[Sneap] Quadrupole lens - Reason for failure

[Ludwig Beck]

Hello,

thanks to all for reply to my recent Email concerning the problems with
our quadupole lens at the exit of our tandem. Meanwhile we have gotten a
set of four coils from the Tandem in Heidelberg. When replacing the four
coils we have found some rust between the pole and the yoke of the coil
with the lower magnetic field. Only a very thin layer of rust which
could not be seen from outside. Perhaps this was the reason for our
problem. The resistance of this coil did not differ clearly  from the
resistance of the other old coils or the new coils. But anyway it was
good to replace the coil because we had in the past a small water leak,
which we could repair only poor. This leak may be present already for a
long time and was not noticed as long as it was very small, so that the
water evaporated before it could be seen somewhere outside the lens.
This water leak was certainly the reason for the rust.

Here now the true reason for our problem with the lens:

Meanwhile we have investigated the old coils. The resistance of all 
coils was nearly equal (0.4 Ohms). We measured additionally the 
inductance of all 4 old coils.  Three had about 800 MikroHenry, but the 
"lower field" coil only 150 MicroHenry. Therefore we opened this coil 
for a closer look inside. In the attached picture you find what we have 
seen. Inside the red insulation the coil was filled with water and as 
you can see there are a lot of corrosion products from copper. This 
water was certainly highly conductive.


The quadrupole is now working. It is  not necessary anymore to use a
steerer to bring the beam to our picture slits. In the past it was not
possible without steering in y-direction before entering the lens. This
is also a hint that the problem with the lens is an old problem, because
nobody could remember that there was a time where this steerer was not
needed.

So every thing is looking fine now.

Thank to all and especially to Roland Repnow from Heidelberg.

Ludwig

--
Dr. Ludwig Beck
Maier-Leibnitz-Labor / Beschleunigerlabor
Am Coulombwall 6
D-85748 Garching

Tel. 089/289-14271
Fax 089/289-14280




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