Ion cyclotron resonance | EPFL Graph Search

Ion cyclotron resonance is a phenomenon related to the movement of ions in a magnetic field. It is used for accelerating ions in a cyclotron, and for measuring the masses of an ionized analyte in mass spectrometry, particularly with Fourier transform ion cyclotron resonance mass spectrometers. It can also be used to follow the kinetics of chemical reactions in a dilute gas mixture, provided these involve charged species. Definition of the resonant frequency An ion in a static and uniform magnetic field will move in a circle due to the Lorentz force. The angular frequency of this cyclotron motion for a given magnetic field strength B is given by :\omega = 2\pi f = \frac{zeB}{m}, where z is the number of positive or negative charges of the ion, e is the elementary charge and m is the mass of the ion. An electric excitation signal having a frequency f will therefore resonate with ions having a mass-to-charge ratio m/z given by :\frac{m}{z} = \frac{eB}{2\pi

Self-Consistent ICRH Distribution Functions and Equilibria in Magnetically Confined Plasmas

Martin Jucker

The deployment of high power radio frequency waves in the ion cyclotron range (ICRF) constitutes an important operational facility in many plasma devices, including ITER. Any charged particle describes a helical motion around a given magnetic field line, the so-called cyclotron motion. ICRF relies on the interaction between charged particles and an injected Radio Frequency (RF) wave, tuned to be at the same frequency as the helical cyclotron motion. It is applied not only for pure heating of the plasma, i.e. Ion Cyclotron Resonant Heating (ICRH), but also for the generation of non-inductive current through Ion Cyclotron Current Drive (ICCD). The numerical code package SCENIC has been developed for self-consistently simulating the effects of ICRH on the resonant ion species within the plasma, the resulting changes in the plasma equilibrium, and finally the back reaction onto the injected wave field. SCENIC is an iterated scheme, which advances the resonant ions' distribution function, the equilibrium and the wave field iteratively until a converged solution, representing a steady state, is reached. The constituents of SCENIC are the MagnetoHydroDynamic (MHD) equilibrium code VMEC,1 the full wave code LE-Man2 and the Hamiltonian guiding centre drift following code VENUS.3 All of these codes are capable of dealing with 3D geometries, and have recently been updated to handle pressure anisotropy, where the energy density parallel and perpendicular to the magnetic field differ. This is important since the RF field resonates mainly with the particle's motion perpendicular to the magnetic field, thus creating pressure anisotropy. After the introduction and description of the different codes and their interfaces, this work verifies the consistency of the numerical results with expected results for simple cases, and a benchmarking effort against the similar code package SELFO is shown. After this validation, SCENIC is applied to different heating scenarios, which are relevant to present (Joint European Torus, JET) and future (ITER) devices. Low power heating simulations with a 1% helium-3 minority in background deuterium plasmas demonstrate that a pressure anisotropy is induced. We show that the hot particle distribution function can be adequately approximated with a particular bi-Maxwellian for the equilibrium and wave field computations. For high power, 3% hydrogen minority heating scenarios, the heating scheme alters the background equilibrium state. This justifies one of the main novelties introduced in this work, namely the inclusion of the equilibrium computation in the self-consistent scheme. Effects due to asymmetric wave injection and different heating locations on the hot particle distribution function, the hot dielectric tensor and the equilibrium will be studied. Here, the emergence of a high energy tail in the minority species distribution function is shown explicitly, and some of its exotic features are observed via the RF driven current, the density and the pressure evolution.

EPFL2010

Analysis and modelling of momentum transport based on NBI modulation experiments at ASDEX Upgrade

Basil Duval, Emiliano Fable, Giovanni Tardini

The prediction of plasma rotation is of high interest for fusion research due to the effects of the rotation upon magnetohydrodynamic (MHD) instabilities, impurities, and turbulent transport in general. In this work, an analysis method was studied and validated to reliably extract momentum transport coefficients from neutral beam injection (NBI) modulation experiments. To this end, a set of discharges was created with similar background profiles for the ion and electron temperatures, the heat fluxes, the electron density, and the plasma rotation that, therefore, should exhibit similar momentum transport coefficients. In these discharges, a range of temporal perturbations were imposed by modulating and varying the power deposition of the NBI, electron-cyclotron-resonance heating (ECRH), and ion-cyclotron-resonance heating (ICRH). The transport model including diffusion, convection, and residual stress was implemented within the ASTRA code. The Prandtl number Pr = chi(phi)/chi(i) was assessed via the GKW code. A convective Coriolis pinch was fitted and the intrinsic torque from the residual stress was estimated. The obtained transport coefficients agree within error bars for sufficiently small imposed temperature perturbations, as would be expected, from the similar background profiles. This successful validation of the methodology opens the door to study the parametric dependence of the diffusive and convective momentum transport of the main ions of the plasma as well as the turbulent intrinsic torque in a future work.

IOP Publishing Ltd2022

Sawtooth control in ITER using ion cyclotron resonance heating

Otto Asunta, Jonathan Graves, Martin Jucker, Olivier Sauter

Numerical modelling of the effects of ion cyclotron resonance heating (ICRH) on the stability of the internal kink mode suggests that ICRH should be considered as an essential sawtooth control tool in ITER. Sawtooth control using ICRH is achieved by directly affecting the energy of the internal kink mode rather than through modification of the magnetic shear by driving localized currents. Consequently, ICRH can be seen as complementary to the planned electron cyclotron current drive actuator, and indeed will improve the efficacy of current drive schemes. Simulations of the ICRH distribution using independent RF codes give confidence in numerical predictions that the stabilizing influence of the fusion-born alphas can be negated by appropriately tailored minority He-3 ICRH heating in ITER. Finally, the effectiveness of all sawtooth actuators is shown to increase as the q = 1 surface moves towards the manetic axis, whilst the passive stabilization arising from the alpha and NBI particles decreases.

2011

Self-Consistent ICRH Distribution Functions and Equilibria in Magnetically Confined Plasmas

Martin Jucker

EPFL2010