We have designed and constructed a magnet surrounding a cylindrical volume of superfluid helium-3 to isolate a region of metastable, supercooled A phase, entirely surrounded by bulk A phase - isolating the ‘bubble’ from rough surfaces that can trigger the transition to the stable B phase. We outline the design of the experimental cell and magnet and show that the performance of the magnet is consistent with simulations, including the capability to produce the high field gradient required for generating a bubble. Future plans include the investigation of possible intrinsic mechanisms underpinning the A-B transition, with potential implications for early-universe cosmological phase transitions.