Internship at Commonwealth Fusion Systems 2021

In the spring of 2021, I worked at Commonwealth Fusion Systems on the applications team, supporting the manufacture of mirror coils for plasma confinement in the upcoming Wisconsin High-Field Axi-Symmetric Mirror (WHAM) fusion experiment. While the manufacturing process and magnet I worked on are trade secrets, I also spent some time on a side project for the company: A device to aid in cutting intermediate lengths (50mm to 3m) of High-Temperature Superconducting tape (HTS). It uses a belt and pinion linear actuator to concentrate engineering complexity all within the mobile carriage, necessitating on-board power management and motor driving.

Partially assembled mobile carriage. Visible is the toggle clamp, retaining a segment of HTS (bottom center), the crawler drive pulley, motor and encoder (right), and the UI (top center).

Partially assembled mobile carriage. Visible is the toggle clamp, retaining a segment of HTS (bottom center), the crawler drive pulley, motor and encoder (right), and the UI (top center).

Before ordering the device PCB, I tested all device functionality on a breadboard model.

Before ordering the device PCB, I tested all device functionality on a breadboard model.

The tape positioning jig is demonstrated in this short clip.

A PCB (desgined in KiCAD) provided mounting for the motor controller, power management systems and teensy 4.1 microcontroller, as well as connections for the UI buttons and screen.

A PCB (desgined in KiCAD) provided mounting for the motor controller, power management systems and teensy 4.1 microcontroller, as well as connections for the UI buttons and screen.

In this still of the carriage in motion, a black wire is visible on the right. This was the solution to the most persistent failure mode of the device. Through a week of bug testing and thinking, the root cause was found to be a difference in static potential between the stepper motor body and the guide rail. When this potential discharged it would power cycle the entire device. This simple wire provided an easy path for electrons to flow between the motor body and the rail via one of the crawler bearings.

In this still of the carriage in motion, a black wire is visible on the right. This was the solution to the most persistent failure mode of the device. Through a week of bug testing and thinking, the root cause was found to be a difference in static potential between the stepper motor body and the guide rail. When this potential discharged it would power cycle the entire device. This simple wire provided an easy path for electrons to flow between the motor body and the rail via one of the crawler bearings.