Was Beta=1 conditions actually measured in WB6?

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D Tibbets
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Joined: Thu Jun 26, 2008 6:52 am

Was Beta=1 conditions actually measured in WB6?

Post by D Tibbets »

Beta =one testing in WB6 and earlier machines. In WB6 the method of determining Beta=1 was described as holding E-gun current and voltage (Magrid) steady with a given background gas pressure and varying the B field wile measuring the PMT (photo multiplier tube)measured light output of the plasma. This seems straight forward and almost error proof. This assumes that the PMT brightness signal grew predictably as the Beta =1 condition was approached, and subsequently fell as Beta>1 was exceeded. There has been some question of the validity of PMT measurements as a measure of density, but Nebel stated that they were consistent with an alternate method.

The aspect that may be confounding though is the assumption that electron emitter current was equal to electron density inside the machine while the B field was varied. As has become apparent, electron injection efficiency is a moving target. As the B field increases the mirror rejection of e-gun electrons may increase in some linear to exponential fashion. Also, with increased B field and / or Beta, the internal contained electron density will increase some interactive amount. This increases the internal negative space charge also impedes electron injection.

What I think this means is that the Beta tests described above are not really measuring when Beta=1 is achieved, but an intermediary value that is the result of decreasing electron injection efficiency (with increasing B), better electron confinement due to Beta increasing up towards one, and then less confinement as one is exceeded. As such the greatest internal density achieved (as measured by PMT or interferometry) is the cross product of these two competing processes. You are indeed measuring the peak density , but with two variables you are measuring the associated peak. How close to Beta=one this may be is unknown (by me) Is it 99% of Beta =1 (or Beta=0.99) or is it 80%, or 50%?

This changes things some and complicates interpreting the results and predictions. On the plus side if actual brightness due to Beta/ electron injection efficiency occurred at a Beta of 0.8, then there is room for improvement if you can somehow boost the electron injection efficiency.

Another measurement method may be neutron yields from D-D fusion. The density, temperature and B field strength peaks at the highest density (squared) whether this is at Beta=1 or some lower value. Calculations may point to an appropriate value, though the degree of thermal spread, degree of ion confluence, instrument accuracy, etc. complicates this measurement also, perhaps to the extent that it has little ability to resolve the situation. You can calculate the density at Beta=1 and calculate the fusion rate from that if temperature is constant and if ion confluence, if any, is constant. The latter may be variable also though. Measuring fusion would tell you if you are doing good or very good, but not necessarily if you have reached the best theoretical conditions.

If Beta =1 tests were conducted with E-gun current and voltage held constant while B field strength was swept up and also swept down from both sides of predicted Beta=1, the peaks in density may match ,or not. If not then I think the above consideration is significant. If the peaks do match, I'm uncertain what the conclusion would be.

Dan Tibbets
To error is human... and I'm very human.

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