The flux loop is common on tokamaks, magnetic mirrors, Field-reversed configurations, the Levitated dipole experiment and the polywell. In tokamaks a set of loops is used, and these are spaced slightly off-center and non-concentrically. Placing the loops intentionally asymmetrically allows the users to find the magnetic field density at different points inside the tokamak. The distance between the loops was determined by shafranov, and is sometime called the "shafranov distance".