Description
Plenary sessions collect all contributions invited or accepted by the IPAC for a complete in depth plenary session.
The reserved time slot for invited talks is 35 minutes (25' for presentation and 10' for discussion).
The reserved time slot for oral talks is 25 minutes (18' for presentation and 7' for discussion).
Recent DIII-D experiments show that small variations in neutral beam modulation period, even with constant time averaged power input, can have a dramatic impact on the beam driven Alfven eigenmode spectrum and resultant fast ion transport. Neutral beam modulation is a common technique used in fusion experiments for regulation of injected power and various diagnostic applications, however, the...
Characteristics of fast ion profile with MHD activities have been investigated in LHD deuterium experiments. The beam deposition profiles are changed by means of the selection of the operational ion source in tangential NBIs. Two ion sources are mounted on tangential NBIs with different tangential radius, therefore, the combination of ion sources operation and plasma position control enables...
An extended version of the 3-ion scheme relies on using fast NBI ions as resonant species for heating mixed plasmas[1,2]. NBI ions can efficiently absorb RF power at the mode conversion (MC) layer, where the wave polarization is particularly favourable for ion cyclotron heating, through their Doppler-shifted resonance. This advanced ICRH+NBI scheme was earlier observed in D-3He plasmas on...
Transport due to plasma turbulence determines the energy content and thus the performance of a tokamak reactor. A recent striking observation in experiments [1,2] and numerical gyrokinetic simulations [3] is the particularly interesting link between the presence of fast particles and a substantial improvement of energy confinement. These findings are intriguing in view of reactor-grade...
In Tokamak plasmas, the modification of magnetic shaping can cause significant influence on both magnetohydrodynamic (MHD) and drift-wave instabilities, and thus affects the confinement performance to a large extent. For instance, the effect of elongation has been proved to increase the global energy confinement time as seen in the ITER IPB98(y, 2) H-mode confinement scaling: τ_E∝κ^0.78. In...
The internal transport barrier (ITB), Alfven Eigenmodes (AEs) and double tearing modes (DTM) have been observed during the off-axis sawteeth oscillation in EAST.
The ITB of electron temperature T_e is modulated by the sawteeth oscillation, and the formation of ITB can be divided into three stages: (1) the transport produced by sawteeth final crash is suppressed at the first stage with steep...
Recent simulations of so-called Abrupt Large-amplitude Events (ALE) driven by beam ions in JT-60U show evidence of transient changes in the magnetic topology on the sub-millisecond time scale, giving rise to moderately sized magnetic islands [1]. Since the configuration at hand is magnetohydrodynamically (MHD) stable with respect to reconnecting instabilities in the range of toroidal mode...
Although the stability of ellipticity, toroidal and reversed-shear Alfven eigenmodes (EAE, TAE, RSAE) is relatively well understood, less is known about the stability of lower-frequency modes such as the beta-induced Alfven eigenmode (BAE), the beta-induced Alfven-acoustic eigenmode (BAAE), and the energetic-particle geodesic acoustic mode (EGAM). Because they are often unstable in present...
The energy and momentum transfer across a magnetic field realized by destabilized magnetohydrodynamic (MHD) eigenmodes - the phenomenon named Spatial Channeling (SC) - can be an important factor affecting the plasma performance [1]. It takes place when sources and sinks (s&s) of energy are located in different regions, i.e., when the region where particles (e.g., fast ions) drive the plasma...
In magnetic confinement devices, pellet injection is used to refuel the core of the plasma, control edge localised modes, and mitigate disruptions. These varied applications require drastically different pellets. As a result, the timescales of pellet assimilation can vary significantly depending on the experiment and machine. Diagnosing the effect of the pellet on the plasma represents an...
Significant variations in MHD activity and fast-ion transport are observed in high-beta, steady-state hybrid discharges with a mixture of Electron Cyclotron (EC) waves and Neutral Beam Injection (NBI). For neutral-beam-only heating, many Alfven Eigenmodes (AE) are observed at frequencies of 100-250 kHz that cause a ~35% degradation in the neutron rate. With both NBI and EC, the AE activity is...
In a reversed magnetic shear (RS) plasma produced by tangential counter neutral beam injection (NBI) having high beam energy of ~160 keV in LHD [1], bulk ion temperature at the plasma center Ti(0) measured by soft X-ray crystal spectrometer (XICS) often increases linearly in time for ~0.3-0.4 s by a factor of ~ 1.5-1.7 in the constant electron density and NBI absorbed power phase. The...
Residual zonal flow level $R_{ZF}$ [1] is one of the key relevant quantities which determine turbulence and transport of tokamak plasmas [2]. While there have been various theoretical extensions of the original work in Ref. [1] including the isotopic dependence [3], most previous works have assumed Maxwellian equilibrium distribution function $F_{0}$ with rare exceptions, for instance Refs...
Radial currents, which occur when energetic particles are expelled from the core of a tokamak plasma, produce torques on the plasma in both toroidal and poloidal directions, due to return currents that maintain quasi-neutrality [1]. The poloidal component of this rotation is predicted to be damped on the ion-ion collision time [2], whilst the toroidal rotation component relaxes more slowly on...
Observations of beam-ion acceleration during edge localized mode (ELM) crashes have been recently reported in the ASDEX Upgrade tokamak [1, 2]. In this work, fast-ion transport during ELMs is investigated using full orbit simulations with the ASCOT code [3] and measurements from a fast ion loss detector (FILD) [4, 5, 6, 7].
Time-evolving 3D electromagnetic fields have been coded up in ASCOT to...
The nonlinear dynamics of shear Alfv{\'e}nic wave fluctuations have become a major concern in magnetically confined fusion, since they can be driven unstable by energetic particles (EPs).
In the present paper, the nonlinear dynamics of toroidal Alfv{\'e}n eigenmodes (TAEs), including nonlinear wave-particle and wave-wave interactions, have been observed in the HL-2A NBI H-mode plasmas. It is...
A strong interplay between edge perturbations, such as edge localized modes (ELMs) and fast-ions has been observed experimentally [1]. Furthermore, beam-ion acceleration during an ELM was observed for the first time in the ASDEX Upgrade tokamak [2]. All these findings indicate that kinetic effects of fast-ions should be considered in ELM modelling. For this purpose, non-linear hybrid...
We report the first observation of chirping instabilities driven by runaway electrons (REs) in a tokamak. Energetic particles often drive instabilities through wave-particle resonances. The frequency of an instability can sweep gradually as background plasma parameters evolve or it can change rapidly (known as “frequency chirping”) due to nonlinear evolution of the energetic-particle...
Injection of high-Z pellets is now a part of the disruption mitigation strategy for ITER. Pellets are seen as favorable to massive gas injection due to deeper penetration of the impurity material into the plasma and the ability to adjust the cooling properties via mixing fractions.
The ablated material surrounding the pellet contains electrons that are much colder
and denser than the ambient...
In a reactor level device such as ITER, a disruption mitigation system is necessary because a considerable level of magnetic energy is transferred to runaway electrons (REs), which seriously damages the tokamak device. Massive material injection techniques considered as a disruption mitigation method in ITER are based on pitch-angle scattering through the Coulomb collision. However, this...
Deuterium experiment was started since March, 2017 on the Large Helical Device (LHD). One of the objective of the deuterium experiment is to explore the physics of energetic particles (EPs) in helical plasmas, but the experiment is also beneficial to the comprehensive understanding of EP physics in toroidal devices.
The EP physics study on LHD is characterized by the use of negative-ion...
In magnetically confined plasmas, energetic particles from Neutral Beam injection, fusion reactions or RF acceleration are susceptible to enhanced transport by several classes of instabilities, thus potentially leading to degraded plasma performance. Depending on its properties (e.g. frequency, mode number spectrum and radial structure), each type of instability can affect the fast ion...
In MAST dedicated experiments were carried out to study the redistribution and loss of neutral beam injected fast ions due to their interaction with Toroidal Alfvén Eigenmodes (TAEs) and Fish-Bones (FBs) by integrating observations from Fast Ion D-alpha diagnostics, a multi-channel Charged Fusion Product Detector (CFPD) and a Neutron Camera (NC) [1]. The experimental observations were modelled...
The evaluation of fast-ion confinement is indispensable for the prediction of the heating efficiency in fusion reactor. The fast-ion confinement depends not only on the collisional transport but also on the fast-ion driven magnetohydrodynamics (MHD) instabilities such as Alfvén eigenmodes (AEs) which induce the fast-ion transport and losses. Therefore, it is an important issue to identify the...
Authors: S.E.Sharapov, M.Garcia-Munoz, B.Geiger, A.Karpushov, P.Schneider, R.Coelho, M.Dreval, J.Ferreira, D.Gallart, P.Lauber, M.Mantsinen, F.Nabais, A.Snicker, G.Tardini, D.Testa, M.A.Van Zeeland, the AUG and TCV Teams and the EUROfusion MST1 Topic 13 Team
See author list of S. Coda et al 2017 Nucl. Fusion 57 102011
**See author list of H. Meyer et al 2017 Nucl. Fusion 57...
In magnetically confined fusion devices, super-thermal particles must be well confined until they slow down to the plasma bulk. Fusion born alpha particles as well as energetic particles produced by external heating systems such as neutral beam injectors (NBI) or ion cyclotron resonance heating (ICRH) are, however, a source of free energy that can destabilize a rich spectrum of Alfvén...
Energetic electron driven toroidal Alf$\rm {\acute{ven}}$ eigenmodes (TAEs), which have been observed in many devices (COMPASS-D[1], C-MOD[2], HL-2A[3]) with high-power ECW and LHW heating, are investigated using a hybrid simulation code MEGA in a tokamak plasma [4]. Considering the interaction between energetic electrons and Alf$\rm {\acute{ven}}$ eigenmodes, energetic electron effects on TAE...
The complex dynamics have been observed in the spectra of the electron cyclotron emission of a nonequilibrium plasma created by powerful microwave radiation of gyrotron (37.5 GHz, 80 kW) under electron cyclotron resonance (ECR) conditions and confined in a tabletop mirror trap [M.E. Viktorov, et al. // EPL V.116, P.55001 (2016)]. The dynamic spectrum of the emission is a set of highly chirped...
Non-thermal ions can drive waves in ion cyclotron range of frequency (ICRF). Excitation of ICRF waves has been observed in several tokamaks and stellarators when fast ions are produced. This emission is called ion cyclotron emission (ICE). A possible driving source for ICE is the ion velocity distribution having significant non-thermal components, such as a bump-on-tail structure and strong...
The 2018 operation phase (OP 1.2b) of the stellarator Wendelstein 7-X (W7-X) included, for the first time, neutral beam injection (NBI) to heat the plasma. During longer phases of NBI injection, with the primary purpose to study the heating efficiency of this system, Alfvén eigenmodes (AEs) were observed by a number of diagnostics, including the phase contrast imaging (PCI) system, the...
The TGLF-EP [1] and Alpha [2] codes for the critical-gradient model (CGM) of energetic-particle (EP) transport have been unified and verified by nonlinear gyrokinetic simulations and validated against five DIII-D H-mode scenarios for ITER. This reduced model predicts the degree to which Alfvén eigenmodes (AEs) destabilized by EPs—in this case fast ions from neutral beam injection—radially...
The recently developed imaging neutral particle analyzer (INPA) on DIII-D enables fast ion velocity-space tomography of unprecedented fidelity, as well as resolution of local phase space dynamics under the action of classical and non-classical transport mechanisms. The INPA itself measures charge-exchanged energetic neutrals by viewing an “active” neutral beam through essentially a 1D pinhole...
Toroidal Alfvén eigenmode (TAE) bursts are often observed in the low magnetic field ($B_t$<1T) experiments in LHD with tangential neutral beam (NB) injection [1-4]. In order to measure the behavior of the energetic particles (EPs) during the TAE bursts, a tangential E-parallel-B type neutral particle analyzer (E//B-NPA) has been used. In the experiments with the E//B-NPA, the hole-clump pair...
Understanding of interplay between energetic particle (EP) and EP-driven magnetohydrodynamic mode is of the greatest importance in order to reduce the anomalous transport and/or loss of EPs in current fusion machines and in a fusion reactor. In high-ion-temperature discharges performed in relatively low-density plasma on the Large Helical Device (LHD), helically-trapped energetic-ion-driven...
Authors: V.G.Kiptily, Ye.Kazakov, M.Nocente, M.Fitzgerald, S.E.Sharapov, A.E.Shevelev, and JET Contributors
Excitation of Elliptical AEs (EAEs) and TAEs has been observed in hydrogen-rich (nH/nH+nD ~70-90%) JET discharges of so-called “three-ion scenario”, i.e.D-(3He)-H three ion ICRH scenario [1]. This scenario is characterized by a strong absorption of radio frequency waves at very...
To understand the dynamics of multiple Alfvén Eigenmode (AE) instabilities excited simultaneously by energetic beam ions we developed a heuristic Predator-Pray (PP) model where two PP systems each consisting of a predator (AE) and a prey (resonant ions) are coupled together. The first PP system works as a source of particles for the second system which in its turn plays a role
of a sink of...
