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.
Ultra-stable flexure driven slit system.
Slit gap controlled by one motor, with translation controlled by a second motor.
Slit gap range of -0.1mm to +2.0mm with sub-µm accuracy.
Translation travel range 8mm.
Ground tungsten slit blades with parallelism to <5µm.
Installed on an ultra-stable granite block with a measured amplification factor of
1.0.
Optional photo diode array can be installed to create an integrated back scatter
beam position monitor from blades.
Below: Secondary Source Aperture installed immediately downstream of the Quad Diode
BPM on the XFM beamline at the Australian Synchrotron.
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:
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
