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

heavy ion beam probes (already in use in the lhd stellarator experiment in Japan), Faraday rotation,
polarimetry, motional stark effect, and high-resolution charge-exchange recombination.
however, these will require substantial commitments of resources for successful deployment.
such diagnostics would have cross-cutting use since they would also be applicable to studies of
core turbulence and transport. measurements of the instability mode structures are a critical step
toward accurate prediction of alpha particle confinement. a second element of the advanced diagnostics
effort is the high-fidelity measurement of the fast ion profile and temporal resolution
of intermittent transport events. This information is necessary to understand the detailed power
flows of fast ions, predict losses to the wall, and infer the alpha particle heating profile. a third
element is the improved measurement of escaping fast ions. This involves covering more of the
first wall and plasma facing components with energetic ion loss detectors so that greater spatial
resolution of the heat loads is possible. such information will be critical in predicting localized
hot spots and in validating simulations of energetic particle losses. These three diagnostic efforts
are expected to originate on existing non-ignited experiments, which will provide useful developmental
test beds during the period (~ 15 years) leading up to d-t operation of iteR. The parallel
development of neutron-hardened diagnostics for iteR will be necessary. These may be more
limited in capability than what is possible on non-ignited devices; a greater reliance on simulation
and synthetic diagnostic reconstruction will likely be required. alpha particle-driven instabilities
may also be useful in high-neutron-fluence fusion devices to infer q-profile information (via mhd
spectroscopy) from the narrow, easily identified spectral lines of such fluctuations.
Experimental Studies and Collaboration
access to experimental facilities is essential for the diagnostic and simulation developments that
are mentioned above. in addition to Us experiments (diii-d, c-mod, and nstX), there exist international
collaborations with Jet and Jt-60U, and future collaborations are anticipated with emerging
devices such as kstaR and east. also, the capabilities developed in this Thrust are expected
to be well suited to future d-d and d-t facilities that might be constructed as part of the Us fusion
program. The non-tokamak concepts (e.g., stellarator, reversed field pinch, field-reversed configuration)
will provide further useful test beds for alfvénic instabilities and energetic ion physics.
as new devices and plasma regimes become available, the detailed validation of ideal mhd predictions
(n-number, radial structure, mode frequency), which has been successful on existing devices,
will continue. Recent diagnostic advances in electron cyclotron emission, beam emission
spectroscopy, and interferometry will allow the mode structure to be measured in greater detail.
The future diagnostic challenge is to measure the perturbed currents and electric fields associated
with these modes. The experimental challenge is to validate theory predictions of the internal
structure over a wider range of parameters.
Quantitative understanding of the fast ion drive is improving; however, more systematic studies
with greater variation of parameters will be required. Recent advances in fast ion d-alpha,
Thompson scattering, neutral particle analyzers, and scintillator detectors are providing more
qualitative information on profiles and fast ion losses. The diagnostic challenge for fast ion drive
measurements is to provide more quantitative information on fast ion profiles and velocity distributions.
The experimental challenge is to more directly calculate the instability drive and to compare
this to the measured mode spectra.
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