The dominant power flow for steady-state hybrid operation is suggested in Fig.

15.2 and the corresponding station electrical output is given by

Pnet ~ Ць Ph, t Pin • (15.6)

Here Pbit* is the thermal power extracted from the blanket and converted into electrical form with efficiency г|ь while Pin is the input power supplied with efficiency Г|щ to the device in order to sustain the fusion reactions.

Using an obvious definition for the blanket energy multiplication, we write

Pl, t = MbPn (15.7)

where Pn* is that component of Pdt* associated with the energy of the fusion — source neutrons entering that blanket; that is

p;=o.8p;(. (15.8)

The remaining 0.2 Pdt component associated with the alpha particles is assumed to be retained in the plasma.

Next, we define an effective fusion-component input power multiplication by

Note that upon introduction of the fusion plasma Q-value, Eq. (8.6), which here for steady state is

the effective fusion-component input power multiplication is represented by

Mju. e=0-SVinVbQP

The significant result here is that the condition for energy viability of a hybrid is now

MbMfU, e>l (15.13)

and contrasts to a stand-alone fusion reactor for which, evidently, it is necessary to have MfUie > 1. Since the attainment of Mfux. > 1 is a demanding technical problem and since Mb > 1 seems readily possible, the hybrid would have the possible advantage that some critical plasma parameters could be relaxed when compared to a pure fusion system. This could be an important motivation for hybrid operation in the early development of fusion systems.

The important consequences of Eq.(15.10) for the hybrid are depicted in Fig. 15.5. Note that for Mb > 1, the energy multiplication of the fusion reactor, that is Mf^, can be less than unity and still provide for an energetically viable
overall system.