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Author: Alexander Ross Meadows Publisher: ISBN: Category : Languages : en Pages : 276
Book Description
A two-year experimental campaign is described during which diamond-like carbon and plastic targets with thicknesses from 20 nanometers to 15 micrometers were irradiated by the Texas Petawatt Laser. Target composition and thickness were varied to modify the specifics of the laser-matter interaction. Plasma mirrors were selectively implemented to affect the contrast of the laser system and provide additional control of the physical processes under investigation. A number of particle diagnostics were implemented to measure the distribution of laser accelerated ions and electrons. In addition, optical diagnostics were fielded to measure the intensity profile of the laser and measure the density of the target pre-plasma. The results of these experiments suggest that the Texas Petawatt laser pulse has pre-pulse and pedestal features with intensities at least 10−8 of the main pulse. Micronscale targets were able to survive these features and maintain a relatively sharp density gradient until the arrival of the main laser pulse, allowing for ion acceleration. Electron spectra measured in this configuration show an average temperature of 10 MeV, with no v angular dependence out to at least 60 degrees. By contrast, interferometric plasma density measurements and a lack of any observable ion acceleration suggest that nanoscale targets were destroyed well before the main pulse. In this case, the peak of the laser pulse interacted with a cloud of plasma between 10−3 and 10−2 of critical density. The contrast improvement offered by the implementation of plasma mirrors was seen to increase the maximum energy of laser accelerated protons from targets thicker than 1 micrometer. In addition, the plasma mirrors allowed nanoscale targets to survive pre-pulse and pedestal features and support the production of ion beams. Proton spectra show that ions were accelerated to greater maximum energies from nanoscale targets than from more traditional micron-scale targets. This effect can be attributed to a reduction in the target pre-plasma scale length upon the introduction of plasma mirrors. These results indicate that the manipulation of target properties and laser contrast can significantly affect the interaction between an ultrahigh intensity laser and a target.
Author: Alexander Ross Meadows Publisher: ISBN: Category : Languages : en Pages : 276
Book Description
A two-year experimental campaign is described during which diamond-like carbon and plastic targets with thicknesses from 20 nanometers to 15 micrometers were irradiated by the Texas Petawatt Laser. Target composition and thickness were varied to modify the specifics of the laser-matter interaction. Plasma mirrors were selectively implemented to affect the contrast of the laser system and provide additional control of the physical processes under investigation. A number of particle diagnostics were implemented to measure the distribution of laser accelerated ions and electrons. In addition, optical diagnostics were fielded to measure the intensity profile of the laser and measure the density of the target pre-plasma. The results of these experiments suggest that the Texas Petawatt laser pulse has pre-pulse and pedestal features with intensities at least 10−8 of the main pulse. Micronscale targets were able to survive these features and maintain a relatively sharp density gradient until the arrival of the main laser pulse, allowing for ion acceleration. Electron spectra measured in this configuration show an average temperature of 10 MeV, with no v angular dependence out to at least 60 degrees. By contrast, interferometric plasma density measurements and a lack of any observable ion acceleration suggest that nanoscale targets were destroyed well before the main pulse. In this case, the peak of the laser pulse interacted with a cloud of plasma between 10−3 and 10−2 of critical density. The contrast improvement offered by the implementation of plasma mirrors was seen to increase the maximum energy of laser accelerated protons from targets thicker than 1 micrometer. In addition, the plasma mirrors allowed nanoscale targets to survive pre-pulse and pedestal features and support the production of ion beams. Proton spectra show that ions were accelerated to greater maximum energies from nanoscale targets than from more traditional micron-scale targets. This effect can be attributed to a reduction in the target pre-plasma scale length upon the introduction of plasma mirrors. These results indicate that the manipulation of target properties and laser contrast can significantly affect the interaction between an ultrahigh intensity laser and a target.
Author: Craig Franklin Wagner Publisher: ISBN: Category : Languages : en Pages : 472
Book Description
This dissertation examines the motion of the electron critical density surface during interactions between a relativistically intense laser pulse and a solid density target. On short time scales the laser field increases the electron quiver velocity, increasing the effective electron mass which increases the plasma frequency at a given electron density. This leads to transmission of a given laser frequency deeper into the target, known as relativistic self induced transparency with the effective critical density surface propagating quickly into the target bulk. On longer time scales, the ponderomotive force from the laser leads to large light pressure which pushes a sheet of electrons into the target bulk. This leads to a strong electric potential between the electron sheet and ions that are left behind. These ions are accelerated by the potential in a process known as hole boring. Both processes are present during laser-solid interactions, but relative contributions to critical surface motion depend on the density profile of the target and the da0/dt of the laser pulse. We have conducted experiments which use the spectral shift in second and third harmonic light generated at the target surface to measure the velocity of the laser reflection point for plastic, copper, and gold targets. This data is time integrated, with the signal limited to the period of high laser intensity. The measured second harmonic spectra show a unique two peak structure which indicates the existence of two velocity regimes in the critical surface dynamics. Qualitatively, there is a small difference between the target types. In shots on gold, the signal in the high velocity peak is slightly greater than that in the low velocity peak, and this trend is reversed for plastic targets, with copper somewhere in the middle. There is more variation in the third harmonic spectrum as spectra from gold are generally high velocity dominant, copper is transitional and show both velocity peaks, and spectra from plastic targets have only the low velocity signal. This two velocity structure is explained by observing that there is a plasma density gradient in front of the solid density target on shot. This preplasma electron density profile is measured via interferometry up to 300 ps before peak intensity arrival on shot for gold and plastic targets. This data is used to evaluate contrast enhancement through adjustments to the pumping of the Texas Petawatt OPA stages, showing that a small adjustment leads to a significantly steeper plasma profile on shot. In addition, the plasma measurements taken are used to validate hydrodynamic simulations of the plasma density profile on shot. 1-D particle in cell simulations have been performed using the code EPOCH to evaluate the influence of preplasma on critical surface movement during the TPW interaction. Simulations with simplified preplasma profiles show two things. First, the cold critical density surface barely moves during the interaction. Second, for a preplasma with two scale lengths, one shallow and one steep, there is an initial phase of swift relativistic critical surface movement due to a relativistic self-induced transparency (RIT) front propagating into the plasma bulk. This is followed by a period of slower velocity hole boring. We also find that in simulations using the simulated preplasma profile, these features are also present. The simulation shows two velocity regimes which correspond to the velocity peaks seen experimentally in the time integrated spectra. Further simulations show that, for a given density profile and peak intensity, changing the pulse profile of incident laser can shift the transition between RIT and hole boring. A pulse with a longer rise time means that ions behind the laser front are less shielded by electrons bypassed in the RIT process. This means that hole boring plays a larger role in interaction with longer rise time pulses. Further explorations of the transition between RIT and hole boring at the Texas Petawatt Laser are proposed to investigate changes in front dynamics due to differing pulse rise time. Time resolved surface dynamic measurements are also proposed using an ultra-broadband GRENOUILLE which has been fielded, and is described in this thesis. Finally, initial studies on the feasibility of using laser wakefield electron accelerators to generate high fluence muon beams are described.
Author: Publisher: ISBN: Category : Languages : en Pages : 15
Book Description
Laser plasma interaction experiments have been performed using a fs Titanium Sapphire laser. Plasmas have been generated from planar PMMA targets using single laser pulses with 3.3 mJ pulse energy, 50 fs pulse duration at 800 nm wavelength. The electron density distributions of the plasmas in different delay times have been characterized by means of Nomarski Interferometry. Experimental data were compared with hydrodynamic simulation. First results to characterize the plasma density and temperature as a function of space and time are obtained. This work aims to generate plasmas in the warm dense matter (WDM) regime at near solid-density in an ultra-fast laser target interaction process. Plasmas under these conditions can serve as targets to develop x-ray Thomson scattering as a plasma diagnostic tool, e.g., using the VUV free-electron laser (FLASH) at DESY Hamburg.
Author: S. Nakai Publisher: American Institute of Physics ISBN: 9781563964459 Category : Technology & Engineering Languages : en Pages : 792
Book Description
Papers from the April 1995 conference (formerly called a "workshop") are contained in two volumes. The first volume (623-9) comprises contributions arranged in sections on ICF programs and energy drivers; critical elements for ignition--target experiment, physics, and design; laser-matter interaction physics; and high intensities, short pulse interactions. The second volume (624-7) begins with papers on optical technologies and various kinds of lasers--free electron, LD and LD pumped, gas, nuclear pumped, and short pulse. Following these are sections on particle beams--light and heavy ion beam fusions; and applications of laser and plasma. Edward Teller Award lectures complete the proceedings. Not indexed by subject (contains only an author "index"). Annotation copyrighted by Book News, Inc., Portland, OR
Author: Jonathan Lee Peebles Publisher: ISBN: Category : Languages : en Pages : 248
Book Description
Relativistic laser plasma interactions in conjunction with an underdense pre-plasma have been shown to generate a two temperature component electron spectrum. The lower temperature component described by "ponderomotive scaling" is relatively well known and understood and is useful for applications such as the fast ignition inertial confinement fusion scheme. The higher energy electrons generated due to pre-plasma are denoted as "super-ponderomotive" electrons and facilitate interesting and useful applications. These include but are not limited to table top particle acceleration and generating high energy protons, x-rays and neutrons from secondary interactions. This dissertation describes experimental and particle-in-cell computational studies of the electron spectra produced from interactions between short pulse high intensity lasers and controlled pre-plasma conditions. Experiments were conducted at 3 laser labs: Texas Petawatt (University of Texas at Austin), Titan (Lawrence Livermore National Laboratory) and OMEGA-EP (University of Rochester). These lasers have different capabilities, and multiple experiments were carried out in order to fully understand super-ponderomotive electron generation and transport in the high intensity laser regime (I > 10^18 W/cm^2). In these experiments, an additional secondary long pulse beam was used to generate different scale lengths of "injected" pre-plasma while the pulse length and intensity of the short pulse beam were varied. The temperature and quantity of super-ponderomotive electrons were monitored with magnetic spectrometers and inferred via bremsstrahlung spectrometers while trajectory was estimated via Cu-K[alpha] imaging. The experimental and simulation data show that super-ponderomotive electrons require pulse lengths of at least 450 fs to be accelerated and that higher intensity interactions generate large magnetic fields which cause severe deflection of the super-ponderomotive electrons. Laser incidence angle is shown to be extremely important in determining hot electron trajectory. Longer pulse length data taken on OMEGA-EP and Titan showed that super-ponderomotive electrons could be created without the need for an initial pre-plasma due to the underdense plasma created during the high intensity interaction alone.
Author: Dongsu Du Publisher: ISBN: Category : Languages : en Pages : 204
Book Description
Since 2004, table-top laser-plasma accelerators (LPAs) driven by ~30fs terwatt laser pulses have produced colimated, nearly mono-energetic eletron bunches with energy up to 1 GeV in laboratories around the world. Large-scale computer simulations show that LPAs can scale to higher energy while retaining high beam quality, but will require laser pulses of higher energy and longer duration than current LPAs. The group of Prof. Mike Downer, in collaboration with the Texas Petawatt (TPW) laser team headed by Prof. Todd Ditmire, is setting up an experiment that uses the TPW laser (1.1 PW, 150 fs) to drive the world's first multi-GeV LPA. This thesis provides a general overview of the TPW-LPA project, including several diagnostic systems for the beam, plasma and laser pulse. Special attention is given to three of the diagnostic systems: (1)A transverse interferometry diagnostic of the plasma density profile created by the TPW laser pulse; (2)A Thomson scattering diagnostic of the self-guided path of the TPW laser pulse through the plasma; (3)An optical transition radiation diagnostic of the accelerated electron bunch exiting the plasma. In each case, basic principles, theoretical background, calculation and simulation results, and preliminary experimental results will be presented.
Author: Gregory Elijah Kemp Publisher: ISBN: Category : Languages : en Pages : 202
Book Description
This work was performed under DOE contract DE-AC52-07NA27344 with support from the Lawrence Scholar Program, OFES-NNSA Joint Program in High-Energy-Density Laboratory Plasmas and an allocation of computing time from the LLNL Grand Challenge and the Ohio Supercomputing Center.
Author: Alexander Ross Meadows
Author: Alexander Ross Meadows
Author: Craig Franklin Wagner
Author: 
Author: S. Nakai
Author: Jonathan Lee Peebles
Author: Dongsu Du
Author: Timothy Robinson
Author: Thomas Gangolf
Author: 
Author: Gregory Elijah Kemp