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

• if a disruption becomes unavoidable, can we then predict the onset, evolution and final
termination of disrupting discharges due to all possible instability mechanisms (e.g.,
density limit radiation collapse, vertical displacement event, beta-limit, etc.) in a demo
device and use this capability to design a mitigation scheme that will perform with high
confidence?
research requirements
The fundamental question of disruption probability can only be definitively answered by a new
generation of very long pulse (likely many days long) discharges coupled with extensive operational
experience of such devices. no such experiment exists today. integrated modeling of disruptions,
which would feature nonlinear mhd simulations for realistic tokamak geometry, including
core, scrape-off layer, plasma facing components, and eventually even coil structures to
calculate halo currents, must occur. such a capability could first be developed and experimentally
validated for elms, then resistive wall modes (RWms), and finally disruption events. modeling
must eventually successfully predict performance of disruption mitigation techniques with sufficient
confidence to make design selection for demo. Reduced physics disruption models must
be integrated into a real-time control system for disruption prediction and detection, avoidance,
and mitigation. improved diagnostics of disruptions, including runaway electron generation and
transport, as well as development and study of potential mitigation techniques, must be performed
in existing experiments. validation experiments using emerging models of unmitigated
and mitigated disruption events can provide predictive capabilities for iteR and then demo.
Pedestal and ELM
Science Opportunities:
• can we accurately identify the physics trigger(s) for formation of the edge transport barrier,
and translate this into a physics-based “l-h mode” transition threshold prediction?
• can these predictions then be extended to fully saturated, steady-state wall conditions?
can we predict the height of the pedestal with a physics-based understanding? can we
accurately predict elm onset, dynamics and the associated heat and particle load on
PFcs?
• can we understand the behavior of elm control and mitigation schemes sufficiently well
to confidently predict their performance and impact upon the pedestal conditions that
will occur in a demo?
• can we predict the coupling of radiofrequency, beam and pellet sources across the
pedestal?
research requirements
a successful predictive pedestal model is inherently a multi-scale problem involving the long-time
evolution of a turbulent system coupled with the evolution of the plasma profiles. new approaches
are needed if a first-principles model of this system is to be created. validation will require new
measurements (e.g., neutral fueling of the pedestal, field penetration from elm control coils) as
well as significantly improved multipoint measurements of turbulent density, potential, magnetic
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