A magnetic field exerts a sideways force on a moving electric charge, causing it to turn sideways. As long as the magnetic field is on, this turning continues, causing the electric charge to travel in spirals. Once traveling in spirals, an electric charge acts like a small, oriented, permanent magnet and is therefore repelled from regions of high magnetic field gradient. Therefore, electric charges tend to spiral around magnetic field lines and be pushed away from regions where magnetic field lines bunch up. These two effects cause electric charges to get trapped along magnetic field lines that are strong enough. Examples of this effect include ions trapped in earth's ionosphere, radiation trapped in earth's radiation belts, hot plasma looping over the sun's surface in solar prominences, and plasmas contained in the laboratory using magnetic traps.