1. Progress and New Results from the H-1NF Scanning Interferometer Scott Collis, George Warr, John Howard

2. 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

4. 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:

5. Motor and Grating

6. 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

7. F osc > F scan

8. Aliased Data

9. Calibration We need a transform from temporal position in scan to spatial position in the H-1NF tank

10. A 2.5cm absorber was placed at three positions on the bottom mirror

11. At 40cm above the centre

12. In the centre of the mirror

13. And at 40cm below the centre

14. Top Diagonal Results Beam width: 1.3cm

15. Bottom Diagonal Results Beam width: 3.2cm

16. Calculated Beam Positions

17. High Density ICRH Shot Fundamental ICRH resonance of Hydrogen B=0.5T Peaked density profile Highest B 2 n e product observed in H-1NF

18. 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

19. 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

20. 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 n e but T e T i and ion velocity

21. 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