Summary

{{Information

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English: Magnetic field around a three-loop Barker coil consisting of three round current loops with identical radius ${\displaystyle R}$ aligned along a cylinder. Distances and currents are optimized to remove variations in the central magnetic field, up to its 5th-order derivative with respect to the center.

The inner loop is placed around the center and carries the current ${\displaystyle 0.531463\,I}$. The outer loops have an axial position ${\displaystyle z=\pm 0.760051\,R}$ and current ${\displaystyle I}$. The central magnetic field is ${\displaystyle B_{0}=0.770361\mu _{0}I/R}$.

The dots symbolize where the current flows out of the image plane, whereas the crosses are where the current flows into the plane.

|date=2018-03-13 |source=Own work |author=Geek3 |permission= |other versions= |other fields={{Igen|VectorFieldPlot|0|+|c1=

1. paste this code at the end of VectorFieldPlot 1.7

doc = FieldplotDocument('VFPt_barker3_coil', commons=True) field = Field({'ringcurrents':[[-0.7601,0,0,1,1], [0,0,0,1,0.5315],

                              [0.7601,0,0,1,1]]})

y0 = 0.952 Fsum = ig.quad(lambda y: field.F([0., y])[0], -y0, y0)[0] nlines = 16 ystart = [op.brentq(lambda ys: ig.quad(lambda y: field.F([0., y])[0],

   -y0, ys)[0] / Fsum - (0.5+i)/nlines, -y0, y0) for i in range(nlines)]

for x0, y0 in [ [0, y] for y in ystart]:

   line = FieldLine(field, [x0, y0], directions='both', maxr=10)
   doc.draw_line(line, arrows_style={'dist':2,
       'min_arrows':2, 'max_arrows':4, 'offsets':[0,0.5,0.5,1]})

for x, y in [ [-0.7601, -0.87], [0.7601, -0.87], [-0.7601, 0.87], [0.7601, 0.87] ]:

   line = FieldLine(field, [x, y])
   doc.draw_line(line, arrows_style={'min_arrows':1, 'offsets':[0.5,0.5,0.5,0.5]})

doc.draw_currents(Field({'ringcurrents':[[-0.7601,0,0,1,1], [0.7601,0,0,1,1]]})) doc.draw_currents(Field({'ringcurrents':0,0,0,1,0.5315}), scale=sqrt(0.5315)) doc.write() }} }}

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