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Formation Studies, Axial Target Field interaction, and new diagnostic development in the CTIX Injector Project
| Author: | Hwang D.Q. |
| Coauthor: | R. D. Horton, S. J. Howard, S. J. E. Brockington, R. W. Evans, J. N. Johnson, A. Graf |
| Institution : | University of California, Davis |
| Abstract text: | Several experiments had been carried out on the passively switched spheromak-like compact toroid (SCT) accelerator at the University of California, Davis/Livermore. The main formation experiment was to understand the initial SCT formation process, especially the role of the initial solenoidal seed field. A special apparatus was constructed to map out the seed field during the formation time, including the eddy current effect from the electrode wall. We find that in the acceleration process, the seed poloidal field is amplified by several orders of magnitude. At the same time, it was observed that the seed field is absolutely essential for the SCT formation regardless of its low level at formation initiation.
To better understand the accelerated SCT with a target field, we have also installed a set of axial solenoidal target field coils that can generate an axisymmetric target field, which is directed either parallel or anti-parallel to the internal SCT magnetic fields at its leading edge. Depending on the alignment direction, resistive MHD predicts that the interaction should result in reconnection of the two fields for the case of anti-parallel alignment, or a compression effect in the case of parallel alignment. The interaction of SCT with the target field was studied using magnetic field probes, laser interferometry, and a fast multi-frame 2-D camera that views the plasma along an axial line of sight. The interaction dynamics have been well characterized, and we have several new findings about the phenomenon of magnetic reconnection in the presence of the fast plasma flow. It is found that the experimental observations are consistent with the results of a simple 2-D MHD code in which magnetic compression and reconnection mechanisms are simulated. We are currently working to reproduce these axisymmetric results using a 3-D MHD code; fully three-dimensional models will follow as the new code is validated.
We will present preliminary measurements using a new plasma density diagnostic that we call a laser deflectometer. It uses a low-power diode laser beam to measure gradients of plasma density by means of detecting the beam’s angular deflection due to refractive bending along the beam’s chord within the plasma flow. In addition, we will show the latest spectroscopic data from the moving SCT.
Finally, the integration of a high spectral resolution transmission grating visible spectrometer is underway. We will extract a time integrated impurity survey and measure Doppler shifts of various ions.
Acknowledgement: This work is supported by the DOE Office of Fusion Energy # DE-FG03-99ER54558 and DE-FG02-03ER54732
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