Magnetic field lines

The problem with all the mirror approaches is that none has achieved the degree of confinement quaUty that the closed systems have. Closed systems ate characterized by magnetic field lines that close on themselves so that charged particles following the field lines remain confined within the system. 

Magnets with associated magnetic field lines. 

In the schematic the detector coil (hatched boxes) and its associated field lines are shown (dotted) and are seen to be always orthogonal to the permanent magnet field lines (solid). The magnitude of the static field is constant in the horizontal plane (thick black line). A stepper motor and gear-drives for raising the whole assembly relative to the external surface are visible in the photograph. 

Twenty years later, in 1933, the German physicist Walter Meissner (together with his co-worker Robert Ochsenfeld) discovered that superconductors cannot be crossed by magnetic field lines. This property is today defined as the Meissner effect. 

The Meissner Effect and Levitation. Besides the absence of electrical resistance, a superconducting material is characterized by perfect diamagnetism. The exclusion of magnetic field lines from a material when it passes from a normal state to a superconducting state is shown schematically in Figure 3. 

Figure 3 The Meissner effect. A superconductor (here in a circular section) excludes the magnetic field lines when it is frozen below the critical temperature...

Scientists are interested in superconductors because they have a number of properties that arise from their lack of resistance. For example, once a current is induced in a circuit made with a superconducting material, the current continues to flow through the circuit indefinitely, without ever diminishing. Also, superconductors have the ability to completely repel magnetic field lines. This means that a magnet placed over a superconductor hovers in mid-air, as shown in Figure 4.25. 

Whenever matter is placed in a magnetic field, electromagnetic interactions alter magnetic field lines, which are stretched or accumulated. The magnetic susceptibility of the bulk medium influences the individual magnetic resonance frequencies so that there is an extra frequency shift called the BMS shift. 

On study of the equation related to the magnetic field, and taking into account all the previous remarks, both current density lines and magnetic field lines appear to be orthogonal with one another. 

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