Artist view of the momentum spectrometer: The deuterium molecules, prepared in a supersonic jet going from the bottom to the top, are intersected with the pulsed photon beam in the middle of the copper rings which define a homogenous electric field. The large coils are a Helmholtz pair that establishes a uniform magnetic field parallel to the spectrometer axis. The charged nuclei (ions) are guided to a position sensitive detector to the left while the electrons spiral to the right in the magnetic field to a similar detector. Unlike the light electrons, the motion of the heavy ions is not significantly influenced by the magnetic field. Credit: Lawrence Berkeley National Laboratory