18,199 research outputs found
Radial convection of finite ion temperature, high amplitude plasma blobs
We present results from simulations of seeded blob convection in the
scrape-off-layer of magnetically confined fusion plasmas. We consistently
incorporate high fluctuation amplitude levels and finite Larmor radius (FLR)
effects using a fully nonlinear global gyrofluid model. This is in line with
conditions found in tokamak scrape-off-layers (SOL) regions.
Varying the ion temperature, the initial blob width, and the initial
amplitude, we found an FLR dominated regime where the blob behavior is
significantly different from what is predicted by cold-ion models. The
transition to this regime is very well described by the ratio of the ion
gyroradius to the characteristic gradient scale length of the blob.
We compare the global gyrofluid model with a partly linearized local model.
For low ion temperatures we find that simulations of the global model show more
coherent blobs with an increased cross-field transport compared to blobs
simulated with the local model. The maximal blob amplitude is significantly
higher in the global simulations than in the local ones. When the ion
temperature is comparable to the electron temperature, global blob simulations
show a reduced blob coherence and a decreased cross-field transport in
comparison with local blob simulations
The influence of temperature dynamics and dynamic finite ion Larmor radius effects on seeded high amplitude plasma blobs
Thermal effects on the perpendicular convection of seeded pressure blobs in
the scrape-off layer of magnetised fusion plasmas are investigated. Our
numerical study is based on a four field full-F gyrofluid model, which entails
the consistent description of high fluctuation amplitudes and dynamic finite
Larmor radius effects. We find that the maximal radial blob velocity increases
with the square root of the initial pressure perturbation and that a finite
Larmor radius contributes to highly compact blob structures that propagate in
the poloidal direction. An extensive parameter study reveals that a smooth
transition to this compact blob regime occurs when the finite Larmor radius
effect strength, defined by the ratio of the magnetic field aligned component
of the ion diamagnetic to the vorticity, exceeds unity.
The maximal radial blob velocities agree excellently with the inertial velocity
scaling law over more than an order of magnitude. We show that the finite
Larmor radius effect strength affects the poloidal and total particle transport
and present an empirical scaling law for the poloidal and total blob
velocities. Distinctions to the blob behaviour in the isothermal limit with
constant finite Larmor radius effects are highlighted
Post-harvest sown catch crops – results from two years of organic field trials
Post-harvest sown catch crops should be sown as early as possible in order to obtain maximum biomass and nutrient uptake in the harvested crop, as biomass production decreased by 2-3.5 percent per day, when time of sowing was postponed throughout August. Furthermore, the winter hardy species included in these experiments had a tendency to yield less than the non-winter hardy catch crops. These experiments imply that early sown catch crops may become a biomass supplement for organic biogas production, provided sufficient yields are obtained and costs for harvest, transportation and storage are adequately low
High-harmonic generation from arbitrarily oriented diatomic molecules including nuclear motion and field-free alignment
We present a theoretical model of high-harmonic generation from diatomic
molecules. The theory includes effects of alignment as well as nuclear motion
and is used to predict results for N, O, H and D. The results
show that the alignment dependence of high-harmonics is governed by the
symmetry of the highest occupied molecular orbital and that the inclusion of
the nuclear motion in the theoretical description generally reduces the
intensity of the harmonic radiation. We compare our model with experimental
results on N and O, and obtain very good agreement.Comment: 12 pages, 8 figures, 2 tables; legends revised on Figs. 1,3,4,6 and
- …