Pellet Injection for Fusion Engines
Currently i’m having some fun playing around with hydrogen gas gun configurations but I am not investigating them for the usual application. Instead, I am looking at them for the potential of delivering an inertial confinement fusion pellet into a reaction target chamber within a fusion engine. The pellets of thermonuclear fuel have to be accelerated at high velocity into the target chamber so that a bank of lasers can then fire at them to initiate the fusion reaction. This must happen many times per second in what is known as pulse repetition frequency.
The initial concept for a single gas gun design is shown below and it includes many pistons acting in sequence to supply the injection barrel. It is a bit like a giant machine gun.
This is for the application to the large interstellar Pegasus spacecraft I have been designing as a part of Project Icarus. With a pulse frequency of 1,000 Hz, and an injection length of 1 m the pellet would have to be injected with a velocity of 1 km/s which is credible. Lowering the pulse frequency results in a lower injection velocity requirement. Increasing the injection length increases the velocity requirement.
In the current setup I am using a 72 mg pellet which has an energy of 36 J or a power of 36 kW. But here is the thing, this is on a spacecraft that has four parallel thrust engines, so you need four of this units operating simultaneously. Each unit has 100 pistons They are positioned onto a large rotating 10 m disc where the units are aligned with the pellet injection line to the target chamber of each reaction chamber. The whole system has an associated moment of inertia 1.25 million kgm2, kinetic energy 0.422 MJ and a power requirement of around 5.275 kW.
The calculations are suggesting that the quantity of hydrogen and oxygen gas required to operate these would be too excessive. It also requires an assumption of an unrealistic high efficiency of operation with negligible energy losses. For these reasons for the particular design I am looking at they may not be appropriate. But it sure is a lot of fun attempting to do engineering design on the application of existing machines to envisaged ones. After all, this is how the future is made.
