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Rev. Sci. Instrum. 87, 11E703 (2016)
FIG. 4. Charge-exchange loss distribution versus time for doped (90% H2, 10% D2) NBI into deuterium-filled C-2U confinement vessel.
There is greater uncertainty in the calibrations at the lowest channels due to small signal levels. This is a result of the reliability and stability of the ion source and sensitivity of the MCP at lower energies. We also expect that fringe field e↵ects and beam energy width should contribute to increased scatter for the lowest channels. However, these uncertainties do not inhibit measurement analysis.
V. MEASUREMENTS ON C-2U
The NPA was installed at a neutral beam injection plane, with its view oriented to collect charge-exchanged fast ions moving in the diamagnetic direction. The view is oriented 20 from normal to the z axis of the experiment (identical to the neutral beam injection angle) with an impact radius of 49 cm. The location and orientation were chosen for optimal signal based on simulations of charge-exchange losses.
For initial measurement tests on C-2U, signal on the NPA was recorded during routine beam-into-gas shots. For these conditions there was no plasma discharge but confinement re- gion magnets were engaged, the C-2U chamber was pre-filled with deuterium gas, and five neutral beams were engaged with a mixture of 90% hydrogen and 10% deuterium. Fig. 4 shows
the distribution measurements from the NPA for a beam-into- gas shot. Shown overlaying the NPA data is the time trace of the nominally 15 keV beam injection energy. Clearly visible is the excellent agreement between the injected energy and the measured particle distribution. The 1/2 and 1/3 energy components of the beam are visible for hydrogen and to a lesser degree for deuterium, as well as 2/3 energy component from DH dissociation.
Measurements of the charge-exchange loss distribution in C-2U discharges and the inferred fast ion behavior will be presented in a forthcoming paper.
VI. FUTURE DEVELOPMENT
The largest deficiency in the NPA, and hence interpret- ing charge-exchange loss signals, is the lack of an absolute response calibration. Presently, a more sophisticated ion beam system is being constructed at TAE to better calibrate particle detectors. In particular, the absolute flux of the beam system will be well characterized allowing absolute response calibra- tions of particle diagnostics, including the NPA. In addition, the beam system will be more stable with larger beam current and reduced fractional energy components which will reduce the uncertainties in E/E, particularly for the lowest channels.
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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