Shock compressed plasma

Incidence of compression plasma flow on the silicon surface causes a shock-compressed plasma layer to form. The energy absorbed by silicon depending on the sample location ranges from 5 to 25 J per pulse, which corresponds (in our experimental conditions) to an increase in power density of plasma flow from 0.510 to 310 W/cm. In its turn, the density of charged particles in plasma varies from 10 cm at the maximum contraction to lO cm in the area of compression flow divergence. Under these conditions, the impact pressure developed by incident plasma flow on the silicon surface ranged from 10 to 30 bar. 

The analysis carried out by AES showed that the films formed by one pulse of plasma treatment possess the complex composition (Fig. 2a) N, C and W from vacuum chamber atmosphere, Fe and C from the shock compressed layer. Further increase of the pulse numbers leads to more homogeneous distribution of elements (Fig. 2b). This effect is associated with high temperature of the surface during the plasma treatment resulting melting and subsequent liquid phase... 

A series of five silicon samples has been prepared for research. Monocrystalline Si(lll) wafers (10x10x0.28 mm) were exposed to plasma. The initial MPC voltage changed from 2.8 up to 3.6 kV, with steps of 0.2 kV. The incident compression flow gives rise to a shock-compressed plasma layer near the sample surface. 

In one application of eFF we smdied the thermodynamics of shock-compressed liquid hydrogen, characterizing molecular, atomic, plasma, and metallic phases at temperatures up to 200,000 K and compressions up to fivefold liquid density (see Fig. 9). We found reasonable agreement with data from both static compression (diamond anvil) and dynamic compression (shocks from explosives, magnetically pinched wires, lasers) experiments. 

A plasma is an appreciably ionized gas(about 1% or more) having no net charge, and may have a wide range of densities. Plasmas are of particular interest because of the possibility of initiating nuclear fusion in them, but they also appear in such phenomena as a neon sign, a lightning stroke, the ionosphere about the earth, shock waves, and the compressed layer of hot gas about an object entering the earth s atmosphere They appear in flames and detonation waves. It seems well established that free radicals and ions are present at well over equilibrium concentrations in flames (Ref 1). The ions appear to be produced not by thermal processes but by chemical factors which cause abnormal electronic excitation... 

Plasmas are of particular interest now because of the possibility of initiating nuclear fusion in them but they also appear in phenomena ranging from those found in a neon sign, a lightning stroke, the ionosphere about the earth, shock waves, and the compressed layer of hot gas around an astronaut s capsule as he comes back thru the earth s atmosphere ... 

Figure 5-43. Energy efficiency of plasma-chemical CO2 dissociation in supersonic flow, taking into account energy cost of compression, as a function of specific energy input at different Mach numbers (1)M=2.5 (2)M = 3 (3) M=4 (4)M=5 (5)M=7 (6)M=8. Solid lines correspond to pressure restoration in a ditfuser, calculated based on Oswatieh theory dashed curves correspond to diffuser eonsidera-tion as a normal shock.

In conjunction with the above experiments, hydrodynamic computer models have been developed to provide a detailed description of the liner motion [18]. The effect of the compressibility of the liner fluid becomes particularly important in thick liners moving at high velocity. If the turnaround time is much less than the transit time of a sound wave through the liner, compression waves will be set up which modify the motion and can cause severe shock loading of the driving mechanism. It is desirable to operate a reactor under conditions where these waves are not significant, and this sets an upper limit on the final pressure to which the plasma may be compressed. 

Production of a foreplasma with the required parameters in a closed cylindrical compression chamber is a rather complex problem. Four different schemes have been considered. The easiest one is that offered by J.G. Linhart [13]. It consists of liner acceleration up to a velocity, at which shock waves in a D-T mixture, would produce foreplasma with the required temperature and density. The inconvenience of this method is in the rigid dependence of the liner velocity on the foreplasma parameters. Besides, plasma production by shock waves decreases compression. 

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