HIGH-DENSITY WINDOWLESS GAS-JET TARGET

A high density gas target has been developed using a focussing effect in slightly underexpanded supersonic free-jets which are produced by axisymmetric Laval nozzles. Under constant pressure conditions the first density focus, a cylindrical flow portion of 3 mm diameter and of a length of about 5 mm and an almost homogeneous density distribution, is spatially fixed. By varying only the pressure of the gas in the entrance of the nozzle, the target thickness can be changed from less than 1 μg/cm2 to more than 100 μg/cm2. To avoid window foils in the target device, the secondary gas load is reduced by a three-stage dynamical pumping system which is built concentrically around the gas jet and which allows unrestricted 360° access to the target area. © 1979 North-Holland Publishing Co.