Page 5 - Jet outflow and open field line measurements on the C-2W advanced beam-driven field-reversed configuration plasma experiment

10D120-5
Sheftman et al.
Rev. Sci. Instrum. 89, 10D120 (2018)
FIG. 9. (a) Simulated spectrum of O4+ doublet transition line for ions in the C-2W inner divertor. (b) Resulting fringe pattern from the spectrum.
the imaging optics. The FWHM of a spectral line was mea- sured at 0.11 nm. The resulting resolving power λ/δλ = 4250 is an order of magnitude larger than the classical limit of a Fourier transform spectrometer, R = 2π/Ω, where Ω is the field solid angle. Thus, enhancement of light throughput by the field widening prisms has been demonstrated. The SHS system (as seen in Fig. 6) is planned to be installed at a line of sight through the field expanded plasma in the inner divertor, offset from the center of the vessel (see Fig. 8).
The reason for the offset is to avoid collecting light from the relatively dense portion of the jet plasma, which termi- nates at the outer divertor. The region of interest includes dilute plasma, terminating at the inner divertor plates. Assum- ing a symmetric radial plasma density profile of Gaussian form
the imaging lens is 1 . Spectral resolution and range of the system are calculated to be ∼0.05 nm and 1.5 nm, respectively. As can be seen in Fig. 9, this instrumental broadening is within the FWHM of the simulated spectral lines. Thus, SHS provides a promising technique for measuring the velocity profiles of ions in the inner divertor. Let us note that in this configuration, deriving the velocity distribution of ions is heavily dependent on knowing the plasma distribution (which is measured by the MW interferometer, see Sec. II B) and the magnetic configu- ration inside the divertor. The SHS system will be operational on C-2W at the latter half of 2018.
n = n0 exp(−r2/r02), an ion temperature of 1 keV, and a par- allel velocity of 420 km/s, equal to the ion sound velocity at that temperature, a simulated spectrum was obtained for the Doppler shifted O4+ impurity ions (see Fig. 9). The spec- trum is obtained by integrating the individual contributions of radiation along the line of sight as follows:
􏰀
n2(r) cos θdl, (5) ity vector, A is a constant, and the radiation is assumed to be
I(λ) = A
where θ is the angle between the line of sight and the ion veloc-
2
proportional to n . The SHS system design for C-2W consists
of 600 g/mm gratings, 5◦ wedge prisms, an image intensifier, and two sets of imaging lenses. The diameter of optics before
′′
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).
2H. Gota et al., Nucl. Fusion 57, 116021 (2017).
3L. C. Steinhauer, Phys. Plasmas 18, 070501 (2011).
4D. Sheftman, D. Gupta, T. Roche, M. C. Thompson, F. Giammanco,
F. Conti, P. Marsili, and C. D. Moreno, Rev. Sci. Instrum. 87, 11D432 (2016).
N. L. Aleksandrov, S. V. Kyndysheva, A. A. Kirpichnikov, I. N. Kosarev, S. M. Starikovskaia, and A. Y. Starikovskii, J. Phys. D: Appl. Phys. 40, 4493–4502 (2007).
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6J. Harlander, R. J. Reynolds, and F. J. Roesler, Astrophys. J. 396, 730–740 (1992).