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1 Brianna Thorpe Arizona State University Controls for Polarimeter Converters

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What are we doing? 2 Experiments at Jefferson Lab use controls for polarimeter converters This minimizes problems in the experiments We want to make a cheap, simple to use control This will require: Developing hardware Writing software

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Converter Issues: Electron Scatter 3 What is this? As an electron moves through the source, it bumps against other atoms. Why is this an issue? As the thickness of the source increases, the ratio of scattering centers to electrons detected increases.

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Converter Issue: Delta Rays 4 What is this? As an electron travels through the source, it bumps against other atoms. This knocks off other electrons. Why is this an issue? These other electrons (Delta rays) hit the detector at angles different than the recoil electron. Because both have similar kinematics, we have no way of knowing which is the recoil electron.

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Converter Issues: Our Solution 5 The Solution: make the target (converter) really thin. Our converter three different sources: Beryllium Slightly thicker Beryllium Carbon

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6 How Do We Control the Converters?

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7 Distance in beam direction between converter and detector is 35 mm

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8 Detector supports attached to plate with screws

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9 Rack guide supports attached to plate with screws

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The Converter Control 10 Motor The motor moves the converter tray. Control the motor and you control the converters. Carbon Beryllium Thicker Beryllium Converters

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Step One: The Hardware 11 We want cheap and simple: Arduino: Open source electronics Works with Linux Programs written in C or C++ Lots of example code on the internet Cost: $99

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12 Motor shield Microcontroller The Arduino board is our microcontroller Our code tells the Arduino what to do The Arduino relays our commands to the shields Shields: Electronics that are stacked on the microcontroller Our motor shield speaks to our motor Cost: $27 Our Ethernet shield allows for Ethernet communication Cost: $35 Ethernet Shield

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13 Hardware Issues: The Arduino motor shield had a pin conflict with the Ethernet shield This prevented communication between the shields Our Solution: An inexpensive pin-reassignment shield We used solder to reassign the pins

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14 We hooked our stacked Arduino and shields to a cheap test motor Bipolar 200 steps per revolution 12 Volt Cost: $20 (including shipping)

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Step Two: The Software 15 Installed on lc64 Linux box Installed on my Windows laptop Used example code for testing. The code for Arduino is called a sketch Compiled using Linux and Windows. We are fully platform independent.

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16 The code to control the motor was written in the Arduino program. The Graphical User Interface was written in Vpython. The GUI allows for communication between the sketch and the Arduino

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GUI Position: retracted 17

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18 GUI Position: One

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19 GUI Position: Two

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20 GUI Position: Three

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Application at Jefferson Lab 21 The GUI will live here

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Cost Effectiveness 22 Controller: $595Controller chassis: $4750 Total Cost: $181 Total Cost: $5345

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Putting it all Together 23

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The Finished Product 24

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Acknowledgments Dr. Mike Dugger Dr. Barrie Ritchie Ross Tucker Todd Hodges Ben Prather 25

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27 Converter Stick assembly Color code: 1.5 mm thick 3.0 mm thick 1.4 mm thick Material: Aluminum All units in mm Hole 1-3: 8x8 Hole 4: 8x42 Screw holes on converter tray are threaded Weight ~ 0.41 oz Hole 3 Hole 2 Hole 1 Hole 4 1 1 1 16 1 1 33 8 22 42 67 22 Converter trayConverter plate

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28 Converter retracted Mounting plate Rack stop Rack Rack stop Converter tray Converter leg Detector card Teeth on rack not shown Converter tray 11 mm from beam center Converter tray detail shown later 11 mm

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29 Converter position 1 102 mm 176 mm 5 mm 10 mm

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30 Converter position 2

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31 Converter position 3

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32 Different view

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33 Front view 3 mm 10 mm

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34 View from downstream, detector removed Weight of rack ~ 0.97 oz Weight of arm ~ 0.26 oz Weight of converter tray assembly ~ 0.41 oz Weight of rack+arm+converter tray assembly = 1.64 oz 91 mm

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35 Gear added Gear has outer diameter of 15 mm (can be a bit smaller) with a minimum of 18 teeth Teeth on gear not shown Precision in linear motion per step (200 steps per revolution is standard for stepper motors): ~1/4 mm

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36 Rack guide added If rack guide is aluminum then coefficient of static friction between rack and rack guide is between 1.05 and 1.35. Using 1.35 as conservative estimate of coefficient of static friction, then the force needed to break static equilibrium is 1.35*1.64 oz ~ 2.2 oz

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37 Motor added Since gear has radius of 7.5 mm (~ 0.3 inch) and force needed to break static friction is 2.2 oz, then minimum torque required of motor is ~ 0.7 oz-inch Motor that Im interested in has holding torque of 7.5 oz-inch Motor details shown later.

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38 Motor mount added Motor mount attached to plate with screws (not shown) Want two cm clearance between upstream chamber wall and motor Upstream