Page 4 - Achievement of Sustained Net Plasma Heating in a Fusion Experiment with the Optometrist Algorithm

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Parameter
Shot 46366
Typical Shot
BExt, Con ning B Field
750 G
760 G
FP, Poloidal Flux
5.6 mWb
4.8 mWb
rΔΦ, Plasma Radius
33 cm
31 cm
n, Average Density
1.9 * 1013 cm−3
2.7 * 1013 cm−3
Ti, Ion Temperature
680 eV
370 eV
Te, Electron Temperature
125 eV
110 eV
Table 1. Average plasma parameters at 1.5 ms within the plasma radius from Shot 46366 as well as a ‘typical’ shot. is typical shot (47778) is the median of the distribution shown in Fig. 3 and has the most common time evolution of the plasma energy.
Figure 2. Plasma ion temperature climbs rapidly a er 1 ms and reaches values of ∼1 keV by 3 ms into the discharge on Shot 46366. Typical temperatures are lower and show little to no rise in time.
Figure 3. (a) Normalised distribution of the number of shots as a function of net heating power in C-2U based on over 1800 shots with at least 2 kJ of stored thermal energy (Eth). Typical power losses are between 0.6 and
1 MW. Power is taken as the peak value in a rolling 1 ms time window between 1 and 3 ms. (b) Net power into the plasma exceeded 0.1 MW in Shot 46366 due to a reduction in cooling rates.
adjustment, which was not common. We did not go below about 15 MPs because this was deemed the minimal set to describe the machine.
Over an experiment run of 3.5 weeks in September 2015, we used this technique over seven experiment days and 150 plasma shots. is does not include the shots used to establish reference settings at the start of each experiment day (totalling approximately 40 for this run).
Before we started optimisation, the plasma would be stable for a small number of milliseconds, and the ion temperature would gradually decay with time. Typical plasma parameters for these conditions are shown in Table 1. We started using the Optometrist Algorithm to extend the stability of the plasma (ignoring the ion tem- perature). However, during the exploration of parameter space, the human operator noticed some experiments
Scientific REPORTS | 7: 6425 | DOI:10.1038/s41598-017-06645-7 4