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: Doppler Broadening
Date: Jun 19, 08:54 am
Poster: Richard Hull

On Jun 19, 08:54 am, Richard Hull wrote:

I recently had access to a wonderful Ocean Optics 2000 spectrometer. This allowed me to check out some of the laws of ion physics and help the owner of the spectrometer calibrate and check out his instrument by the use of my fusor.

The unit itself is all contained on a single PC card and includes software to place the spectrographic data on a common windows PC both in graphic and tabular form. The killer low price of $2000.00 belies the incredible accuracy and possible resolution of the device.

He had spec'd his device for a 2400line/mm grating and a 10 micron slit. This limits his spectrometer to the blue end of the spectrum (350-500nm) but makes it very high resolution within that range.

I loaded my chamber up with deuterium at 20u pressure and used only enough voltage to get the internal cathode glow ball which I have called the poissor. (~3.4KV).

The spectrometer's fibre optic glass input cable was just set up outside the bell jar to stare at the poissor on a ring stand holder. The room lights were turned out and the classic hydrogen beta line (spike) appeared near 485nm. increasing the resoltion on the PC software allowed us to measure the doppler broadening at the base of the Hb line It was on the order of 15-17 angstroms.

This broadening of the line occurs due to ion velocity in the gas plasma, and is ,thus, related to ion energies. Basically it is a ratiometric formula which states that the ratio of delta lammba to lamba center is equal to the ion velocity divded by the speed of light. The delta lamba is the 15-17 angstrom broadening. This is divded by the center wavelength (Hb line center). Next the result is multiplied by the speed of light to get the ion velocities. By measuring the base spread (widest point) as our delta we are looking at only the fastest ions. Naturally, in most any plasma there are a range or distribution of velocities. Nonethless, this will allow us to back figure to the acceleration voltage for those fastest ions.

In the case of our test, the energy calulations came out right on the money! This was most gratifying for all in that 1. The laws of plasma physics proved themselves and 2. His spectrometer was dead on and nicely calibrated. He rewarded me with a nice steak dinner for assisting him.

No fusion, but a little side trip into the physics of plasmas with a fusion capable device.

Richard Hull