Re: Tektronix 7104 and 7D20 showstopping?


Don Black <donald_black@...>
 

Thanks for the excellent description of their construction and manufacture. I guess the electrons entering each pore initiated secondary emission? Were the tubes lined with a conductor or the glass chosen (doped?) to be conductive, maybe with a voltage gradient. I haven't had a chance to read the article about them yet so maybe that will answer "all" (like the magazine articles "all about ....  ;-) ).

Don Black.

On 07-Apr-13 5:46 PM, Craig Sawyers wrote:
 

==========================
Is there a concept book that describes the micro-channel tube and how it
works?

Don Black.
==========================

Hi Don

Don't think so. But the concept of using a multi-channel plate for electron
multiplication actually comes from military image intensifier tubes. In
fact I got to know the British guy who developed the prototype MCP's for Tek
, now working for Photonis in Brive, France. Ray was working at Mullard at
the time, and the technology was transferred to Tek eventually. At that
time, and pretty much still, this was the largest MCP ever made.
Generically, they are made by using two types of glass - a leachable core,
and a non-leachable cladding. These are around 6mm solid for the core and
10mm tube with a 6mm hole for the cladding. Length is around 50cm to 100cm.
The fit is precision, and the individual rods and tubes are expensive.
These are assembled into a stack maybe 50mm in diameter and put in a fibre
drawing machine. The resulting rod is cut and re-stacked, and re-drawn, and
the process repeated. Eventually a large number of these approx 5mm solid
preforms are assembled by hand into a jig, inserted into a furnace and fused
together to make a solid block the final size of the MCP with the correct
number of pores. This preform is then diamond sawn into the correct
thickness slices. With the Tek MCP the slices are taken at a bias angle of
about 23 (I think it was that) degrees, so electrons can never go straight
through - they always suffer multiple reflections from the inside of the
tiny pores. After slicing, the solid slices are then immersed in
exceptionally controlled conditions in etchant to remove the leachable
parts.

For a "regular" size MCP, these are circular with maybe 25mm to 50mm
diameter. The Tek one was 100mm x 80mm.

For what it is worth the same sort of technology was used to make flexible
fibre image bundles in medical endoscopes (before the days of video
endoscopes), except this time there were three glasses. An inner and outer
of different refractive indices (ie the normal sort of optical fibre) made
of non-leachable glasses, and an outer cladding of leachable glass. Reverse
of the MCP process (stack-draw-cut-restack-etc, then cut stack fuse), after
masking the ends to prevent leaching, what you ended up with were solid
stubs that you could form an image on at one end and look at with an
eyepiece at the other, but with every fibre individual and floppy in the
metre of so between.

Craig


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