Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: Re: pulsing and potential well
Date: Nov 3, 12:44 pm
Poster: Jim Lux

On Nov 3, 12:44 pm, Jim Lux wrote:

>why is pulsing important for the fusor to work correctly as farnsworth hoped?
>after some earlier discussions, i have seen pulsing articles about high currents and melting of the grid. but i read about nasa using pulsing and the potential well to get near breakeven. is this possible?

I don't think that pulsing, per se, is necessary. The idea is that if you get a high enough current, the ions clump in the middle (in that second potential well), forming a higher density of fast moving ions which can fuse. Miley talks about going from a x^1 regime to a x^2 regime in terms of fusions per unit input power.

It seems to me that the pulsing is to overcome the practical problems of such high currents: the grid can't take the sustained power and will melt; and generating sustained currents of many amps at several hundred kV in a lab is very expensive. If you are just trying to find out if it will work at all, then doing it for a millisecond at a crack is plenty long enough to reach steady state. Megawatt pulse powers (and low average powers) are easy, megawatt continuous powers are expensive.
You'll observe that for all of the "fusion power too cheap to meter" schemes (including commercialization of the Farnsworth unit, except as a neutron source), everyone proposes that "there is a nonlinear relation between power out and power in, and if only we can make the box big enough, with enough input power, we'll get over the breakeven level, and be generating more than we feed in." Generally, there are reasonably sound physics reasons why this is theoretically true. (sometimes overlooking practical details like that you'll need the entire world resources of Vanadium to make the thing)

Of course, the "in 2 (or 5, or 10, or..) years, we'll have enough input power to reach breakeven" statement has been made many a time over the past 30 years. Nobody even claims that the big laser inertial confinement thing is to generate power anymore, but rather, it's for "stockpile stewardship."