A review of the dense Z-pinch

Plasma Phys. Control. Fusion 53 (2011) 093001
Topical Review
from the extra viscous heating which occurs at high temperature. It should be noted that all
the results here are for masses below the break-point for onset of the efficient regime. A triple
nested array was explored and gave up to 200 TW total x-ray power for a 4:2:1 mass and
radius ratio, with T e ≃ 3.8 keV and a narrower pulse. It was noted that radiative cooling in the
L-shell complicates the simple model and reduces the efficiency of K-shell radiation.
A transition from I 4 to I 2 scaling of keV radiation found by Sorokin et al [653]at4MAin
a double shell gas-puff experiment in argon. They claim this is due to a very high compression
of the pinch to a diameter of 0.2 mm when the inner and outer shells had mean radii of 4 mm
and 13 mm, respectively, i.e. a 45-fold radial compression. This might be based on the timeintegrated
pinhole photographs of the pinch. A similar result was found by Sze et al [654].
There is a tendency for the hotter electrons to drift preferentially towards the axis (see
sections 2.6 and 2.7). Indeed runaway electrons can only exist in a Z-pinch within one Larmor
radius of the axis (section 2.2). Combined with m = 0 instabilities bright micro-pinches have
been observed by Alikhanov et al [655] with pulsed gas injections. Indeed Kr xxxv–Kr xxxvI
ions with ionization potentials ∼17 keV suggest electrons with 3–5 keV temperature. Choi et al
[656] distinguished hard and soft x-rays from a gas-puff Z-pinch, the former being associated
with bursts of ∼10 keV electron beams and emission from the anode. Li and Yang [657] showed
that a thinner gas sheath gave a higher velocity of compression and a higher x-ray yield, while
Bayley et al [658] injected argon through a hole in the anode of the speed 2 plasma focus to
obtain soft x-rays from micro-pinches along the axis. Chuvatin et al [659] considered a two
stage heating of an argon gas fill. The first stage was shock heating and thermal conduction from
an imploding shell, and the second is an adiabatic compression to the required temperature.
Bergman and Lebert [660] varied parameters to find the optimization of Lyman-α emission in
a plasma focus. In section 7.2 the x-ray emission from a plasma focus is discussed in detail.
The X-pinch (see section 7.6) is also a very useful source of 1–10 keV photons, and
its small volume of emission (