DC linac #1 My first linac

For posts specifically relating to fusor design, construction, and operation.
Post Reply
3l
Posts: 1866
Joined: Sat Jul 07, 2001 3:51 pm
Real name:

DC linac #1 My first linac

Post by 3l »

Warning: The following post contains procedures that should not be attempted with out a thorough and COMPLETE understanding of the radiation hazard involved.
High vacuum is required to make this method work.
Remote operation procedure HAVE to be in place from the beginning.
Appropriated warning signs with a flashing warning light are necessary.
High voltage safety will be stringent due to the extra high potentials involved.
The radiation is short range but very intense close to the linac and the experintal area
Proper safety interlocks with keys are a must.
The local radiation will be on the order of 100 Rads or above.
It exceeds the lifetime permissible dose many fold.

Well I started trying to do an ac aproach to the trusty linac but
when Dave Cooper posted the idea of a solid state cascading voltage multiplier.... well it was all over but the shouting.

The posts are in the HV forum under:
2003-15-02 01:41 Re: High frequency high voltage generation (Dave Cooper)
2003-15-02 08:51 Re: High frequency high voltage generation (larry leins)
2003-16-02 02:49 Re: High frequency high voltage generation (Dave Cooper)

I was against any voltage drop scheme due to the losses and the resistors get hairy near the output!
Telsa coils are mean to tune and make nasty xrays when diodes are used.
The beauty of his suggestion was to tie in at each point on the voltage multiplier circuit where the voltage doubles and run the dees* at those voltages.
I didn't even think this way because I knew the history and had a mental picture of the massive set that disintegrated lithium. the 1932 cascading voltage multiplier filled a building. The Walton Crockcroft accelerator with modern parts will fit on a desk!
His idea (Dave's) is such a neat solution.
No longer do you calculate the dee* (electrode) length or sychronise anything.
No arc over due to very high potential....stages at a relatively low voltage to each other. No xrays generated during acceleration. But you are on your own bub after that!
The only critical factor is to gap the dees* (electrodes) so not to arc to it's neighbor but the dee could be a ring or very small length of pipe.
The particle could take it's own sweet time to move.
Uses availible parts that are still being manufactured.

New*******
Got glass pipe?
Build the classic electrostatic accelerator tube system w/o the Van de Graff generator.
No need for the sphere to shield the ion source
You can use the linear accelerator design of the voltage drop system by attaching wires on the bulkhead that holds the electrode.

I like metal systems so,,,,

I am currently drilling all the feedtru hole for the dees*.
A 3/8 " copper rigid tube will be cut at .5 " and soldered into a two inch copper pipe that is 12 inches long. My dees* are 1" long 3/4" copper pipe.
Yes my first unit will be soldered with silver solder at first to test the idea.
The first unit will run at 15 kv @30 ma from the dreaded neon sign transformer. Caps are 30 kv units of .0006 uf. The diodes are two microwave diodes in series.
Humm to test the p-b fuel set at 15 kv will take 5 stages to get
240 kv pretty close to the 500kv energy (collisional) required to test it out.
So the linac would need 5 dees* of one inch with a separation
of about 5 " total for ten inches total .
My pipe dealer sells by the foot.. more junk I guess.
For insulation for the dee* lead sylgard epoxy mix or vacuum epoxy.
The running pressure will be 10^-6 torr break out your diffusion pumps!
If this is your cup of tea see this post also in the HV forum

2003-15-02 15:51 DC Linac 1 power supply (larry leins)

* Sorry I was thinking cyclotron when I labeled the electrodes .

Fusion is fun!

Larry Leins
Fusion Tech
Attachments
linac dc1.ppt
(34 KiB) Downloaded 274 times
grrr6
Posts: 217
Joined: Mon Sep 16, 2002 11:10 pm
Real name:

Re: DC linac #1 My first linac

Post by grrr6 »

im not getting this, how can you have a dc accelerator with more than one stage?

Have you thought about using a van de graaff generator? Would be easy to get around 1-2 mev, with only microamps though.
DaveC
Posts: 2346
Joined: Sat Jun 30, 2001 1:13 am
Real name:

Re: DC linac #1 My first linac

Post by DaveC »

Greg -

By connecting each of the drift tubes (I think that's what Larry means by "dees") ..to a stage of the multiplier, you get progressively higher voltages as you go down the LINAC . Since the stage voltages of the multiplier are typically in 10 to 30 kV range, high voltage breakdown problems are not so severe.

You can always do the same thing with a single drift tube electrode connected to the top end of the multiplier, but the stage by stage connections tend to grade the electrical stresses more uniformly and life is just a little more pleasant...

Dave Cooper
pfostini
Posts: 124
Joined: Wed Nov 13, 2002 9:38 pm
Real name:
Contact:

Re: DC linac #1 My first linac

Post by pfostini »

Larry check this out, Hope it can give you some ideas. I built this before the fusor. Thats how I got hooked. I never thought of using the multiplier directly.
http://www.paradigmenergy.us/accelerator.htm
pfostini
Posts: 124
Joined: Wed Nov 13, 2002 9:38 pm
Real name:
Contact:

Re: DC linac #1 My first linac

Post by pfostini »

One other thing. I found those cheap high frequency solid state NST work best with the multiplier I built. I used a smaller 5 KV unit.
3l
Posts: 1866
Joined: Sat Jul 07, 2001 3:51 pm
Real name:

Re: DC linac #1 My first linac

Post by 3l »

Hi Greg:
I have used Van de Graff in the past and the accelerator would only work on dry cold days...it is a dead loss in wet weather.
Unless you put it in an enclosure in an enviroment the generator likes it is not reliable. The multiplier circuit will provide ample current for the linac (10 ma -100amps!) It works like throwing a light switch if the parts are good it will go.



Hi Phil:

Thats good news I'm using a solid state neon former for a bookend in my computer room.
Nice to know it might be good for something after all.
I have grown beyond Xformers tho.
Ripping a page from the homemade arc furnace that I did in sixth grade , I now power mine straight from the wall with no transformer.
Good breakers are needed of course!
Two chokes prevent any funny business on my power line.
I started using 220 off the main breaker but used 110v instead
so I could use a 12v inverter to power my linac.
Using this method allows you to apply solar power in order to do fusion testing for the price of nada. Well the operational cost anyway.

Re:Portability

Has anyone thought about a propane powered diff pump? I have thought for a while now that if you had a battery to run the inverter for high voltage and rough pumping and a small bottle of propane to run the diff pump. You would have a portable
fusion power unit when we get this sorted out.

Fusion is fun!
Coming Soon "Fusion Too Cheap to Meter" :p)

Larry Leins
Fusion Tech
grrr6
Posts: 217
Joined: Mon Sep 16, 2002 11:10 pm
Real name:

Re: DC linac #1 My first linac

Post by grrr6 »

I never thought about using a drift tube for each rung in the ladder of the multiplier, i would have just connected the bottom to one electrode and the top to another, and let the full potential out right there.

If you put a small van de graaff in strong enclosure, you could pressurize it, that way, you could get extra voltage out of a small top sphere. Definitely more trouble than its worth im guessing.
3l
Posts: 1866
Joined: Sat Jul 07, 2001 3:51 pm
Real name:

Re: DC linac #1 My first linac

Post by 3l »

I used a small vg generator in a tall tupperware plastic clothes container. The trouble starts over 150kv. It is very hard to control the arcs with out a steel container...at 1 mev the container is 1/2 inch thick to contain the 30-40 psi needed for arc suppression.
The unit they used at North Texas was a little over a ton in the basement lab.

Fusion is fun!

Larry Leins
Fusion Tech
DaveC
Posts: 2346
Joined: Sat Jun 30, 2001 1:13 am
Real name:

Re: DC linac #1 My first linac

Post by DaveC »

Pressurizing a Vande Graaff generator is a tried and true way to get much higher and more consistent output. Several different gases have been used. Nitrogen, Hydrogen (excellent insulator) and Nitrogen-SF6 mixes .. are probably the most common. Works well for Wimshurst machines too, especially the sectorless types. Can easily double the output voltage, with a couple atmospheres pressure.

Since the maximum voltage of electrostatic machines is related to either surface leakage or gas ionization at the high voltage electrode, raising pressure has a direct increase on output voltage.

But... the output bushing can get quite large.

Dave Cooper
Post Reply

Return to “Fusor Construction & Operation (& FAQs)”