ION BEAM ???

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
Post Reply
pfostini
Posts: 124
Joined: Wed Nov 13, 2002 9:38 pm
Real name:
Contact:

ION BEAM ???

Post by pfostini »

Below are some preliminary pictures of what I think is ions impacting on a quartz window at 10-5 torr. This is with D2 metered slowly into the test chamber. The test chamber used is the one in the multipactor thread. So - is this an ion beam?
Attachments
ionbeam.jpg
3l
Posts: 1866
Joined: Sat Jul 07, 2001 3:51 pm
Real name:

Re: ION BEAM ???

Post by 3l »

Hey Phil:

Looks like you made it.
The beam I played with at school was only a microamp.
When a proton beam hits quartz,it emits blue light just like your photos.
At a microamp you need a really dark room to see it.
Your ion cone is well defined... good focus.
You are in the 10 ma range from the intensity your pictures seem to show.

Looks Good
Fusion is fun!
Larry Leins
Fusion Tech
hellblazer
Posts: 157
Joined: Wed Sep 18, 2002 12:16 pm
Real name:

Re: ION BEAM ???

Post by hellblazer »

Certainly looks like one to me. If the accellerator is negatively biased, it can't be electrons.

Something interesting would be to make a negative target for the beam, and then measure the current. The current would have to come from the ions.
pfostini
Posts: 124
Joined: Wed Nov 13, 2002 9:38 pm
Real name:
Contact:

Re: ION BEAM ???

Post by pfostini »

> Something interesting would be to make a negative target for the beam, and then measure the current. The current would have to come from the ions.

I am not sure how to do that. I already have a feedthru on the far end on the gun. I know I need to put a meter in series but when I do this would it not arc from this end to the gun.

The RF that is needed. There is no mention on the wattage required. I have stuff that goes from 10 - 2000 watts.

Starting the gun is a trick in itself because I did not include a cathode or other source of electrons. I think what I will do since my station has to ports on it is to use the other for gun testing and focusing.
hellblazer
Posts: 157
Joined: Wed Sep 18, 2002 12:16 pm
Real name:

Re: ION BEAM ???

Post by hellblazer »

Attached is a schematic for measuring electron beam current I found on the net. The set up for measuring ion current should be identical, but with the polarity reversed ('natch). No need for a suppressor supply - that's just there (I think) to prevent secondary electron emission from the collector. Nor do you need the three drift tubes.

All you really need - I believe - is just a piece of metal as the target where you have the quartz window (for example) at a negative potential (more negative than the accellerator sleeve) and connected to the positive of the accellerator power supply - similar to the schematic attached. I think you can set the accellerator potential to 400 volts or so - no need for 2,000. Perhaps this will help prevent the arcing you're seeing?

The current is measured between the positive of the accellerator / multipactor supply point and the metal target. This should be the current carried by the generated ions in the gun. If the beam is tight enough, and there's not many neutrals in the beam, the measured current should be pretty close to the ion beam current.

Well, at least that's my story and I'm sticking to it Naturally, normal disclaimers apply.
Attachments
current-measurment.gif
current-measurment.gif (6.99 KiB) Viewed 4560 times
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: ION BEAM ???

Post by Richard Hull »

All D2 ion beams are the lavender pink seen here. If at any time the beam prior to impacting the target goes blue or changes hue, you now longer have an ion stream of deuts. Blue beam means electrons and neutrals and some lower energy ions. Keep all beams focused and lavender pick right to target impact.

A dead giveaway to reduced target ion beam current is the reduction of intensity of the pink line from the gun to target.

The normal methodology has the ion gun guts at the absolute highest pressure that the filament can possibly handle. ~10e-3 torr or higher! The output of the gun traditionally dumps into a high vacuum of 10e-5 MINIMUM! 10e-6 or 10e-7 is better. Note, at deep vacuums the beam may be faint to the eye.

In this manner, the beam dispersal and interference to target is reduced considerably and the actual currrent from the guns is really what is impacting the target.

Keep the distance GUN to TARGET at the absolute minimum needed to avoid arcing due to accelerating potential. Note that this distance is more determined by the AIR spacing outside the assembly than the inside vacuum travel distance.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Post Reply

Return to “Ion Gun Design and Construction (& FAQs)”