Of course, quasi-neutrality demands that [18]
We can estimate typical particle speeds in terms of the so-called thermal speed [18],
The typical gyro-radius of a charged particle gyrating in the magnetic field of a tokamak is given by
(2.18) |
(2.19) |
The electron-ion and ion-ion collision times are written
respectively [18]. Here, is the Coulomb logarithm [42]. Note that is the typical time required for the cumulative effect of electron-ion collisions to deviate the path of an electron through . Likewise, is the typical time required for the cumulative effect of ion-ion collisions to deviate the path of an ion through .The electron and ion collision frequencies are simply the inverses of the corresponding collision times:
(2.22) | ||
(2.23) |
Finally, the mean-free-paths between collisions (i.e., scattering events) for electrons and ions are
(2.24) | ||
(2.25) |
Table 2.1 gives estimates for some of the fundamental plasma parameters defined in this section in a low-field and a high-field tokamak fusion reactor. Here, use has been made of the data shown in Table 1.2. It has also been assumed that , for the sake of simplicity.