FOCUSING COLLIMATORS FOR A MICROFOCUS X-RAY SOURCE. U.W. Arndt¹⁾, A. Inneman²⁾ and L. Pina³⁾, ¹⁾MRC LMB Cambridge CB2 2QH, UK, ²⁾Koma, K Lesu 965/4 14200 Prague 4, Czech Republic, ³⁾Czech Technical University, Bréhová 7, 11519 Prague 1, Czech Republic

We have constructed two types of specularly-reflecting focusing mirrors for 8keV X-rays: ellipsoidal mirrors made by an electroforming replication of appropriately shaped mandrels, and double Kirkpatrick-Baez-Franks mirror-blocks containing two pairs of orthogonal elastically-bent planar-elliptical mirrors. They are used with a magnetically focused X-ray tube, produced in collaboration with JVP Long and P Duncumb, which allows the mirrors to be mounted within 10 mm of the electron focus of which an image is formed on the specimen 600 mm from the source. This arrangement permits a large collecting angle at the source and a small crossfire at the sample: our best collimators produce a flux per unit tube power more than 100 times that obtained with a pin-hole-collimated beam with the same cross-fire of about 0.001 radians. We have tested our system at low tube-power; we expect to be able to dissipate more than 25 watts in our X-ray tube, at which point we should exceed the X-ray intensity at the sample obtained with conventional collimation of a 2.5 kW rotating-anode X-ray generator beam.