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As a simple example from the physics of magnetically confined plasmas, consider an axisymmetric system with circular, concentric magnetic flux surfaces of radius (a crude approximation to the magnetic field geometry in an early tokamak but topologically equivalent to any toroidal magnetic confinement system with nested flux surfaces) and denote the toroidal angle by and the poloidal angle by .
In electromagnetism, a toroidal moment is an independent term in the multipole expansion of electromagnetic fields besides magnetic and electric multipoles. In the electrostatic multipole expansion, all charge and current distributions can be expanded into a complete set of electric and magnetic multipole coefficients. However, additional terms ...
Because the toroid is a closed-loop core, it will have a higher magnetic field and thus higher inductance and Q factor than an inductor of the same mass with a straight core (solenoid coils). This is because most of the magnetic field is contained within the core.
= V·s/(A·m) is the magnetic constant, is the major radius of the toroid, is its minor radius. This formula assumes the turns are evenly spaced and that these turns are small relative to the radius of the coil itself.
In a toroidal fusion power reactor, the magnetic fields confining the plasma are formed in a helical shape, winding around the interior of the reactor. The safety factor, labeled q or q(r), is the ratio of the times a particular magnetic field line travels around a toroidal confinement area's "long way" (toroidally) to the "short way" (poloidally).
In the tokamak design the total field is a combination of the external toroidal field and the current-induced poloidal one, so the "beta poloidal" is sometimes used to compare the relative strengths of these fields. And as the external magnetic field is the driver of reactor cost, "beta external" is used to consider just this contribution.
The magnetic vector potential, , is a vector field, and the electric potential, , is a scalar field such that: [5] = , =, where is the magnetic field and is the electric field. In magnetostatics where there is no time-varying current or charge distribution , only the first equation is needed.
The most common definition of toroidal coordinates (,,) is = = = together with () = ().The coordinate of a point equals the angle and the coordinate equals the natural logarithm of the ratio of the distances and to opposite sides of the focal ring