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Chuang Ren
Assistant Professor of Mechanical
Engineering and Physics
Scientist, Laboratory for Laser Energetics
Hopeman 214
Phone: (585) 275-2048, Fax: (585)
256-2509, chren@me.rochester.edu.
Ph.D,. University of Wisconsin-Madison
(1998), M.S. and B.S., Tsinghua University (China)
My research interest is generally in the
area of theoretical and computational plasma physics. In particular, I
work to apply plasma physics to a wide range of applications including
astrophysics, inertial confinement fusion (ICF), plasma-based
accelerators, and new radiation sources. Since these applications
usually involve a very high energy density driver, my research also
falls under the so-called High Energy Density Physics (HEDP) umbrella.
A key characteristic of my research in this complex and highly
nonlinear area of physics is the interplay between theoretical analysis
and large-scale Paricle-in-Cell (PIC) simulations. Currently I am
actively seeking students to work in this exciting new field.
Laser-underdense
plasma interactions
I have been interested in what could be called the
nonlinear optics of plasmas. For example, there can be effective
attractive and repulsive forces between two laser beams in a plasma
[1]. The attractive force between the two lasers can cause them to
spiral around each other and form a braided pattern. This work is
useful in understanding the interaction between individual filaments of
a large laser beam or between individual speckles in a random phase
plate beam in ICF. It may also find applications in studying Gamma-ray
bursters, where the radiation can filament and the filaments can
interact. Another example is that laser pulses can be deflected by an
applied magnetic field in a plasma [2], which may possibly lead to
steering intense laser pulses using plasmas.
Figure 1 
The iso-surfaces and calculated centroids
of the electric field of two lasers from a PIC simulation show the
braiding of the lasers.
The lines on the box walls are projections of the centroids.
Laser-overdense plasma interactions
One of the new ideas in ICF is the fast
ignitor concept, which requires a beam of energetic electrons produced
by intense laser heating to penetrate the overdense region of a
compressed pellet and deposit its energy to the dense core. The
deposited energy would produce a hot spot and thus ignite the fuel. For
a hot spot with a temperature of 10 keV and density of 300 g/cm3,
its energy density exceeds 1011 J/cm3. Under
these extreme conditions, there is much new physics to be explored. For
example, in what fashion will the mega-ampere current of the energetic
electron beam transport through the overdense region? The current
transport depends critically on the electric and magnetic fields
generated by the beam itself and the return current in the background
plasma. In a recent paper [3] we have presented some large-scale 2D PIC
simulations (12000 by 12000 grids) using the parallel code OSIRIS. The
results show that the boundary conditions and the pellet geometry can
have profound effects on the energetic electron flow, which spreads
with a wide angle instead of coalescing into a single filament as in
the earlier smaller-size simulations. Furthermore, even assuming that
the fast electrons can eventually reach the core, it remains to be seen
whether these electrons can deposit their energy in the core region
through either collision or collective motion. To correctly model this,
one may have to supplement the intrinsic physical collisions of a PIC
code by adding suitable collisional models to the code.
Figure 2 
Plasma electron density profile from a 2D
PIC simulation of the fast ignition shows the laser-plasma interface.
The University of Rochester hosts the Fusion Science
Center for Extreme States of Matter and Fast Ignition Physics
(http://fsc.lle.rochester.edu/) funded by the Department of Energy. The
60-beam Omega laser and the new Omega-EP short-pulse laser at the
Laboratory for Laser Energetics (http:www.lle.rochester.edu) will
provide the unique capability to compress and heat a target and create
a state of high energy density. All these make the University of
Rochester an exciting place to study fast ignition and high energy
density physics.
Representative Publications
[1]. PDF
"Mutual attraction of laser beams in plasmas: braided light," Phys.
Rev. Lett. 85, 2124 (2000); PDF "On the mutual interaction between laser beams
in plasmas," Physics of Plasmas 9, 2354 (2002).
[2]. PDF
"Nonlinear and three dimensional theory for cross-magnetic field
propagation of short-pulse lasers in underdense plasmas," Phys. Plasmas
11, 1978 (2004).
[3]. PDF
"A global simulation for laser driven MeV electrons in fast ignition,"
Phys. Rev. Lett. 93, 185004 (2004).
[4]. PDF
"Compressing and focusing a short laser pulse by a thin plasma lens",
Phys. Rev.
E, 026411 (2001).
[5]. PDF
"Proton shock acceleration in laser-plasma interactions", Phys. Rev.
Lett. 92, 015002 (2004).
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