Progress and New Results from the H-1NF Scanning Interferometer Scott Collis, George Warr, John...
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Transcript of Progress and New Results from the H-1NF Scanning Interferometer Scott Collis, George Warr, John...
Progress and New Results from the H-1NF Scanning
InterferometerScott Collis, George Warr,
John Howard
A Time Multiplexed Interferometer
• The System is basically described as two Michelson Interferometers with a time varying viewing path viewing
• The phase shift induced by the plasma is given by
• The signal is time multiplexed, which means we only need one detector per probe beam
dlnλr2Δφ ec
Beams are swept by a grating wheel
• Wheel speed can be varied from 0-6000rpm
• At 6000 rpm with a 6 partitioned wheel one scan of the plasma takes 1.8ms
• The wheel also Doppler shifts the beam:
dmRf /
Motor and Grating
Continuous Grating allows viewing of small structures
• The grating constant changes linearly across a sector
• Possibility of seeing small structures, of order 1cm (beam size) such as islands and transport barriers
• Data can aliased when frequency of plasma oscillations approaches the scan frequency of the interferometer
Fosc > Fscan
Aliased Data
Calibration
•We need a transform from temporal position in scan
to spatial position in the H-1NF tank
A 2.5cm absorber was placed at three positions on the bottom
mirror
At 40cm above the centre
In the centre of the mirror
And at 40cm below the centre
Top Diagonal Results
Beam width: 1.3cm
Bottom Diagonal Results
Beam width: 3.2cm
Calculated Beam Positions
High Density ICRH Shot
•Fundamental ICRH resonance of Hydrogen
•B=0.5T
•Peaked density profile
•Highest B2ne product observed in H-1NF
Possibilities
• With the wheel running at high speed it is possible to get temporally and spatially resolved information on the plasma decay
• From this it will be possible to solve the two dimensional diffusion equation
• With the new ICRH mode it is possible to study the physics of fully ionized plasmas in H-1NF
But first….
• To tomographically reconstruct density maps of the H-1NF plasma we need a greater coverage of the plasma
• We will be expanding the fan of the diagonal views and installing a central view
Using the interferometer to understand particle transport
• Using a gas puffer it is possible to modulate the source term in the continuity equation
• By modulating the gas flow and using the high temporal and spatial resolution of the interferometer it is possible to gain an insight into how particle transport occurs in H-1NF
• Information can be combined with other instruments to gain not only ne but Te Ti and ion velocity
Conclusion
• The H-1NF Scanning interferometer can make spatially and temporally resolved measurements of the plasma with resolutions of up to 1cm and 1.8ms
• As the system is upgraded the data it produces will provide physical insight into the behavior of flexible Heliac plasmas