THE THEORY AND SIMULATION OF RELATIVISTIC ELECTRON BEAM TRANSPORT IN THE ION-FOCUSED REGIME. PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download THE THEORY AND SIMULATION OF RELATIVISTIC ELECTRON BEAM TRANSPORT IN THE ION-FOCUSED REGIME. PDF full book. Access full book title THE THEORY AND SIMULATION OF RELATIVISTIC ELECTRON BEAM TRANSPORT IN THE ION-FOCUSED REGIME. by STEPHEN BRIAN SWANEKAMP. Download full books in PDF and EPUB format.
Author: STEPHEN BRIAN SWANEKAMP
Publisher:
ISBN:
Category :
Languages : en
Pages : 258
Get Book Here
Book Description
and provides a new and interesting view of IFR beam transport.
Author: STEPHEN BRIAN SWANEKAMP
Publisher:
ISBN:
Category :
Languages : en
Pages : 258
Get Book Here
Book Description
and provides a new and interesting view of IFR beam transport.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 62
Get Book Here
Book Description
The resistive hose instability can disrupt propagation of self- pinched beams in dense gas. To reduce growth of the instability, beams can be conditioned prior to propagation. The objectives of beam conditioning are to center the beam in order to reduce initial transverse perturbations which seed the hose instability, and to tailor the beam emittance in order to detune the head-to-tail coherence of the instability. Emittance tailoring can be performed by transporting the beam through a passive ion-focused regime (IFR) cell, which induces a head-to-tail taper of the beam radius; the radius taper is then converted to an emittance taper by passing the beam through a thick exit foil which scatters the beam. Beam centering can be accomplished by transporting the beam through either: (1) a passive IFR cell which is narrow enough to provide wall guiding, or (2) a laser-ionized active IFR cell, or (3) a wire cell in which the centering is provided by a current-carrying wire. We report here on axisymmetric particle simulation studies of IFR tailoring cells, alone and in tandem with each of these types of centering cells, and also on the effect of supplementary focusing lenses and conducting foils. We discuss the parameter choices that are conducive to effective beam conditioning. The emphasis is on conditioning configurations and beam parameters that have actually been tested in experiments with the ATA and SuperIBEX accelerators.
Author: J. R. Smith
Publisher:
ISBN:
Category :
Languages : en
Pages : 36
Get Book Here
Book Description
This report presents observations on propagation of a mildly relativistic electron beam (gamma = 2.4) in several different gases (air, Helium, Nitrogen, Argon) at low pressure (10-320 mTorr). At such low pressures, and with beam currents of several kiloamperes, beam induced ionization may result in self focusing of an electron beam. Beams propagating under this condition are said to be in the ion focusing regime of propagation. The injected beam has an rms radius of 0.7 cm and a transverse temperature of 35 keV. Beam transport efficiency was measured for He, N2 and Ar. A simple calculation was performed to determine the space charge neutralization fraction as a function of time. Using the results of this calculation, the charge transport efficiency is found and compared with the experimentally measured quantity. Keywords: Electron Beam; Ion Focused Regime.
Author: Nikita Wells
Publisher:
ISBN:
Category : Electron beams
Languages : en
Pages : 100
Get Book Here
Book Description
Soviet research on the propagation of intense relativistic electron beams (IREB) through fairly high-pressure air (pressure range 0.1 to 760 Torr) since the early 1970s has included the study of the plasma channel created by the passage of the electron beam through air, the resistive hose instability and its effect on beam propagation, the effect of self-fields, current enhancement, gas expansion, return currents, inherent beam energy spread, and other factors. This report covers Soviet developments in IREB propagation through air where the beam is not focused by external magnetic fields. The information was obtained from Soviet open-source publications with emphasis given to the last ten years of beam propagation in the Soviet Union. The volume of papers published on this subject in recent years indicates a significant increase in Soviet research in this area.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 5
Get Book Here
Book Description
This paper reviews the transport of the 19-MeV, 700-kA, 25-ns Hermes-III electron beam in long gas cells filled with N2 gas spanning six decades in pressure from 103 to (approximately)103 Torr. We show through measurements and theoretical analyses that the beam has two windows of stable transport: a low-pressure window (between (approximately)1 and (approximately)100 mTorr) that is dominated by propagation in the semi-collisionless IFR (ion-focused regime), and a high-pressure window (between (approximately)1 and (approximately)100 Torr) that is dominated by propagation in the resistive CDR (collision-dominated regime). In the CDR, 79"1.5% of the beam energy is transported over 11 m at 20 Torr. In the IFR, we show that intense radiation fields with controllable rise times and pulse widths can be generated on axis at a bremsstrahlung target. In summary, the measurements and analyses presented here provide a quantitative description of the Hermes-III beam transport over six decades in pressure.
Author: JOEL DAVID MILLER
Publisher:
ISBN:
Category :
Languages : en
Pages : 227
Get Book Here
Book Description
unity.
Author: Joshua Joseph May
Publisher:
ISBN:
Category :
Languages : en
Pages : 250
Get Book Here
Book Description
The continued development of the chirped pulse amplification technique has allowed for the development of lasers with powers of in excess of $10^{15}W$, for pulse lengths with durations of between .01 and 10 picoseconds, and which can be focused to energy densities greater than 100 giga-atmospheres. When such lasers are focused onto material targets, the possibility of creating particle beams with energy fluxes of comparable parameters arises. Such interactions have a number of theorized applications. For instance, in the Fast Ignition concept for Inertial Confinement Fusion \cite{Tabak:1994vx}, a high-intensity laser efficiently transfers its energy into an electron beam with an appropriate spectra which is then transported into a compressed target and initiate a fusion reaction. Another possible use is the so called Radiation Pressure Acceleration mechanism, in which a high-intensity, circularly polarized laser is used to create a mono-energetic ion beam which could then be used for medical imaging and treatment, among other applications. For this latter application, it is important that the laser energy is transferred to the ions and not to the electrons. However the physics of such high energy-density laser-matter interactions is highly kinetic and non-linear, and presently not fully understood. In this dissertation, we use the Particle-in-Cell code OSIRIS \cite{Fonseca:2002, Hemker:1999} to explore the generation and transport of relativistic particle beams created by high intensity lasers focused onto solid density matter at normal incidence. To explore the generation of relativistic electrons by such interactions, we use primarily one-dimensional (1D) and two-dimensional (2D), and a few three-dimensional simulations (3D). We initially examine the idealized case of normal incidence of relatively short, plane-wave lasers on flat, sharp interfaces. We find that in 1D the results are highly dependent on the initial temperature of the plasma, with significant absorption into relativistic electrons only possible when the temperature is high in the direction parallel to the electric field of the laser. In multi-dimensions, absorption into relativistic electrons arises independent of the initial temperature for both fixed and mobile ions, although the absorption is higher for mobile ions. In most cases however, absorption remains at $10's$ of percent, and as such a standing wave structure from the incoming and reflected wave is setup in front of the plasma surface. The peak momentum of the accelerated electrons is found to be $2 a_0 m_e c$, where $a_0 \equiv e A_0/m_e c^2$ is the normalized vector potential of the laser in vacuum, $e$ is the electron charge, $m_e$ is the electron mass, and $c$ is the speed of light. We consider cases for which $a_0>1$. We therefore call this the $2 a_0$ acceleration process. Using particle tracking, we identify the detailed physics behind the $2 a_0$ process and find it is related to the standing wave structure of the fields. We observe that the particles which gain energy do so by interacting with the laser electric field within a quarter wavelength of the surface where it is at an anti-node (it is a node at the surface). We find that only particles with high initial momentum -- in particular high transverse momentum -- are able to navigate through the laser magnetic field as its magnitude decreases in time each half laser cycle (it is an anti-node at the surface) to penetrate a quarter wavelength into the vacuum where the laser electric field is large. For a circularly polarized laser the magnetic field amplitude never decreases at the surface, instead its direction simply rotates. This prevents electrons from leaving the plasma and they therefore cannot gain energy from the electric field. For pulses with longer durations ($\gtrsim 250fs$), or for plasmas which do not have initially sharp interfaces, we discover that in addition to the $2 a_0$ acceleration at the surface, relativistic particles are also generated in an underdense region in front of the target. These particles have energies without a sharp upper bound. Although accelerating these particles removes energy from the incoming laser, and although the surface of the plasma does not stay perfectly flat and so the standing wave structure becomes modified, we find in most cases, the $2 a_0$ acceleration mechanism occurs similarly at the surface and that it still dominates the overall absorption of the laser. To explore the generation of relativistic electrons at a solid surface and transport of the heat flux of these electrons in cold or warm dense matter, we compare OSIRIS simulations with results from an experiment performed on the OMEGA laser system at the University of Rochester. In that experiment, a thin layer of gold placed on a slab of plastic is illuminated by an intense laser. A greater than order-of-magnitude decrease in the fluence of hot electrons is observed when those electrons are transported through a plasma created from a shock-heated plastic foam, as compared to transport through cold matter (unshocked plastic foam) at somewhat higher density. Our simulations indicate two reasons for the experimental result, both related to the magnetic field. The primary effect is the generation of a collimating B-field around the electron beam in the cold plastic foam, caused by the resistivity of the plastic. We use a Monte Carlo collision algorithm implemented in OSIRIS to model the experiment. The incoming relativistic electrons generate a return current. This generates a resistive electric field which then generates a magnetic field from Faraday's law. This magnetic field collimates the forward moving relativistic electrons. The collisionality of both the plastic and the gold are likely to be greater in the experiment than the 2D simulations where we used a lower density for the gold (to make the simulations possible) which heats up more. In addition, the use of 2D simulations also causes the plastic to heat up more than expected. We compensated for this by increasing the collisionality of the plasma in the simulations and this led to better agreement. The second effect is the growth of a strong, reflecting B-field at the edge of the plastic region in the shock heated material, created by the convective transport of this field back towards the beam source due to the neutralizing return current. Both effects appear to be caused primarily by the difference is density in the two cases. Owing to its higher heat capacity, the higher density material does not heat up as much from the heat flux coming from the gold, which leads to a larger resistivity. Lastly, we explored a numerical effect which has particular relevance to these simulations, due to their high energy and plasma densities. This effect is caused by the use of macro particles (which represent many real particles) which have the correct charge to mass ratio but higher charge. Therefore, any physics of a single charge that scales as $q^2/m$ will be artificially high. Physics that involves scales smaller than the macro-particle size can be mitigated through the use of finite size particles. However, for relativistic particles the spatial scale that matters is the skin depth and the cell sizes and particle sizes are both smaller than this. This allows the wakes created by these particles to be artificially high which causes them to slow down much faster than a single electron. We studied this macro-particle stopping power theoretically and in OSIRIS simulations. We also proposed a solution in which particles are split in to smaller particles as they gain energy. We call this effect Macro Particle Stopping. Although this effect can be mitigated by using more particles, this is not always computationally efficient. We show how it can also be mitigated by using high-order particle shapes, and/or by using a particle-splitting method which reduces the charge of only the most energetic electrons.
Author: Valery B. Krasovitskii
Publisher: Nova Publishers
ISBN: 9781600215292
Category : Science
Languages : en
Pages : 218
Get Book Here
Book Description
This volume presents the non-linear theory of electrostatic focusing of an electron beam split into bunches under conditions when the plasma permittivity at the modulation frequency is negative and the effective Coulomb force acting on the electron bunches is reversed. Conditions for the spatial equilibrium between the bunch and plasma emission, as well as the dynamics of the formation of focussed bunches, are confirmed by solving (both analytically and numerically) the self-consistent set of equations.
Author:
Publisher:
ISBN:
Category : Power resources
Languages : en
Pages : 486
Get Book Here
Book Description
Author: J. King
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
The transport of intense relativistic beams in solid density plasma presently is actively being studied in laser laboratories around the world. The correct understanding of the transport enables further application of fast laser driven electrons to a host of interesting uses. Advanced x-ray sources, proton and ion beam generation and plasma heating in fast ignitor fusion all are owed their eventual utility to this transport. We report on measurements of relativistic transport over the whole of the transport region, via analysis of x-ray emission. Our experiments cover laser powers from Terawatt to Petawatt. Advances in transverse imaging of fluorescent k-alpha x-rays generated along the electron beam path are used to diagnose the electron emission. Additionally the spatial pattern of Bremsstrahlung x-rays provides clues into the physics of electron transport in above Alfven current limit beams. Issues regarding the electron distribution function will be discussed in light of possible electron transport anomalies. The initial experiments performed on the Nova Petawatt Laser System were those associated with determining the nature of the electrons and x-rays in this relativistic regime especially those useful for advanced radiography sources suitable for diagnostic use in dense high-Z dynamic processes or as the driver of a relativistic electron source in the Fast-Ignitor Inertial Confinement fusion concept. The development of very large arrays of thermoluminescent detectors is detailed along with their response. The characteristic pattern of x-rays and their intensity is found from detailed analysis of the TLD detector array data. Peak intensities as high as 2 Rads at 1 meter were measured with these shielded TLD arrays. An average energy yield of x-rays of 11 Joules indicates a very large fraction of 45-55% of the laser energy is absorbed into relativistic electrons. The pattern of x-ray distribution lends insight to the initial relativistic electron distribution function and subsequent transport inside solid density material. A theoretical-computational model (MPK) combining laser focal spot data with ponderomotive kinematics with Monte Carlo collisional transport is developed here, and is presented which associates the laser interaction to the observed x-ray data. There is good agreement between the MPK model and data exhibiting ponderomotive like x-rays is found. Additional agreement is had in comparison to recent electron transport experiment utilizing Cu fluorescence to map the electron flow.
