Speaker
Jakub Bielecki
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1014.pdf
New methods of neutron emissivity tomographic reconstruction for
fusion plasma
J. Bielecki 1
1 Institute of Nuclear Physics Polish Academy of Sciences (IFJ PAN), PL-31-342 Krakow,
Poland
Reconstruction of the neutron emissivity distribution in fusion devices is a useful tool for
retrieving information on spatially resolved fusion rates. The reconstruction is performed
from a limited number of line-integrated quantities measured by a set of neutron detectors.
Usually the coverage of a plasma cross-section is very sparse. Thus, the problem of
tomographic reconstruction is very challenging due to its ill-posed character. Several
approaches to the reconstruction of neutron emissivity in magnetic-confinement fusion
devices have been developed.
In this work two recently developed methods are presented: (i) the method based on genetic
algorithms (GA) and (ii) the method based on Metropolis–Hastings Monte Carlo (MC)
algorithm.
GA are inherently parallel and the search is performed from a population of points.
Therefore, the method has the ability to avoid being trapped in a local optimal solution.
The developed MC method is based on a biased random walk. The algorithm generates
pseudo-random samples within the domain that contains the solution. The properly chosen
objective function ensures the convergence to the desired solution. The applied Metropolis–
Hastings algorithm can overcome the problem of trapping of the random walk in local
minima, because it offers a possible method for jumping out of them by accepting, with
some finite probability, changes in the direction opposite to indicated by the objective
function.
Both methods have been tested using a set of synthetic models. The methods have been
validated in terms of accuracy, speed and resilience against the noise present in the line-
integrated input data. The obtained results show that both methods provide accurate
reconstruction results, comparable with those obtained by the standard methods routinely
used for tokamak plasma (e.g. Tikhonov Regularization, Minimum Fisher Information,
etc.)
Acknowledgement:
The author gratefully acknowledges the financial support of the Polish National Science
Centre (NCN), (grant no. DEC-2017/01/X/ST2/00126.) which financially supported this
research.
