Langmuir Probe

4 01 2010

If you wish to replicate the Sydney experiment, you must first obtain a Langmuir Probe.

I have requested quotes for these commercial Langmuir Probes:


Automated Langmuir Probe (ALP) System


BTW, how do you pronounce Langmuir? I imagine it rhymes with “pang-doer” or maybe “ma-doer”. ANSWER: it rhymes with lang-meer.

Q&A with Joe Khachan about copper coil Polywell

4 01 2010
To gather more information on the Sydney copper coil Polywell, I emailed the project leader Joe Khachan with some questions:


Q) What journal will this research be published in?
A) We haven’t decided yet.


Q) When will that journal article be published?
A) We have not written it. We need to obtain some final results before publishing.


Q) Is your ceramic magrid made from off the shelf parts?
A) The formers for the coils are made from Teflon. This is readily available and easy to machine.


Q) Are the copper coils in your magrid at positive potential or ground potential?
A) They are floating. The coils are not running at high voltage. Moveover, they are made of enamelled copper wire so biasing them will not help. By floating I mean they are electrically isolated from the whole system. The cathode that produces the beam is negative with respect to the chamber. A better way to do this is to make the Bussard polywell, where the rings are biased positively. As I say, we are doing it in this way to understand some of the physics before committing ourselves to a final design. The way we are doing it enables changes to be made very quickly.


Q) Are you only injecting electrons at this point? no deuterons?
A) Yes, electrons. There is hydrogen background gas in order to produce electrons from it.


Q) Why is the electron beam entering the magrid at an angle instead of being aimed right in the center?
A)That was one particular experiment of many. Other experiments had the beam going in normal to the faces. One reason for the angle is so that the electron beam doesn’t touch the langmuir probe at the center. Other reason is to see if the depth of the well changes with angle of beam.


Q) How are you measuring the depth of the electron well?


Q) What are you using for your electron gun?
A) A metal cylinder (as shown in the photo) placed at -10 kV in a few millitorr of hydrogen gas will produce the beam that you see.


Q)  How deep was your vacuum prior to electron injection?
A) Our base pressure is 10^-3 millitorr but we operate at a few millitorr, so we are not replicating Bussard’s polywell exactly since he operated at lower pressures, but at a few millitorr we can gain valuable insights before committing ourselves to a more involved experiments.


Q) What are the dimensions of the magrid?
A) The dimensions we have are quite arbitrary and are unlikely to produce any substantial fusion at this stage since the well may not be deep enough. However, the space between the inner faces of the spools is about 5 or 6 cm – very small.

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