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Yet more Horrors in the fusion story.

Posted: Mon Aug 27, 2007 9:26 pm
by Richard Hull
Steve Blasing and I chatted the other night as I was getting my facts in line and rechecking some data related to the ITT effort.

Steve is a d-mned good tech and knows his stuff. Now in his late seventies, his memory is almost as sharp as Genes was on specific events.

Steve and I chatted about the electron multipaction method and its abortive result. Steve told me something I never knew even though the perfesser and I sat down with he and Gene a few year ago in Fort Wayne for a full day long interview.

Steve said that so far as he was concerned the actual workability story on the Farnsworth electron multipactor concept was not really in! As he went into the technical elaboration for this bizarre statement, I realized he might just be right, at least as far as good data gathering went during the tests.

I seems that in those early days when Farnsworth was working with the top hat system, (bell jar, solid hollowed dynode), they looked to a capacitive coupled, choke blocked, modulated HV using a 1-2KW RF amp driven by a generator that could go up to 800mhz for attaining the multipactor mode.

Steve came on as a part time, inter-departmental "share, as needed", tech right at the tail end of the Mark I system. He, said that he was specifically brought in to help with the great difficulties they were having with the RF gear. He said he was floored to see what was happening. He yelled to me that "there was no match" and no way to match the system at all frequencies and no one had a clue!

Apparently, there was a long encased and encapsulated capacitor used for coupling that no member of the team knew the value of, nor did they know the value of the choke. (also entombed in the guts of the device).

No one would allow the device to be taken apart as the ITT people were coming for the grand inspection and they did not want to take it apart with the associated issues involved with re-bakeout and possible damage of the now working system.

Steve said that he assembled an incident and reflected power hook up and tweaked the system as best he could at the frequency they were interested in at that moment. He noted that after he did this, they never bothered to readjust in any future test and he was constantly having to repair the power amp which cooked due to mismatch or the RG-9 cable that fried several times due to a voltage node or reflection. He was always called only after a disaster to clean up.

Thus, as Farnsworth envisioned electron multipaction in the system, it may never have been optimally tested!!! GEEZ Louise! Or as Steve said, "Garsh, those guys just didn't have a clue!"

His efforts ultimately were recognized by Farnsworth, who tended to recognize talent. But it was only after they switched over to ion based fusors that Steve was called upon to work full half days on loan as an actual part of the fusion effort. Ultimately, in late 1963, he was yanked or transfered permanently to the fusor team as the techical aide to the just hired, Bob Hirsch.

So was electron multipaction and the super virtual cathode viable? Maybe not, but it looks as if the original fusor team did not do the job to a level that Farnsworth perhaps envisioned.

Oh well, more sadness.

Richard Hull

Re: Yet more Horrors in the fusion story.

Posted: Mon Aug 27, 2007 10:48 pm
by Starfire
Like most of the fusion effort, it is a big jig-saw and the full over-all picture never seen. It would appear that the Farnsworth team ( before Steve Blasing ) did not understand RF techniques - which was a refined technology at the time. Any Rado Amateur of the day, worth his salt would have understood load matching. Or as Steve said, "Garsh, those guys just didn't have a clue!"
- it was physicists presuming they understood radio and RF but did not have the technology skills to apply it if they did.

Technology, Engineering and Science go hand in hand and woe be it to anyone from one discipline, who does not respect the other disciplines.

A great report Richard and a valuable archieve insight into the early fusion effort. It is vital that such narrative is recorded and I applaud your effort and record.

Re: Yet more Horrors in the fusion story.

Posted: Mon Aug 27, 2007 11:34 pm
by DaveC
Fascinating, Richard!! Who'd a thunk it, eh? Thanks for yet another gem.

Was wondering, would you like to steeer a thread here or maybe, better up in the theory section, on the Multipactor as it applies to early fusion efforts of Farnsworth?

I am not clear, myself, on the need for the UHF HV drive in the multipactor. Since there have been discussion off and on here about resonance methods and etc, might be appropriate to have a thread to collect these useful discusiions.

Dave Cooper

Re: Yet more Horrors in the fusion story.

Posted: Tue Aug 28, 2007 12:59 am
by mheslep
Richard -

Great bit of history; thanks for sharing it here.


Re: Yet more Horrors in the fusion story.

Posted: Tue Aug 28, 2007 1:09 am
by tligon
I don't have any so dramatic to share, but maybe one day I'll tell y'all about the expectations that electrons have a positive charge.

Or not paying any heed to Nyquist.

Or unprotected +/- 5V instrument amps hooked directly to plasma experiments, no MOVs, no clamping, no input limiting, no filtering ...

Physicists need techs.

Re: Yet more Horrors in the fusion story.

Posted: Tue Aug 28, 2007 1:23 pm
by Richard Hull
This is in reply to Dave's general request related to electron multipacting.

Farnsworth recognized a use for the long noted problem in some UHF systems of electron knotting, which he termed multipacting. For a short while Farnsworth and later, ITT made a small multipactor vacuum tube! (use unknown and now a collector's item)

The multipaction scheme is simple in theory. If one switches the plus and minus connections (alternating current) at just the right speed in any vacuum geometry where electrons are emitted from a hot cathode towards a plate system, a bunching or electon knot can be created. A form of electrostatic, physical, electron resonance is created, hopefully, with a single, well controled, nodal point

This was first noted and caused great damage in early UHF tubes, mainly power output tubes as grids and plates and even some cathodes were melted or damaged coupled with effective shutdown of the device, even if not damaged. The problems were solved by mostly geometric considerations. (making the devices smaller, internally.)

Farnsworth sought to create a physical, spherical, electron knot or virtual cathode in the center of his "Mark I" device, (1960-62). It was hoped this massive current locked wad of electrons would accelerate deuterons to itself and, if missing the electrons, would collide with the usual infalling deuterons from the opposite direction and fuse. (gridless fusor)

This is a tricky business, at best, and while sounding theoretically simple is very difficult to physically achieve. While multipacting accidentally happened to detrement in vacuum tubes, there was not the additional requirement of symetrical co-acceleration of positive nuclei into the knot thrown into the mix.

This latter demand is the sticking point.

More history:

There was a single tube that was designed, hand blown and constructed to Farnsworth's personal specs in 1959 Just after the program's inception. Unfortunately, it was such a horrid kludge that it was never used or tested according to George Bain. He did note that the tube lab at Pontiac Street spent over three months on the tube, discarding several models as Farnsworth almost daily had a design change. The tube lab quickly learned to drag its feet on Farnsworth requests, but it had to do so strategically as the Admiral was instantly prepared to crush and fire anyone impeding Farnsworth's progress.

Like many of Phil's brain storms, this early fusor tube turned out to be a brain fart and was never utilized, but occupied a place in a cabinet or on a shelf along with many similarly conceived and constructed bretheren.

Stories similar to Bain's were told by every team member that I have ever interviewed.

Richard Hull

Re: Yet more Horrors in the fusion story.

Posted: Tue Aug 28, 2007 1:47 pm
by Starfire
-- and Engineers :)