Hello

enclosed Zdenek and my first proposal about the B0-collimator in vacuum.
A few remarks:
    - Our original plan to build this collimator into a NW160 vacuum 
pipe is not possible because of the length of the PMTs. Therefore we 
went to NW200 and a thickness of 60mm.
    - However, NW200 gives a problem in connecting to the beam pipe and 
the use of an internal beam window. The problem is not of principal 
manner but if we want to stay with NW200 we have not only to produce the 
pipe holding the collimator but also all the other pieces for to connect 
to the beam line and the internal window. After discussing that subject 
with Michael Koller (vacuum group) he suggest to use NW250. The enclosed 
drawings are all done assuming NW200. If we use NW250 we have two 
options: a) enlarge the collimator to NW250 meaning an increase in 
weight from about 22kg to 34kg, or b) using the NW200 collimator as an 
inlet into a plastic disk which would hold the collimator at the axis 
position.
    The difference in costs between version a or b are probably not very 
large. The higher costs for the lead are somehow compensated by the 
plastic costs and costs for machining. Therefore its mainly the larger 
weight which  we should consider.

Now to the drawings:
- "B0-Pb-collimator.pdf" shows the lead collimator NW200. The beam hole 
we assumed 18mm diameter almost fitting to the existing B0 scintillator 
(20mm wide).  4 holes will  be  made to mount holds in order to 
move/carry the beast. The 4 slots for gliding rods are not necessary if 
we place the collimator within a larger plastic disk. One can see the 
thread which shall hold the B0-PMT-support. There one needs some space 
to get Lemo cables on the PMT. The design as shown would require for 
each PMT 4 Lemo elbow pieces to get out of the lead. When enlarging the 
Pb to NW250 or when using an outer plastic disk one can reduce this 
space as we than have enough radial space to get directly with a Lemo 
cable into the PMT.
- "B0-PMT-support.pdf" is a tube holding the PMT (rather tight). Outside 
it has a thread to be turned into the lead to hold the PMT in place. The 
PMT itself is fixed inside the support tube with a single small screw 
(Madenschraube M4). The piece is made of brass.
- "B0-W-collimator" is the piece holding the scintillator. The 
scintillator is put into the slit. It is extending the Tungsten on both 
sides by 1mm for to couple to the PMTs. Beam hole again 18mm. Material 
is Tungsten. The main reason for Tungsten is that the slit has to be 
eroded and the workshop does not like to erode lead for safety reasons. 
Of course, Tungsten has also some advantages when used as the inner beam 
collimator.

With the threads in lead one has the possibility to adjust the beam hole 
axis a few mm up/down. This, however, would require a somewhat larger 
beam hole in the lead collimator, or, alternatively, a similar 
adjustment of the PB-collimator in up/down position. Do you feel it 
necessary?
One more question: Does somebody remember what the typical distance 
(horizontally) between e and pi beam is?

I'm glad to get your opinions on that subject.
Best regards
    Willi