Plasma power density

These and further economic requirements have dictated the trend towards reducing the reactor size for a given thermal power. In order to achieve an adequate increase of the plasma power density higher values of P (Eq. 8) have to be used (Eq.9). A convenient way to achieve this requirement is to use plasmas of a noncircular cross section (Fig. 7). 

Most reliable are the data on neutron fluxes which are determined by the plasma power density, reactor geometry and structural parameters. Most of the conceptual power reactor design studies contain a detailed neutronics analysis giving the energy as well as the spatial distribution of neutron fluxes. 

The importance of the specific wall loading should now be apparent. It is the key parameter linking our three regions of option space. From the capital cost we determine the desired value of P for the reactor to be economically acceptable, technology tells us whether and how such a level can be handled for a reasonable life and plasma physics has to see whether a sufficiently high plasma density can be achieved to match the required wall loading. Plasma power density (P ) is directly related to the station size ... 

The mean volumetric power density of a DT fusion reactor depends on the plasma power density B ) and the sum of the volumes... 

The wall load constraint would disappear for neutron-free fuel cycles and the mean reactor power density attainable would only depend on the plasma power density, provided that the thermal and particle loads on the wall can be kept sufficiently low. 

To achieve high cleaning rates, high plasma densities are needed together with a large number of reactive species at reasonable plasma power densities. These plasma properties can be increased by increasing the electron-atom collision probability by ... 

The decrease of the silane partial pressure and the concomitant increase of the hydrogen partial pressure as a function of plasma power can be understood in terms of the increased electron density and electron energy. Both lead to a higher dissociation of silane and hydrogen. The silane radicals and atomic hydrogen thus... 

Luft and Tsuo have presented a qualitative summary of the effects of various plasma parameters on the properties of the deposited a-Si H [6]. These generalized trends are very useful in designing deposition systems. It should be borne in mind, however, that for each individual deposition system the optimum conditions for obtaining device quality material have to be determined by empirical fine tuning. The most important external controls that are available for tuning the deposition processs are the power (or power density), the total pressure, the gas flow(s), and the substrate temperature. In the following the effects of each parameter on material properties will be discussed. 

Fig. 1. Deuterium concentration profiles in bulk n-type GaAs Si after exposure to a rf deuterium plasma for 90 min. at various temperatures (rf power density = 0.2 W/cm2). 

Fig. 6. Deuterium concentration profiles in LPE grown p-type GaAs Si (p 7x 1018 cm-3) exposed to a rf deuterium plasma for 90 min. at different temperatures (rf power density = 0.2 W/cm2). For these diffusion temperatures, the plateau region is well defined with a deuterium solubility slightly above the silicon acceptor concentration. J. Chevallier era/., Mat. Res. Soc. Symp. Proc. 104, 337 (1988). Materials Research Society. 

Fig. 7. Deuterium concentration profiles in a GaInAs/InP Zn OMVPE structure after exposure to a rf deuterium plasma for 20 min. at different temperatures (rf power density = 0.08 W/cm2). The dashed line represents the active zinc concentration profile as deduced from a POLARON semiconductor profiler. Note that the deuterium concentration matches the zinc concentration at all investigated temperatures. J. Chevallier et al., Materials Science Forum, 38-41, 991 (1989). Trans. Tech. Publications Semicond. Sci. Technol. 4, 87 (1989). IOP Publishing Ltd.

It allows the laser radiation to be focused onto a small area 10 cm ) and the power density to be considerably increased (up to 10 watt cm with continuous argon-lasers, and more than 10 watt cm with pulsed glass lasers) 22). This is, for instance, important for microspectrometric investigations (see Section III. 9) and for production of high-temperature plasmas. 

Glow discharge or "cold" plasmas are gaining increased currency for the deposition of novel and potentially valuable macromolecular coatings. The range of properties attainable by a plasma-polymer is wide, and depends critically on such variables of the plasma deposition process as choice of monomer, substrate temperature (T ), power density (p), the excitation frequency (v), and others incluSing monomer flow rate, reactor geometry, etc... Control over these variables can produce crossllnked, dense deposits which adhere tenaciously to... 

---