Sorry for the long post buuut... Here it is.
Ah, the engine. Now this manmade star is one of the components
that give BattleMechs part of their allure. Well, it did
at least during the Succession Wars, when fusion engines
Fusion and Fusion Fuels
Fusion reactors generate their vast quantities of power by,
well, fusing light elements like hydrogen together into heavier
elements like helium. Contrast this with nuclear fi ssion, which
splits heavy elements, like uranium, into lighter materials. The
fuel of choice for modern fusion engines is normal hydrogen,
the protium isotope if you want to be fancy.
In the past, other fuels were used by early fusion reactors—
from the heavier hydrogen isotopes deuterium and tritium, to
the helium-3 isotope and even lithium. But these types gradually
lost ground to protium users. It was almost a century after
the Terran—sorry, the Western Alliance—harnessed fusion that
a reactor capable of burning protium was built. Though other
fuels would’ve allowed simpler reactors, and backwater planets
continued to use such primitive systems for that reason,
militaries are fascinated with the newer reactor technology.
Normal hydrogen is a fairly clean nuclear fuel in terms of
radioactive waste, at least compared to fusion with other fuels
or fi ssion. In fusion reactors today, this normal hydrogen
is easily extracted from any number of sources, especially
water. This is why most military fusion engines include a
small electrolysis unit to extract hydrogen from water. Those
tales you may have heard, of MechWarriors “refueling” their
BattleMechs with urine? They aren’t myths.
Containment and Power Generation
So, you’ve got this super-hot ball of hydrogen plasma being
turned into helium. What keeps it from melting the engine?
Magnetic fi elds. Plasma is electrically charged, so it can
be pushed around by magnetic fi elds. There are fi elds in the
plasma itself and fi elds generated outside the plasma. The
plasma doesn’t touch the wall. In fact, outside the plasma, the
reactor chamber is a vacuum for insulation.
How does the power come out of the plasma? Two ways.
The fi rst way is a tongue twister called “magnetohydrodynamics,”
MHD for short. The short and semi-correct description
is that the plasma is like a dynamo, stirring up electrical currents
in loops of conductors that wrap around the reactor. MHD directly
converts heat from the fuel into electricity—unlike, say, a
gas turbine, which burns fuel to spin a turbine, and the turbine
spins a dynamo. By cutting out the middleman and operating
at extreme temperatures, MHD power generation can exceed
90 percent effi ciency in turning heat into electricity.
The second way of generating power is only a secondary
system, called regenerative cooling. Regenerative cooling
uses some of the waste heat it’s handling to generate power.
The typical format is a closed-cycle gas turbine or even a
steam turbine. Most BattleMech designers and MechWarriors
view this as part of the cooling system, even calling it “heat
sinks hidden in the engine.” In fact, the regenerative cooling
machinery is quite diff erent from real heat sinks, even though
it can benefi t from the same advances in materials that make
the recovered double strength heat sinks possible. This system
adds negligible volume to the engine, as it mostly uses
the existing plumbing of the engine’s cooling system, though
weight starts to add up on larger engines when designers attempt
to scavenge every last scrap of waste heat.