Pages

December 20, 2008

General Fusion: Almost has Second Round of Funding


The January 2009 issue of Popular Science has several pages on General Fusion.

32 page patent for acoustic generator for nuclear fusion.

24 page patent for magnetized target fusion generator

Popular Science indicated that General Fusion has raised $7 million of their $10 million second round which would fund an almost full scale version (2 meters instead of 3 meter diameter).

A prototype device with a tank diameter of ~2 m and an input energy of ~120 MJ could provide interesting fusion gain. Such a system could be built at a reasonable cost of ~10 $M in about 3 years. (For a prototype with low repetition rate, no tritium re-breeding, no heat exchanger and no turbo-generator).


This would suggest 2010-2011 as the timeframe for completion of the tests and work associated with that device.

The third phase for General Fusions is to raies $50 million for a net energy gain device with a target date of 2013 if the second/third phase are roughly on schedule.

Then they try to raise $300-500 million for commercialization.

The company's ultimate plan is to build small fusion reactors that can produce around 100 megawatts of power. The plants would cost around $50 million. That could allow the company to generate electricity at about 4 cents per kilowatt hour, relatively low.

UPDATE:
M Simon has performed an analysis of the patents

MTBF is Mean Time Between Failures, which is described at this wikipedia link. The reliability of the pistons is a key aspect.

When they go to pistons they will pressurize the pistons and use triggered latches to let them all go at the same time. The final velocity of the piston will be 100 m/S and the shock wave it induces will be traveling at 2.5 km/S. If we assume 100nS timing to assure reasonable addition of all the induced waves you get a distance variation at that speed of 10 um. Which is 2X what his measurement system can do. Good. And the measurement system will require laser diodes for the light source and gratings to do a linear encoder.

He plans to control the timing and velocity by repeated shots to adjust the parameters. Clumsy but OK.

Can it be made to work? There is an outside chance. Repeatedly and reliably? I doubt it. Wear is going to be a killer on the latches. He proposes to fix the piston/cylinder wear with an air bearing. The problem is that the space in front of the cylinder must be evacuated before every shot.

I'd want to see a dummy steam powered machine with 2 or 3 cylinders operating reliably for a day or two meeting all specifications for timing and velocity before I set up the full machine. Given that he expects to run the whole 200 cylinders on 100 Mj or so a 2 MW steam boiler ought to suffice for experiments.

I will say that he seems like a careful experimentalist so he might pull it off. He might even get the machine to function for a few shots. Continuous operation for a year?

That would require a 2,000 year MTBF or better for each cylinder and its associated electronics for a reasonably good probability of 1 year of operation. that is roughly better than 20 million hour MTBF. That is space rated electronics parts and space rated assembly or better because the mechanical parts have to have a failure rate on that order as well.

Let us think in terms of an auto engine. 4,000 hour MTBF at 5,000 rpm. 8 cylinder. Say 10 billion piston strokes VS 200 pistons at 1 stroke per second at 3,600 strokes an hour at 24 hrs a day at 365 days a year. About 6.5 billion strokes. So the ball park is right. Except for one minor detail. The piston in the auto is not slamming into the cylinder head every time it reaches TDC [top dead center]. Its timing is constrained by the crank shaft.

Let us look at timing in the auto at 5,000 RPM [revolutions per minute] it completes a revolution in 200 uS (microseconds). To get the timing of the spark right it must be controlled to within 1/2 uS. (about 1 deg) . But in the auto you have rotational inertia helping keep things constant and feedback from gas sensors to tell you when the timing is right.

So I would not put making all this work outside the realm of possibility. It will not be easy. Not easy at all. And the MTBFs of every part in the cylinder assembly must be beyond space rated.


Although having a system for monitoring the pistons and system for wear and having an easy method to rapidly swap out pistons could maintain a sufficiently high operating reliability. Keeping 90% uptime throughout a year with an average of one piston or some other component replaced every day with a 15 minute hot swap would be doable. Quality and cost of components would need to be balanced against overall costs.

Nasa has stirling free piston cryocoolers with mean time between failure of over 500,000 hours Aircraft engines wiith 40,000 hours of mean time between failure are common and microturbines have 14,000 hours of mean time time between failure. Twice weekly and even daily maintenance can be doable if the maintenance can be fast (using a robotic arm to pop a piston assembly out and replace it). Faulty units can be refurbished and put back into service if that keeps costs down without sacrificing overall reliability.






FURTHER READING
Previous update: General fusion had completed proof of concept experiments and performed full scale computer simulations.

First article by this site on General Fusion's and magnetized target approach
blog comments powered by Disqus