Solenoid
A large 5 Tesla superconducting solenoid unquestionably transcends present experience in magnet design. It has been suggested that mechanical considerations lead to an upper limit of about 60 T2m for the figure-of-merit B2R for superconducting solenoids. For the solenoid for the proposed SiD
detector at the ILC this quantity is 62.5 T2m, suggesting that
the feasibility of such a magnet is best determined by appeal to
experience and careful engineering extrapolation where required. The CMS
solenoid, nearing completion at the CERN Large Hadron Collider, will
provide a 4 T field in a bore 5.9 m in diameter and 13 m long. This
magnet provides a substantial proof-of-concept for the SiD solenoid. The
CMS conductor consists of a 32-strand NbTi cable, stabilized by a co-extrusion
of high-purity aluminum, which is welded to two bars of strong aluminum
alloy. CMS achieves its design field with four winding layers; SiD will
require six layers using the same conductor. The smaller aspect ratio
(magnet length divided by diameter) of SiD vs. CMS -- approximately one
for SiD but more than two for CMS -- means that more linear current
density than simple proportionality of the higher field is required. CMS
operates at 19.5 kilo-Ampères (kA) and its windings provide a linear
current density of approximately 3500 A/mm; SiD requires 4800 A/mm, a
factor of almost 1.4 more than CMS for a field only 25% more intense
Description of the work done to date in a contribution (pdf) to the Genoa conference.
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