Speaker
Description
Heat exhaust in the boundary region of fusion experiments remains to this day the biggest challenge towards harvesting fusion power. Transport of particles and heat in this region is dominated by radial motion of coherent structures known as blobs [1].
Long time series obtained by fixed point probe measurements in recent experiments reveal highly intermittent fluctuations in the ion saturation current. These measurements are well described by a super-position of uncorrelated exponential pulses with exponential decay and exponentially distributed pulse amplitudes [2; 3; 4]. In previous numerical simulations of boundary plasma turbulence the statistical properties of plasma fluctuations were investigated [5; 6; 7]. In order to validate this modeling approach we run simulations in the boundary turbulence code BOUT++ [8; 9] to obtain long time series that can be compared to time series obtained from experimental measurements. These simulations use a two dimensional fluid model describing the evolution of the plasma density and vorticity in the two dimensional plane perpendicular to the magnetic field.
We find that the radial particle density profile is exponential with a radially constant scale length. The probability density function for the particle density fluctuations has an exponential tail. Radial motion of blob-like structures leads to large-amplitude bursts with an exponential distribution of peak amplitudes and the waiting times between them. The fluctuation statistics obtained from the numerical simulations are in excellent agreement with recent experimental measurements from magnetically confined plasmas.
References
[1] D. A. D’Ippolito, et. al., Phys. Plasmas, 18, 060501 (2011).
[2] A. Theodorsen, et. al., Plasma Phys. Contr. Fusion, 58, 044006, (2016). [3] R. Kube, et. al., Plasma Phys. Contr. Fusion, 60, 065002, (2018).
[4] O. E. Garcia, et. al., Nucl. Mater. Energy, 12, 36-43 (2017).
[5] Y. Sarazin, et. al., J. Nuclear Mater., 313, 796-803, (2003).
[6] N. Bisai, et. al., Phys. Plasmas, 12, 072520, (2005).
[7] O. E. Garcia, et. al., Phys. Plasmas, 12, 062309, (2005).
[8] B. D. Dudson, et. al., Comp. Phys. Commun., 180, 1467-1480, (2009). [9] F. Militello, et. al., Plasma Phys. Contr. Fusion, 59, 125013, (2017).
