Printed Circuit Board Coils for the Mirror Neutron Oscillation Experiment*

When ordinary neutrons are sent through a magnetic field, they may be converted into mirror neutrons. These particles behave like their Standard Model counterpart, but are not visible in the ordinary world, much like dark matter. To detect these particles, we need two magnetic fields, one to oscillate from neutrons to mirror neutrons, and the other to convert them back into neutrons.  To create this field, we constructed a prototype with three slanted solenoid coils that can produce a weak, uniform magnetic fields in an arbitrary direction by tuning the three individual currents. Each sub-coil is made of a flexible printed circuit board (PCB), wrapped around a cylindrical contour, with a rigid PCB, connecting each trace of the flex PCB to the next loop in the sequence. Each of these flex PCBs has a sinusoidal shape so that the axis of the elliptical loops are at an angle with respect to the cylinder. Each sub-coil is at an angle of 120^○ to the other two in a symmetric arrangement yielding three independent field components.