Helical motion. A particle of mass m and charge q moves in a uniform magnetic field B = Bk?. Assume that the particle is initially in the x-y plane and that its velocity is v = v0 ?i + u0k?. It follows from problem 3 that in the x-y plane the particle will move in a circle of radius r = mv/qB and at the same time it will move along the z-axis at a uniform speed u. Thus the particle moves along a helix. Notice that the axis of the helix is a field line

3. Magnetic Mirror. taxis 2 -Ax 15 helix In Spired Figure 5: Particle in a uniform field (left) and non-uniform field (right). *(a) Helical motion. A particle of mass m and charge q moves in a uniform magnetic field B = Bk. Assume that the particle is initially in the z-y plane and that its velocity is v = wi + unk. It follows from problem 3 that in the r-y plane the particle will move in a circle of radius r = mv/qB and at the same time it will move along the z-axis at a uniform speed u. Thus the particle moves along a helix. Notice that the axis of the helix is a field line