temperature and impurity density,

Provides toroidal and poloidal rotation, through the analysis of spectral moments of an impurity line radiation

Line populated by charge exchange reaction between intrinsic impurity (carbon) and a diagnostic neutral beam (DNB), which is weak enough to not perturb the plasma significantly. This permits CX measurements in the absence of auxiliary ion heating and external input torque.

Optimized for plasmas vertically centered in the vacuum vessel.

 

 Evolution of the rotation profile as a function of the ECRH deposition

 

Contact person: Alexander Karpushov

 

 

 Hard-X rays tomography spectrometer

 

The Hard X-Ray Tomographic Spectrometer (HXRS) is a tomographic hard x-ray (HXR) camera system that measures the bremsstrahlung emission (typically in the 10-200 keV energy range) coming from a poloidal slice of plasma along a discrete set of different anglular views. The radiation detected is fed to a tomographic routine that returns the 2D poloidal bremsstrahlung emission profile. HXR bremmstralhung emission comes from collisional slowing down of fast electrons (with energy exceeding the thermal energy and therefore also called suprathermal) on ions. The spectroscopic grade CdTe detectors proposed for this camera system permit the determination of the bremsstrahlung photon energy distribution

Reference: S. Gnesin, Electron Cyclotron Heating and Suprathermal Electron Dynamics in the TCV Tokamak

 

Contact person: Stefano Coda

 

 

 

Tangential phase contrast imaging

The Tangential Phase Contrast Imaging diagnostic is a CO2-laser based system that generates an image of line-integrated density fluctuations on a plane perpendicular to the beam. It is conceptually similar to an interferometer, but the reference beam is not external but internal. Plasma waves scatter the beam inducing phase variations which are transformed into amplitude variations by means of a phase-contrast filter. An image of the plasma is then created using an optical system.

The tangential geometry makes it possible, in combination with an additional filter selecting a specific fluctuation wave-vector direction, to localize the measurement to a small fraction of the length of the beam, hence a small region in plasma minor radius. A resolution of 1% of the minor radius can be achieved. By varying the orientation of the filter, different regions from the core to the edge can be imaged, along with a mainly radial or poloidal component of the fluctuation under consideration. The adjustability of the launching and receiving mirrors adds further flexibility, allowing the magnetic axis to be reached if wanted.

The 10.6-µm wavelength, 7-W CO2 laser beam is 7 cm in diameter and the image is obtained through a 30-element linear detector array. By varying the imaging system magnification, wave numbers from 1 to 60 cm-1 can be resolved. Typical wave numbers around 0.5 cm-1 are expected for TEM’s, 16 cm-1 for ETG. The bandwidth is approximately 2 MHz (expected ~250-1000 kHz for TEM, 5-8 MHz for ETG) and the sensitivity to density fluctuations is of the order of 1×1016 m-3.

 

Contact person: Stefano Coda