Positron plasmas

Fig. 6.6. Schematic illustration of the electrode structure of the positron trap of Greaves, Tinkle and Surko (1994). The variation of the electrical potential along the trap, together with the gas pressure in the various regions, is also shown. The letters A, B and C indicate energy-loss collisions of the positrons with the N2 buffer gas. Reprinted from Phys. Plasmas 1, Greaves et at, Creation and uses of positron plasmas, 1439-1446, copyright 1994, by the American Institute of Physics.

Although positron plasmas can be considered to be systems containing many positrons, and as such technically fall within the scope of this section, we will not consider them here. Rather, we will concentrate on the theory of, and the possibilities of observing, assemblages of particles containing both positrons and electrons. These include the positronium molecule and a Bose-Einstein (BE) condensate of positronium atoms. 

A discussion of some applications of positron plasmas in atomic-physics investigations is given in Chapter 6, and more general information can be found in the review of Greaves, Tinkle and Surko (1994). 

Following the same procedure outlined for the cold plasma, we can specialize the system of (10.17) and (10.18) in Part I to the one-dimensional case with circular polarization and zero group velocity. The explicit forms of the relevant equations are given in [39], where RES in an electron-positron plasma were studied. Since the two species have equal masses and absolute values of charge, the plasma does not develop any charge separation for Te = Tp = T0 and so (j> 0. A single second-order nonlinear differential equa-... 

A kinetic approach to the study of one-dimensional RES in a hot plasma was developed in [44] and applied to RES in an electron-positron plasma [44], electron-ion plasma [45], and electron-positron-ion plasma [46]. A highly anisotropic particle distribution function for each plasma species j (where j = e for electrons and j = i for ions) was considered, with a finite constant... 

We can summarize the main results from the previous investigations in the following points (i) soliton solutions have been found under general conditions for an electron-positron plasma and by assuming quasi-neutrality in an electron-ion plasma (ii) sub-cycle nondrifting solitary waves represent an equilibrium in a multicomponent warm plasma that is, half-wavelengths of the EM radiation can be trapped inside a plasma density well (iii) the... 

For the accumulation of the positron plasma we plan to use a system based upon the positron accumulator presently operated at the University of California in San Diego, in which 108 low energy positrons are routinely accumulated in... 

The formation will be done by pushing antiprotons through a rotating positron plasma. The rotation is an unavoidable result of the E x B drift of the positrons in the magnetic field. The rotation frequency depends on the spatial density of the plasma [34]. 

We now turn to reaction (8.14), the trapped plasmas combination reaction, in which the excess energy is removed by an extra positron as shown in Figure 8.9(c). The use of this ternary reaction for antihydrogen formation was first suggested by Gabrielse et al. (1988), who noted that its matter equivalent had been studied, mainly in relation to high temperature plasmas, for some time. These authors were therefore able to write the antihydrogen production rate, which corresponds to the recombination rate in conventional plasma physics, as... 

Fedichev, P.O. (1997). Formation of antihydrogen atoms in an ultra-cold positron-antiproton plasma. Phys. Lett. A 226 289-292. 

Figure 9 Effect of cyclosporin A on the brain (A) and plasma (B) concentration of nC verapamil in healthy volunteers. (A) 1 -Verapamil ( 0.2 mCi/kg) was administered to healthy volunteers intravenously, approximately one minute before and after one-hour infusion of cyclosporin A (2.5 mg/kg/h). (B) PET images of a normal human brain after nC-verapamil administration in the absence or presence of cyclosporin A. Images shown are in SUV summed over a period of 5 to 25 minutes, which is an index of regional radioactivity uptake normalized to the administered dose and weight of the subject. Abbreviations PET, positron emission tomography SUV, standardized uptake value. Source From Ref. 218.

A hot fluid model would be highly desirable for applications in astrophysics. As we have already mentioned, the formation of RES in the primordial plasma could be an important source of large-scale nonuniformities in density and temperature, which seeded the formation of galaxies and clusters of galaxies [4], In particular, it is conjectured that in the early universe matter was present in the form of a mixture of electrons, positrons and photons in thermal equilibrium at a temperature above me2. It is evident that the propagation of relativistic EM waves in such peculiar environment should be addressed in the framework of a hot-plasma model. 

The above reactions require that two plasmas of opposite charge (antiprotons and positrons) are trapped and brought into contact. Alternatively, recombination by crossing a beam of positronium (either in the ground state or in low-lying excited states) with antiprotons has been proposed (see references [23,24,25,26]) ... 

This formula for the rate per trapped antiproton per second is notable for its very strong, T-9/2 (in degrees K), positron temperature dependence and the presence of the positron density, ne+ (in cm-3), to the second power. In their analysis Gabrielse et al. [21] assumed that a plasma of 107 e+ cm-3 would be produced at 4.2 K which yields a production rate of Rfj 600 s-1. Glinsky and O Neil [37] have re-examined this problem from a plasma physics viewpoint. They find that the combination rate given by equation (9), which is actually that pertaining to... 

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