My research interests are in advanced accelerator concepts, intense laser-plasma interaction and the basic equilibrium, stability, and radiation properties of intense charged particle beams. The research includes basic theory, simulation and the development of proof-of-principle experiments.
My current research is on wake excitation and pulse propagation in plasma channels, muon colliders, the development of simplified models of intense laser-plasma interactions, two-dimensional turbulence in nonneutral plasmas, and free-electron laser oscillators.
High energy accelerators have served as the main tool with which physicists have explored the building blocks of matter for more than sixty years. During this time there has been an exponential increase in the energy of accelerated particles. This increase has been made possible by a combination of improvements in existing machines and the invention of new acceleration techniques. Historically, whenever a given type of accelerator has reached the limit of its performance, an innovative idea for particle manipulation, storage, cooling or acceleration has made possible experiments at ever higher energies. The US High Energy Physics community faces serious challenges over the next decades. While a new high-energy Hadron Collider, the LHC, is being built at CERN, there is a significant risk, especially if 1 TeV center-of-mass energy electron-positron collider is constructed in Japan, that no new high-energy facility will be constructed in the United States beyond the TeVatron and the B-factory. This situation lends some urgency to innovation and the serious examination of new ideas.
I work on advanced accelerator concepts, in particular laser-plasma accelerators and muon colliders. These nascent concepts may turn into the workhorses of high-energy physics in the 21st century. Plasma accelerators may have applications, at lower energies, to other fields, such synchrotron radiation sources, as well. A major challenge facing researchers on laser-driven plasma accelerators is to overcome laser diffraction, the most severe limit on the energy to which particles can be accelerated. A second challenge is to accelerate a well-collimated electron bunch with a small energy spread. Theoretical investigations have shown that a hollow plasma channel can potentially achieve both challenges. In collaboration with the LBL Center for Beam Physics we are theoretically and experimentally investigating plasma channel accelerators.
The concept of Muon-Muon Colliders originates in the 70's. More recently, a collaboration led by BNL, FNAL and LBNL has undertaken detailed studies of the muon collider. As part of this collaboration, we have responsibility for coordinating the collider ring research and are studying collective phenomena in the collider ring of a muon collider. This ring has many unique features. The luminosity requires that the muon bunches have a high current and small energy spread, and the muons only live for around one thousand turns. Such a ring will need to operate above instability thresholds and must rely on a variety of innovative techniques for beam control. In a work that has applications to storage rings in general, we have found that the periodic temporal variation of ring parameters, such as magnet field strengths, can be used suppress collective instabilities.
The propagation of intense short-pulse lasers in underdense plasmas in strongly influenced by parametric instabilities, such as Raman scattering. Nonlinear Raman scattering is usually studied with particle-in-cell simulations. We are developing a simplified nonlinear model of Raman backscattering that preserved the important physics but has a much faster numerical implementation. Backscatter may be an important diagnostic in future inertial confinement experiments.
A final area of research is on the theoretical understanding of nonneutral plasmas under conditions where the plasma dynamics closely resemble that of a two-dimensional Eulerian fluid.
In the News
Scientists at Lawrence Berkeley National Laboratory have played leading roles in designing and operating ALPHA, the CERN experiment that was the first to capture and hold atoms of antihydrogen, a single antiproton orbited by a single positron.
The ALPHA experiment at CERN in Geneva has successfully trapped rare antihydrogen atoms for 1,000 seconds, or more than 16 minutes. This is long enough to start experimenting for the first time on antimatter atoms to determine whether they act like normal matter.
The particle accelerators at CERN in Geneva produce scads of antiprotons, which five years ago were combined at high speed with positrons to create for the first time antimatter atoms: antihydrogen. Those atoms annihilated with normal matter within microseconds, but an international team involving UC Berkeley and LBNL physicists has succeeded in slowing such atoms down and trapping them for a tenth of a second. This will allow experiments on a type of matter that hasn't been available since shortly after the Big Bang 14 billion years ago.