Liquid nitrogen is pumped on and freezes into a sponge of solid nitrogen.
The liquid nitrogen is in a 600 or 800 ml beaker under a shielded bell jar on top of the red vacuum cart. A cold trap is not necessary if only nitrogen is being pumped on.
It is important that the beaker of liquid nitrogen not have frozen water vapor on its side, as the view is impaired. A camera is zoomed in on the beaker, which is in a thick glass bell jar and an acrylic tube shield.
With the pump running and the bell jar vent open, pour the nitrogen and cover the beaker with bell jar. Open up...
Read more about Nitrogen Phase Change