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

Figure 3. Spectrogram of the time-varying frequency
of magnetic fluctuations showing the onset
of toroidal Alfvén eigenmode activity after t = 220
ms, followed by an avalanche at t = 282 ms (detailed
in the inset) in NSTX. (Figure reproduced from M.
Podestà et al., Phys. Plasmas 16 [2009] 056104.)
how well are the alpha particles confined by the magnetic configuration, including 3-D fields?
iteR and demo devices will have various sources of magnetic field non-axisymmetry, such as
toroidal field ripple, ferromagnetic materials, blanket modules, control coils for edge localized
modes and resistive wall modes, and internal mhd and alfvén modes. such asymmetries and
time-varying fields can sensitively affect alpha particle confinement. improved monte carlo simulation
codes will need to be developed that take all of these effects into account. although particle-following
codes currently exist that can include a prescribed field of spatially non-axisymmetric
and time-varying modes, the level of transport from such calculations often significantly
underestimates the observed losses. also, alpha particle confinement calculations in the future
should be based on 3-d equilibrium calculations that include magnetic islands and self-consistently
account for the effects of external ferromagnetic materials.
existing methods for internal (confined) fast ion and lost particle measurements are inadequate
to reconstruct a large fraction of the spatial and velocity space distribution of the fast ions. also,
present measurements cannot resolve the collective motion of the fast ions on the time scale of
the wave period. These limitations must be overcome, both for confined and lost particle measurements.
Resolving the phase space distribution of the energetic ions and their motion on the wave
period time scale will lead to major advances in the understanding of the physics of anomalous
fast ion transport in advanced confinement regimes.
Fast ion losses are currently measured on many experiments using scintillator detectors at a few
locations just outside the plasma edge. however, since alpha particle losses in future burning plas-
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Figure 4. Radial structure of toroidal
Alfvén eigenmodes measured in DIII-D
with electron cyclotron emission diagnostic
and compared to NOVA-K synthetic diagnostic
simulation predictions. (Figure
reproduced from M.A. Van Zeeland et al.,
Phys. Rev. Lett. 97 [2006] 135001.)