Radius		(m)
Current		(MA)
Radial Position		(m)
Axial Position		(m)

Calculate!

# BA Wire Circle
# 2025-4-25 Kiyoshi Yoshida
from scipy.special import ellipk, ellipe
from numpy import abs, pi, sqrt, sin, cos, arctan2
small_dist = 1.00e-6

def main():
  print("Magnetic Field and Vector Potential from Circular Wire Ring")
  ra=0.5; ia0=1.0; rp=0.01; zp=0.01
  while True:
    ia0 = inpfuncf("Current (MA), stop<0", ia0)
    if ia0 <0: break
    ra = inpfuncf("Radius (m)", ra)
    rp = inpfuncf("rp (m)", rp)
    zp = inpfuncf("zp (m)", zp)
    ia= ia0*1.0e6
    br, bz, at = ba_wirecir(rp, zp, ia, ra)
    print("Br (T): {:.6f}".format(br))    
    print("Bz (T): {:.6f}".format(bz))    
    print("At (Tm): {:6f}".format(at))    

def ba_wirecir(r, z, i, ra):  # Smythe
  cn = i*1.0e-7
  if r < small_dist:    # on axis
    at = 0.0
    br = 0.0
    bz = 2.0*cn*pi*ra**2 / (z**2 + ra**2)**1.5
  else:
    if r==ra:
      r= ra - small_dist
    a2 = (ra + r)**2 + z**2
    a1 = sqrt(a2)
    b2 = (ra - r)**2 + z**2
    k2 = 4.0*r*ra/a2
    k1 = sqrt(k2)
    km = float(ellipk(k2))   # K(m): Complete elliptic integral 1st
    em = float(ellipe(k2))   # E(m): Complete elliptic integral 2nd
    at = 4.0*cn/k1*sqrt(ra/r)*((1 - k2*0.50)*km - em)
    br = 2.0*cn*z/(r*a1)*(-km + (ra**2 + r**2 + z**2)/b2*em)
    bz = 2.0*cn/a1*(km + (ra**2 - r**2 - z**2)/b2*em)
  return br, bz, at

# keyboard input float
def inpfuncf(msg,x):
  s=input(msg+" : "+str(x)+" : ")
  if s=='':
    y=x
  else:  
    y=float(s)
  return y

if __name__ == "__main__":
  main()