摘要:

The growth of an unstable electrostatic ion Bernstein mode in a uniformly magnetized, homogeneous plasma is simulated by time averaging the equations of motion over a cyclotron period. (AIP)

ISSN:0094-243X    

DOI:10.1063/1.46547

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

An analytical model and a numerical procedure are presented which give a kinetic nonlinear description of the Alfve´n‐wave instabilities driven by the source of energetic particles in a plasma. The steady‐state and bursting nonlinear scenarios predicted by the analytical theory are verified in the test numerical simulation of the bump‐on‐tail instability. A mathematical similarity between the bump‐on‐tail problem for plasma waves and the Alfve´n wave problem gives a guideline for the interpretation of the bursts in the wave energy and fast particle losses observed in the tokamak experiments with neutral beam injection. ©American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46559

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

One‐dimensional electrostatic particle simulations have been performed to investigate the formation and sustaining mechanisms of ion acoustic double layers. Double layers spontaneously evolve out of thermal noise when electrons with a subthermal drift velocity (Vd<Vth) are injected into a long and open system. The simulation model is so designed that the system is in contact with an external agent with an ability of emitting a steady current. Three phases are noted in the nonlinear development. In the first place, a stairs‐like structure is formed for the electrostatic potential, where each stair consists of an ion acoustic double layer of the order of an electron thermal potential (e&fgr;/Te≲1).After a while, this stairs‐structure is destroyed by emitting soliton‐like modes, and another similar stairs‐like structure is reconstructed. This second stairs‐like structure also subsides meanwhile. After that, amazingly enough, there appears a ‘‘giant’’ double layer, which exceeds ten times of the electron thermal potential (e&fgr;/Te≳10). This ‘‘giant’’ double layer generates an unexpectedly high energy electron beam (Vb≳5Veth) on the downstream side, in spite of the fact that the applied electron drift speed is less than the electron thermal speed (Vd<Veth). ©American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46546

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The ‘‘dormant’’ and ‘‘fishbone’’ modes of excitation are considered in D‐T fusion reactions. (AIP)

ISSN:0094-243X    

DOI:10.1063/1.46560

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The resonant excitations of high‐n magnetohydrodynamic (MHD) instabilities by the energetic ions/alpha particles in tokamaks are theoretically analyzed. Here, n is the toroidal mode number. Since, typically, the MHD modes consist of two‐scale structures; one singular (‘‘inertial’’) region and one regular (ideal) region, the energetic particle contributions in the singular region are suppressed by the finite‐size orbits. Analytical dispersion relations can then be derived via the asymptotic matching analysis. The dispersion relations have the generic form of the ‘‘fishbone’’ dispersion relation and demonstrate, in particular, the existence of two types of modes; that is, the MHD gap mode and the energetic‐particle continuum mode. Specific expressions are given for both the kinetic ballooning modes (KBM) and the toroidal Alfve´n modes (TAM). It is suggested that the stability property may be qualitatively regarded as the ‘‘hybrid’’ of conventional MHD tokamaks and field reversed ion rings. ©American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46548

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The stability of toroidicity‐induced Alfve´n eigenmodes is investigated in general tokamak equilibria with finite aspect ratio and finite plasma beta. The finite orbit width of the hot particles and the collisional damping of the trapped electrons are included. The critical hot particle beta values for the stability threshold are numerically calculated for deuterium‐tritium thermonuclear plasma experiments. ©American Institute Physics

ISSN:0094-243X    

DOI:10.1063/1.46549

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Both the slowing down and the neoclassical diffusion of high energy ions are discussed in a self‐consistent manner. The basic equations, which describe the temporal development of distribution function in a real and velocity spaces, are formulated. ©American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46550

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The stability properties of the toroidal Alfve´n eigenmode excited by energetic neutral‐beam ions are investigated in a divertor tokamak configuration, with the use of the Bishop magnetic flux equilibrium model and a population of trapped/passing fast particles. The location of the separatrix X‐point affects the mode behavior noticeably. Physical interpretation of the results and comparison with some experimental observations are discussed. ©American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46551

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Several possibilities to diagnose fusion‐produced fast particles have been considered; such as, high energy beam probe method, low energy beam probe method, charge exchange spectroscopy method, pellet injection method, collective Thomson scattering method, etc.. As a diagnostics for the velocity distribution of fusion‐produced fast particles, especially in the higher energy range, the high energy beam‐probe method or the collective Thomson scattering method will be a good candidate. Concerning to the density profile of high energy particles, however, it seems to be rather difficult to measure by one method, and we might have to have two (or three) different methods in order to obtain those kind of information.Relating to the pellet injection method for confined fast particle diagnostics, experiments of pellet acceleration by laser irradiation have been carried out. The total momentum of a plasma ablated from a pellet by the laser irradiation has been examined and confirmed to be consistent with the pellet momentum accelerated by the reaction of the plasma. Also the dependences of pellet momentum on laser energy have been studied with various pellet mass/size and pellet species, and the scaling has been studied especially in the region of small pellet size.In addition, a preliminary study about the possibility of simulation experiments have been carried out for the study of high energy particle physics in the LHD project. ©American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46552

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Placing anl=1 continuous helical coil with a significant pitch modulation in axisymmetric toroidal magnetic field, we obtained a helical‐axis configuration with characteristics similar to the Helias. In the four pitch case, a device with apect ratio of 5 ∼ 6 and good accessibility becomes possible, although a very weak magnetic hill exists. In a particular MHD equilbrium, the magnetic well appears in the whole region for central beta of &bgr;(0)≥1%.Collision‐less particle orbit is studied by the guiding center drift equation taking into account of the finite beta effect. Though about one fourth of particles launched from the magnetic surface located at half radius are lost due to the bumpy component of the magnetic field spectrum in the vacuum, both the radial electric field and the finite &bgr; effect improve the particle orbit confinement significantly. Loss rate reduces more than 40% due to the diamagnetic effects on the magnetic field when ⟨&bgr;⟩≳3%. ©American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46553

出版商:AIP    

年代:1994

数据来源: AIP