Strike Rail

From:  Jim Lux [SMTP:James.P.Lux-at-jpl.nasa.gov]
Sent:  Thursday, June 18, 1998 12:45 PM
To:  Tesla List
Subject:  Re: Strike Rail

Tesla List wrote:
> ----------
> From:  Julian Green [SMTP:julian-at-kbss.bt.co.uk]
> Sent:  Thursday, June 18, 1998 4:22 AM
> To:  tesla-at-pupman-dot-com
> Subject:  Re: Strike Rail
> > The strike rail is not a complete turn with about 2" gap to avoid shorted
> > turn problems.
> > I changed it from the picture.  This time my plumbing came up to the rail
> > via a nice curve then fitted into a right angle joint (running
> > horizontally).  I concluded it could only be due to this.  So instead of the
> > right angle pipe joint I curved it with a radius of about 3".  Now the
> > problem has gone away.
> >
> > The reason for passing on this info is that I know some people have suffered
> > from breakout in the middle of the secondary but I do not recall any mention
> > of strike rail geometry's as possible problems.
> >
> > Regards
> >
> > Viv Watts UK.
> I have had a similar problem and found that any objects comming near to the
> secondary can cause corona discharge.  

Anything that disturbs the nonuniformity of the field will increase the
local Efield, and if it gets above 30kV/cm, you'll get corona or
sparks.  I control the voltage of my Van deGraaf generator by bringing a
small diameter sphere that is grounded close to it. It doesn't spark
over, but it does bleed off the charge.  In fact, this is a standard
technique for controlling VDG output, you put some sort of variable
resistance (e.g. a vacuum tube) in series with the corona point driven
by something that measures the voltage (typically the position of an ion
beam going through some magnets).