4,415 research outputs found
A Long Duration Orbital Simulator (LDOS) Utilized in Technical Planning Activities
This paper describes the development and use of a long duration orbital simulator (LDOS). The LDOS capabilities, options, accuracy, and central processing unit (CPU) usage are discussed. The applications described using the LDOS are associated with (a) Manned Space Flight Network (MSFN) support of long duration missions, (b) environmental effects on high earth orbits and (c) long term orbit decay. The appendix depicts the salient portions of the math model
Ion-scale turbulence in MAST: anomalous transport, subcritical transitions, and comparison to BES measurements
We investigate the effect of varying the ion temperature gradient (ITG) and
toroidal equilibrium scale sheared flow on ion-scale turbulence in the outer
core of MAST by means of local gyrokinetic simulations. We show that nonlinear
simulations reproduce the experimental ion heat flux and that the
experimentally measured values of the ITG and the flow shear lie close to the
turbulence threshold. We demonstrate that the system is subcritical in the
presence of flow shear, i.e., the system is formally stable to small
perturbations, but transitions to a turbulent state given a large enough
initial perturbation. We propose that the transition to subcritical turbulence
occurs via an intermediate state dominated by low number of coherent long-lived
structures, close to threshold, which increase in number as the system is taken
away from the threshold into the more strongly turbulent regime, until they
fill the domain and a more conventional turbulence emerges. We show that the
properties of turbulence are effectively functions of the distance to
threshold, as quantified by the ion heat flux. We make quantitative comparisons
of correlation lengths, times, and amplitudes between our simulations and
experimental measurements using the MAST BES diagnostic. We find reasonable
agreement of the correlation properties, most notably of the correlation time,
for which significant discrepancies were found in previous numerical studies of
MAST turbulence.Comment: 67 pages, 37 figures. Submitted to PPC
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