Another type of containment is the magnetic mirror method. This method is considered to be the 'open' type. In this system, an electric current generates a magnetic field, which "pinches" the plasma and contains it within the field. Because of the way the magnetic fields act, the plasma contained was cylindrical. Two stronger magnetic coils were placed at the ends to lessen plasma loss (the Tokamak's donut shape was to prevent this). The coils create a bottleneck effect to the plasma, which prevents the plasma from escaping.