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We develop next-generation accelerators and radiation sources based on the interaction of lasers and plasmas. Our staff has extensive expertise in plasma, laser, accelerator and radiation physics. We study laser-plasma interactions experimentally; with analytic modeling; and via simulations using high performance computing. The ultimate goals include useful all-optical accelerators (latest milepost: 1 GeV of monoenergetic electrons) and applications such as a “hyperspectral” light source in which terahertz radiation, x-rays, and laser beams are all inherently synchronizable. | |
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Most of today's particle accelerators use the same basic principle: ions or electrons surf on waves of intense radio energy. These machines have reached a high state of sophistication and have been remarkable tools of both discovery and application. Unfortunately their size, cost, and complexity go up with the desired energy: at the frontiers of high-energy physics, their scale is measured in kilometers. Accelerator scientists and users alike have long dreamed of a simpler and much more compact way to achieve high-energy beams of the requisite quality. |
| Our program in Laser Optics and Accelerator Systems Integrated Studies (LOASIS) has made remarkable progress in recent years. In 2004 we observed mono-energetic beams in the 100 MeV class from a channel-guided wakefield accelerator. In 2006, with improvements in the theoretical and practical understanding of laser-plasma interaction, we achieved the GeV (giga-electron-volt) class and began laying the groundwork for a push toward 10 GeV. |
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Besides their direct thrust toward useful accelerators, these investigations help lay the groundwork for a future in which many of the things one now does with rf energy will call for the shorter wavelengths and time structures available by using light. | |
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An important part of the capillary-discharge-guided laser wakefield experiment that achieved 1 GeV is “T-Rex” (left), an amplifier of the 100 terawatt class. The green pump beams are produced by eight commercial Nd:YAG lasers for a total average pump power of 120 W. The main amplifier (inside a vacuum chamber, and operated cryogenically at a temperature of 100 kelvins) gives 35 W average power at the infrared wavelength of 800 nanometers. We are commissioning an upgrade to 40-50 W. Simulations (as in this example result from a 1-GeV fluid-code wakefield simulation at right ) and theory are integrated with experiment in our work. |
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| Our 1-GeV laser wakefield accelerator is already being used as a driver for experiments that could lead to applications in the fairly near future—perhaps even a “hyperspectral” source that provides coherent terahertz radiation, laser light, coherent light at the “hard” end of the ultraviolet spectrum, and electron bunches, all inherently synchronized with one another. |
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One new application is the generation of coherent terahertz radiation. Sometimes called T-rays, this output is intermediate in wavelength between microwaves and infrared rays, giving it has a wide variety of potential uses in the sciences. For example, this combination of radiation sources could provide information on the density and temperature of materials in regimes that are inaccessible to other forms of electromagnetic radiation, such as that from conventional lasers. For example, the way materials respond to being shocked by a laser could be studied by backlighting them with an x-ray source and measuring the spectrally resolved opacity or the diffracted x-ray spectrum. Pulse durations shorter than the characteristic time for motion of the material—as in melting or shock compression of high-atomic-weight targets—would permit time-resolved dynamics studies. The intrinsic synchronization (available because all these pulses originate with the same drive laser) would allow precise pump-probe experiments.
Of the several means of generating THz radiation that are being investigated worldwide, the technique pioneered by LOASIS has some especially attractive features. When electron bunches from the laser-plasma accelerator leave the plasma and go into vacuum, transition radiation is produced, and is in the THz range of the spectrum. This THz pulse is coherent, short (tens of femtoseconds), and inherently synchronizable with the electron bunch, other optical laser pulses, and femtosecond x-ray pulses (which could be produced from high-current, GeV-class electron beams in a high-gain free-electron laser, in a facility based on hoped-for future progress with laser wakefield acceleration). |
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| Shown above is a concept for an intense THz source that might involve accelerating gradients of 0.01 to as much as 10 megavolts per centimeter at the focus (with as much as tens of microjoules in the THz pulse), whereas traditional laser-based sources deliver less than 100 kV/cm. Thus far, in early experiments we have shown generation of terahertz radiation, with good agreement between electro-optical measurements and the predictions of computer modeling. |
| There is worldwide interest in free-electron lasers that give ultrashort pulses of light in the vacuum-ultraviolet region of the spectrum. With a combination of proposals, we plan to use the electron bunches from our GeV laser wakefield accelerator to drive an FEL whose higher harmonics are in the VUV range. The concept is illustrated below. This facility would provide scientifically useful light and would also serve as an LBNL testbed for FEL concepts. A key component, the THUNDER undulator from Boeing, has been delivered to LBNL. Modeling is in progress as part of this project, which takes excellent advantage of work already done on the laser wakefield accelerator. | |
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As we pursue improvements of the present GeV-class system, and applications of its beams (such as an FEL and terahertz radiation), we are also looking toward the next major step: 10 GeV. This will be a substantial effort both scientifically and technologically, conducted over several years in three phases with our characteristic synergy of theoretical analysis, supercomputing, and experimentation. The first phase will consist of a parametric study of the 1-GeV system using the existing T-Rex and Godzilla lasers, along with development of techniques and technologies appropriate to larger systems, just a few of which are staged acceleration; coupling-in the laser power; development of long (tens of centimeters, rather than the present few cm) capillaries; and diagnostics. We will then need to add a petawatt laser system (40 joules delivered in a 40-femtosecond-long pulse once a second, giving a power of 10 The third phase would be production and then use of 10 GeV beams with this “vacuum snapping” (nonlinear quantum electrodynamics) capability. This multiyear endeavor, BELLA (Berkeley Lab Laser Accelerator), is presently at the stage of a “white paper” presented to the Department of Energy. We hope for a near-future proposal opportunity in order to remain leaders in this worldwide, competitive, and fast-moving field. | |
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In 1995, AFRD’s Center for Beam Physics started a leading-edge research
effort, one of several in the world, exploring advanced accelerators
based on the interactions of lasers and plasmas. This effort focused on
the development of advanced acceleration and radiation concepts.
dedicated facility was built that became known as the LOASIS
Laboratory. Wakefield accelerators became the predominant effort. In 2005,
we were spun off from the Center and designated as an AFRD program in our own right.
The LOASIS Program has a total FY07 budget of ~$3M and a staff of approximately 23 full- or part-time members, including scientists, postdoctoral researchers, engineers, technical and administrative support staff, and students. Training of postdoctoral fellows and students is an important part of the Program; there are presently 4 postdoctoral researchers, 4 PhD students, 2 Masters students, and 2 undergraduates. LOASIS has maintained an exceptional record for productivity, which is reflected by a large number of high-quality publications. The work done here since January 2004 has been reported in approximately 60 publications, most of these appearing in refereed journals. In 2006 through mid-2007, we placed 14 publications in the refereed literature and another 10 in unrefereed conference proceedings. The staff of the LOASIS Program also contribute extensively to the national and international accelerator communities through a variety of service and leadership roles. These include participation on program and organizing committees of major accelerator conferences and workshops; facility advisory committees; and various program and proposal review committees; service as journal referees; and service to the International Committee on Future Accelerators, the American Physical Society, and various executive and technical boards. |
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Administrative and legal information on the AFRD homepage is applicable to this page.
Approved by Wim Leemans and posted August 28, 2007. Nature link added 13 September 2007. Pageowner: Joe Chew.