Page 3 - Fast imaging diagnostics on the C-2U advanced beam-driven field-reversed configuration device

11D428-3 Griswold et al.
Rev. Sci. Instrum. 87, 11D428 (2016)
FIG. 5. (a) Ion current density measured by the GEA compared to ions lost from the core. (b) Power density measured by the bolometer compared to power lost from the core.
diagnostic operated successfully and provided experience for a future iteration that is currently in design. Current and power density measured by the ELA during a representative shot are shown in Fig. 5. The measurements agree with an estimate of power and particle loss from the core plasma, which is derived from measurements of density and excluded flux in the core as well as power and particle input from the neutral beams. Total outflows from the core are converted to current and power densities by dividing by an e↵ective area of 1 m2, a free parameter that is slightly less than the real electrode area of 1.2 m2. The true radial profile of current and power at the divertor is unknown because the ELA only measures at one radial location.
The ELA uncovered the unexpected result that power lost to the inner electrode deviated from expectations when the plasma gun bias voltage dropped below 350 V. Fig. 6 shows quantities that are time-averaged over the main part of each shot as a function of the plasma gun bias for the shot. At bias voltages less than 350 V, the power measured by the bolometers was significantly less than expected given the level of core losses, while the current density continued to agree with expectations. Future work will investigate how spatial changes in the power lost to the walls may account for this result.
FIG. 6. (a) Power loss from the core and power density measured by the bolometers vs. plasma gun bias voltage. (b) Particle loss from the core and ion current density measured by the GEA vs. plasma gun bias voltage. Quantities are time averaged over the shot.
ACKNOWLEDGMENTS
We thank our shareholders for their support and trust, and all fellow TAE sta↵ for their dedication, excellent work, and extra e↵orts.
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