Introduction

A new facility for Detector Testing. Many of the future detectors will have a 4 T magnetic solenoid and possibly a number of compensating solenoid and final focus elements. For testing and measuring magnetic elements, a general purpose 4 T test facility is required to replace or complement the outdated systems available at CERN's North Area providing maximum fields of 1.9 and 3 T, respectively. The efforts in this R&D programme are restricted to a conceptual design study of such a facility while its implementation will require funding from other sources.

Split-solenoid design

The design effort is currently focused on two types of superconducting dipoles, each producing a magnetic field of 4 T over a volume of about 1 m3.

The split solenoid type is a design utilizing a concept similar to M1, albeit with a center field of 4 T (Fig. 1). The design features two solenoids, where a field of 4 T is produced in the center between the two coils. Similar to M1, the magnet can be rotated with respect to the direction of the beam, so that it may either generate a 4 T solenoid or a dipole field over the beam axis.

The shape of the iron around and inside the coils is optimized to limit the peak field inside the coil (important as this peak field approaches the limits of Nb-Ti conductor technology for superconducting detector magnets) and to limit the stray field (Fig. 2).

Various properties of this design are given in Table I. The split-solenoid design is compatible with the iron end-plates used for M1, so that certain parts of M1 may be repurposed for this new magnet to reduce the overall cost.

Preliminary quench protection studies of the split-solenoid design were completed and it was concluded that this magnet may be protected either with energy extraction or quench heaters. Here quench heaters are considered as the preferred option given that the associated construction and maintenance costs are favourable with respect to energy extraction. In general it was concluded that quench protection of this magnet design is straight-forward and not too challenging (Fig. 3).

Fig. 1. 4 T Split-solenoid magnet in the style of M1

Fig. 2. Iron shaping of the split solenoid design, for the purpose of limiting the stray field.

Table I. Properties of the split-solenoid design

Fig. 3. Quench protection studies of the split-solenoid design were completed.

Magnadon dipole design

An alternative to the split-solenoid design is the so-called Magnadon dipole design (Fig. 4). The name of this design is derived from its resemblance to a Megalodon prehistoric shark (Fig. 5). This design features flared-end superconducting coils that are located around a 1.4 m free bore, with a central field of 4 T.

This design is compatible with the iron yoke of the H8 Morpurgo dipole, so that its yoke may be repurposed for a reduction in overall cost of construction (Fig. 6).

Similar to the split-solenoid design, the Magnadon dipole was optimized to minimize the peak field on the conductor, and the limit the stray field. The stray field of this design is very favorable, reaching just 11 mT at a distance of 5 meters from the center of the magnet.

Various properties of the magnet design are given in Table II.

Fig. 4. Magnadon flared-end dipole design

Fig. 5. Fossil of a ‘Megalodon’ prehistoric shark

Fig. 6. The Magnadon design is compatible with the H8 iron yoke (here in red).

Table II. Properties of the Magnadon dipole design