Laser Wakefield Acceleration Driven by a CO2 Laser (STELLA-LW) - Final Report PDF Download
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Languages : en
Pages : 56
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The original goals of the Staged Electron Laser Acceleration - Laser Wakefield (STELLA-LW) program were to investigate two new methods for laser wakefield acceleration (LWFA). In pseudo-resonant LWFA (PR-LWFA), a laser pulse experiences nonlinear pulse steepening while traveling through the plasma. This steepening allows the laser pulse to generate wakefields even though the laser pulse length is too long for resonant LWFA to occur. For the conditions of this program, PR-LWFA requires a minimum laser peak power of 3 TW and a low plasma density (10^16 cm^-3). Seeded self-modulated LWFA (seeded SM-LWFA) combines LWFA with plasma wakefield acceleration (PWFA). An ultrashort (~100 fs) electron beam bunch acts as a seed in a plasma to form a wakefield via PWFA. This wakefield is subsequently amplified by the laser pulse through a self-modulated LWFA process. At least 1 TW laser power and, for a ~100-fs bunch, a plasma density ~10^17 cm^-3 are required. STELLA-LW was located on Beamline #1 at the Brookhaven National Laboratory (BNL) Accelerator Test Facility (ATF). The ATF TW CO2 laser served as the driving laser beam for both methods. For PR-LWFA, a single bunch was to probe the wakefield produced by the laser beam. For seeded SM-LWFA, the ATF linac would produce two bunches, where the first would be the seed and the second would be the witness. A chicane would compress the first bunch to enable it to generate wakefields via PWFA. The plasma source was a short-length, gas-filled capillary discharge with the laser beam tightly focused in the center of the capillary, i.e., no laser guiding was used, in order to obtain the needed laser intensity. During the course of the program, several major changes had to be made. First, the ATF could not complete the upgrade of the CO2 laser to the 3 TW peak power needed for the PR-LWFA experiment. Therefore, the PR-LWFA experiment had to be abandoned leaving only the seeded SM-LWFA experiment. Second, the ATF discovered that the chicane bifurcated the incoming bunch into two compressed bunches separated in time and energy. With the available equipment it was not possible to stop the bifurcation. In an attempt to still deliver a single compressed bunch to the experiment, a slit was used to block one of the bunches, but this also blocked any witness bunch. Third, the loss of the witness bunch meant a different method for detecting the effect of the laser beam on the wakefield had to be implemented. Hence, a coherent Thomson scattering (CTS) diagnostic was designed and assembled. Unfortunately, further tests with blocking one of the double-bunches showed that wakefield generation was too unstable and difficult to control for the seeded SM-LWFA experiment. Luckily, it was found that a fast-rising (~50 fs) bunch could be created along Beamline #2 that was capable of generating wakefields, did not use the chicane, and was more stable. Thus, as the fourth major change, the entire STELLA-LW apparatus, including the CTS diagnostic, was moved from Beamline #1 to Beamline #2. Because this move occurred near the end of the program, only a single 2-week run could be performed. During the run it was found the laser beam transmission through the capillary discharge was severely degraded when the plasma was on. This loss of transmission appeared to be due to defocusing of the laser beam probably caused by laser-induced ionization creating a lens effect inside the capillary. Defocusing could also cause laser light to strike the capillary wall, thereby producing ablation and localized changes in the plasma density. Any changes in the plasma density would disrupt the plasma resonance condition for the wakefield. It was also discovered after the run that the ATF laser was producing multiple output pulses. The leading pulse could have caused ionization that interfered with transmission of the following pulses. Worse yet, the peak power in each of the pulses was several times smaller than if all the pulse energy wa ...
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 56
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Book Description
The original goals of the Staged Electron Laser Acceleration - Laser Wakefield (STELLA-LW) program were to investigate two new methods for laser wakefield acceleration (LWFA). In pseudo-resonant LWFA (PR-LWFA), a laser pulse experiences nonlinear pulse steepening while traveling through the plasma. This steepening allows the laser pulse to generate wakefields even though the laser pulse length is too long for resonant LWFA to occur. For the conditions of this program, PR-LWFA requires a minimum laser peak power of 3 TW and a low plasma density (10^16 cm^-3). Seeded self-modulated LWFA (seeded SM-LWFA) combines LWFA with plasma wakefield acceleration (PWFA). An ultrashort (~100 fs) electron beam bunch acts as a seed in a plasma to form a wakefield via PWFA. This wakefield is subsequently amplified by the laser pulse through a self-modulated LWFA process. At least 1 TW laser power and, for a ~100-fs bunch, a plasma density ~10^17 cm^-3 are required. STELLA-LW was located on Beamline #1 at the Brookhaven National Laboratory (BNL) Accelerator Test Facility (ATF). The ATF TW CO2 laser served as the driving laser beam for both methods. For PR-LWFA, a single bunch was to probe the wakefield produced by the laser beam. For seeded SM-LWFA, the ATF linac would produce two bunches, where the first would be the seed and the second would be the witness. A chicane would compress the first bunch to enable it to generate wakefields via PWFA. The plasma source was a short-length, gas-filled capillary discharge with the laser beam tightly focused in the center of the capillary, i.e., no laser guiding was used, in order to obtain the needed laser intensity. During the course of the program, several major changes had to be made. First, the ATF could not complete the upgrade of the CO2 laser to the 3 TW peak power needed for the PR-LWFA experiment. Therefore, the PR-LWFA experiment had to be abandoned leaving only the seeded SM-LWFA experiment. Second, the ATF discovered that the chicane bifurcated the incoming bunch into two compressed bunches separated in time and energy. With the available equipment it was not possible to stop the bifurcation. In an attempt to still deliver a single compressed bunch to the experiment, a slit was used to block one of the bunches, but this also blocked any witness bunch. Third, the loss of the witness bunch meant a different method for detecting the effect of the laser beam on the wakefield had to be implemented. Hence, a coherent Thomson scattering (CTS) diagnostic was designed and assembled. Unfortunately, further tests with blocking one of the double-bunches showed that wakefield generation was too unstable and difficult to control for the seeded SM-LWFA experiment. Luckily, it was found that a fast-rising (~50 fs) bunch could be created along Beamline #2 that was capable of generating wakefields, did not use the chicane, and was more stable. Thus, as the fourth major change, the entire STELLA-LW apparatus, including the CTS diagnostic, was moved from Beamline #1 to Beamline #2. Because this move occurred near the end of the program, only a single 2-week run could be performed. During the run it was found the laser beam transmission through the capillary discharge was severely degraded when the plasma was on. This loss of transmission appeared to be due to defocusing of the laser beam probably caused by laser-induced ionization creating a lens effect inside the capillary. Defocusing could also cause laser light to strike the capillary wall, thereby producing ablation and localized changes in the plasma density. Any changes in the plasma density would disrupt the plasma resonance condition for the wakefield. It was also discovered after the run that the ATF laser was producing multiple output pulses. The leading pulse could have caused ionization that interfered with transmission of the following pulses. Worse yet, the peak power in each of the pulses was several times smaller than if all the pulse energy wa ...
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Languages : en
Pages : 7
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A new experiment has begun that builds upon the successful Staged Electron Laser Acceleration (STELLA) experiment, which demonstrated high-trapping efficiency and narrow energy spread in a staged laser-driven accelerator. STELLA was based upon inverse free electron lasers (IFEL); the new experiment, called STELLA-LW, is based upon laser wakefield acceleration (LWFA). The first phase of STELLA-LW will be to demonstrate LWFA in a capillary discharge driven by the Brookhaven National Laboratory Accelerator Test Facility (ATF) terawatt CO2 laser beam. This will be the first time LWFA is conducted at 10.6-[mu]m laser wavelength. It will also be operating in an interesting pseudo-resonant regime where the laser pulse length is too long for resonant LWFA, but too short for self-modulated LWFA. Analysis has shown that in pseudo-resonant LWFA, pulse-steepening effects occur on the laser pulse that permits generation of strong wakefields. Various approaches are being explored for the capillary discharge including polypropylene and hydrogen-filled capillaries. Planned diagnostics for the experiment include coherent Thomson scattering (CTS) to detect the wakefield generation. This will be one of the first times CTS is used on a capillary discharge.
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Languages : en
Pages : 6
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Particle accelerators enable scientists to study the fundamental structure of the universe, but have become the largest and most expensive of scientific instruments. In this project, we advanced the science and technology of laser-plasma accelerators, which are thousands of times smaller and less expensive than their conventional counterparts. In a laser-plasma accelerator, a powerful laser pulse exerts light pressure on an ionized gas, or plasma, thereby driving an electron density wave, which resembles the wake behind a boat. Electrostatic fields within this plasma wake reach tens of billions of volts per meter, fields far stronger than ordinary non-plasma matter (such as the matter that a conventional accelerator is made of) can withstand. Under the right conditions, stray electrons from the surrounding plasma become trapped within these "wake-fields", surf them, and acquire energy much faster than is possible in a conventional accelerator. Laser-plasma accelerators thus might herald a new generation of compact, low-cost accelerators for future particle physics, x-ray and medical research. In this project, we made two major advances in the science of laser-plasma accelerators. The first of these was to accelerate electrons beyond 1 gigaelectronvolt (1 GeV) for the first time. In experimental results reported in Nature Communications in 2013, about 1 billion electrons were captured from a tenuous plasma (about 1/100 of atmosphere density) and accelerated to 2 GeV within about one inch, while maintaining less than 5% energy spread, and spreading out less than 1/2 milliradian (i.e. 1/2 millimeter per meter of travel). Low energy spread and high beam collimation are important for applications of accelerators as coherent x-ray sources or particle colliders. This advance was made possible by exploiting unique properties of the Texas Petawatt Laser, a powerful laser at the University of Texas at Austin that produces pulses of 150 femtoseconds (1 femtosecond is 10-15 seconds) in duration and 150 Joules in energy (equivalent to the muzzle energy of a small pistol bullet). This duration was well matched to the natural electron density oscillation period of plasma of 1/100 atmospheric density, enabling efficient excitation of a plasma wake, while this energy was sufficient to drive a high-amplitude wake of the right shape to produce an energetic, collimated electron beam. Continuing research is aimed at increasing electron energy even further, increasing the number of electrons captured and accelerated, and developing applications of the compact, multi-GeV accelerator as a coherent, hard x-ray source for materials science, biomedical imaging and homeland security applications. The second major advance under this project was to develop new methods of visualizing the laser-driven plasma wake structures that underlie laser-plasma accelerators. Visualizing these structures is essential to understanding, optimizing and scaling laser-plasma accelerators. Yet prior to work under this project, computer simulations based on estimated initial conditions were the sole source of detailed knowledge of the complex, evolving internal structure of laser-driven plasma wakes. In this project we developed and demonstrated a suite of optical visualization methods based on well-known methods such as holography, streak cameras, and coherence tomography, but adapted to the ultrafast, light-speed, microscopic world of laser-driven plasma wakes. Our methods output images of laser-driven plasma structures in a single laser shot. We first reported snapshots of low-amplitude laser wakes in Nature Physics in 2006. We subsequently reported images of high-amplitude laser-driven plasma "bubbles", which are important for producing electron beams with low energy spread, in Physical Review Letters in 2010. More recently, we have figured out how to image laser-driven structures that change shape while propagating in a single laser shot. The latter techniques, which use t ...
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Languages : en
Pages : 28
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The possibility of utilizing the fields of an intense laser beam to accelerate particles to high energies has attracted a great deal of interest. The study of laser driven accelerators is motivated by the ultrahigh fields associated with high intensity laser pulses. The peak amplitude of the transverse electric field of the laser pulse is given . A laser driven accelerator that has a number of attractive features is the laser wakefield accelerator (LWFA). In the LWFA, a short intense laser pulse propagates through an underdense plasma. The ponderomotive force associated with the laser pulse envelope expels electrons from the region of the laser pulse. If the laser pulse is sufficiently intense, virtually all of the plasma electrons will be expelled. When the laser pulse length is approximately equal to the plasma wavelength, large amplitude plasma waves (wakefields) will be excited with phase velocities approximately equal to the laser pulse group velocity. The axial and transverse electric fields associated with the wakefield can accelerate and focus a trailing electron beam. The ratio of the accelerating field, E sub z, to the laser field in the LWFA is given.
Author: Chalk River Nuclear Laboratories. Accelerator Physics Branch
Publisher: Chalk River, Ont. : Chalk River Laboratories, Accelerator Physics Branch
ISBN: 9780660160849
Category : United States
Languages : en
Pages : 5
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Author: M. Kando
Publisher:
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Category :
Languages : en
Pages : 15
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Author:
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Category :
Languages : en
Pages : 3
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Monoenergetic laser acceleration of trapped microbunches has been demonstrated for the first time. An inverse free electron laser (IFEL) is used to create microbunches, which are then accelerated by a second IFEL using a tapered undulatos. An adjustable magnetic field chicane is located between the two IFELs and is used to control the phase of the microbunches with respect to the laser field in the second IFEL. The IFELs are driven by a single lases beam from a high peak power CO2 laser. During the experiment, the trapped portion of the microbunch electrons had an energy gain of>16% with an energy width of -0.86% (full width at half-maximum).
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Languages : en
Pages : 17
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A summary of the talks, papers and discussion sessions presented in the Working Group on Plasma Based Acceleration Concepts is given within the context of the progress towards a 1 GeV laser driven accelerator module. The topics covered within the Working Group were self-modulated laser wakefield acceleration, standard laser wakefield acceleration, plasma beatwave acceleration, laser guiding and wake excitation in plasma channels, plasma wakefield acceleration, plasma lenses and optical injection techniques for laser wakefield accelerators. An overview will be given of the present status of experimental and theoretical progress as well as an outlook towards the future physics and technological challenges for the development of an optimized accelerator module.
Author: Heinrich Schwoerer
Publisher: Springer Science & Business Media
ISBN: 3540302719
Category : Science
Languages : en
Pages : 258
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Lasers and Nuclei describes the generation of high-energy-particle radiation with high-intensity lasers and its application to nuclear science. A basic introduction to laser--matter interaction at high fields is complemented by detailed presentations of state of the art laser particle acceleration and elementary laser nuclear experiments. The text also discusses future applications of lasers in nuclear science, for example in nuclear astrophysics, isotope generation, nuclear fuel physics and proton and neutron imaging.
Author: National Research Council
Publisher: National Academies Press
ISBN: 030908637X
Category : Science
Languages : en
Pages : 177
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Recent scientific and technical advances have made it possible to create matter in the laboratory under conditions relevant to astrophysical systems such as supernovae and black holes. These advances will also benefit inertial confinement fusion research and the nation's nuclear weapon's program. The report describes the major research facilities on which such high energy density conditions can be achieved and lists a number of key scientific questions about high energy density physics that can be addressed by this research. Several recommendations are presented that would facilitate the development of a comprehensive strategy for realizing these research opportunities.
