Present: Fritz Caspers, Alex
Grudiev,
Tom Kroyer, Elias Métral, Federico Roncarolo,
Benoit Salvant.
Tom is leaving very soon, and won't be
available much until he leaves (we have no confirmation
whatsoever that this has to do with the short hair). Federico
and I will try to run a few examples so that his studies can be
carried on if needed. In particular, we could assess the effect
of the height of the plates on the impedance, as it seems the
agreement is not perfect. Also, we should crosscheck we use the
right Yokoya factor (Pi^2/12 or Pi^2/8) to relate cylindrical
pipe to flat jaws.
The distance of the external boundary
condition to the setup was looked at in a couple of simulations
by Tom. We should also assess its effect with analytical
calculations.
We should check the effect of the
presence of dielectric next to the coil on the impedance
measurements.
We presented on Feb 4th at the
collimation working group the consistency of simulations, theory
and bench measurements. However, is it really the impedance the
beam sees? In fact, theory assumes a ring beam source, while
measurements and simulations rely on an analogy between a free
particle beam, and an eletron RF current circulating in loops of
copper wire.
The main opening from the observation of
a non monotonic impedance with frequency is that it may open up
possiblities of reducing the impedance through using combination
of materials.
Fritz suggested we should study
collimators made of ceramics and litz wire (to carry the average
image current away from the beam, and thereby reduce the
impedance). Analytical calculations or simulations seem hard to
perform, but we could try to measure the impedance of Litz wire
plates with the coil.
We could also look more at the physics
behind the transition from an imaginary impedance (Z~j) at DC to
an impedance in Z~(1+j) in the classical regime.