After installing some magnetic shielding, and reinstalling the superconducting magnet, I thought I’d put a picture of the entire dilution fridge assembly being lowered into the dewar, as it looked quite impressive.
At the bottom you can just see the top of the outer mu-metal shield. It’s actually quite a lot longer than this, I’d already lowered it a fair way into the dewar. Inside this shield is a second, inner one, and inside that is the superconducting magnet (solenoid). Inside the bore of the solenoid is the IVC, inside which is the sample box, and inside that the Josephson junction is mounted. Which makes it sounds a bit like one of those childrens’ pop-up books or interactive posters where you ‘look under’ parts (I should really make one of those, it would be cool to show to visitors).
I’m thinking of adding a third mu-metal shield. I do have one that will fit, but it will involve some ‘fridge modification’ (aka a hacksaw to the Lambda coil) so I think I’ll see how it does with 2 layers for now.
Addition of the magnet allows the critical current of the Josephson junctions to be changed in persistent mode (with less flux noise from the magnet itself) and the shields should help attenuate external magnetic interference.
So we’re ready to rock!