Fast ion conductor | EPFL Graph Search

In materials science, fast ion conductors are solid conductors with highly mobile ions. These materials are important in the area of solid state ionics, and are also known as solid electrolytes and superionic conductors. These materials are useful in batteries and various sensors. Fast ion conductors are used primarily in solid oxide fuel cells. As solid electrolytes they allow the movement of ions without the need for a liquid or soft membrane separating the electrodes. The phenomenon relies on the hopping of ions through an otherwise rigid crystal structure. Mechanism Fast ion conductors are intermediate in nature between crystalline solids which possess a regular structure with immobile ions, and liquid electrolytes which have no regular structure and fully mobile ions. Solid electrolytes find use in all solid-state supercapacitors, batteries, and fuel cells, and in various kinds of chemical sensors. Classification In solid electrolytes (glasses or crystals), th

Experimental investigation of fast ion dynamics in TORPEX toroidal plasmas

Boris Roulet

The goal of the present diploma work is to experimentally investigate the fast ion physics in TORPEX plasmas, in which interchange modes with flute characteristics and intermittent transport events, i.e. blobs, are observed to dominate the plasma dynamics. During the first part of the diploma, the Candidate will test different fast ion emitters on a test bench, which will be then mounted into the BN casing to form the fast ion source. In parallel, the Candidate will design an innovative in-vessel movable system, which will displace toroidally the fast ion source, thus allowing 3D measurements of the fast ion beam. In the second part of the diploma, the detector will be mounted onto the existing 2D position system and the Candidate will focus on energy-resolved 2D measurements of the fast ion beam. Provided that the in-vessel movable system is timely and successfully constructed, the measurements will be repeated at different toroidal positions of the source, thus providing first 3D and energy resolved measurements of fast ion profiles. The measurements will be performed together with sets of movable Langmuir probe arrays, which provide complete monitoring of the plasma dynamics with fine spatial and temporal resolution.

2010

Phonon-Ion Interactions: Designing Ion Mobility Based on Lattice Dynamics

Sokseiha Muy

This review is focused on the influence of lattice dynamics on the ionic mobility in superionic conductors in particular solid-state Li-ion conductors. After a succinct review of the static view of ionic conduction, the role of polarizability as the underlying cause of lattice softness is discussed in connection with the anharmonicity and the roles of lattice dynamics on ionic conductivity as proposed in early theories in the 70's and 80's by Mahan, Zeller, Rice and Roth are reviewed with the emphasis on various proposed correlations between Debye and Einstein frequency as well as other specific vibrational modes with the activation energy. The role of lattice dynamics on the correlation between the pre-exponential factor and activation energy, i.e. the Meyer-Neldel rule is also presented with emphasis on the entropy of migration and its dependence on the vibrational spectrum of the lattice. Moreover, a recent computational high-throughput screening based on the average vibrational frequency is also discussed to illustrate the application of lattice dynamics descriptors to design new lithium conductors. Finally, several open questions regarding the fundamental understanding of the role of lattice dynamics and new strategies to tune ionic conductivity based on these concepts are presented.

WILEY-V C H VERLAG GMBH2020

A Fast Ion Loss Detector for the TCV Tokamak

Lorenzo Stipani

A Fast Ion Loss Detector (FILD) was designed, assembled, installed and commissioned for TCV. This is a radially positionable, scintillator based detector that provides information on the 2D fast-ion velocity space lost at the probe's location. The collected particles are collimated inside the probe head and impinge upon a plate coated with a scintillator material that emits light. The photon flux is relayed to two acquisition systems: a sCMOS camera for high spatial resolution measurements of the emission locations in the scintillator, and fast photo-multipliers that allow time-correlation studies of fast-ion losses with high-frequency electromagnetic fluctuations. From its position with respect to the confined plasma and the fast-ion sources on TCV, FILD probes a small portion of the lost fast-ion phase space with high velocity-space and temporal resolution. Therefore, it naturally complements other available diagnostics such as neutral particle analysers, spectroscopy techniques for light emission from energetic particles following CX reactions, or neutron counters, which feature a broader, but less resolved, spatial coverage of fast-ion dynamics.The TCV-FILD design introduces some novelties for exploring new ranges of operation that may be adopted in similar systems for other Tokamaks, such as ITER. Two entrance slits can collect particles that circulate in co- and cntr-plasma current directions. This will be particularly useful when the second NBH system, injecting in the opposite toroidal direction, with particle energies that can excite strong Alfvénic modes, will be operated on TCV. A controlled pneumatic linear actuator radially positions the detector to expose the slits to the particle flux up to 9mm inward of the vessel wall. A plug-in design was conceived to facilitate diagnostic installation. The diagnostic was installed and commissioned during TCV experiments in 2020. The sensitivity of the detector to the local magnetic field line direction was investigated. The direction of the plasma current was found to select which of the two slits may be traversed by lost particles. The operational limits in discharges with NBH with total delivered energies up to 1MJ were assessed with the help of sensors monitoring the temperature of the probe head and cameras detecting visible light emissions resulting from the graphite shield heating by particle fluxes. Using FILD, fast-ion losses were detected for the first time on TCV in plasma discharges exhibiting strong MHD modes. Ejections of energetic ions were found correlated in time with Sawtooth crashes, as a sequence of individual events, and in strong phase coherence, as a continuous loss in time, with magnetic perturbations of a saturated and toroidally rotating magnetic island of a NTM. These observations, in addition to providing initial results on the relevant physics phenomena, stimulating further experiments and comparisons with theory, demonstrate the ability of TCV-FILD to provide valuable information in plasma discharges of interest for fast-ion studies. These measurements and additional information from other TCV diagnostics may now be combined to reconstruct, with tomographic inversion techniques, more of the fast-ion phase space. This will be used to identify the conditions for the excitation/suppression of magnetic instabilities, develop methods for their real-time control with heating and/or shaping actuators and investigate their dependencies on plasma parameters.

EPFL2021

A Fast Ion Loss Detector for the TCV Tokamak

Lorenzo Stipani

EPFL2021