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Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Wed Oct 11, 2017 5:43 pm
by Shireesh Apte
We are in our first preliminary stages of building a plasma (not necessarily a fusion reactor) at this point.
We are still trying to get a low enough vacuum. We obtained a Fieldspace micron vacuum pressure gauge but we have been unable to pump down to below 500 microns (its upper set reading). I am going to change out the plastic tubing we are using for SS tubing sometime this week. We are using a 2 stage, 4 CFM rotary vane vacuum pump for now. The pump indicates that it can go down to 3 X 10^-1 Pa, or 2.25 X 10^-3 mmHg (2.25 microns). I realize that this magnitude may not be reached, but it seems to me that it should be able to pump down to <100 microns, where one could get a plasma. I have attached the gauge to the vacuum pump inlet.

My objective is to get plasma before I plunge into the fusion part of this project. Is it at all possible to get a vacuum of < 500 microns using silicone tubing? I am currently using garage door grease on the barb fittings before inserting the tubing over them (I received a reply as to why this was the incorrect approach so I will abandon it) to hopefully get an airtight seal but I am beginning to have serious doubts as to whether this is possible - hence the planned change to SS tubing with proper NPT adapters.

As regards the fusion part, I have a 4 way SS cross (2.75 inches) with CF flanges. I have ordered three CF to female NPT adapters with copper gaskets and one CF quartz view port. We have a deuterium supplier that we found and contacted thanks to these posts. Our Chinese Electroprecipitator unit is still functioning and the (extremely) brief user-guide on ebay says it can do a maximum of 60 KV, but we have never measured the output voltage. We will order a diffusion pump when we have plasma.

Best,
Shireesh Apte

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Wed Oct 11, 2017 6:55 pm
by ian_krase
Regarding the electroprecipitator: This may work, or it may not -- to do fusion you must be able to run negative polarity with high current (5-50 mA) and high voltage (25-100 kV) at the same time. Please keep in mind that safety precautions for these very high voltages are much more stringent than those for lower voltages to the tune of 5 to 15 kV. Voltage measurement above 40 kV is likely to be expensive or homebrew. Keep in mind that at these voltages the electricity can leak through the air, cause corona, blow through a good many mm of insulating material, and attract lightweight objects with electrostatic attraction. It can also leak along the surface of an insulator.

A much safer option for initial tests is a neon sign transformer or oil burner ignition transformer (often cheaper and easier to find in the old-fashioned iron core type which is needed).

Can you post a picture of your setup and your parts? While NPT connections can be used in vacuum, they are generally considered undesirable because they are sometimes tricky to get leak-free (the best option is to glue them together with Loctite 209).

Silicone hose would probably work for what you are planning to do, as long as it seals to the hose barbs and does not collapse, but it's generally avoided in high vacuum because air can seep through it. Other rubbers (such as Buna-N and Viton) are better.

I am curious what kind of stainless tubing you are planning to use. If it's just "a tube made of stainless", that's great. If it's flex hose, you'll want to be careful that it is actually stainless on the inside as well as the outside and capable of being reliably connected.

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Sun Oct 15, 2017 5:08 am
by Jerry Biehler
Silicone tubing should be fine as long as you can get it in a thick enough wall that it wont collapse or shove a spring down the length to support it. Even generic pvc tubing is fine at roughing pressures as long as you can keep it from collapsing. Tygon vacuum tubing is just a flexy PVC. Gum rubber too, that is the traditional vacuum line from way back, it's a reddish rubber.

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Sun Oct 15, 2017 11:34 am
by Shireesh Apte
Thank you Ian, Jerry,

The pictures - second iteration (without the vacuum set up - as that is at school) are below:

https://drive.google.com/drive/folders/ ... sp=sharing
https://drive.google.com/drive/folders/ ... sp=sharing

My first iteration was mason jars with playdough as vacuum holder. I have moved on to the second iteration. I went to the container store and bought SS containers with acrylic lids. I drilled holes for the high-voltage feed-through and for the vacuum line into the acrylic lid and JB welded the vacuum hose barb. For the high-voltage feed-through, I have a flared 1/8th inch compression fitting that I JB welded to the acrylic. I acquired 1 foot, 0.094 inch ID ceramic tubing from McMaster and cut it into 2, 6 inch sections using a dremmel with a 1 inch diamond tipped cutting blade. I then inserted an 11 gauge (diameter 0.0907 inches) copper wire through the ceramic tube and joined one end to the inner grid (that i made from 18 gauge galvanized steel wire. The other end of the copper wire was JB welded to the ceramic tube (away from the plasma locale) so that some copper wire projected out of the ceramic tube. This apparatus was then fed through the compression fitting and the nut tightened at the appropriate spot on the ceramic tubing such that the inner grid was approximately in the center of the SS jar. ( I might add that I also applied JB weld to the compression fitting to ensure a vacuum seal).
The acrylic lid with the vacuum fittings and the high-voltage-feed-through was then JB welded to the SS container (see pictures for details). I plan to use this next week with the silicone tubing and the pump with my chinese electro-precipitator to see if I can get plasma. The center grid will be negative and the SS container itself will be positive. I will post pictures of the whole set up next week.
I realize that this content is better suited for the "fusor construction" forum so I will post it there as well. I thought I would post it here so that there is continuity when I post the vacuum set up (and the complete set up) pictures.
As you can see from the pictures, this apparatus will be used to generate a plasma. The 4 way 2.75 inch cross with the CF flanges and 1/4 inch, 1.5 inches hex bolts, nuts, washers and copper gaskets are for the fusion part of the project. For the fusion, I plan to use a 1 mm thick tungsten wire that I acquired from ebay-china. I also need to get a diffusion pump. I have a deuterium gas supplier that I found on these forums. Is there a store that I can get SS rigid tubing (for starters -I am looking at 1/8th inch male fitting to connect to my 1/8th inch female built in the CF flange).
Best,
Shireesh

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Sun Oct 15, 2017 2:30 pm
by John Futter
Shireesh
we prefer that pictures are embedded on this site not a link o another picture sharing host.
Some time in the future the external host will dissapear leaving dead links making this whole post somewhat worthless
To get to the required size use irfanview a free picture manipulation app that you can resize resample to 1024 x 768 which is the best size for this forum

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Sun Oct 15, 2017 8:29 pm
by Shireesh Apte
Image,
Obviously, this method of inserting the link between two Image HTML tags does not work.
John, This is going to take me some time until I can figure out how to do this. Best, Shireesh

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Mon Oct 16, 2017 4:56 am
by John Futter
Shireesh
you are not getting it
no links
put the picture on this site natively
check out the attachments button directly below (next to options) all of this that we type
go and select file
then put it inline

no links to external sources!!!

all should be internal to this site

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Mon Oct 16, 2017 6:54 am
by Shireesh Apte
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Testing to see if this works for inserting pictures. Shireesh

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Mon Oct 16, 2017 4:19 pm
by Dennis P Brown
Acrylic lids will not work very well - even for a simple plasma. It will allow you to get a plasma but it will be a mess after a while. Do make a glass lid system sooner rather than later.

Also, as the electrode heats up, epoxy will really out gas and the acrylic lid may melt. All that may even fail rather quickly so be aware of those issues.

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Mon Oct 16, 2017 7:25 pm
by Shireesh Apte
Thanks Dennis. Is there a way to cut holes in glass similar to my acrylic set up please?
I ran the reactor today in my lab. I do not think I obtained a plasma but did get some very good ionization glow. As you can see from the pictures, the plasma seems to be confined to the region in between the central grid and the bottom of the SS container. I suspect this may be because, I made the central grid too 'dense' with more metal than air (partial vacuum) so that there is hindered acceleration in the grid ( I may be dead wrong about this and I welcome corrections and suggestions). I operated the Variac at 120 V. The white (step up transformer) device you see plugged into the variac increases the voltage to 230 V that the Chinese electroprecipitator (CE) unit operates on. I operated the CE at full voltage. Again, I am unable ( thus far) to measure the actual voltage fed into the fusor. I taped the positive to the SS vessel and the negative was alligator clipped to the copper wire that jutted out of the high-voltage feedthrough from the ceramic tube.
Since this is a vacuum post, I come finally to the pictures of my vacuum pump. I tried to pull a vacuum in the morning with the Fieldspace micron gauge attached to the inlet but it did not get past an overload (OL) reading. I hence swapped out the micron gauge for a coarse vacuum gauge. This is what is depicted in the pictures. It read approximately -29.5 inches Hg. I don't know why one would have a gauge that is supposed to be read with a negative sign. However, I figured, that -29.5 inches Hg was equivalent to -(29.5 x 2.54 x 10) mm Hg or -749.3 mm Hg. I took this to mean that the actual pressure in the vessel was [768.1 (barometric pressure today in Euless, TX) -749.3] = 18.8 mm Hg or 18800 microns Hg. This is my real conundrum as to why the pressure does not decrease to at least in the 100 micron region range (especially when the pump says it can pull to 5 microns).
I then shut off the vacuum pump. The pressure remained steady at -29.5 inches Hg for a good 10 minutes indicating that I did not have any major leaks in the system. The plasma is when we ran the apparatus in the afternoon. By the way, I used glycerine to attach the silastic tubing to the hose barbs on the vacuum pump and on the reactor.
At this point, I think I will make another version of the same reactor with the following design changes: make the inner grid so that it has a lesser metal/air ratio, position the inner grid so that the distance between the inner grid and the bottom wall of the SS container is increased. I still need a way to get to at least 1000 microns ( don't know how yet but will ruminate on this). Suggestion welcome.
Best,
Shireesh Apte


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Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Tue Oct 17, 2017 12:16 am
by John Futter
Waterjet cutting shop will cut glass of any normal thickness up to at least an inch thick

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Tue Oct 17, 2017 7:05 am
by Dennis P Brown
I cut holes in glass plates up to 3/4 inch thick by up to one inch in diameter easily; I bought an inexpensive set of diamond abrasive hole saw bits from china (these work very well.) I put plumbers putty around the area to be drilled. Then I fill in about 1/2 inch of water and include a drop of dish washing soap (add water as needed.) Using a hand drill (but a drill press makes straighter/cleaner cuts) - I drill through the glass slowly: raise and re-engage the glass hole with the bit often to let the bit/glass drilled area cool. I have done many cuts and never had an issue except when using a hand drill: using such a drill allows the bit, at first,to try and "walk" away across the surface. A steady hand and trying to get the bit edge to bite into the glass (don't push too hard but rather, very, very slightly, favor a side) to anchor the cut is all you can do; a drill press avoids this issue. If you have a drill press, always use the highest speed setting.

Well, I guess Richard can add your name to the plasma club. You should PM him with the request and reference your plasma results.

Looks like your pump has issues or else the vacuum gauge has issues; or both. My guess is the pump since it does not appear to be a two stage unit. Do show a picture of your vacuum gauge system (the micron unit.) You should easily get below 1 torr with most vacuum pumps. Micron gauges, cheap ones or TC ones do have issues with pressures in the high range close to 1000 microns. So you could be near 800 microns and the gauge would still not record this. Maybe a better gauge (there are good gauges that read in the low torr range to sub-torr accurately but cost can be an issue.) That is why most here get a high end two stage pump and use inexpensive TC gauges to read microns since our pumps easily get down to a few microns or less. It all depends on ones available funds, knowledge and skill set/experience. One only gets experience by trying like you are now doing.

A few minor notes: we do not use inches of Hg here; torr is often used here (or one can use SI units: Pascal or Bar.) There is absolutely no such things as "-749.3 mm Hg"; yes, refrigerator people use negative inches of Hg to spec the difference from atmospheric pressure but do not use those units in high vac work nor use them here; you need to learn what units are and mean. Atmospheric pressure is about 760 torr; 1 torr equals 1000 microns. At and below 1.0 micron one uses scientific notation for torr units; i.e. 1 micron equals 1*10^-3 torr.

One does not refer to a vacuum chamber as a fusor unless one has a system that can handle real attempts at fusion (i.e. will need deuterium, and at least the ability to create the required power/voltage in an acceptable vacuum.) Nor is it a reactor unless one is doing real fusion - a very high bar to achieve because one must prove that statement (this issue is not relevant here.) However, do keep at it. You are making progress and that's how one can achieve a goal of getting in the neutron club.

Don't get discouraged: I have generated and detected neutrons and I am still struggling to learn elementary aspects about high voltage multipliers (lol.)

To get started in any real high vacuum work the first two absolute requirements are a good two stage pump that gets down to a few microns (i.e. below 2 or 3 mircons; generally mfg will claim sub-micron) and a gauge that accurately measures microns (100 and below.)

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Tue Oct 17, 2017 11:11 am
by Shireesh Apte
Thanks Dennis, John,

I am using a 2 stage, 4 CFM rotary vane vacuum pump. The pump indicates that it can go down to 3 X 10^-1 Pa, or 2.25 X 10^-3 mmHg (2.25 microns). I realize that this magnitude may not be reached, but it seems to me that it should be able to pump down to <100 microns, where one could get a plasma. I have attached the gauge to the vacuum pump inlet. If I indeed have generated a plasma, then it would seem that the pressure is much lower than what the roughing gauge displays (calculated to be 18800 microns or 18 mmHg). The issue I am having is that when I attach the micron gauge to the pump, it always reads OL(overload) ( I have seen it read 5000 microns before). Therefore, I am going to attach the micron gauge to my set up again and tighten the connections. I should be able to do this today.
An accurate pressure reading will help me when I eventually run a diffusion pump and start to work toward fusion.
I have pictures of my roughing pressure gauge, vacuum pump and micron gauge below.
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Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Tue Oct 17, 2017 11:34 am
by Shireesh Apte
Here are pictures showing the micron vacuum gauge connected to the pump. I have been pumping for about 2 minutes now with the gauge still reading overload. I will try for about 15 minutes later.
Best,
Shireesh Apte
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Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Tue Oct 17, 2017 12:55 pm
by Dennis P Brown
Well, a number of issues: the connections you are using are not suitable for vacuum work - those compression fittings are extremely difficult to get a good quality seal and it is best if you abandon them. Your "micron" vac gauge is not using a standard connector either and those types that it has may cause issues with high vac.

Unless you can get below 50 microns, a diffusion pump should not be used.

The plastic line you are using isn't suitable for vacuum work - the plasticizer will out gas badly.

You need to look at kf flange systems (they use o-rings) and work very well for most fusors. These can be had rather inexpensively on ebay - especially used systems. Mating to your gauge isn't going to work so maybe best to get a conventional TC gauge that reads in the microns (but are fairly useless above 200 microns.)

Try pumping just on your vacuum gauge - having a plastic line still connected isn't the proper method - use just the gauge head. See what the pump can do. If it still can't read then either those compression fittings are leaking terribly or else the gauge is no good or the pump is no good or some/all of these.

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Tue Oct 17, 2017 3:20 pm
by Richard Hull
Dennis is correct. How are you to diagnose your pump and find how low it will go when also pumping your system??? Your system might be the source of leaks. Attach the gauge and only the gauge to the pump inlet.... no hose allowed.

Richard Hull

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Tue Oct 17, 2017 9:01 pm
by Shireesh Apte
Thanks Dennis and Richard,

I actually did do this some weeks ago with ambiguous results - I don't remember what the exact reading was on the micron gauge ( my apologies, I have too many students clamoring for grade betterment now that it is almost the end of the quarter). However, I am going to do this again by removing the barb fitting and mating the pump with a proper screw on end-cap. I agree, I want to see the micron gauge read between 1 and 10 microns or slightly above so that I can then install the diffusion pump between the fusor and the rotary vane pump and move on with the fusion part of the project.

Best,
Shireesh Apte

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Tue Oct 24, 2017 12:46 pm
by Shireesh Apte
As you can see, after attaching the micron gauge (still with a compression joint) to the pump inlet, I get a reading of approximately 1.4 mmHg (1400 microns) after pumping for 20 minutes with a 2 stage 4 CFM rotary vane pump. The pump comes with a female flared threaded 3/8th inch to which I have attached the compression fitting of the micron gauge. The next step will be to apply loctite to the joints and check pressure again.
I am in the process of ordering NPT to KF-25 adapters but I don't know if they will work with a flared fitting. I am shooting for a vacuum of at least <100 microns using the rotary pump alone.
Best,
Shireesh Apte
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Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Tue Oct 24, 2017 2:26 pm
by Nnnnnnn
Shireesh, my pump is 1/4" flare. If you want to go to any other connection type you need a special adapter. I got a flare to 3/8" BSP adapter it comes with a piece of copper that you have to put in between the flare and the adapter to get a good seal. I had to contact the pump manufacturer to get the adapter. In the thread I started on my TC gauge you can see I got about 4 out of 10 mV out of the gauge. This is because I did not use a sealing ring on the BSP connectors. This is more than good enough to start my turbo though.

Which secondary pump do you plan on using? Afaik a diffusion pump will need a lower fore pressure than a turbo (mine is rated at 14 mbar)

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Tue Oct 24, 2017 2:52 pm
by Dan Knapp
From your pictures, it looks like your tubing is Tygon rather than silicone. Tygon tubing is commonly used on vacuum systems for forevacuum lines, but in larger diameter than yours. The tubing you are using is very small for a forevacuum line; the low conductance of the narrow tubing will significantly reduce your pumping speed. Tygon forevacuum lines must be heavy wall or have a metal spiral spring inside to keep the wide bore tubing from collapsing under vacuum. The plasticiser in Tygon is usually dioctyl phthalate, which has a vapor pressure in the 10e-7 Torr range; thus it is not a problem in forevacuum lines. Hose barb fittings are commonly used with Tygon forevacuum lines, but with hose clamps. Properly assembled compression fittings are adequate for forevacuum lines, but again yours are very narrow bore for this application.

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Tue Oct 24, 2017 3:27 pm
by Dennis P Brown
Then either the pump has issues, the gauge does or more likely, your connector system is leaking very badly.

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Tue Oct 24, 2017 8:52 pm
by Richard Hull
This close to the pump, even a 1/4" hole should yank down to well below 100 microns in seconds! (assuming all clamping is good, which it may well not be.) Even a rotten trashed out pump, at the head, sealed well, should sink below a torr!

Richard Hull

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Tue Oct 24, 2017 9:06 pm
by Shireesh Apte
Thanks Niels, Dan, Dennis,

I put loctite on the fittings and started the pump after the loctite had hardened (approximately 4 hours later). The micron gauge almost immediately read 110 microns (a significant improvement from 1400 microns), but began to creep up so that it was reading about 400 microns a minute later. At this point, I stopped the pump and could distinctly hear the hiss of air ingress. The micron gauge immediately displayed overload.
Hence, I have liberally applied loctite to all the fittings and will start up the pump again tomorrow. I find this highly encouraging as it indicates that the micron gauge and the pump are apparently functioning as intended. If I stop all the leaks, then I should be able to try my 'container store' plasma chamber again, hopefully with a plasma being generated this time.
Once I am confident that I can produce a plasma , and the rotary vane does go below (or hovers at) 100 microns, then I will purchase a diffusion vacuum pump (still costly with >$400 for a rebuilt one on dunway) but I will query ebay as well. I already have a 2.75 4-way SS with 3 conflat flanges adapted to 1/8th inch female NPT. I have ordered 3, 1/8th inch male NPT to KF-25 adapters. I also have a 4th conflat flange view port. I have the necessary hardware, copper gaskets, and 1/4th inch hex bolts and nuts to assemble the fusion chamber. I am going to go with the same design for the high voltage feedthrough as I have for the plasma chamber (please see an earlier post for details)
If the tubing starts to collapse; as suggested I will either put a spring or hard material inside to hold it up or switch to a Teflon or SS tubing. For the fusion part of the project, I aim to switch to SS 1 inch with KF-25 flanges that adapt to whatever tubing I have coming out of the pump/fusor.
Thanks again and I will post pictures again sometime this week. Still a long way to go but getting there slowly but surely.
Best,
Shireesh

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Wed Oct 25, 2017 2:07 am
by ian_krase
I highly suggest searching for diffpumps on ebay, repeatedly, over time -- and also at local surplus stores if they exist where you live. It is *very* hard to ruin a diffpump except by losing the jet chimney from the inside. This is in blatant contrast to every other kind of vacuum pump or vacuum equipment except simple pipe fittings. Of course, repairing one assumes some degree of tools and skills.

I don't know if anybody here, except a few super-experimenters with deep pockets, ever buy anything but pipe fittings new or factory refurbished.


Diff pumps of the size you want on ebay are now somewhat uncommon and sell at a high-ish price -- or periodically sell at a very low price from people who don't know what they are selling or do not care.

As far as connecting your fusor chamber to your diffpump, this is almost always done by directly attaching the fusor to the pump flange (ideally with a valve in between). High vacuum does not like flowing through narrow pipes at all, and your pump is only as good as the smallest diameter aperture.

Since you have a micron gauge (almost certainly some form of "thermocouple gauge") you can try spraying Dust-Off or isopropyl alcohol on your pipe fittings to find the leaks -- this will cause a change in the gauge reading. If you have a plasma running, it will also change the color and appearance of the plasma almost immediately. I also like applying loctite or other sealants while under vacuum.

Re: Silicone tubing with hose barbs OK to pull low vacuum?

Posted: Wed Oct 25, 2017 5:53 am
by Dennis P Brown
Hello and welcome to the world of vacuum leak detection/control - seriously, this is an issue that can plague anyone but making matters worse is not the solution here - i.e. using sealants to patch worthless hardware. Until leaks are in the micron class, chemical detection isn't the method - ones ears (as you now know) works best.

Your fittings are beyond useless as you are seeing only too well; so wasting time and effort on "sealing" them isn't worth the trouble because they will continue to fail. Having a decent vacuum pump - while the central purchase and minimum requirement to start on real vacuum work - is a necessity, it isn't sufficient as you have now discovered (no doubt to your aggravation. Many of us have had similar issues so don't get discouraged.)

Relative to getting a diffusion pump (DP), hold off. If a "steal" for a DP appears on ebay, do get it (but remember THREE critical points about those devices: the heater must work, the main opening must be something you have the ability/funds to connect to, and one will need DP oil (it isn't included.)) If you can handle water cooling that is a big plus since there are more of these types of pumps available and often at good prices. Do note what I said to start - only buy one if the price is really good (and they guarantee a working pump or money back w/shipping.) However, you are not ready for high vacuum - you are struggling to still get below a torr! Also, getting below 100 microns (barely) is not acceptable for a DP's health and operation. Your system should get below 10 microns with a good two stage vacuum pump like you have. Until that, your system is leaking too much and oxygen will steadily fry your DP oil.

There is no way around the need for proper vacuum fittings with high vac - zero. That gauge will NOT work (seal) properly with that worthless connection fittings. Get a proper thermal couple (TC) or similar gauge (They can be had for low cost if one is careful.) Richard offers these, I believe.

What you need bare minimum for HV if you are serious about making a real fusor (before a DP is obtained):
1) Your pump and system reaches below 10 micron and leak back rate (a subjective measure here) really shouldn't exceed a micron/second and rapidly slow and plateau so that over a few days, the system will then reach a few torr- that implies your system is tight but undergoing normal out gassing issues.
2) A gauge that measure accurately (below 50 microns and doesn't make connecting to std fittings an issue.)
3) A coupling to your fore pump that converts it to the std vacuum fittings you select for your arrangement.
4) Decide upon your chamber design and be certain you fittings work with what you settle upon.

Remember: a high vac system does not need sealants, or loc-tight, or even vacuum grease (except possibly for o-rings but follow std vac techniques for applying) to hold a good level of vacuum; if one uses those, then something is wrong: either a bad connection or a damaged seal system.

Ian is correct - one must use as large a diameter as possible from a fusor to a DP. A gate valve of some type is essential if you plan on using deuterium (otherwise, usage will be extreme.) Your chamber will be, I assume, the four-way connector. That should work well but the DP will have to couple with that "chamber".

A plasma can easily be produced even at a torr using a neon-sign transformer (NST.) Again, these units are worthless for fusion but good for many other applications (I have two on hand and use them all the time: one powers a voltage multiplier (which I am posting too much on), another I use to test diodes and voltage dividers.) However, I got them very cheap - otherwise, no way since these are specialized devices unique to my needs.