A doublet C0 IR solution using existing magnets Page: 2 of 13
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It does not appear possible to create triplet final-focus optics at CO with existing Tevatron IR
magnets. Currently at CDF/DO the IP to triplet distance is 7.363 m. The BTeV detector requires
that this space be expanded to at least 12.192 m. By eliminating the Q1 magnet plus its
accompanying TSP spool, and replacing them with a single short (49.91") TSS spool, an extra
2.008276 m of space can be created. It's difficult to imagine, though, how an additional 2.8209 m
of space could be generated, producing sufficient room for both a triplet plus the detector.
Quad Location Magnetic Length Max. Gradient Max. Current
(in) (T/m) (A)
Q4 / Q2 132 145 5000
[Q3]  [ 145] [5000 ]
[Q1 ] ['55.19 ] [ 145] 
Q5 55.19 145 5000
Q6 23.875 145 5000
QT7/QT9/QTO 25 58 1000
Table 1. Magnet parameters of the available high-gradient DO quadrupoles.
(Shaded entries are not used in the present CO design).
While doublets do have the advantage over triplets of requiring less space & generally lower
gradients, they have the glaring drawback that Pmax is 3-4 times larger than it would be in a triplet
for the same 1*. Doublet optics at CO can be created with the Q4 & Q2 quadrupoles or, if the
Q1+TSP combination is removed as described above, with the Q3 & Q2 quadrupoles.
In Run II the Tevatron operates with tunes near the half-integer; at (sx, y) = (20.585, 20.575).
There are two simple approaches that maintain the nominal operating point. The obvious solution is
to leave CDF tuned to its Collider mode injection lattice. By simply moving the other IR from DO
to CO the overall machine tune is unaffected. Another option is to re-tune CDF to the Fixed Target
lattice, in this case the BO insert becomes a "Collins-like" straight. The additional half-integer of
tune is then generated by the regular tune-quad strings and becomes distributed uniformly around
the ring. The CDF Lattice functions & gradients for these 2 options are provided in Appendix A.
The first option has the advantage that BO can be easily re-tuned for collisions when CO is not in
use. However, it will be seen later that this solution creates significant difficulties for maintaining
adequate beam separation around the ring. The second approach - re-tuning BO to Fixed Target
optics - is greatly preferred from the standpoint of beam separation. Unfortunately, the drawback
in this case is that a shift or so of labor is required to physically switch powering at BO between
Fixed Target & Collider optics.
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Johnstone, John A. A doublet C0 IR solution using existing magnets, report, August 19, 2002; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc734632/m1/2/: accessed March 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.