Speaker
Report on the experience (or the proposed activity). It would be very important to mention key services which are essential for the success of your activity on the EGEE infrastructure.
We have developed a computer code, ISDEP, that solves the
guiding-centre
equations in the presence of collisions. One million particles
are followed
in a realistic TJ-II magnetic configuration for a time (for the
first time in
TJ-II) comparable to the discharge duration. The large number of
trajectories
as well as a careful data analysis allow us to obtain accurate
estimates of
the time evolution of several quantities of interest. The method
is specially
appropriated for a complex magnetic configuration like that of
TJ-II.
Global features of transport, not present in the customary
neoclassical
models, appear: a monotonic increasing of heat and particle
fluxes with
minor radius, the non-diffusive character of transport, the
appearance of
asymmetries on the magnetic surfaces and the non-Maxwellian
character of the
distribution function.
Describe the added value of the Grid for the scientific/technical activity you (plan to) do on the Grid. This should include the scale of the activity and of the potential user community and the relevance for other scientific or business applications
The customary neoclassical transport estimates assume that the
transport
coefficients depend only on the local plasma characteristics. In
TJ-II, the
ion particle orbits include large radial excursions in a single
collision
time. The very same particle thus visit plasma regions of widely
differing
conditions, which invalidates the local approximation. Therefore,
global
plasma characteristics must be taken into account in more
accurate transport
estimates for TJ-II. With this in mind, one can find an
equivalence between a
Fokker-Planck equation (which in our case describes the evolution
of the
particle distribution a plasma in the presence of electric field
and
collisions) and a Langevin equation. This approach it is ideally
suited for
massive parallel computing in Grids. We expect the Langevin
approach to be useful to study transport in devices where
deviations from the
local hypothesis are sizeable.
Describe the scientific/technical community and the scientific/technical activity using (planning to use) the EGEE infrastructure. A high-level description is needed (neither a detailed specialist report nor a list of references).
The study of ion trajectories in low collisionality plasmas is
very important
for understanding transport in tokamaks and stellarators. Several
issues make
this study useful to understand the confinement in those devices.
One of them
is the kinetic transport and the behaviour of particles in a
given magnetic
configuration. We make a transport estimate for the TJ-II device,
which is a
medium size flexible heliac characterized by a complex magnetic
configuration.
With a forward look to future evolution, discuss the issues you have encountered (or that you expect) in using the EGEE infrastructure. Wherever possible, point out the experience limitations (both in terms of existing services or missing functionality)
The next step will be to let the background plasma vary due to the
evolution of the test particles followed by the code. The
approach consisting on keeping
constant the background does not allow the study of evolving
plasmas and dissipates any
perturbation. The application must, hence, be modified to be able
to be run iteratively and
self-consistently in the Grid.
