Heat-engines that do not need containers (was A buck a squafoot)

> Space is the perfect place to [...] build [...] fusion reactors.
>
> If [a fusion-based heat-engine were] built in space or the moon
> [it] wouldn't need any container and [would] not have to worry
> about losing plasma.

How do you figure? Are you talking about an external-combustion
engine? For example:

A stream of glass microspheres containing deuterium/tritium, is
lit by Laser Inertial Confinement. The resulting power is
captured and converted by thermophotovoltaic cells or by a
fluid-charged heat-exchanger attached to a standard mechanical
heat-engine. Most of the power simply shines, untapped, into
space.