EM waves inside is not coherent
1 mm
Our micron sized cavity is much smaller than
Focusing of laser light by small hollow cone
applied to
ion acceleration
Jiaotong University, Shanghai
Trapping and focusing of laser light
by small solid cavity targets and
ion acceleration
Main point
Hollow sphere and cone of similar size
Ponderomotive force of light
d r v
dt
v eE0 (r) sin t me
B dt E

1



E0
sin
t
Taylor expand
PF is independent of the sign of the charge, and dependent on the gradient of the field energy
Shanghai Institute of Optics and Fine Mechanics (SIOM), Shanghai
National University of Defense Technology (NUDT), Changsha
Institute for Applied Physics and Computational Mathematics (IAPCM), Beijing
Optimum-intensity regime
No focusing!
a0 5
w 2
L 20T
Ray tracing
with cone wall acting like mirror
Poor transmission and no focusing
Ion acceleration using
Nonlinear laser-plasma interacton
Electron density
Radial profile of EM energy density, as the peak of light pulse passes the left and right openings
a0 5
and heats the ions in a surface layer 5. Compressed plasma expands into the cavity 6. High-pressure ion region forms at center
electrons ions
t 50T0
EM energy
t 100T0
t 300T0
t 50T0
Pi
ni Ey
In the plane z =10
t 300T0
t 100T0
t 300T0 Ti
At cavity center Ion temperature
ni Ti
Similar to ion focusing in inertial electrostatic confinement
謝謝！
Intense (>1020 watt/cm2) short-pulse (10-15 s)
laser interaction with matter
Short pulse (chirped)
Ultra short-pulse (~ 1 fs) pulse
(only the highest- density parts are shown)
Explains why a cone guide leads to better emission (electron heating)
2.45-MeV thermal neutrons
R. Kodama et al., Nucl. Fusion 44, 276 (2004)
(IEC)
Ashley, et al.
Fusion Technology Institute
University of Wisconsin
Anode 40-50 cm 100V ac @ 245kHz
Cathode 10cm - 25 to - 60 kV
A neutron Source
Not the same as hohlraum
Nonlinear light-matter interaction initiated by the ponderomotive force
(light-pressure force)
on the electrons
f p m0 v2
Relativistic:
f p m0c2
cone focused light
Put a foil target in front of the open cone tip
2m, 10nc foil
EM energy density
ion density
Mono-energetic ion bunch
a0 = 4
Ion energy density
w 2
L 20T
The light is focused into a tiny spot of 1m
radius, with large intensity enhancement!
Can greatly improve the pulse contrast!
Percentage of reflected and transmitted light energy
西湖国际聚变理论与模拟研讨会
M. Y. Yu 郁明阳 Institute for Fusion Theory and Simulation
Zhejiang University
Hangzhou 2008.12.26
with
W. Yu, H.B. Zhuo, X. Wang, L.H. Cao, H. Xu, B.F. Shen, Z.M. Sheng, J. Zhang, etc.
as the short laser pulse
Boundary modified by the light pulse Trapped light is still coherent!
Light pulse becomes a “nonlinear cavity mode”?
Need definition and analytical theory!
Physical process
1. Laser pulse enters the cavity 2. Pulse edge ionizes the cavity surface 3. Light pressure drives out plasma electrons in surface 4. Resulting space-charge field accelerates, compres1 a02
Same form as the kinetic or hydrodynamic pressure force
short pulse large force
Trapping of laser light in small spherical cavity
applied to
ion acceleration
Laser pulse and cavity are of similar dimension
a0 5
w 2
L 20T
Solid density target
Laser pulse
Cavity
w (FWHM)
Ri 4 Ro 6
Short-pulse laser interaction with matter
1. Electrons strongly driven by EM wave field 2. Ionization of target by pulse front 3. Strong light pressure on plasma electrons 4. Almost all affected electrons driven away 5. Strong space-charge field formed 6. Ions are driven by the space-charge field or
Coulomb explode 7. In 2D and 3D: everything also in the
transverse direction
Ponderomotive force
Space dependent
Particles are always pushed to the lower-field region
Short laser pulse and hollow cone
w = 10 m D =15m D = 1m
a0= 4
= 25T
2m
n=10nc
EM energy density in 30 deg cone
Laser light becomes a thin high-intensity needle-like spot before defocusing
n 4nc
Laser-light trapping by mircrocavity
at t 50T