SUPER STRONG ADJUSTABLE PERMANENT MAGNET QUADRUPOLE FOR THE FINAL FOCUS IN A LINEAR COLLIDER

A permanent magnet quadrupole (PMQ) with variable strength was fabricated for a feasibility study for its use as the final focus lens in a linear collider. An over 120T/m field gradient over a bore diameter of 20mm was achieved by the introduction of saturated iron and a "double ring structure". The integrated gradient was 24T with 20cm length and the outer magnet diameter was ø100 mm. A recent change is to raise the absolute field gradient further by reducing the bore diameter down to ø15mm. This paper describes the modification and the variable PMQ from the viewpoint of linear collider final focus application.