161 research outputs found
Assessment of Independent Fuelling and ELM Pace Making by Pellet Injection in ITER
Abstract. The possibility of independent plasma fuelling by high field side (HFS) DT pellet injection and ELM pace-making by low field side (LFS) D pellet injection is considered for ITER. The model used in the analysis takes into account the outward drift of the ablated pellet substance. The simulations show that the residual fuelling efficiency from the LFS injection is a non-monotonic function of the pellet size. It is shown that it can be possible to use the pellets of similar size, speed and frequency for HFS fuelling with ELM pace-making and for LHS ELM pace-making with low residual core fuelling to keep particle fluxes to the divertor on the same level. The relations between pellet size and speed and frequencies for the HFS and LFS pellet injection, which provide desirable residual fuelling and tolerable divertor loads are determined
Superconducting-coil--resistor circuit with electric field quadratic in the current
It is shown for the first time that the observed [Phys. Lett. A 162 (1992)
105] potential difference Phi_t between the resistor and the screen surrounding
the circuit is caused by polarization of the resistor because of the kinetic
energy of the electrons of the superconducting coil. The proportionality of
Phi_t to the square of the current and to the length of the superconducting
wire is explained. It is pointed out that measuring Phi_t makes it possible to
determine the Fermi quasimomentum of the electrons of a metal resistor.Comment: 2 pages, 1 figur
Saturation of fishbone instability by self-generated zonal flows in tokamak plasmas
Gyrokinetic simulations of the fishbone instability in DIII-D tokamak plasmas
find that self-generated zonal flows can dominate the nonlinear saturation by
preventing coherent structures from persisting or drifting in the energetic
particle phase space with mode down-chirping. Results from the simulation with
zonal flows agree quantitatively, for the first time, with experimental
measurements of the fishbone saturation amplitude and energetic particle
transport. Moreover, the suppression of the microturbulence by fishbone-induced
zonal flows is likely responsible for the formation of an internal transport
barrier that was observed after fishbone bursts in this DIII-D experiment.
Finally, gyrokinetic simulations of a related ITER baseline scenario show that
the fishbone induces insignificant energetic particle redistribution and may
enable high performance scenarios in ITER burning plasma experiments
The `Friction' of Vacuum, and other Fluctuation-Induced Forces
The static Casimir effect describes an attractive force between two
conducting plates, due to quantum fluctuations of the electromagnetic (EM)
field in the intervening space. {\it Thermal fluctuations} of correlated fluids
(such as critical mixtures, super-fluids, liquid crystals, or electrolytes) are
also modified by the boundaries, resulting in finite-size corrections at
criticality, and additional forces that effect wetting and layering phenomena.
Modified fluctuations of the EM field can also account for the `van der Waals'
interaction between conducting spheres, and have analogs in the
fluctuation--induced interactions between inclusions on a membrane. We employ a
path integral formalism to study these phenomena for boundaries of arbitrary
shape. This allows us to examine the many unexpected phenomena of the dynamic
Casimir effect due to moving boundaries. With the inclusion of quantum
fluctuations, the EM vacuum behaves essentially as a complex fluid, and
modifies the motion of objects through it. In particular, from the mechanical
response function of the EM vacuum, we extract a plethora of interesting
results, the most notable being: (i) The effective mass of a plate depends on
its shape, and becomes anisotropic. (ii) There is dissipation and damping of
the motion, again dependent upon shape and direction of motion, due to emission
of photons. (iii) There is a continuous spectrum of resonant cavity modes that
can be excited by the motion of the (neutral) boundaries.Comment: RevTex, 2 ps figures included. The presentation is completely
revised, and new sections are adde
LOCUST-GPU predictions of fast-ion transport and power loads due to ELM-control coils in ITER
The LOCUST-GPU code has been applied to study the fast-ion transport and loss caused by resonant magnetic perturbations in the high-performance Q= 10 ITER baseline scenario. The unique computational efficiency of the code is exploited to calculate the impact of the application of the ITER ELM-control-coil system on neutral beam heating efficiency, as well as producing detailed predictions of the resulting plasma-facing component power loads, for a variety of operational parameters—the toroidal mode number n0, mode spectrum and absolute toroidal phase of the imposed perturbation. The feasibility of continually rotating the perturbations is assessed and shown to be effective at reducing the time-averaged power loads.Through careful adjustment of the relative phase of the applied perturbation in the three rows of coils, peak power loads are found to correlate with reductions in NBI heating efficiency for n= 3 fields. Adjusting the phase this way can increase total NBI system efficiency by approximately 2-3% and reduce peak power loads by up to 0.43 MWm-2. From the point of view of fast-ion confinement, n= 3 ELM control fields are preferred overall to n= 4 fields.In addition, the implementation of 3D magnetic fields in LOCUST is also verified by comparison with the SPIRAL code for a DIII-D discharge with ITER-similar shaping and n= 3 perturbation
- …