A 30 Tesla hybrid magnet with 5 cm bore: A French-German project

In order to generate continuous magnetic fields it is advantageous to combine a resistive inner magnet and an outer superconducting coil. Such a system is commonly called a hybrid magnet. Recently the C.N.R.S. and the M.P.G. agreed to build a hybrid system in Grenoble. A study of the project was made, taking into account several options. For various reasons it was decided to make the superconducting coil from Nb-Ti with a capability to generate a 10-11 Tesla in a room temperature bore of 42 cm and to operate at 1.8 K at atmospheric pressure. The inner part of the Grenoble hybrid will be a 10 MW duplex coil. This construction consists of an inner polyhelix magnet and an outer Bitter-magnet with a capability to generate more than 20 Tesla in an outer field of 10 Tesla. The polyhelix concept has the advantage that a magnet can be optimized with respect to stress and heat flux and that the power can be shifted away from the center to achieve tolerable stress levels. The essential points of the hybrid project are outlined and the actual state of the construction is reported.