Upgrade to PEM based gas generation system. Gas chiller/dryer added.

[Rich Gorski]

PEM based electrolysis systems are inherently wet as some amount of D2O molecules get through without being split apart. The addition of the heavy water vapor contaminant into the vacuum chamber both reduces the fusion production rate as well as creating high voltage instabilities. One solution to this problem is to dry out the gas before it enters the vacuum chamber. Indicating zeolite is one possibility but that may add its own chemical contamination. My choice was to design and build a thermoelectric gas chiller/dryer to condense out the water vapor in the gas on its way to the mylar gas storage balloon. The chiller is constructed out of 24” long 1/8” diameter copper tubing bent around into a serpentine shape. The serpentine copper tubing then is soldered to a copper plate above and below creating a sandwich. Four 1 ½” X 1 ½” cooling chips are placed two on each copper plate with the cold side facing inward. Two water cooled heat sinks are then mounted on the hot side of the cooling chips. The entire assembly is then clamped together forming the complete unit. Water through the heat sinks keeps the hot side near room temperature (25C) while the cold copper loops reached -3 Celsius with a power input of about 100 Watts (10V , 10A) applied to the thermoelectric chips. The last photo below shows frost building up on the cold regions indicating proper temperature to condense out the water vapor.

Fusor performance results with new gas chiller/dryer installed:
1) Increased NPR by 1.5 to 2.0X
2) Better HV stability
3) Longer gas storage time in mylar balloon before it becomes contaminated and the NPR drops.
4) Best NPR for the planar radial acceleration fusor was about 120 CPS as measured with a B10 proportional tube running with 3 ion source producing 18mA current, pressure of 1.8mTorr and at -40kV. With my best guess at the B10 sensitivity of 1.7CPS/nv this implies 0.57*120*4*π20^2 = 3.4 x 10^5 NPS or 6.84 x 10^5 fusions/s isotropic.


The entire PEM based gas generation system with the newly constructed chiller installed (blue). The PEM cell is to the left in the photo with the silver mylar gas storage balloon below.

Close up of the thermoelectric chiller showing a side view with the 4 thermoelectric cooling chips (white) visible.

Disassembled cooler showing interior parts. Cooling chips, copper plates, serpentine tubing and blue water cooled heat sinks.
Cooling chips FD117V1 size = 1 ½ x 1 ½”
Copper plates: 2” X 5” X 1/16”
4 cooling chips connected in parallel require 10V at 10A (100W) to reach a interior temperature of -3C. Water cooling flow rate was about 1L/min.

Close up showing frost that has built up on the cold copper sections of the gas chiller/dryer.

[Frank Sanns]

This topic came up at the HEAS this year. Jim Kovalchick and I had an in depth discussion about this.

It is very important to differentiate what "water" is in a Fusor. Water is typically thought of the H2O bound to metallic and glass surfaces. It can be quite bound and deep and be difficult to remove. That is one of the reasons for high temperature bake outs on ultra high vacuum systems. Yes other gasses come out but water can be more problematic because of its relatively strong bonds with metals.

Nothing new there except that the water is protium hydrogen. It is not fusible.

At Fusor voltages, water is going to mostly be hydrogen and oxygen and not water. The hydrogen gets accelerated very much like deuterium so it interferes in paths that lead to fusion. It dilutes down greatly the small amount of deuterium fuel that is in an operating Fusor and imbeds in the walls.


In sharp contrast, deuterium "water" does not dissociate into protium to interfere. It dissociates into deuterium and some oxygen. While the oxygen presence will reduce the fusion a bit, there are not twice the number of protium ions getting dumped into the plasma.

I postulated that D2O might not hurt fusion much at all for this reason. It seems you have demonstrated that it does degrade the neutron numbers a bit but nothing like having conventional protium water in there.

NIce work, Thanks.

[Jim Kovalchick]

Rich,
I'm curious if your tests were succession and reverse succession. We've all seen improving neutron runs with succeeding runs from chamber conditioning. Did you try immediately removing your dryer system to see if numbers went back down?

[Rich Gorski]

Frank,
Interesting.
It never occured to me that protium water would be worse for fusion rate than deuterium water but it makes sense.


Jim,
My numbers reflect the NPR before install of the dryer and after. However I will purge the mylar balloon of the "dried" gas and refill with the chiller unit turned off. Then run the fusor system again at hopefully the same conditions and report back with those results in a few days.

Rich

[Rich Gorski]

More data on NPR with and without thermoelectric chiller/dryer. Forward and reverse direction below. Confirms my expectation that the chiller/dryer improves NPR.

NPR data at 40kV, 1.8mTorr D2, 16-18mA PSU current, 3 ion sources active
Fresh D2 gas used in below data. Test run just after filling mylar balloon. Less than 1 hour storage time in balloon.

Prior to chiller/dryer
95CPS

Chiller added
125CPS

Chiller inline but not activated (3 runs)
82, 90, 83 CPS Avg = 85CPS

Chiller activated (2 runs)
133CPS, 150CPS Avg = 142CPS

Noted better HV stability with dry gas! Easier to maintain constant PSU current over time.
I also want to note that the gas stored in the mylar balloon degrades over time. NPR reduced to 1/2 over a 72 hours storage time. Contamination from balloon or D2 leaking out and being replaced with N2 ??

Rich G.

[Frank Sanns]

Interesting results.

It is still not too bad.

Considering that even at 100% RH, the amount of D2O in the D2 stream would only be around 4% by weight (if it tracks air data). This is not a massive sum of contaminate. Drops of neutron production of %50-100% is not terrible.

In contrast, starting up a fusor that has been open to the air and picked up a ton of protium water will totally kill neutron numbers. Literally by a factor of 10 or maybe even 100. A fusor that has sat open to the atmosphere for a while will really struggle to get even to 10^4 in the first half an hour of operation. Not saying that only protium is contaminating and killing the numbers but there is way more protium water on the surface of a chamber and its parts thank any D2O dragged in from a PEM cell.

Your drying system works well. It was a worthwhile project to get the highest neutron number possible.

Thanks for posting.

[Richard Hull]

Nice report. This shows the positive effect of a chiller, all other things held equal. Thanks for the good news.

Richard Hull