Losses of neutral beam injected fast ions due to adiabaticity breaking processes in a field-reversed configuration

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We performed trajectory analysis of beam ions in such a magnetic field structure having a weak magnetic field region over a wide range by canceling the magnetic field created by the solenoid coil with a Helmholtz coil. The rate at which the beam ions injected in the axial direction are trapped in the magnetic field structure is statistically examined. In addition, by adjusting the Helmholtz coil current, the position of the field-null point is changed, and the influence on the ion trapping rate is also investigated. As a result, it is found that the larger the beam dispersion, the higher the trapping rate, and the higher the energy, the lower the trapping rate. Furthermore, it is also found that in the case where the magnetic field is not completely canceled at the center of the device, there is an energy which extremely decreases the trapping rate.

Section: Introductionmentioning

confidence: 99%

Trapping Efficiency of a Non-Adidabatic Confinement Device

Adachi

Matsui

Iwata

et al. 2018

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“…At the same time, the trajectory deviates from a regular circular motion. However, it can be seen that the trapped particles are subject to more changes of the velocity direction, i.e., collisionless pitch angle scatterings [2,3], which depend on the gyrophase when ions enter and exit the weak magnetic region. For a small trapped rate, ions entering the weak magnetic field region are un- likely to cause perturbation of their trajectory and exhibit regular motions.…”

Section: Resultsmentioning

confidence: 99%

“…By creating a region where the magnetic field becomes zero at the center, it can be expected that the adiabatic invariance in a charged particle motion will be broken. Charged particles, in particular ions, will suffer from collisionless pitch-angle scatterings [2][3][4] and will be able to move all over the accessible region that is specified by the constant of motion such as the Hamiltonian and the canonical angular momentum. By connecting multiple non-adiabatic traps in the axial direction, it becomes possible to extend a net confinement time because of statistical properties shown in random walk processes [1].…”

Section: Development Of Particle Control Technologies By Ap-mentioning

confidence: 99%

Lyapunov Exponent Analysis for Stochastic Ion Motion in a Non-Adiabatic Trap

Matsumoto

Iwata

Urano

et al. 2019

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The Lyapunov exponent analysis is carried out for ion motions in a non-adiabatic trap where the axial magnetic field from a solenoid is partially cancelled by that from a Helmholtz coil. In particular, relation between the Lyapunov exponents and the trapped rate of ions injected in the axial direction is numerically studied. It is found that there exist energy minimizing the particle trapped rate, and the Lyapunov exponent for the axial velocity is found to be minimized with that energy.

“…The form of pressure function and the boundary conditions are the same as Ref. [4], and plasma parameters, such as, the plasma size, the confinement field, the temperature, etc. are determined by reference to the FRC experiment on the NUCTE-III [5].…”

Section: Perturbation Of Electron Fluid In An Frcmentioning

confidence: 99%

Electron-Fluid Perturbation and Its Interaction with Electrons in a Field-Reversed Configuration

Iizima

Takahashi

Watanabe

et al. 2012

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Electron-fluid perturbation fields of a field-reversed configuration plasma is investigated by assuming the source of a electromagnetic wave is the electron current fluctuation. Electron trajectories in the prescribed perturbation field are calculated, and the toroidal flow velocity and velocity distribution and estimated by the particlein-cell method. It is found that electrons are heated and enhancement of the end-loss of electrons is observed when the perturbation field is present. Keywords: field-reversed configuration, electron-fluid perturbation, wave-particle interaction DOI: 10.1585/pfr.7.2403057 InroductionThe origin of resistivity in field-reversed configuration (FRC) plasmas has been unidentified as yet because of difficulties in diagnostic technique to measure pulsing events. In the history of transport study of FRC, the lower hybrid drift instability has believed to be the dominant process [1], however, it is disproved by Carlson's experiment [2]. Since obtainable data are restricted by an experimental approach, a numerical study is very convenient to investigate the transport phenomena in FRC plasmas. We are also interested in spontaneous toroidal spin-up mechanism, which may relate with resistive flux decay [3]. According to Ref. [3], the poloidal flux decrement directly changes to the kinetic angular momentum of both ions and electrons. If the current of both species increases, the poloidal flux maintains and no flux decay is observed. We suppose that the angular momentum of electrons is rapidly lost by some kind of transport mechanism. In the present paper, we assume the presence of electron fluid fluctuation with relatively high frequency, and study its interaction with electrons. Electron trajectories in the prescribed fluctuating fields are calculated, and response to the fluctuation and associated transport is discussed by collection of their motion. Perturbation of Electron Fluid in an FRCThe wave equations of electromagnetic fields areauthor 's e-mail: t-tak@el.gunma-u.ac.jp * ) This article is based on the presentation at the 21st International Toki Conference (ITC21).Here, all the quantities above are fluctuating components and have the relations with the oscillating fields in the formNow, let us assume that the field perturbation is caused by plasma current fluctuations. Since an FRC plasma has a high beta value, the confinement field is sustained mainly by the plasma current containing fluctuation coming from typical electron motions. Since electrons are affected and ions are unable to follow, we choose the fluctuation frequency is 0.1 ω ec , where ω ec is the electron cyclotron frequency. Then the source terms in Eqs. (1) and (2) are given asAmplitudes ofρ(r, z) andj(r, z) are assumed to be proportional to the equilibrium quantities, theñThe fluctuation ratios δ n and δ j are chosen small values, such as 10 −3 . There is no experimental evidence that fluctuating fields in an FRC plasma originate from the above assumptions (7) and (8). However, it is reasonable to consider that the ...