We got a kilo of dry ice pellets from BOQ in Welshpool and used a small aquarium with black felt from Spotlight, lining the bottom of the aquarium and Isopropyl alcohol (100%) to moisten the felt. You then tip the aquarium upside down on top of the lab tray containing polystyrene foam insulator, the dry ice, a metal plate and a thin sheet of cardboard covered with black PVC tape.
We used double sided tape to hold the felt to the bottom of the aquarium. A better idea is to use pairs of rare earth magnets, some inside and some outside the aquarium to hold the felt securely. It worked fabulously and we saw hundreds of tracks of particles over more than half an hour.
We used a very old slide projector from the side for illumination. It is important to use 100% Isopropyl alcohol, not the 60% often sold as a cleaning solution.
You tube link is https://www.youtube.com/watch?v=BeohJbfgp_M