Low-loss top terminal design

From:  Gary Lau  03-Jul-1998 1142 [SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent:  Friday, July 03, 1998 11:06 AM
To:  tesla-at-pupman-dot-com
Subject:  Low-loss top terminal design

>The resistance of the top terminal has recently gained
>new importance considering the high frequency nature of output arcs.  There
>is evidence that a highly conductive, RF friendly top terminal will support
>longer arcs much better than a sloppy resistive terminal.

The construction method most frequently suggested in the archives uses
some toroidal form, covered with adhesive-backed aluminum tape, applied
in consecutive and detached strips.  There would appear to be no good
connection between adjacent strips, due to the insulating nature of the
adhesive, except for chance contact at the edges and capacitive coupling,
and adhesive breakdown under high voltage differentials.  When I built
mine, I used a conductive center disk, sized so that it was a secure
press-fit with a length of conductive EMI gasketing mesh between the disk
and the ID of the toroid.  This connected all of the individual strips to
the center disk.  Then I covered the joint with hot melt glue to keep it
stable.  I wonder if lacking such a strip-joining method compromises the
top terminal performance?

Gary Lau
Waltham, MA USA