Ultra High Precision Monochromatic Slit (SLT-600)

This unit is identical to SLT-700 except it does not come with water cooling capabilities. This unit consists of vertical and horizontal slit mechanisms, a vacuum vessel which houses the individual blades, stepper motors, limit switches and electrical connections for beam monitoring and a stand (optional) for the vacuum chamber to attach to.

These slits employ ADC's newly redesigned linear actuator providing highly accurate linear travel and are based on a standard DN150 cross. Each slit is customized to meet the needs of the client including aperture, heat load, resolution, accuracy, beam position monitoring, etc.

Each of the four blades are individually controlled and motorized. For the base design, the fully scannable aperture can be up to 35mm square with a maximum aperture of 50mm square. For custom designs, the aperture can be significantly larger, though it requires moving actuators to adjacent flanges.

Cross-roller bearing technology is used for exceptional straightness of travel. Standard micro stepped stepper motors are used that could be controlled with a wide array of controllers/drivers available on the market. The design incorporates limit switches and linear encoders. All blades can travel past each other without interference (Overlapping/Zero Beam).

• Micron precision
• Linear Encoder
• Beam monitoring
• Blades can go "past closed" without clashing (Overlapping/Zero beam)
• Blade material;
• Synchrotron Application:
  • Tungsten (TU) 95%W, 2.5%Ni, 2.5%Cu
  • Tantalum (TA) ASTM-B-7-8 R05200

An easily visible linear scale for each blade is attached to its translation system to provide an alternate way of reading the blade position. Limit switches and hard stops prevent damage by over-travel. The four blades are electrically conductive and insulated from the vacuum vessel. Each blade is connected to a feedthrough with a standard BNC connector. The drive assembly uses stepper motor actuation and crossed-roller bearings. Two fiducial marks are provided per slit unit as well as height references on the vacuum chamber. All UHV sections are vacuum tested to better than 5x10^-10 torr and have a leak rate of less than 2x10^-10 mbar 1^-1s^-1. An optional stand is available to mount the slit system. This stand has holes in the steel tubes so it can easily be filled with sand for added stability. Kinematic mounts on the base offer fine adjustment when lining up the slit to the beamline.

 

Actuators

The actuator is a slightly modified form of ADC's DS200-150-E with linear encoder. The illustration below shows the typical actuator.

This linear actuator provides an open loop positioning accuracy of 5um per 25mm and a closed loop positioning accuracy of up to 3um per 1000mm. Linear accuracy is assured by the highest precision crossed roller linear bearings with straightness of travel up to 2um per 100mm of travel.

The standard DS200-150-E actuator uses a 200 step per revolution NEMA17 motor with 10% step angle accuracy. The modified version for use in the white beam slits employs a 400 step per revolution. Coupled with a 1mm lead preloaded class T7 provides a full step resolution of 2.5um and a half step resolution of 1.25um with 10% accuracy.

For situations that require a finer full step resolution than 2.5um, ADC can further modify the DS200 to use a 5.5:1 planetary gear head. This combination will give a full step resolution of .45um.

The encoder available with this actuator is made by Numerik Jena and has scale accuracy of +/-5um per meter with a grating period of 20um. A 10x interpolation after quadrature yields .5um resolution.

 

Bakeout

One key feature of ADC's white beam slit is the ability to remove the actuators in approximately 10min for bakeout with the ability to replace them in an equal amount of time within microns of their original position. This allows for easy vacuum system maintenance while preserving the accuracy of the system.

The illustration to the right shows the assembly of the actuators and coupling between the linear feedthroughs and blade holder mechanisms.

Using a three-point mount, the actuator weldment engages the main feedthrough flange in a kinematically determinate fashion that provides quick removal and attachment. A pin and slot, pin and hole, and three flat surfaces locate the support weldment on the feedthrough plate.

 

 

 

The actuator is coupled to the linear feedthrough shaft using a three ball, three groove style coupling that has been optimized for the loading condition seen by the feedthrough rods. The illustration below shows this coupling.

The springs shown are used to bind the coupling in place when used in a condition without the vacuum preload. For example, during testing and shipping, the 125N force from the vacuum preload will not exist and the springs must hold the joint together.

 

 

 

 

 

 

Beam Monitoring

Each blade is electrically isolated from ground using aluminum nitride spacers. A single wire is attached to each blade and fed through the vacuum chamber with a floating shield BNC coaxial feedthrough. This is used to determine the position of the beam. Four independent electrical connections are used. The minimum DC resistance between the blade and earth is >10¹⁰ ohms. Typically, these are attached to a cluster flange on one of the remaining ports, but if necessary, the 6-way cross is modified to add additional ports.

 

Fiducialization

For beamline component alignment, ADC provides fiducial points on precision surfaces. Ultra High UHV Slits, for example
are shipped with both scribe lines at the X and Y locations of the beam center and precision holes for mounting of tooling balls.

 

Temperature Measurement

Each blade has a K type thermocouple to be able to monitor the temperature of both the blade holder and the blade. This data can be used to include compensation for thermal growth in the support structure and further increase the accuracy of the system. These are also typically attached to a cluster flange on an adjacent port, but in special cases the vacuum chamber is modified to add ports.

Encoders

Numerik Jena Optical Linear Encoder
PN: LIK21-M52-WZ.

• Square wave output, RS 422 with interpolation out to a 15pin D-Sub connector
• Supply voltage 5V DC ±10%
• High resolution and accuracy
• High interpolation accuracy due to electronic offset and amplitude control

 

ORDERING INSTRUCTIONS:

Ultra High UHV Precision Slits can be ordered with different options. Please use the following chart for ordering.

For example: To order an SLT-600 slit with tungsten blades, a stand, and RGA the model number would be SLT-600-TU-S-R.

NOTE: Custom/Neutron application blades are available in boron carbide, cadmium, boron nitride or a sandwich combination structure.