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Research Needs for Magnetic Fusion Energy Sciences - US Burning ...

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4. based on the outcome of actions 1-3, a new experiment capable of demonstrating the<br />

integration of confinement, current sustainment, active control of mhd stability, and<br />

boundary control is essential to establish the scientific basis <strong>for</strong> an RFP burning plasma.<br />

This could be a two-stage, upgradeable facility that first emphasizes the integration of<br />

confinement and current sustainment at moderate plasma current. a 2 ma first stage<br />

could attain sufficiently high-S to robustly test confinement scaling, ac current drive,<br />

and the hybrid scenario. The second stage will push per<strong>for</strong>mance at the 4 ma level to<br />

test confinement and current-drive up to S=10 9 and r* less than 1% with fully integrated<br />

boundary control and near-burning plasma conditions. The pulse length requirement<br />

<strong>for</strong> both stages will demand active control of resistive wall modes (RWms). high-power<br />

plasma control using mW-level neutral beams and radiofrequency are required, and the<br />

experiment must be well-diagnosed to validate our understanding of the important<br />

physical processes.<br />

similar to the RFP, spheromaks have shown transient control of magnetic fluctuations leading to<br />

electron temperature of 0.5 kev and core energy confinement time of 10 ms. continuous sustainment<br />

compatible with good confinement has not been demonstrated and is a focus of near-term<br />

activities. at present there are no large-scale experiments that can address this issue or other limits<br />

to confinement. The development path shown in Figure 2 will fill this gap, facilitate innovation<br />

to increase <strong>for</strong>mation efficiency, and address technology needs.<br />

1. Upgrades of existing and construction of new ce-level experiments will foster innovation<br />

in <strong>for</strong>mation and current drive studies. With support from analytics and computation,<br />

<strong>for</strong>mation experiments will investigate methods <strong>for</strong> exceeding the flux amplification and<br />

current multiplication factors obtained in past experiments. They will also improve our<br />

understanding of mhd activity excited by ac current drive and refluxing techniques <strong>for</strong><br />

steady, quasi-steady, and pulsed operation.<br />

Figure 2. CE spheromaks emphasize innovation to address specific needs prior to PoP development.<br />

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