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Secondary Source Aperture

The IDT Secondary Source Aperture (SSA) is a highly stable motorised slit with polished tungsten rods as slit blades. The SSA is a proven design with high stability, highly parallel blades and ultra-stable operation.

A stepper motor is used to open the slit gap by moving the blades in equal increments, driven by a flexure design. A second stepper motor is used to translate the pair of slit blades so that the beam profile can be scanned.

The flexure and the back plate are made of beryllium copper and are thermally matched. The stepper motors are thermally isolated from the flexure to prevent thermal drift. Each motion is encoded and can be driven in closed loop.

A second aperture can be mounted orthogonally to provide a horizontal and vertical SSA.

The ability to drive the slit position independently of the slit gap is a key advantage of the IDT SSA design. This provides the ability to scan the monochromatic beam.

Secondary Source Aperture mechanism Secondary Source Aperture labelled

Below: Secondary Source Aperture installed immediately downstream of the Quad Diode BPM on the XFM beamline at the Australian Synchrotron.

SSA diffraction pattern SSA diffraction pattern

Right: This is a diffraction pattern produced by an 88µm vertical SSA slit, viewed at the sample position. This demonstrates the fantastic slit blade alignment.

Image of beam using a YAG screen on table 5x objective. Camera resolution = 3.75µm/pixel.

XFM Beamline SSA performance data:

SSA accuracy measurement SSA photo diode BPM linearity

Left: Accuracy measurement for slit aperture mechanism demonstrating the fantastic performance over 3 ±100µm cycles. Unidirectional accuracy of 0.15µm.


Right: ​Demonstration of integrated photo diode beam position monitor linearity. The beam was scanned ±170µm across a 100µm slit aperture. This response is clearly ideal for a closed loop feedback.​

Technical Data Quad Diode & Secondary Source Aperture System installed on XFM beamline