Re: [Phys-L] Child's Law & the Limits on Scaling Arguments & Dimensional Analysis (long)

[bernard cleyet <bernardcleyet@redshift.com>]

> On 2021/Nov/29, at 10:35, David Bowman <David_Bowman@georgetowncollege.edu <mailto:David_Bowman@georgetowncollege.edu>> wrote:
>
>  Unfortunately, essentially nobody builds vacuum tube diodes like this. Rather, they tend to use a cylindrical geometry with the much smaller cathode on the inside and a much larger anode on the outside.  



A common exception is a vacuum gauge.  Where the directly heated cathode outside a grid (+ HV to attract the emitted electrons.  Since a wire spiral many continue on and ionize the residual gas.  The + ions are coiled by the anode wire.  The resulting current is a function of the gas pressure.  


https://en.wikipedia.org/wiki/Hot-filament_ionization_gauge <https://en.wikipedia.org/wiki/Hot-filament_ionization_gauge>    

more:   https://mmrc.caltech.edu/Vacuum/Teledyne%20Hastings/Ion%20Gauges.pdf <https://mmrc.caltech.edu/Vacuum/Teledyne%20Hastings/Ion%20Gauges.pdf>  


bc   used another type in his research, the vac-ion pump.  The fore pump two sorption pumps.