Technical Notes > Applications in Electromagnetics > Magnetostatics > A Magnet Coil in 2D Cylindrical Coordinates

As a first example, we will calculate the magnetic field created by a coil, using 2D cylindrical (r,z) geometry. We will apply current only in the azimuthal direction, so the only nonzero component of will be the azimuthal component. With only a single component normal to the computational plane, the gauge condition is automatically satisfied, since .

In the descriptor which follows, note that we have chosen to align the cylindrical axis with the horizontal plot axis. FlexPDE uses a right-hand coordinate system, so in this case positive is outward from the plot page.

Descriptor 2.1: Magnet_Coil.pde

Title 'AXI-SYMMETRIC MAGNETIC FIELD'

Coordinates

xcylinder(Z,R)

Variables

Aphi { azimuthal component of the vector potential }

Definitions

mu = 1 { the permeability }

J = 0 { global source term defaults to zero }

current = 10 { the source value in the coil }

Br = -dz(Aphi) { definitions for plots }

Bz = dr(r*Aphi)/r

Equations

Curl(curl(Aphi)/mu) = J

Boundaries

Region 1

start(-10,0)

value(Aphi) = 0 { specify A=0 along axis }

line to (10,0)

value(Aphi) = 0 { H x n = 0 on distant sphere }

arc(center=0,0) angle 180 to close

Region 2

J = current { redefine source value }

start (-0.25,1)

line to (0.25,1) to (0.25,1.5)

to (-0.25,1.5) to close

Monitors

contour(Bz) zoom(-2,0,4,4) as 'FLUX DENSITY B'

contour(Aphi) as 'Potential'

Plots

grid(z,r)

contour(Bz) as 'FLUX DENSITY B'

contour(Bz) zoom(-2,0,4,4) as 'FLUX DENSITY B'

elevation(Aphi, dr(Aphi), Aphi/r, Bz)

from (0,0) to (0,1) as 'Near Axis'

vector(Bz,Br) as 'FLUX DENSITY B'

vector(Bz,Br) zoom(-2,0,4,4) as 'FLUX DENSITY B'

contour(Aphi) as 'MAGNETIC POTENTIAL'

contour(Aphi) zoom(-2,0,4,4) as 'MAGNETIC POTENTIAL'

surface(Aphi) as 'MAGNETIC POTENTIAL'

viewpoint (-1,1,30)

End