What is the mechanism for plasma compression in the video below?

I provide a still from the video and a link to the actual video on YouTube.

[![enter image description here][1]][1]


https://www.youtube.com/watch?v=gsjWGz3YE5o

BTW, is there a gradient in the magnetic field, meaning that it is stronger near the axis of the glass tube? Like in the picture below?

[![enter image description here][2]][2]


  [1]: https://i.sstatic.net/FPGb8.jpg
  [2]: https://i.sstatic.net/iQ051.png