Beam on Target Progress

This forum is for other possible methods for fusion such as Sonolumenescense, Cold Fusion, CANR/LENR or accelerator fusion. It should contain all theory, discussions and even construction and URLs related to "other than fusor, fusion".
Post Reply
George Schmermund
Posts: 262
Joined: Tue Aug 15, 2006 8:51 pm
Real name: George Schmermund
Location: Carlsbad, CA

Beam on Target Progress

Post by George Schmermund »

The beam on target system that I'm caught up in building right now has expanded into several different, though related, areas. I've redesigned the diffusion pump and this next generation is a much better performer than the steampunk version previously described. The steampunk approach was designed to be an absurdity anyhow and seems to have fulfilled that roll rather nicely. The new design is intended to demonstrate that a DP, with modern oil, can operate in an unexpected way. This simplified arrangement has reduced the machining time to about 2 hours and the brazing time is about 1 hour. Pressures routinely get down to the low 10^-6 Torr. A compact, working DP in an afternoon!

The pump and manifold are arranged to assist in the vacuum testing of the new accelerator electrode assembly. The electrode/insulator parts need to be tested for safe hold-off voltage, so I'll just test a single section at first. The new Delrin/ Cu fitting parts were He leak tested and this time they were tight. The compression assembly method is now very acceptable for this application.

In the course of measuring any high voltage sources that I'll be using it has become clear that good numbers are not trivially aquired. The Spellman 40 KV supply that I've chosen for the vacuum break down tests has a somewhat reliable pair of meters on the front panel. This supply has an added advantage of a floating ground which allows measuring currents far below that which can be displayed by the front panel ma meter. This will assist in evaluating various stages of any breakdown modes. A Brandenburg 139D HV meter will be used to accurately follow the voltage on the DUT side of a high value resistor. This meter has an input resistance of 30 Gohms and good specs for overall testing. Its recorder output will also be handy.

Since I'll be using a Van de Graaff (proper spelling) generator for the HV supply when the fully assembled tube is finished, the need arises for a means to measure 150 KV with far less loading then any meter that requires actual contact with the measured source. Having a good collection of Keithley, Monroe, and Simco instruments in the lab makes HV measurements relativity easy. The Monroe electrostatic voltmeter uses a vibrating reed probe and can be converted into a field mill rather simply. This will allow non-contact measurements of the VdG HV terminal up to several hundred KV with good accuracy. We'll see how that plan works out.

In the mean time I decided to sacrifice a Bruel &Kjear 4145 1" microphone and preamp to the cause. With the diaphragm cut away (I did shed a few tears) the backing plate can be used as a very high impedance probe for the Keithley 610C electrometer. The world of electrostatic measurements is sort of an orphan area of science. There's a lot to be learned before one can say that they really know how to make the measurements. I'll have to say that I find non-contact instruments fascinating to work with!
Attachments
6-P1030887.JPG
5-P1030888.JPG
4-P1030891.JPG
3-P1030881.JPG
2-P1030874.JPG
1-P1030870.JPG
Anything obvious in high vacuum is probably wrong.
User avatar
Dennis P Brown
Posts: 3160
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Beam on Target Progress

Post by Dennis P Brown »

The Diff Pump looks great; however, to get into the mid/low 10-6 torr you may need a cold trap. I never ran my DP since I obtained a extremely inexpensive turbo that works well but I did install a baffle to block oil vapor. The cold trap (I was going to build) was dropped when I got the turbo.

My Van de Graaff has become a strange breast that refuses to now work (???) ... since I must have a positive charge to "repeal the deuteron's" , the unit uses a NST/diode (max 12 kV) or a voltage multiplier (70 kV) to charge (depending on my desired charging points), which it doesn't for reasons that baffle me (used that twice!) ... that is holding me up. Otherwise, my unit is ready to go. Aggravating to say the least ...
George Schmermund
Posts: 262
Joined: Tue Aug 15, 2006 8:51 pm
Real name: George Schmermund
Location: Carlsbad, CA

Re: Beam on Target Progress

Post by George Schmermund »

The saturated vapor pressure of DC 704 is about 2X10^-8 Torr @ 25 deg. C. An optically dense baffle is all that's needed to easily get down into the 10^-6 - 10^-7 Torr range with a DP. An LN2 trap is for freezing out the condensable vapors (mostly H2O) that haunt most high vacuum systems. At this point the goal is to test the DP characteristics and to find the breakdown limit of the tube electrodes. The pressures that I'm working with now are in the low 10^-6 Torr range and that's fine for the time being.

The VdG That will provide the HV for a beam on target system is triboelectrically charged and generates about 50 microamps of current. Further tests are underway to see how much the current can be increased by changing the roller materials. The belt is made from Nylon. The charging rate is controlled by the drive motor speed.
Anything obvious in high vacuum is probably wrong.
User avatar
Dennis P Brown
Posts: 3160
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Beam on Target Progress

Post by Dennis P Brown »

Using triboelectrically charging method for a Van de Graaff (VdG) can be problematic since an ion accelerator requires a specific polarity. Of course the direction of the ions relative to the VdG also determines the needed/required VdG polarity, as well.

Assuming you are using the standard method for your accelerator system (VdG as the voltage source with the ions released at the VdG), then generating the correct polarity by the VdG for the given ion is critical. Depending on roller materials for the triboelectrical charging, your system's polarity will not necessarily be correct - while some claim that the desired polarity can be achieved using a given bearing material at a given place in the VdG, that is dicey. Most sources recommend that a desired "charge" polarity be sprayed on the lower belt. Most all author's claim that at least the base roller in the VdG be metal to create enough charge transfer to created the desired polarity (haven't had time to test that issue so I can't say one way or the other.) Some say both should be metal (appears to be correct following the logic of triboelectric charging) if a charge is sprayed onto the belt. This, along with the emitter material type/design gets complex or simple depending on the source; this has proven rather problematic for adapting a commercial unit.

This was the issue that has plagued my VdG system for the last year and what I referenced in the post - the designs on line just didn't work as shown. While I recently fixed the problem with my VdG so that the emitter/collector now enable my upper globe to hold 200 kV VdG with the correct polarity (positive for my system to accelerate deuterons), the fix did not follow any standard design - while the emitter electrode for my VdG does use the classic HV NST power supply w/diode (and anything above 7 kV appears dangerous to belt operation) my system also has a rather unusual (currently) emitter design -more strangely, I was forced to set the emitter electrode in direct contact with the VdG belt - that does not directly follow any design I've seen or read about. But it works, so I'll use it. Of course, the poor design of the upper roller bearing for this commercial VdG has now failed and needs a major redesign (of course.) That has been completed but remains untested - so far.

The bottom line is that for any ion accelerator system that will use a VdG system the polarity issue is critical.

Aside - the very hot oil in the DP when it is running creates a far higher vapor pressure that can back flow causing contamination issues so I hope you are correct and a cold trap isn't necessary. That could be a concern for a accelerator and its electrodes even with a baffle system.
George Schmermund
Posts: 262
Joined: Tue Aug 15, 2006 8:51 pm
Real name: George Schmermund
Location: Carlsbad, CA

Re: Beam on Target Progress

Post by George Schmermund »

Dennis - You have such interesting insights into many areas of Science and Technology! I just wish that I could grasp their meaning.
Anything obvious in high vacuum is probably wrong.
User avatar
Dennis P Brown
Posts: 3160
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Beam on Target Progress

Post by Dennis P Brown »

Glade to read your posts on this subject (seriously) and your very interesting project. I see you do not care for my posting's relative to your work so I'll cease.
Bruce Meagher
Posts: 148
Joined: Thu May 12, 2011 11:25 pm
Real name: Bruce Meagher
Location: San Diego

Re: Beam on Target Progress

Post by Bruce Meagher »

I'm impressed how you’ve shrunk the size of your diffusion pump, and your latest design appears to be smaller than Agilent’s little AX-65. It’s been nearly a century since Gaede first invented what would become the modern diffusion pump so I have to ask what is a “new [diffusion pump] design...that can operate in an unexpected way?”
George Schmermund
Posts: 262
Joined: Tue Aug 15, 2006 8:51 pm
Real name: George Schmermund
Location: Carlsbad, CA

Re: Beam on Target Progress

Post by George Schmermund »

Bruce - Thanks for the inquiry. I'll start a new thread over in the vacuum forum and explain the new pump design.
Anything obvious in high vacuum is probably wrong.
Post Reply

Return to “Other Forms of Fusion - Theory, Construction, Discussion, URLs”