Page 4 - A mass resolved, high resolution neutral particle analyzer for C-2U

FIGURE 5: (Color online). (a) Representative data from each bolometer for a single shot. (b) Average power density measured by each bolometer vs. Vbias. The power density is time-averaged over the main part of each shot (0.5-1.5 ms) and QCL is the power density that should be measured at the bolometer calculated from measurements of the
core plasma and 0D power balance.
radiated power density measured by similar pyrobolometers in the confinement vessel is only .01 MW/m2, so we can safely assume that this is particle power. Overall, the measured end loss power agrees with what we expect based on measurements of the core plasma and 0D power balance (QCL, Fig. 5 (b)). However, we note several issues: first, the bolometers and their signal cables are mounted next to a plasma gun that is used to bias the edge of the FRC, which introduces a large amount of noise to the signal. Furthermore, the average power density measured by each bolometer can differ by as much as a factor of 2.5, even though they are mounted at the same radius. Finally, when the machine is operated with Vbias < 400 V the power measured by the bolometers is significantly lower than QCL. All of these factors introduce uncertainty in our measurement and will be addressed with future work. Nevertheless, we consider here the average of the signal from both bolometers in the range Vbias > 400 V.
Energy Per Ion
The energy lost per ion calculated from data presented in the previous sections is Eie = qQ/Ji = 2.6 keV, where Q is the power density measured by the bolometers, Ji is the ion current density measured by the GEA, and both quantities are averaged over the main part of each shot (0.5-1.5 ms), and then over the 28 shots in the database with Vbias > 400V (Fig. 5). Using Te = 40 eV which was measured on the SOL by a Helium Jet imaging diagnostic[11] gives the result that Eie/Te = 65. This value is much larger than the case of an isolated and collisionless mirror, which was expected because sources of cold electrons were not carefully controlled in the C-2U divertor. It is difficult to interpret this result further because it was taken in in a limited time frame during an abnormal operating condition on C-2U. In particular, the electrodes and plasma gun on the north side of the machine (opposite the ELA) were replaced with an emissive LaB6 cathode that injected energetic electrons into the plasma and drove currents across the machine. As such, we present this result as a preliminary estimate subject to further refinement.
REFERENCES
[1] M. W. Binderbauer et al., AIP Conference Proceedings 1721, p. 030003 (2016).
[2] A. V. Anikeev, P. A. Bagryansky, G. I. Kuznetsov, and N. Stupishin, Plasma Phys. Reports 25, p. 775 (1998).
[3] D. D. Ryutov, Fusion Sci. Technol. 47, p. 148 (2005).
[4] R. Post, J.Nucl. Mater. 76, p. 112 (1978).
[5] P. A. Bagryansky, A. G. Shalashov, E. D. Gospodchikov, A. A. Lizunov, V. V. Maximov, V. V. Prikhodko,
E. I. Soldatkina, A. L. Solomakhin, and D. V. Yakovlev, Phys. Rev. Lett. 114, p. 205001 (2015).
[6] A. A. Ivanov and V. V. Prikhodko, Plasma Physics and Controlled Fusion 55, p. 063001 (2013).
[7] L. Galeotti, D. C. Barnes, F. Ceccherini, and F. Pegoraro, Phys. Plasmas 18 (2011).
[8] A. W. Molvik, Rev. Sci. Instrum. 52, p. 704 (1981).
[9] G. Fiksel, J. Frank, and D. Holly, Rev. Sci. Instrum. 64, p. 2761 (1993).
[10] J. Cooper, J. Sci. Instrum. 39, p. 467 (1962).
[11] D. Osin and T. Schindler, Rev. Sci. Instrum 87 (2016).
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