The field measurements of the dipole magnet at the GSI in Darmstadt has been carried out (see fig. 4) and the magnet is now arranged in the B1 area (fig. 5). The first tests with 1340A were performed successfully!
The central part of the spectrometer is a dipole magnet. Very fortunately, it was possible to get an MD type magnet on permanent loan basis from DESY, which has practically ideal geometry. The magnet was transported to the experimental area at beam line S (fig.1) in April 2007 and was taken into operation for test purposes.
The magnet is featured with a variable gap in vertical direction. For largest possible acceptance in forward direction we decided to extend the gap. With an acceptable amount of work and cost it was possible to increase the height from 54cm to 84cm. The size of the gap in horizontal dimension is (W × D) ≈ (1500 × 1500)mm2. The outer dimensions of the magnet are (H × W × D) ≈ (2800 × 3900 × 1500)mm3 and the total weight amounts to ≈ 90tons. In march 2009 all modifications of the magnet were completed by an external company. At the foreseen position in the experimental area (2m distance downstream of the target) an acceptance of αhor ≈ 12.1° and αver ≈ 8.2° is covered.
With a current Imax = 1500 A and a vertical gap size of 54cm amagnetic field of Bmax= 0.9 T can be achieved (see fig.2), corresponding to a bending power of ∫B dl ≈ 0.9 Tm. With the maximum current Imax = 1340A of the available power supply unit at ELSA and the gap extended to 84cm, a central magnetic field strength of Bmax = 0.54T (∫B dl ≈ 0.74Tm) is expected from simulations. In fig. 3 the simulated field is shown for I=1340A coil current and both gap sizes. The simulations have been performed with the CST studio suite 2006. For the 54cm gap size the result agrees within a few percent with the previous field measurements at DESY.
Presently field measurements of the dipole magnet with the extended gap are performed at the GSI in Darmstadt. There a professional field mapping device is provided by the magnet technology group. Measurements with variable grid sizes in the range of 10mm - 50mm at different currents are scheduled. At each point all three field components (Bx, By, Bz) can be simultaneously measured with an accuracy in the order of 10-4T.
It is planned to have the magnet back in Bonn around middle of the year. Besides rebuilding and connecting, no additional work is required at ELSA. The device will be ready for first testing in fall 2009.