Introduction

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Introduction

Postby Shireesh Apte » Sun Sep 10, 2017 3:10 pm

I am a high school teacher in Texas. My students and I want to eventually build a fusor. We are currently in the process of building a 'star-in-a-jar' rudimentary apparatus. We ordered a high voltage power supply (claims 60 kV at 12 mA) that is supposed to be for electrostatic precipitators from China on ebay. Its input is 220 V so we have a 110 to 220 V converter plugged into a variac that we keep at 110 V. The high voltage power supply has two potentiometers, one we assume is to turn up the voltage. We do not know what the other one is for. We have this hooked up to a stainless steel coat hanger inner grid with a 1/4 inch copper pipe as outer grid in a large mason jar with a PVC lid. The inner grid is encased in a 25% ceramic plus 75% 'plaster of paris' hardened mixture. We made this by using an outer paper cylinder to drop the wet mixture in. Then we sealed both ends with tape and kept it in a 200 C oven for 24 hours. We then removed the paper and tape. Only the spherical grid at the end is exposed inside the Mason Jar. Our vacuum system is a 3 CFM rotary vane pump that the brochure says will go down to 5 Pa absolute or 38 microns approximately. We are using play-dough to tightly clamp the PVC lid on the mason jar since we cannot exactly find a matching ID. Our gauge on the rotary vane vacuum pump goes down to minimum hence we are assuming that we are operating at approximately < 100 microns; which should be good enough to get a plasma. Our issue is that we do see a plasma but it is at the upper end of the Mason Jar, i.e. where the inlet for the ceramic encased inner grid and the copper tubing is. It is purple in color. I will ask my students to post a video of the plasma as well as pictures next week at this site. We think we may either too deep - or not too much of a vacuum. We are going to run again tomorrow with the vacuum pump shut off to see if we get a plasma at slightly higher pressures. Once we post the pictures and video, any suggestions on how to get the plasma at the center will be welcome.
We realize this is obviously the first step toward eventual fusion. We anticipate at least getting to 'jump off' point by this academic year end (May 2018). We have contacted a deuterium supply that we found on these forums. We have ordered and received a gas regulator. We are in the process of looking at ordering a thermocouple pressure gauge, oil diffusion pump, needle valve, and assorted piping and valves. We also plan to build a (8 inch) stainless steel fusor from ss plates with 4 ports (vacuum, high voltage feedthrough, deuterium supply, and porthole). We will use powdered silver kept in a moderator to detect neutrons. The idea is that thermal neutrons will convert the silver to cadmium with emission of gamma rays, which we can detect using a geiger counter.
We will keep you posted.
Best regards,
Shireesh
Last edited by Shireesh Apte on Sun Sep 10, 2017 3:29 pm, edited 1 time in total.
Shireesh Apte
 
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Posting shared link to video

Postby Shireesh Apte » Sun Sep 10, 2017 3:23 pm

A shared link to our video appears below. The video may not play when you click on the link. However, there is a download option available so that you may download to your computer and play it using your computer apps. This is what I had to do as well.

https://drive.google.com/file/d/0ByEkO9 ... sp=sharing

Best,
Shireesh
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Re: Introduction

Postby Niels Geerits » Mon Sep 11, 2017 3:38 pm

Shireesh, An easy way you guys can estimate the pressure is by measuring the voltage over and current through the fusor. You can check the FAQs on the best way to do this. I just put 100 1W 10M ohm resistors in series (15 cents each) + a single very precise 100k Ohm and a voltage meter in paralell to the 100k ohm resistor. This resistor chain is in paralell with the fusor. The current is measured by putting a 100 ohm resistor in series with the fusor and measuring the voltage across said resistor. If you measure a low voltage you have a high pressure, assuming your power supply is good. See this FAQ viewtopic.php?f=24&t=2795
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Re: Introduction

Postby Shireesh Apte » Tue Sep 12, 2017 12:09 am

Thanks Niels. We will check this out.
Best,
Shireesh
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Re: Introduction

Postby Dennis P Brown » Tue Sep 12, 2017 3:03 pm

Play-dough to seal a vacuum chamber? Really? You appear to be using very low grade stuff to build your system. This concerns me for a high school. While I have read a bit on the Chinese electro-static power supply here (and I have my doubts it will provide the power it claims) it does appear to be capable of producing a dangerous voltage/current and you do not appear to have much knowledge of electrical systems - like safe wiring, standoffs, proper high voltage housing or feed-thru design, grounding, and there is more. While I appreciate using available stuff to build a vacuum system (my first vacuum/sputtering system, also in High School, was a wine bottle with its end cut off and a 'rubber' stopper for a electrode feed-thru), this approach has no place for use with any real (or semi-real) power supply. Be careful - if its rated power can supply even a few milli-amps, then it can kill.

Any attempt at a real fusor will absolutely require you first get a gauge that reads microns and you should wait for that to come in (and this should be one of the first items you get.)

As for getting a good plasma glow, once you achieve a few tens of microns and have a power supply of a few hundred to a thousands volts (no real current required so many cheap ways to do this) a plasma glow will be struck.
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Re: Introduction

Postby Shireesh Apte » Sun Sep 17, 2017 11:52 pm

Duniway has rebuilt diffusion pumps (speed: 105 L/s) at $600. Ebay does not seem to have any diffusion pumps any cheaper either. I searched the forums and it appears that I will need > 60 L/s for a robust vacuum. Is there anywhere else I should be looking for a cheaper diffusion vacuum pump?
Thank You and Best regards,

Shireesh Apte
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Re: Introduction

Postby MatthewL » Mon Sep 18, 2017 12:38 am

Ebay is usually the best place to find a diffusion pump that is inexpensive. With enough searching a good pump can be found for well under $300. Perhaps try different search terms. It can also be helpful to follow a search so that you can get notification emails when new listings appear. LabX.com can also have options as well.

Regards,
-Matthew
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Re: Introduction

Postby Shireesh Apte » Mon Sep 18, 2017 4:12 pm

Thanks Matthew, we will try that.
Best,
Shireesh
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