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: Proton detection
Date: Dec 30, 8:08 pm
Poster: Pierce Nichols

On Dec 30, 8:08 pm, Pierce Nichols wrote:

>The problem comes in that at the wall (positively charged electrons are slammin' hard enough so that virtually 100% of the impacts produce an X-ray photon which will cruise right through the thin aluminum!! Rats!
>What about a negatively charged grid to repel the electrons, or a magnetic field to bend the electrons a different direction.

This is the essence of the so-called Faraday Cup. You use a grid or series of grids to exclude particles of a certain energy and charge. In this case, you would use an positively charged grid at a couple of kV to repel random fuel ions that happen to be going in the wrong direction and a strong magnetic field to bend incoming electrons into the wall. You could also do it with a couple of extra grids in there. The back is a plate of copper connected through a very sensitive ammeter to ground. Every proton hitting that plate produces a tiny pulse of current, which you measure. This is a terribly simplified description; I helped build a much more complex version of this concept with 96 cells as a charged particle imager when I worked in the Columbia University Plasma Lab as a student.