Electromagnetic Simulation Code Research Articles

Microscopic analysis of merging processes of relativistic electron beams propagating in a high-density plasma

The dynamical processes of an energetic electron beam propagating through a high-density plasma have been analyzed using an electromagnetic two-dimensional hybrid simulation code. After an initially solid cylindrical electron beam breaks up into a number of small beamlets, they start to merge with each other by means of their mutual current attractive force. The results show that detailed processes which take place when a pair of beamlets merge into a single one are different for different sizes of beamlets. When the size of the beamlet is small, the merging process is accompanied by magnetic field generation and the energy of the beam electrons then decreases in time. On the other hand, when the beamlet becomes sufficiently large, the merging no longer generates an excess magnetic field, and the energy of beam electrons is kept constant. The difference comes from the magnitude of the return current induced in the surrounding background plasma.

Transverse impedance of axially symmetric tapered structures

We determine the low frequency transverse impedance of axially symmetric tapered structures. Higher-order perturbation theory is used to improve previous estimates due to Yokoya and Stupakov. For linear tapers, accurate numerical results are obtained using the ABCI electromagnetic simulation code. Based upon insight gained from the perturbation calculations, we introduce a simple parametrization that provides an excellent fit to all of our ABCI data---including cases with gradual and steep tapers as well as large and small change in cross section.

Development of the Efficient Electromagnetic Particle Simulation Code with High Performance Fortran on a Vector-Parallel Supercomputer

Development of the Efficient Electromagnetic Particle Simulation Code with High Performance Fortran on a Vector-Parallel Supercomputer

Power-Balance Control by Slug Tuner for the 175MHz Radio-Frequency Quadrupole (RFQ) Linac in IFMIF Project

RF Power-balance control among the quadrants of IFMIF 4-vane radio-frequency quadrupole (RFQ) linac structure is a critical issue, because it may be affected by the fabrication error of the 12m-long RFQ and by the perturbation due to loop antenna installation. The power-balance controllability of slug tuners was measured by a low power test, and the distortion behavior of electric fields profiles at beam bore peripheral was calculated by an electromagnetic field simulation code. From the low power test, it was found that RF power-balance up to 80% can be controlled without overlap of modes. The calculation suggested that the design requirement of distortion limit of 1% can be attained by employing 1cm slug tuner with insertion depth of 1cm or less.

Three-Dimensional Modeling of AC Space Charge for Large-Signal TWT Simulation

We describe a new model for calculating the ac space charge in a linear-beam traveling wave tube (TWT) large-signal simulation code when the true three-dimensional (3-D) geometry of the interaction circuit is taken into account. We use the 3-D electromagnetic simulation code CTLSS to characterize the ac space charge fields generated by a set of test currents placed inside the periodic interaction structure. This information, expressed in matrix form, is used by the large-signal simulation codes CHRISTINE-1D and CHRISTINE-3D to compute self-consistently the additional space charge field terms due to the structure in response to the beam evolution during the simulation. We present the formulation, and describe the implementation in both CTLSS and the large-signal codes. We validate the model by comparison with the analytical sheath helix model, and evaluate the importance of including this correction for modeling a number of helix and coupled-cavity TWT devices.

Development of the Efficient Electromagnetic Particle Simulation Code with High Performance Fortran on a Vector-Parallel Supercomputer

A three-dimensional, relativistic, electromagnetic particle simulation code is developed using the “Exact Charge Conservation Scheme”on a vector-parallel supercomputer. This scheme is a method for calculating current densities. Applying this method, correction of electric fields is not needed. In this paper, some techniques to optimize the above scheme for a vector-parallel supercomputer are shown. The method for vectorization and parallelization in shared memory and in distributed memories are discussed. The code is written in Fortran90 and High Performance Fortran (HPF). Examination of this code is also made.

Short large‐amplitude magnetic structures and whistler wave precursors in a full‐particle quasi‐parallel shock simulation

A one‐dimensional (1‐D) full‐particle electromagnetic simulation code (PIC) is used to investigate the role of upstream whistler and low‐frequency upstream waves during cyclic reformation of a medium Alfvén Mach number quasi‐parallel collisionless shock (magnetic field ‐ shock normal angle = 30°). The ion to electron mass ratio is assumed to be 100. Compared with previous PIC simulations, the upstream region is large enough to allow for the emergence of low‐frequency upstream waves by the interaction of backstreaming ions with the solar wind via an ion/ion beam instability in the far upstream region. It is shown that the low‐frequency upstream waves steepen up into pulsations (or short large‐amplitude magnetic structures (SLAMS)), as has been shown earlier by hybrid simulations. As these pulsations are added to the shock and thus comprise the shock, the upstream edge radiates a phase standing whistler train. This whistler train propagates partway into the newly arriving pulsation. The nonlinear interaction of reflected ions and incoming solar wind ions in the electrostatic potential of the whistler leads to ion trapping and rapid whistler damping. This results in SLAMS consisting of two regions with different ion temperatures. The cyclic reformation is essentially due to the SLAMS being added to the shock and is of larger scale (∼10 ion inertial lengths) as compared with the whistler scale.

Formation of reflected electron bursts by the nonstationarity and nonuniformity of a collisionless shock front

The impact on electron dynamics of the nonstationarity and nonuniformity of a quasi‐perpendicular supercritical collisionless planar shock is analyzed by means of a two‐dimensional full‐particle electromagnetic simulation code. Trajectories of preselected self‐consistent electrons (in contrast with the test particles approach) have been analyzed in order to determine the reflection conditions. Four different classes of reflected electrons have been identified according to the time these spent within the shock front itself before being reinjected into the upstream region. However, the shock front is revealed to be strongly nonstationary and nonuniform (front rippling). Different sources of shock front nonstationarity are shown to take place over different time and spatial scales. The longer time scale is due to the shock front reformation associated to the dynamics of reflected ions. The smaller time scale is due to the propagation of front rippling along the shock front. One key result is that electrons hitting the shock front are not reflected uniformly in time; instead, bursts of energetic reflected electrons are formed by the shock front reformation. In addition, electrons are not reflected uniformly in space, but packs of reflected electrons are formed along the rippled shock front. Comparison of two‐dimensional with one‐dimensional simulation results evidences that nonuniformity (rippling) of the shock front contributes to diffuse electron bursty patterns both in real and velocities space. Persistent (one‐dimensional) and more diffuse (two‐dimensional) electron bursts have different impacts on upstream wave emission, which are also discussed.

Design of Back-bombardment-less Thermionic RF Gun

A new type of compact, back-bombardment-less RF gun is proposed. The new S-band RF gun will be useful for wide pulse operation. The performance of this RF gun is evaluated by using the 3D electromagnetic simulation code; MW-Studio and the beam tracking code; GPT. The simulation results for the new RF gun with the conventional one are presented.

Divergence Correction Techniques for Maxwell Solvers Based on a Hyperbolic Model

Usually, non-stationary numerical calculations in electromagnetics are based on the hyperbolic evolution equations for the electric and magnetic fields and leave Gauss' law out of consideration because the latter is a consequence of the former and of the charge conservation equation in the continuous case. However, in the simulation of the self-consistent movement of charged particles in electromagnetic fields, it is a well-known fact that the approximation of the particle motion introduces numerical errors and that, consequently, the charge conservation equation is not satisfied on the dicrete level. Then, in order to avoid the increase of errors in Gauss' law, a divergence cleaning step which solves a Poisson equation for a correction potential is often added. In the present paper, a new method for incorporating Gauss' law into non-stationary electromagnetic simulation codes is developed, starting from a constrained formulation of the Maxwell equations. The resulting system is hyperbolic, and the divergence errors propagate with the speed of light to the boundary of the computational domain. Furthermore, the basic ideas of the numerical approximation are introduced and the extended hyperbolic system is treated numerically within the framework of high-resolution finite-volume schemes. Simulation results obtained with this new technique for pure electromagnetic wave propagation and for an electromagnetic particle-in-cell computation are presented and compared with other methods.

イオンスラスタプルーム周辺での電磁環境のシミュレーション

An ion thruster emits a high density plasma plume and the electromagnetic noise radiated from the plasma current may affect the spacecraft instrument. An electromagnetic particle simulation code has been developed to investigate the effects of the electromagnetic interference induced from the ion thruster plume. The electromagnetic waves are excited due to plasma instability caused by strong polarization field inside imperfectly neutralized plume. The strength and frequencies of electromagnetic noise radiated by ion thruster plume depend on the distribution of charged particles inside the plume, static magnetic field strength and its orientation.

Collisionless Damping of Low-Frequency Magnetosonic Pulses in a Two-Ion-Species Plasma

Low-frequency mangnetosonic pulses in a two-ion-species plasma are studied theoretically and by simulation with a one-dimensional electromagnetic simulation code based on a three-fluid model, with particular attention to the dynamics of minority heavy ions. It is found that heavy ions can gain some energy from the pulses. Because of this energy transfer, the pulses are damped even if the plasma is collisionless and pulse propagation is perpendicular to the magnetic field.

Full curvature effects of a collisionless shock

Curvature effects of a quasi-perpendicular collisionless shock in a super-critical regime are studied with the help of a 2 - D full particle electromagnetic simulation code, where both ions and electrons are treated as particles moving within self-consistent fields. The curved shock is initiated by using a cylindrical magnetic piston. Main characteristics of quasi-perpendicular collisionless shocks in the angular range 90° to 65° are fully recovered. Full curvature effects allow to follow continously the transition from a narrow and step-like strictly perpendicular shock to wider and more turbulent oblique shock waves. Present preliminary results emphasize the differences between planar and curved shock. For the first time to our knowledge, the formation of electron foreshock is fully recovered without any simplifying assumptions; moreover, loss cone distribution is also reproduced for high energy reflected electrons which is the signature of a dominant fast Fermi acceleration type process.

Acceleration of energetic ions by nonlinear magnetosonic waves

Interactions of nonthermal energetic ions with nonlinear magnetosonic waves are studied by means of a one-dimensional (one space coordinate and three velocity components), relativistic, electromagnetic particle simulation code with full ion and electron dynamics. It is found that, if ions with gyration speeds much greater than the Alfvén speed encounter a shock wave, some of them can gain great energies. The acceleration takes place when the particle velocity becomes nearly parallel to the transverse electric field in the shock. On the basis of a simple physical picture, the increase in the energy is theoretically obtained. Both the theory and simulation show that the ions with higher energies can obtain greater energies. Thus, in a plasma with strong magnetohydrodynamic turbulence some of the ions could be repeatedly accelerated to higher energies by many nonlinear pulses.

Particle Acceleration and Langmuir Waves Triggered by Pair Plasma Cloud Moving Across a Magnetic Field

We have investigated the dynamics of the electron-positron plasma cloud moving perpendicular to an ambient magnetic field in the background plasma by using a three-dimensional, electromagnetic, and relativistic particle simulation code. The simulation results show that large amplitude Alfven waves are excited, while the electromagnetic waves are weakly excited because of the relativistic effect of the cloud particles. Langmuir waves are also excited along the magnetic field, and cloud particles as well as background pair particles are accelerated by Langmuir waves along the magnetic field. The maximum velocities of cloud and background particles exceed the initial cloud velocity.

Electron Acceleration from Electron-Ion Plasma Cloud Moving across a Magnetic Field

The dynamics of the electron-ion plasma cloud moving perpendicular to an ambient magnetic field in the background plasma is investigated by means of a three-dimensional, electromagnetic, and relativistic particle simulation code. The simulation results show that the cloud separates into electrons and ions due to their gyromotions with Larmor radius of V 0 /ω c j ( V 0 is the initial cloud velocity and ω c j is the cyclotron frequency of species j ). Consequently, electromagnetic and whistler waves are excited from the cloud due to coherent gyration of cloud electrons. In addition, Langmuir waves are also excited along a magnetic field. It is shown that cloud electrons are accelerated by Langmuir waves along the magnetic field and the population inversion is created in the velocity distribution of cloud electrons. The acceleration mechanism of cloud electrons is due to Landau resonance between Langmuir waves and cloud electrons. We apply our results to the electron acceleration mechanism from plasma cloud ...

Particle simulation and electron heating effects in plasmas produced by laser pulse

The processes of resonant absorption, vacuum heating, and anomalous skin effect in plasmas produced by a laser pulse are studied using the two-dimensional multi-time-scale, fully electromagnetic relativistic particle simulation code with mobile ions. The mechanisms of electron heating are expounded and compared.

Simulation Studies of Acceleration of Heavy Ions and Their Elemental Compositions

By using a one-dimension (one spatial coordinate and three-velocity components), electromagnetic particle simulation code with full ion and electron dynamics, we have studied the acceleration of heavy ions by a nonlinear magnetosonic wave in a multi-ion-species plasma. First, we describe the mechanism of heavy ion acceleration by magnetosonic waves. We then investigate this by particle simulations. The simulation plasma contains four ion species: H, He, O, and Fe. The number density of He is taken to be 10% of that of H, and those of O and Fe are much lower. Simulations confirm that, as in a single-ion-species plasma, some of the hydrogen can be accelerated by the longitudinal electric field formed in the wave. Furthermore, they show that magnetosonic waves can accelerate all the particles of all the heavy species (He, O, and Fe) by a different mechanism, i.e., by the transverse electric field. The maximum speeds of the heavy species are about the same, of the order of the wave propagation speed. These are in good agreement with theoretical prediction. These results indicate that, if high-energy ions are produced in the solar corona through these mechanisms, the elemental compositions of these heavy ions can be similar to that of the background plasma, i.e., the corona.

Coalescence of two current loops with a kink instability simulated by a 3-D EM particle code

We have studied the dynamics of a coalescence of current loops using a 3-D electromagnetic (EM) particle simulation code. Our focus is the investigation of kinetic processes such as energy transfer, heating of particles, and electromagnetic emissions associated with a current loop coalescence which cannot be studied by MHD simulations. First, the two loops undergo a pinching oscillation due to a pressure imbalance between the inside and outside of the current loop. During the pinching oscillation, a kinetic kink instability is excited and electrons in the loops are heated perpendicularly to an ambient magnetic field. Next, the two current loops collide and coalesce, while at the same time a helical structure grows further. Subsequently, the perturbed current, which is due to these helically bunched electrons, can drive a whistler instability. It should be noted in this case that the whistler wave is excited by the kinetic kink instability and not a beam instability. After two helical loop coalescence with tilting motions in the direction of left-hand rotation. the helical structure relaxes resulting in strong plasma heating mostly in the direction perpendicular to the ambient magnetic field.

The detector response matrices of the burst and transient source experiment (BATSE) on the Compton Gamma Ray Observatory

The detector response matrices for the Burst And Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory (CGRO) are described, including their creation and operation in data analysis. These response matrices are a detailed abstract representation of the gamma-ray detectors' operating characteristics that are needed for data analysis. They are constructed from an extensive set of calibration data coupled with a complex geometry electromagnetic cascade Monte Carlo simulation code. The calibration tests and simulation algorithm optimization are described. The characteristics of the BATSE detectors in the spacecraft environment are also described.