Page 5 - Magnetic diagnostic suite of the C-2W field-reversed configuration experiment

10J107-5
Roche et al.
Rev. Sci. Instrum. 89, 10J107 (2018)
FIG. 8. Mode analysis of a single Mirnov ring of 8 probes at the same axial location (z = 0.48 m). The temporal evolution of MHD modes n = 1 and n = 2 is depicted. Two degenerate principle axes and components, 45◦ out of phase, describe the rotational motion of the modes. Time ranges are the same between contour and magnitude plots.
FIG. 9. Spectrogram of magnetic fluctuations using wavelet analysis of the average of a ring of 8 Mirnov probes. Electron cyclotron and Aflve´nic fluctuations detected as indicated.
The slow chips in the Mirnov probe arrays detect bulk plasma motion. The coherent modes are determined using Sin- gular Value Decomposition (SVD) analysis10 on the individual
rings of probes. Figure 8 shows an example of mode analysis using SVD. The time evolution, spatial structure, and magni- tude of MHD modes n = 1 and n = 2 are depicted as detected by one of the Mirnov rings located at z = 48 m. Data are simply downsampled by a factor of 10–250 kHz without any other manipulation before the SVD analysis is performed. The modes are identified by programmatically examining the num- ber of 0 crossings in the principle axes. Incoherent fluctuations are examined using wavelet analysis on the fast probe signals. An example spectrogram using the averaged signals from 8 probes in a single ring is displayed in Fig. 9. It describes how the fluctuation spectrum changes over time at higher frequen- cies (MHz range). In this example, both electron cyclotron and Aflve´nic fluctuations are detected.
V. SUMMARY
Over 700 magnetic field diagnostics have been installed on the C-2W FRC machine and are providing data which have been used to determine essential parameters of the FRC. This represents an order of magnitude upgrade over C-2U.
ACKNOWLEDGMENTS
We thank our shareholders for their support and trust and all fellow TAE staff for their dedication, excellent work, and extra efforts.
1M. W. Binderbauer et al., AIP Conf. Proc. 1721, 030003 (2016).
2J. A. Romero, S. A. Dettrick, E. Granstedt, T. Roche, and Y. Mok, Nat.
Commun. 9, 691 (2018).
3M. C. Thompson et al., Rev. Sci. Instrum. 83, 10D709 (2012).
4T. Roche et al., Rev. Sci. Instrum. 87, 11D409 (2016).
5C. A. Romero-Talama´s, P. M. Bellan, and S. C. Hsu, Rev. Sci. Instrum. 75,
2664 (2004).
6M. Tuszewski, Phys. Fluids 24, 2126 (1981).
7W. Rogowski and W. Steinhaus, Arch. Elektrotech. 1, 141 (1912). 8L. C. Steinhauer, Phys. Plasmas 18, 070501 (2011).
9N. Rostoker and A. Qerushi, Phys. Plasmas 9, 3057 (2002).
10C. Nardone, Plasma Phys. Controlled Fusion 34, 1447 (1992).