Design and Testing by Undergraduates of a Solenoidal Magnet to Field-Modulate the Critical Current of an all-MgB2 Josephson Junction

We describe the process of designing, building, and characterization, by undergraduates, of a solenoidal magnet to modulate the critical current of all-MgB2 thin film Josephson junctions. Using the magnetic field expression of a solenoid of finite length, the design parameters were determined and used to fabricate several prototypes of a magnet. A three-axis magnetometer was then used to map the field near the solenoid's geometric center, and the field was calibrated as a function of current. The solenoid was then mounted on a cryocooler shield and centered about an all-MgB2 thin film Josephson junction to be cooled down to 2 degrees Kelvin. We discuss the resulting magnetic field modulation of the junction's critical current and the estimated junction geometric area, as well as its impact on our current energy gap measurements in MgB2.