configuration

The present design is a warm magnet (FeCo alloy) of 2.2 m long with the inner radius of 6.86mm and the pole tip field of 1.3 Tesla. It is located at $\ell^*$=2m from IP. For NLC, it consists of two permanent magnets of 1m long each, whose inner (outer) radii are 7(20) and 8(25) mm, respectively, and a superconducting quadrupole magnet(Q1SC) of 0.5 m long. PEP-II also uses permanent magnets. It is also located at $\ell^*$=2m from IP. For the case of the warm magnet, a water cooling must not cause any vibration. Beam-based alignment must be very difficult with the permanent magnets.

For the third option, a superconducting quadrupole magnet can be used with the smallest crossing angle and a clever extraction method of beams. This option is very attractive because no compensating magnet is necessary. So, it should be seriously considered. The parameters of the superconducting quad were given in the JLC-1[1], which are the aperture radius of 6.0cm, the inner radius of coil of 8.0cm, the outer radius of cryostat of 30cm, the field gradient of 117 Tesla/m and the material of NdTi at 1.8 K (superfluid He). The current stability must be less than $4 \times 10^{-6}$.

The longer distance($\ell^*$) of the quad from IP makes a smaller dead cone and less background (back-scattered photons), and it must be benefit if it is set outside the compact detector. If $\ell^*$= 1 (3)m, the final focus system becomes shorter (longer) by 25 (20) % (NLC study).