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

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heavy ion beam probes (already in use in the lhd stellarator experiment in Japan), Faraday rotation,<br />

polarimetry, motional stark effect, and high-resolution charge-exchange recombination.<br />

however, these will require substantial commitments of resources <strong>for</strong> successful deployment.<br />

such diagnostics would have cross-cutting use since they would also be applicable to studies of<br />

core turbulence and transport. measurements of the instability mode structures are a critical step<br />

toward accurate prediction of alpha particle confinement. a second element of the advanced diagnostics<br />

ef<strong>for</strong>t is the high-fidelity measurement of the fast ion profile and temporal resolution<br />

of intermittent transport events. This in<strong>for</strong>mation is necessary to understand the detailed power<br />

flows of fast ions, predict losses to the wall, and infer the alpha particle heating profile. a third<br />

element is the improved measurement of escaping fast ions. This involves covering more of the<br />

first wall and plasma facing components with energetic ion loss detectors so that greater spatial<br />

resolution of the heat loads is possible. such in<strong>for</strong>mation will be critical in predicting localized<br />

hot spots and in validating simulations of energetic particle losses. These three diagnostic ef<strong>for</strong>ts<br />

are expected to originate on existing non-ignited experiments, which will provide useful developmental<br />

test beds during the period (~ 15 years) leading up to d-t operation of iteR. The parallel<br />

development of neutron-hardened diagnostics <strong>for</strong> iteR will be necessary. These may be more<br />

limited in capability than what is possible on non-ignited devices; a greater reliance on simulation<br />

and synthetic diagnostic reconstruction will likely be required. alpha particle-driven instabilities<br />

may also be useful in high-neutron-fluence fusion devices to infer q-profile in<strong>for</strong>mation (via mhd<br />

spectroscopy) from the narrow, easily identified spectral lines of such fluctuations.<br />

Experimental Studies and Collaboration<br />

access to experimental facilities is essential <strong>for</strong> the diagnostic and simulation developments that<br />

are mentioned above. in addition to Us experiments (diii-d, c-mod, and nstX), there exist international<br />

collaborations with Jet and Jt-60U, and future collaborations are anticipated with emerging<br />

devices such as kstaR and east. also, the capabilities developed in this Thrust are expected<br />

to be well suited to future d-d and d-t facilities that might be constructed as part of the Us fusion<br />

program. The non-tokamak concepts (e.g., stellarator, reversed field pinch, field-reversed configuration)<br />

will provide further useful test beds <strong>for</strong> alfvénic instabilities and energetic ion physics.<br />

as new devices and plasma regimes become available, the detailed validation of ideal mhd predictions<br />

(n-number, radial structure, mode frequency), which has been successful on existing devices,<br />

will continue. Recent diagnostic advances in electron cyclotron emission, beam emission<br />

spectroscopy, and interferometry will allow the mode structure to be measured in greater detail.<br />

The future diagnostic challenge is to measure the perturbed currents and electric fields associated<br />

with these modes. The experimental challenge is to validate theory predictions of the internal<br />

structure over a wider range of parameters.<br />

Quantitative understanding of the fast ion drive is improving; however, more systematic studies<br />

with greater variation of parameters will be required. Recent advances in fast ion d-alpha,<br />

Thompson scattering, neutral particle analyzers, and scintillator detectors are providing more<br />

qualitative in<strong>for</strong>mation on profiles and fast ion losses. The diagnostic challenge <strong>for</strong> fast ion drive<br />

measurements is to provide more quantitative in<strong>for</strong>mation on fast ion profiles and velocity distributions.<br />

The experimental challenge is to more directly calculate the instability drive and to compare<br />

this to the measured mode spectra.<br />

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