Toroidal Field Profile Measurements on SSPX Using the Transient Internal Probe Diagnostic
Abstract
The TIP diagnostic will be used on SSPX to directly measure internal spheromak toroidal fields. This will provide F as a function of R, which will be used along with p ( R ) from multi-point Thomson scattering, to obtain flux surfaces using a Grad-Shafranov equilibrium code. These will be spatially resolved measurements along a chord from the flux conserver through the predicted magnetic axis. The diagnostic relies on the Faraday effect, in which the polarization of light is rotated in proportion to the component of the magnetic field along its propagation direction. A 1-cm long probe made of a Faraday effect-sensitive Verdet material encased in sapphire for protection is fired through the spheromak at 1.8 km/s by a light gas gun. The probe is illuminated by a 514-nm laser throughout the trajectory. This light is retro-reflected from the probe back to an ellipsometer (polarization detector), thus determining the component of the magnetic field along the flight path. An expansion tank with fast mechanical and gate valves separates the high gun pressures from the experiment vacuum. The high speed of the probe and the cladding guards against plasma perturbation, ablation, and sputtering. In addition, we will look for the n=1 rotating mode that is often observed in spheromaks.
- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- November 1999
- Bibcode:
- 1999APS..DPP.FP171H