Cornell University Unit Name

"Design of a 5T Solenoid"

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INTRODUCTION

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 SiD solenoid 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-Amperes (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.

GOALS

The SiD detector calls for a five Tesla solenoid. This proposal will carry out the necessary research and development to establish the feasibility of a design, prepare a realistic cost estimate and establish the contacts with industry for construction of the magnet by industry. The R&D proposed consists of the testing of optimized finished stabilized high purity aluminum alloy conductor at the 20kA, 4-6 Tesla scale to establish the conductor design concepts. Under study in this optimization effort are the hardening of the high purity aluminum with specific alloys to improve is behavior in high stress conditions, and the use of better optimized hard aluminum alloy reinforcement for the conductor. These studies would be complemented with 3-d FEA modeling of 5T solenoid using CMS parameters and 3-d FEA modeling of 5T solenoid with results from new conductor tests to establish the proof of principle for a 5T solenoid by the year 2007.

Beam particles entering the detector at a finite horizontal crossing angle will deviate in the vertical plane. This deviation can be corrected by a special dipole field at the intersection region. For maximum efficiency this special field can be provided by saddle coils mounted on the outer support cylinder of the solenoid. This Detector-Integrated-Dipole (DID) corrector can also be used to compensate for rotation of the beam polarization or beam size growth due to synchrotron radiation. Locating the DID coils on the solenoid outer support cylinder offers an ideal environment for them. There is minimal solenoidal field in that region, a slight increase in the size of the solenoid cryostat readily provides for the dipole coils, and the large winding radius of the dipole coils ensures a high quality dipole field on the beam axis with modest attention to the dipole winding geometry. Approximately 550 kA-turns are needed for the required ~ 600 G dipole field from each of the coils. This proposal calls for a continuation of the R&D on the DID and evaluation of its effects on the physics.

COLLABORATION

The conductor R&D would be carried out in collaboration with CERN. CERN is responsible for obtaining samples of new conductors. CERN is in the process of having the extrusion vendor, used for the CMS conductor, perform another extrusion of stabilizer onto some existing leftover CMS superconducting cable. Instead of ordinary high purity aluminum, they will use a leftover billet of Akira Yamamoto's special stabilizer alloy prepared for the ATLAS solenoid, and perhaps another similar alloy under development at CERN. Then leftover reinforcing bars from CMS will be welded onto the extrusion. The yield would be samples of finished conductor at the CMS scale (20 KA, 4-6 Tesla) for further study and measurement which would be shared by CERN and us.

SCHEDULE

The goals for this project to be accomplished within the next two years are to:

• 1) Fabricate “CMS” conductor samples with improved aluminum stabilizer
• 2) Fabricate “CMS” conductor samples with improved aluminum reinforcement
• 3) Test finished stabilized alloy conductor at the 20kA, 4-6 Tesla scale
• 4) Perform 3-d FEA modeling of 5T solenoid using CMS parameters, including DID
• 5) Perform 3-d FEA modeling of 5T solenoid with results from new conductor tests, including optimum conductor design, to establish the proof of principle for a 5T solenoid by the year 2007.

Based on the results of the first phase, a complete conceptual design of cold mass support system and cryogenic cooling technique for a 4-6 T solenoid will be developed in the years following, i.e. 2008 and following years.

SUPPORT

The current level of support is inadequate for carrying out the proposed research. The level of shortfall is listed on the prioritization form.

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Please address the following questions in your statement.

• What are the goals of this R&D project. How does this R&D project address the needs of one or more of the detector concepts?

• If there are multiple institutions participating in this project, please describe the distribution of responsibilities.

• Are there significant recent results?

• What are the plans for the near future(about 1 year)? What are the plans on a time scale of 2 to 3 years?

• Are there critical items that must be addressed before significant results can be obtained from this project?

• Is the support for this project sufficient? Are there significant improvements that could be made with additional support?