The Academy of Sciences of the Czech rebublic - ASCR


Reciprocating probes

 

Measured quantities: Measurement in the Scrape-off-layer region of
  • radial profiles of plasma electric potential, electron density and temperature
  • plasma velocity along magnetic field
  • fluxes of particles and energy towards the wall
  • ion temperature
Spatial resolution: 2-4 mm
Temporal resolution:: 1 µs
Responsible persons: J. Horáček, J. Adámek
Status: Operational since summer 2010
Purpose: Study the physics of plasma at contact with the vessel with general goal to
  • decrease the plasma heat & particle flux on the vessel => increasing lifetime of the internal structures
  • decrease contamination of the core plasma by the sputtered vessel material => improving fusion performance
Physics studied: Turbulent processes causing anomalous plasma fluxes towards the wall and transporting impurities along the magnetic field lines.
Collaboration:
  • The vertical probe was built in Univ. of California San Diego (USA) and later reconstructed at CRPP EPFL (Switzerland). The probe was loaned on long-term basis to IPP Prague.
  • The horizontal probe was built at UKAEA (Great Britain)
  • Both manipulators reconstructed under the EFDA WP08-TGS-01-06 Priority support
  • Sofia University (Bulgaria) is constructing new probe heads

 

 

Diagnostic description:

Since electrostatic probes are in direct contact with the hot plasma, they are mounted on a fast pneumatic manipulator reciprocating quickly (within 0.1 second) in and out to avoid overheating, which would cause the impurity release, and, consequenty, cooling the plasma or the probe head destruction.

 

At parking position the probe is behind gate valve. Therefore, either the probe head or the manipulator itself can be replaced without breaking the tokamak vacuum. Status of the head can also be checked visually through vacuum window after each discharge.


Planned Upgrades: We plan to increase speed of the manipulator and optimization of the probe heads to survive higher heat flux. If successful, we could put both probes at a single magnetic surface inside the pedestal transport barrier during the H-mode, yielding thus worldwide unique opportunity to study Long-range correlations – phenomena that might be responsible for the global plasma transition into the improved confinement H-mode.

 

 

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Fig. 1: Geometry of the horizontal manipulator. The table (in blue) supports the manipulator. In park position the probe head is at position of the vacuum window (see Fig. 4), then penetrates leftward through the gate valve (green) into the tokamak vessel and reaches the plasma separatrix during fast movement.

 

 

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Fig. 2: Geometry of the vertical manipulator. In park position, the head is at position of the vacuum window just above the gate valve. Then, it penetrates vertically inside the chamber to start a fast reciprocation up to the plasma separatrix.

 

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Fig. 3: The vertical probe head.

 

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Fig. 4: View at the horizontal probe head through the vacuum window.