Helical Magnetic Field (Solenoid)

import matplotlib.pyplot as plt
import numpy as np

# Helical magnetic field (like in a solenoid)
n = 5
r = np.linspace(0.5, 2, 3)
theta = np.linspace(0, 2*np.pi, n)
z = np.linspace(-2, 2, n)

R, THETA, Z = np.meshgrid(r, theta, z)
X = R * np.cos(THETA)
Y = R * np.sin(THETA)

# Helical field: B_theta + B_z
U = -np.sin(THETA) * 0.5 / R
V = np.cos(THETA) * 0.5 / R
W = np.ones_like(Z) * 0.8

fig = plt.figure(figsize=(10, 8), facecolor='#0a0a0f')
ax = fig.add_subplot(111, projection='3d', facecolor='#0a0a0f')

ax.quiver(X, Y, Z, U, V, W, length=0.35, normalize=True,
          color='#4ade80', alpha=0.85, arrow_length_ratio=0.3)

ax.set_xlim(-2.5, 2.5)
ax.set_ylim(-2.5, 2.5)
ax.set_zlim(-2.5, 2.5)

ax.set_xlabel('X', color='white', fontsize=10)
ax.set_ylabel('Y', color='white', fontsize=10)
ax.set_zlabel('Z', color='white', fontsize=10)
ax.set_title('Helical Magnetic Field (Solenoid)', color='white', fontsize=14, fontweight='bold', pad=20)

ax.tick_params(colors='#64748b', labelsize=8)
ax.xaxis.pane.fill = False
ax.yaxis.pane.fill = False
ax.zaxis.pane.fill = False
ax.xaxis.pane.set_edgecolor('#1e293b')
ax.yaxis.pane.set_edgecolor('#1e293b')
ax.zaxis.pane.set_edgecolor('#1e293b')

ax.view_init(elev=20, azim=45)
plt.tight_layout()
plt.show()