This tube contains a mixture of argon and neon gas. The tube is connected to electrodes that send an electrical current through the gas, causing it to become plasma. Sliding the magnet shows how the magnetic field affects the plasma.
In a Tokamak fusion reactor, huge electromagnets are used to contain the glowing plasma producing fusion energy. Magnetic fields are used to surround the plasma in the Tokamak because no solid material can withstand the extremely high temperatures of the plasma, which reach 180 million degrees Fahrenheit.