In ideal magnetized plasmas, sheet-like field discontinuities, where current and vorticity peak, naturally form. According to the linear theory, these layers undergo fluid and magnetic instabilities whose strength depends on the amplitude of the local magnetic field and flow. In non-ideal plasmas, in presence of magnetic reconnection, the combined action of the sheared flow and the sheared...
The geodesic-acoustic-mode (GAM) is a plasma oscillation observed in fusion reactors with toroidal geometry (such as the Tokamak or Stellarator) and are recognized to be the non-stationary branch of the zonal flows (ZFs). Similarly to the ZFs, GAMs are understood to regulate cross-field turbulence and thus enhance energy confinement [1]. Still, their direct effect on turbulence is not yet...
SOLPS-ITER modelling of plasma rotation with co-rotating atoms in the Magnum-PSI beam.
H.J. de Blank1 , J. Verstappen1, J. Gonzalez2, I. Classen1, E. Westerhof1
1 DIFFER - Dutch Institute for Fundamental Energy Research. De Zaale 20, 5612AJ, Eindhoven, The Netherlands
2 ARCNL, P.O.Box 93019, 1090BA Amsterdam, The Netherlands
In the ITER divertor heat loads of 10 MWm-2 are expected in...
A numerical tool modelling the excitation and evolution of electron avalanche ionization in the breakdown phase of start-up in tokamaks is presented. We estimate the energization efficiency of the nonlinear interaction between spatially localized Gaussian EC-fields propagating in vacuum with an ensemble of seed electrons. This process is coupled with the acceleration of electrons due to the...
The stellarator is a device designed to achieve controlled fusion by magnetic confinement.
Despite several advantages over tokamaks, its lack of axisymmetry creates some difficulties to confine the plasma: in an unoptimised stellarator reactor, both thermal ions and the fast ions produced by DT fusion would be lost faster than in a tokamak. On the other hand, stellarators are characterised by...
In order to be candidates to fusion power plants, stellarators must be optimized, i.e. the magnetic field needs to be tailored to have sufficiently good confinement properties. When the optimization process is performed to minimize neoclassical losses, the goal is to obtain a magnetic field that is close to omnigeneity. A magnetic field is omnigenous [1] if the radial drift of collisionless...
Quasi-isodynamic (QI) stellarators are a uniquely attractive fusion reactor candidate due to their low neoclassical transport, excellent confinement of fusion-borne alpha particles, and vanishingly small bootstrap currents [1]. Due to the complexity of their geometries, QI stellarators must generally be designed through numerical optimization, which requires an objective metric that quantifies...
In the last experimental campaign of Wendelstein 7-X (W7-X) the new ICRH antenna [1] was brought into operation. With only one of the two antenna straps being operable in the last campaign, the available phasing options as well as the amount of power that could be coupled into the core plasma were limited. Nevertheless, the antenna is expected to be fully functional for the next operational...
Concentrated exhaust power deposition must be avoided in a fusion power plant. A strategy to prevent this is to seed heavy impurities in the divertor, which radiate strongly at the local plasma temperature. This can help to maintain a uniform power deposition over the divertor structure. However, if the impurity migrates upstream, it can produce a number of detrimental effects, including fuel...
The neutral atoms in the plasma edge of nuclear fusion devices are typically modeled using a kinetic approach and more specifically the Monte Carlo (MC) code EIRENE [1]. Although EIRENE has been proved very reliable and effective, there are some drawbacks such as the statistical noise introduced by the MC techniques and the computational cost, which is significantly increased in high...
To accurately model the plasma dielectric properties in presence of rotational transform, most of the theoretical models and full-wave codes addressing radiofrequency wave propagation and absorption in tokamaks are based on toroidal and poloidal Fourier expansions of the RF fields (see for instance [1-4]). A significant drawback of this field representation is its lack of flexibility, in that...
To understand plasma behaviour in the scrape-off layer (SOL), we need to know the boundary conditions for the plasma and electromagnetic fields near a divertor. At the plasma-wall boundary, in the direction perpendicular to the wall, there are four length scales of interest. These are the Debye length $\lambda_D$, the ion gyroradius $\rho_i$, the projection of the collisional mean free path in...
Decades of research has demonstrated the necessity of using kinetic plasma models to accurately model the flux of heat and particles through the closed-field line region of tokamaks. In the much colder open-field-line region beyond the last closed flux surface (LCFS), fluid models are typically used to model the flux of heat and particles to the divertor. Recently, kinetic plasma models have...
Modelling the large amplitude fluctuations of the plasma edge, particularly across the separatrix into the hot scrape-off layers of future reactors, can require costly full-f kinetic simulations, with heavily restricted time-step due to uninteresting fast waves [1]. Here we demonstrate the first steps in the implementation of a method allowing consistent evolution of the system up to the...
Stellarator magnetic configurations need to be optimized in order to meet all the required properties of a fusion reactor. The stellarator Wendelstein-X (W7-X) was optimized to be approximately quasi-isodynamic (QI). In an exactly QI field, trapped particles orbit, on average, in the poloidal direction, and therefore remain confined [1]. Neoclassical transport is thus expected to be low....
This work is based on the variational principle for magnetic field lines introduced in 1983 by Cary and Littlejohn [1]. The action principles for magnetic field lines and for Hamiltonian mechanics are recalled to be analogous. It is shown that the first one can be rigorously proved from first principles without analytical calculations. Not only the action principles are analogous, but also a...
Since the early 90ties, 3D nonlinear MHD studies have been developing a fundamental framework for the understanding of the Reversed Field Pinch (RFP) self-organization. The simple visco-resistive MHD approximation clearly shows that 3D reconnection processes strongly characterize the dynamics in an ample range of the dimensionless Lundquist/Hartmann numbers, as well as in experimental...
Importance of Parallel Dispersion in ICRF Modelling of Travelling Wave Antenna Concept in DEMO-Like Plasmas in 2D Axisymmetry
B. Zaar$^1$, T. Johnson$^1$, L. Bรคhner$^1$, R. Bilato$^2$, R. Ragona$^3$, and P. Vallejos$^4$
$^1$KTH Royal Institute of Technology, Stockholm, SE-114 28, Sweden
$^2$Max-Planck-Institut fรผr Plasmaphysik, Garching, D-85748, Germany
$^3$Department of Physics,...
M. F. F. Nave1, A. Mauriya1, M. Barnes2, E. Delabie3, J. Ferreira1, J. Garcia4 , A. Kirjasuo5, F.I. Parra6, M. Romanelli7 and JET Contributors*
EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK
1Instituto de Plasmas e Fusรฃo Nuclear, Instituto Superior Tรฉcnico, P1049-001 Lisboa, Portugal
2Rudolf Peierls Centre for Theoretical Physics, Oxford University, UK
3Oak...
The dynamics of magnetic islands and the role they play in fusion plasmas are usually approached and predicted using extensions of the original theory by Rutherford [1, 2], on which estimates for their impact on the operation of present and future magnetic confinement devices are based. Likewise, diagnostics to detect their presence [3] and techniques to limit their impact are operated on the...
Implementation of an analytical Jacobian in the MEQ free-boundary tokamak equilibrium code suite
See attached PDF.
Recently, a general theoretical framework for the transport of Phase Space Zonal Structures (PSZS) has been developed \cite{zonca2015,falessi2019}. PSZS are the long-lived toroidal symmetric ($n=0$) structures that define the nonlinear equilibrium in the presence of fluctuations such as Alfv\'enic instabilities. In order to include sources and sinks and collisional slowing down processes, a...
Nonlinear inverse bremsstrahlung absorption (NLIBA) of intense electromagnetic waves in homogeneous plasmas may have significant impact on many physical phenomena through modifications of the electron distribution function (EDF). These modifications depend on the relevant parameter $ \alpha=\frac{v_0^2}{v_t^2\ } $, where $v_0 $ is the quiver velocity and $v_t $ is the electron thermal...
