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White Beam Water Cooled Slit (SLT-700)

This unit consists of vertical and horizontal slit mechanisms, a vacuum vessel which houses them, water cooling lines connected to the individual blades, stepper motors, limit switches and electrical connections for beam monitoring system and an optional stand 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 that are used could be controlled with a wide array of controllers/drivers available on the market. The design incorporates limit switches and come with 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-708 R05200

Each of the four blades are individually controlled and motorized. The range of travel for each blade is customized depending on customer specification from the nominal beam axis. The vacuum vessel, a custom cylindrical chamber, contains ports for an ion pump, roughing pump, fluorescent screen, cold cathode gauge, feedthroughs for drain current measurement, feedthroughs for temperature sensors and spare ports for future use. The slit system is designed in such a way that each of the blades can withstand power loads specified by the customer. A detailed FEA report would be provided during Final Design Review (FDR). The electrical, vacuum and water connections are all housed on custom designed interface units, making attachment to the beamline simple and straight forward.

A spring-extended linear encoder with built-in home position is provided for each individual blade. The accuracy of the linear encoder is better than 1 micron. 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 avaliable 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 to the right 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 if assured by the highest precision crossed roller linear bearings with straightness of travel up to 2um per 100mm of travel.

The modified version for use in the white beam slit 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 gearhead. 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.

One key feature of ADC's white beam slit is the ability to remove the actuators in approximately 10 min. 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.

 

Cooling

ADC has performed a complete thermo-mechanical finite element analysis of this system for use in undulator beamlines with exceptionally high power density about a very small area of the aperture. It documents the resulting stresses and deflections due to thermal loading of the blades as well as verifies the adequacy of the cooling circuit.

The illustration below shows a typical blade holder as well as the cooling path and support structure. Water enters through the 9.5mm diameter outer tube and travels to the copper blade holder. It returns through the annular 6.35mm diameter tube. A sustained flow rate 3.5 GPM will acceptably cool a heat load of up to 300W per blade with minimal thermal strain in the supporting material.

The structural tube provides the vacuum guard for the system with a vacuum brazed joint between the 304SS tube and the C10100 copper blade holder. The supply tube is also vacuum brazed to the blade holder. The inner return tube is floating inside the supply tube and is fastened with a compression fitting at the outboard end.

The blades are fastened to the blade holders with aluminum nitride spacers. This allows for a very high thermal conductivity while allowing for an insulation to ground. In this configuration, each blade can withstand up to 300W of heating. For even more extreme cases, employing an indium foil between the blade and spacer and spacer and copper blade holder can increase the thermal conductivity.

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. Water Cooled 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.

 

Finite Element Analysis

A detailed thermal/mechanical analysis will be performed. A complete FEA report will available and can be provided for customer review.

 

 

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

AS: monitoring signal
NAS: negated monitoring signal
Numerik Jena LIK Encoder DB15 Pin Assignment

 

ORDERING INSTRUCTIONS:

White Beam Water Cooled Slits can be ordered with different options. Please use the following chart for ordering.

For example: To order an SLT-700 slit with tungsten blades, a stand, and RGA the model number would be SLT-700-TU-S-R.

NOTE: Custom/Neutron application blades are available in boron carbide, cadmium, boron nitride or a sandwich combination structure. #2: For a copy of the FEA on high heat load contact ADC.
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