In second case with a magnetic field in the x-direction the initial velocity is zero but there is a check-box so that you can give the particles an initial velocity in the +x direction. In the...In second case with a magnetic field in the x-direction the initial velocity is zero but there is a check-box so that you can give the particles an initial velocity in the +x direction. In the third case the magnetic field is rotated so that it points into the screen (which is now the x direction) and the particles have an initial velocity in the +z direction.