equal to the ion sound velocity C s per unit time. Assuming all laser energy is
absorbed in this region, we can roughly obtain the following relation:
C s P A $ I L ,
ð1:4:3Þ
where the plasma energy density is approximated with its pressure P A , which is
called ablation pressure generated by the expanding plasma. With the use of the
relation that the photon pressure P L satisfies the relation, P L ¼ I/c, a new relation is
obtained:
P A
P L
$
c
C s
ð1:4:4Þ
It is clear that the ablation pressure is 3 ~ 4 order of magnitude higher than the laser
pressure. This is the principle why the laser heating is used to study high-density
plasma by the ablation pressure instead of direct laser pressure. Thanks to the
ablation pressure, the laser implosion fusion is possible as reviewed in a book
[19]. The physical principle of ICF and the present status of laser fusion research
are given in Vol. 2. The present accomplishment of ICF by NIF experiment and its
difficulty compared to the optimistic scenario are reviewed by mainly focusing on
hydrodynamic instability and turbulent mixing.
1.4.2 Collisionless Absorption and Ponderomotive Force
Plasma as a continuous medium has a resonance frequency ω pe .
ω pe ¼
e
2 n e
ε 0 m
1=2
ð1:4:5Þ
It is called electron plasma frequency or plasma frequency in short. The plasma
frequency is only a function of electron density, and the oscillation is kept by the
balance between induced electric field and electron inertia in the fixed ion
background. Since the induced electric field by charge separation is large for higher
density, the plasma frequency is proportional to (electron density)
1/2 . When the
electron oscillating current is evaluated from (1.3.8) and inserting it to (1.3.2), it is
found that the RHS of (1.3.2) cancels each other when the plasma electron density
satisfies the relation
ω pe ¼ ω L
ð1:4:6Þ
This determines the cut-off density already mentioned. Physical meaning is that the
induced current generate coherent electromagnetic wave at the cut-off density so that
18
1 Introduction
absorbed in this region, we can roughly obtain the following relation:
C s P A $ I L ,
ð1:4:3Þ
where the plasma energy density is approximated with its pressure P A , which is
called ablation pressure generated by the expanding plasma. With the use of the
relation that the photon pressure P L satisfies the relation, P L ¼ I/c, a new relation is
obtained:
P A
P L
$
c
C s
ð1:4:4Þ
It is clear that the ablation pressure is 3 ~ 4 order of magnitude higher than the laser
pressure. This is the principle why the laser heating is used to study high-density
plasma by the ablation pressure instead of direct laser pressure. Thanks to the
ablation pressure, the laser implosion fusion is possible as reviewed in a book
[19]. The physical principle of ICF and the present status of laser fusion research
are given in Vol. 2. The present accomplishment of ICF by NIF experiment and its
difficulty compared to the optimistic scenario are reviewed by mainly focusing on
hydrodynamic instability and turbulent mixing.
1.4.2 Collisionless Absorption and Ponderomotive Force
Plasma as a continuous medium has a resonance frequency ω pe .
ω pe ¼
e
2 n e
ε 0 m
1=2
ð1:4:5Þ
It is called electron plasma frequency or plasma frequency in short. The plasma
frequency is only a function of electron density, and the oscillation is kept by the
balance between induced electric field and electron inertia in the fixed ion
background. Since the induced electric field by charge separation is large for higher
density, the plasma frequency is proportional to (electron density)
1/2 . When the
electron oscillating current is evaluated from (1.3.8) and inserting it to (1.3.2), it is
found that the RHS of (1.3.2) cancels each other when the plasma electron density
satisfies the relation
ω pe ¼ ω L
ð1:4:6Þ
This determines the cut-off density already mentioned. Physical meaning is that the
induced current generate coherent electromagnetic wave at the cut-off density so that
18
1 Introduction