Talk-Polywell.org

seems stabilising the plasma with clever control algorithms has been key ... also an interesting helicon RF technology involved

http://spacefellowship.com/News/?p=7153

The helicon first stage of the VX-200 VASIMR plasma rocket prototype has achieved its full power rating of 30 kW with Argon propellant in tests conducted last Wednesday at Ad Astra’s Houston laboratory.

My ISDC talk cites the 27 kW ESEX arc-jet. It also cites the 130-something kW (180 HP) Piper Cub (the latest models, and the power of late-model Cessna 172's)

Each engine of the space shuttle develops 6 GW.

Gotta ways to go.

Last Friday I attended a symposium about deflecting asteroids. They were talking about deflecting Aphophis-sized rocks using the DS-1 Xenon ion motors (typically about 2.7 kW, 93 millinewtons). Given a dozen years of thrust, they figured they might push one about 30 km.

Just out of curiosity, since we're talking whose electric drive is bigger, badder, and meaner, if the polywell was working today, would it be trivial to build a REB or QED engine?

Bussard often discussed those, with some fairly unbelievable T/W and ISP numbers to my mind -- what prevents these engines from being built today-- is there a minimum power threshold below which a REB or QED would not function? What is it?

I find the technologies for controlling the plasma more relevant to the Polywell rather than the size.

For instance could a helicon be used for electron manipulation, aka energy recirculation?

Both developing the relativistic electron beam and imparting the energy to the reaction mass to make a QED engine will be serious engineering challenges, which Dr. Bussard admitted to me he had only a vague notion how to do.

You're in space ... vacuum all around. For the e-beam generation, fine. The e-beam will like a vacuum. However, it needs to fire into gas at a fairly high density, right beside it. Furthermore, you need to heat the gas fast, before it leaks out to space on its own. How to maintain that density while allowing the e-beam to run was not at all clear. He had some notion it might be possible to inject the gas in a vortex, and possibly to place a thin metal barrier between the e-gun and the gas chamber, but no idea if it would work.

What was absolutely clear, especially after melting a few grid wires on our e-beams and fusors, was DS-1 (NSTAR) ion motors will not scale to the hundreds of megawatts.

Control is obviously going to be a huge problem esp in the start up phase of a power producing BFR.

All I can say is - Let me at 'em.

cuddihy wrote:Just out of curiosity, since we're talking whose electric drive is bigger, badder, and meaner, if the polywell was working today, would it be trivial to build a REB or QED engine?

Depends, are we talking

1) A well funded, no frills, risk tolerant, learn by killing test pilots wartime priorities program, or

2) A lavishly funded (to bleed the government), gold plated, absolutely risk adverse program?

Case 1, 30 months. Case 2, 15 years.

Care to guess where I fall?

Duane

In the absence of nuclear fusion, ejecting fuel out at high energy is not completely desireable and has some disadvantages.

Momentum=2*Energy/velocity thus if you have a finite ammount of electrical power coming from your solar cells, then kicking out less mass at high speeds will reduce your thrust in proportion to the speed you eject said mass at. If your power source is nuclear (a uranium reactor pehaps?)
you'll have to carry more uranium aboard to provide the power to accelerate the plasma propellant. This will increase the mass of your vessel.