Interesting Things
Ideas we have not got around to trying
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Field emission pulse X-ray source
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Thermionic emission pulse X-ray source |
High repetition rate gated imaging in synchrotrons |
Looking around corners |
Improving the resolution of proximity focussed
image tubes |
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These are ideas we have had but have not had time to try out.
Someone else may have already had the idea or the idea may be
stupid so we take no responsibility taken for them!
Field emission pulse X-ray source
We could build an avalanche pulser and a transformer to give
a differential voltage in excess of 50kV with a short pulse length.
A suitable vacuum field emission X-ray diode could be driven by
such a pulser to produce a short (sub ns) burst of X-rays. Such
a triggerable pulsed X-ray source may be useful for instrument
characterisation among other things.
Thermionic emission pulse X-ray source
Microwave planar triode tubes are capable of high currents
and relatively fast rise times. It should be possible to persuade
a manufacturer to fit a modified tube with a special anode with
an X-ray transmitting window. We could provide drive electronics
for such a tube. A peak current of around 20 amps and a pulse
width of a nanosecond at an accelerating potential of 10kV is
enough info to work out the X-ray signal. This could be produced
repetitively at, say, 10kHz. A titanium anode with a Be window
would give K-alpha around 5keV, suiting many laser plasma X-ray
diagnostics. If someone feels they would like to try this we would
be happy to share more details of our thoughts
High repetition rate gated imaging in synchrotrons
We can build high repetition rate gated imaging systems with
frequencies in the MHz region (HRI &
GOI). It occurs to us that this fits in
well with the excitation frequency of synchrotrons. It would be
simple to synchronise a 1MHz, few hundred ps exposure optical
camera with such a source. Perhaps there is some good physics
to do here.
Looking around corners --
This idea of ours from the 1990s has recently been tried successfully by a few university labs with streak cameras.
There's a lot of maths involved in the inverse scattering problem.
A point in the hidden image plane produces a specific time
signature for light scattered back onto the ground (expanding
rings). In principal this scattering could be deconvolved to give
info about the hidden object. Changing the initial illumination
point will help the deconvolution process.
Improving the resolution of proximity focussed imaging.
This is now implemented in our latest GOI systems with great sucess.
Whilst proximity focussed tubes can have extremely
high resolution due to the short distances that electrons have
to travel and the very high fields that can now be maintained
across such gaps, there is an issue in gated detectors and also
in imaging devices where the image has to drift somewhat larger
distances.in a gated device during the turn ON and turn OFF phase
the proximity focussing is not so strong as the electrons do
not reach the full energy equivalent to the pulse height voltage.
For gating with pulse lengths significantly longer than the rise
or fall time of the gate pulse this is not significant for most
applications. However, for fast gates where the gate pulse is
nearer triangular or gaussian than rectangular the contribution
to the overall image of these only partially proximity focussed
focussed electrons can be significant.
To over come this a magnetic field could be applied to the tube. The field should primarily be in the direction of image propagation. As the gaps are small in proximity focussed devices the field does no have to be particularly uniform. however, for an improvement in spatial resolution the electron larmor radius in the field should be small enough to stop the electrons spreading during their transit across the gap. The field should also not be so strong that the larmor radius is significantly less than the diameter of a MCP pore hole (if one is used in the image tube). This could cause the electron to miss the wall of the MCP and result in reduced gain