Two Stream Instability: Explaination of the fusor's electron beam
Posted: Wed Jan 05, 2011 3:05 pm
Last year I was able to make a fusor for my senior project for a completion of a physics degree. I also constructed a triple Langmuir probe, which was able to make near instantaneous and repeatable measurements of electron temperature. The process is semi-documented here: viewtopic.php?f=6&t=3022#p12532
My favorite measurements are measurements I got when I placed the probe into the well known 'electron beam' which emanates from the center of the fusor during jet mode. I got excellent data, which I didn't understand at the time. This data is attached.
As you can see, the triple probe recorded a distribution of temperatures in the fusor, which can be placed into a histogram plot, which is very similar to a velocity distribution (temperature instead of velocity, both are basically the same). I didn't understand why my distribution had two bumps until the last week of my graduate plasma physics class this semester while discussing Landau Damping. I have a much better idea right now, one which confirms the theory that this is an electron beam and it contains HOT electrons.
http://en.wikipedia.org/wiki/Two-stream_instability
Its called the two stream instability. (Please don't can me for wikipedia, this is located in Chen and I believe is mentioned in Gurnett as well. Its really easy to show things to everyone on wiki.)
'In the case of the two stream instability, when an electron stream is injected to the plasma, the particle's velocity distribution function has a "bump" on its "tail"'
In my histogram I constantly had the tiny bump on the end in all my measurements. I'm very excited about figuring out what it was and I also think that it is a nice addition to everyone's fusor knowledge base. I'm interested in hearing your comments and criticisms (Is Doug still around??)
I also feel that this makes my triple Langmuir probe all worth it; I feel that it really proves its ability to take measurements in the fusor. More of you should make this probe and see if you can confirm my data. Its really easy.
I'll be checking in for a few days, although i'm afraid i've dropped off this forum due to my project's completion.
My favorite measurements are measurements I got when I placed the probe into the well known 'electron beam' which emanates from the center of the fusor during jet mode. I got excellent data, which I didn't understand at the time. This data is attached.
As you can see, the triple probe recorded a distribution of temperatures in the fusor, which can be placed into a histogram plot, which is very similar to a velocity distribution (temperature instead of velocity, both are basically the same). I didn't understand why my distribution had two bumps until the last week of my graduate plasma physics class this semester while discussing Landau Damping. I have a much better idea right now, one which confirms the theory that this is an electron beam and it contains HOT electrons.
http://en.wikipedia.org/wiki/Two-stream_instability
Its called the two stream instability. (Please don't can me for wikipedia, this is located in Chen and I believe is mentioned in Gurnett as well. Its really easy to show things to everyone on wiki.)
'In the case of the two stream instability, when an electron stream is injected to the plasma, the particle's velocity distribution function has a "bump" on its "tail"'
In my histogram I constantly had the tiny bump on the end in all my measurements. I'm very excited about figuring out what it was and I also think that it is a nice addition to everyone's fusor knowledge base. I'm interested in hearing your comments and criticisms (Is Doug still around??)
I also feel that this makes my triple Langmuir probe all worth it; I feel that it really proves its ability to take measurements in the fusor. More of you should make this probe and see if you can confirm my data. Its really easy.
I'll be checking in for a few days, although i'm afraid i've dropped off this forum due to my project's completion.