[MAP] Be Wall Cavity: on- or off-axis?

[Daniel Bowring]

All,

Is it necessary that the beryllium wall cavity be coaxial with the
magnetic field in the Lab G solenoid?

Debate on this issue has slowed the design effort.  We would like to
finish the design very soon, but one last attempt at consensus seems
warranted.  Our next design meeting with SLAC will probably happen on
Tuesday, June 26.  If you have strong feelings about this issue,
please share those feelings with me before then.  (And please accept
my apologies for the somewhat late notice.)

Please see our recent IPAC paper for background information:
http://199.190.250.75/prepress/THPPC033.PDF
In that design, the cavity center is 2 cm lower than the magnet axis.

Very briefly:

- Some people feel the cavity axis should be aligned with the axis of
the solenoid.  Since we know so little about the physics of breakdown
in strong magnetic fields, it is felt that azimuthal symmetry would
simplify our analysis of future data.  The only way to achieve
azimuthal symmetry is to design a cavity that is coaxial with the
solenoidal fields.

- On the other hand, there's not much room in the solenoid.  Centering
the cavity is surprisingly difficult once you account for nonzero
waveguide thicknesses, bolted flanges, vacuum conductance, etc.  Given
our time and budgetary constraints, a prolonged R&D effort in this
direction may be unwarranted.  Especially because there is not
currently any convincing *physics* argument in favor of such an
effort.

These arguments are expanded in my most recent MTA-RF meeting presentation:
https://indico.fnal.gov/conferenceDisplay.py?confId=5697

Furthermore, Yagmur has provided a link to the solenoid's field map.
Scroll down to the bottom of this page:
http://mice.iit.edu/mta/magnet/magnet.html

If you have input, please send it to me by Tuesday, June 26.  (Please
do not "reply-all" to this email.)

Thanks very much,
Daniel