- Physics Questions
- Applications
- Relativistic Plasma
- Ultrahigh Intensity Laser
- Computer Simulations
- Quantum Plasma Dynamics
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We use the world's most intense lasers, to create extreme fields and temperatures, asking ourselves: Is there a fundamental limit to acceleration? How can we use relativistic plasmas to go beyond the limits of classical particle accelerators? How can we use laser-accelerated particles to image and treat cancer? Can we make Inertial Fusion work in a laboratory?
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We use todays's most powerful lasers to create "relativistic" plasma i.e. plasmas with the electron temperature greater than the rest mass of electron (0.511 MeV).
Such Plasma can sustain electromagnetic fields a billion times stronger than any conventional material.
Fields of this strength are otherwise only found in astrophysical settings like neutron stars, black holes, and supernovas.
These fields can be used to accelerate particles to generate gamma rays.
Using experiments and massively parallel computer siumlations, we study these interactions trying to understand and control them.
A main regime of interest for us is that of relativistic transparent plasmas. Here, a classically overdense plasma, which reflects light, is turned transparent by relativistic effects on a timescale of just a few laser cycles. The electrons in the plasma gain energy of many times their rest mass in just a laser cycle, thus being unable to respond to the fast oscillations of the laser field. Not being able to follow, they cannot screen the field anymore and the plasma becomes transparent. The details of the dynamics of this interaction and the laser-plasma interaction inside such plasmas are subjects of intense study.Projects
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Laser plasma acceleration has a wide range of applications. For example, we use high intensity lasers to create compact and high peak neutron flux, which can be used to do neutron imaging, neutron powder diffraction, neutron resonance spectroscopy and neutron cancer therapy. Lasers can also be used to produce x-ray beams or proton/ion beams. Laser based x-ray sources can be used in fields of laboratory astrophysics, medicine and nuclear security. Proton beams thus generated can be used in treating cancer and establishing compact therapy units in hospitals, making proton beam therapy easily accessible all over the world.
Projects
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For our experiments, we develop and use the world's most powerful and intense lasers. They draw their power from concentrating light in both space and time: to a few micrometer radius and femtosecond duration: 1 femtosecond compared to 1 minute is like 1 minute compared to the age of the universe.
Here at UT we have four such lasers: the Thor and UT3 (Ti:Sapphire lasers) and the Ghost and Texas Petawatt (OPCPA: Glass lasers, one of the most powerful lasers in the world.)
We also perform experiments at off-side facilities and collaborate with the national labs, including Los Alamos, Lawrence Livermore, and Sandia National Laboratories. We are participating in research at the new Linac Coherent Light Source at Stanford, using an optical laser together with the world's most powerful x-ray and collaborate with groups in Germany, China, and Russia. -
We develop and use parallel particle-in-cell codes to simulate the laboratory laser plasma interaction. These simulations are run on the largest existing supercomputers, like Roadrunner at LANL or Stampede at UT, using novel processor architecture, GPU-based computing and new software methods.
A first-principles, 3D calculation requires upwards of a 109 particles, 1016 grid cells and 107 times steps, a challenge even for the largest computers.
We are developing adaptive codes to address this challenge.
We also use GEANT4 to simulate the nuclear process and high energy particle transportation that are related to our laser plasma experiment. -
We are trying to develop a fundamental theory for Quantum Effects in Strong, Classical Potentials and trying to answer these questions:
1. When should we begin to consider Quantum Effects in Strong Classical Potentials?
2. How do we describe them? (Developing a Non-perturbative, Dynamic Quantum Field Theory)
Is a new theory of matter and light needed at the highest energies or the highest intensities? Matter and radiation in the laboratory appear to be extraordinarily well described by the laws of quantum mechanics, electromagnetism, and their unification as quantum electrodynamics. However the universe presents us with places and objects, such as neutron stars and the sources of gamma ray bursts, where the conditions are far more extreme than anything we can reproduce on Earth that can be used to test these basic theories.
Sufficiently strong electromagnetic fields allow fundamentally new quantum processes: electron-positron pairs are created from vacuum; photons split, merge, and convert into pairs; new degrees of freedom may emerge due to breaking the classical conformal symmetry. These are the QED equivalents of Hawking radiation and quark-gluon plasma formation, that are important, hotly discussed questions in how quantum theory and gravity work together and how the theory of strong interactions (QCD) works at long wavelength.
Using PW-class lasers such as the TPW, we can access related nonperturbative effects, such as high-energy photon emission and pair bremsstrahlung from an accelerated electron, that occur at lower field strength. To predict them, we need to be able to separate classical radiation and plasma dynamics from the underlying quantum event. To this end, we are developing the first systematic theory of quantum electrodynamic processes in relativistic laser fields.
This theory and laser experiments offer a unique opportunity to test quantum dynamics at the newly-opened high intensity frontier.
