Page 3 - End loss analyzer system for measurements of plasma flux at the C-2U divertor electrode

11D432-3
Sheftman et al.
Rev. Sci. Instrum. 87, 11D432 (2016)
FIG. 6. Electron temperature (a) and electron density (b) profiles measured at z = 2.25 m.
For an exponential distribution of electron density at the jet, the velocity is calculated as
f
where f is the flux of lost particles. The factor 2 in the denom- inator emphasizes the two symmetric axial jet components, o⇤f which only one is measured. Averaged values of f and
nedl throughout a typical shot, and a calculated above from triple probe measurements, result in v = 2.2 km/s. Let us note that this velocity corresponds to lost deuterium particles, whereas the measured ion velocities from Doppler measure- ments shown in Fig. 5 are of oxygen impurities. Indeed, both results imply a slow jet of Mach number M < 0.1.
III. SUMMARY
Measurements of electron density, electron temperature, ion temperature, and outflow velocity were performed on the C-2U open field line region. MW interferometry provides a high resolution measurement of integrated electron density and shows a detailed behavior of fast fluctuations. Fast fluc- tuations in the form of “microbursts” have been shown to propagate across open field lines at a velocity best fitting the ion-sound velocity. Doppler spectroscopy provides ion impurity temperature measurements at various positions along the longitudinal axis, as well as temporal behavior of the ion outflow velocity. Triple probe measurements provide limited radial profiles of electron density and temperature and show reasonable fitting to an exponential density profile. Measured jet velocity is consistent with calculated expectations, evident of slow jet outflow.
ACKNOWLEDGMENTS
We thank our shareholders for their support and trust, and all fellow TAE sta↵ for their dedication, excellent work, and extra e↵orts.
1M. W. Binderbauer et al., Phys. Plasmas 22, 056110 (2015).
2L. C. Steinhauer, Phys. Plasmas 18, 070501 (2011).
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4T. Ohtsuka, M. Okubo, S. Okada, and S. Goto, Phys. Plasmas 5, 3649 (1998). 5C. Theiler, I. Furno, A. Kuenlin, Ph. Marmillod, and A. Fasoli, Rev. Sci.
Instrum. 82, 013504 (2011).
v = 2p⇡a⇤ nedl, (4)
FIG. 5. Ion temperature (a) and ion axial velocity (b) measured by Doppler spectroscopy. Solid line is for z = 4.65 m and dashed line is for z = 2.65 m.
C. Triple Langmuir probe measurements
A triple Langmuir probe was inserted inside the confine- ment vessel at z = 2.25 m, providing limited radial scans of electron density and temperature, with a minimal scanned radius of 20 cm. For a detailed description of the triple probe measurement technique, see Ref. 5. Triple probe measure- ments (see Fig. 6) show an exponential profile of electron density and an approximately uniform temperature profile. The electron density was fitted to an exponential profile ne = n0 exp[ (r/a)2], where r is the radial distance from the z axis, n0 is the electron density at r = 0, and a is the e↵ective jet radius. A fitting parameter 2 = 0.83 was achieved for the latter profile, with an e↵ective radius r = 11.5 ± 5.6 cm. Indeed, lack of data at the jet center and relatively large error margins limit adequate data fitting. A multi-chord interferom- eter, currently in planning stages, will enable measurement of electron density inside the jet center with increased resolution.
An estimate of average jet velocity can be obtained from the particle loss flux from the FRC plasma. The latter flux is obtained by the time derivative of the particle inventory, which is a function of the average electron density and FRC radius and length, all obtained from measurements in the confinement section. Also, it is assumed that all lost particles flow in the jet.