The Twin Arm Dipole Spectrometers will guide the scattered particles from the interaction point to the detectors positioned in the focal plane of the magnetic system. The specific design of the spectrometer's magnets focus particles of different moment and scattering angle on different positions of the focal plane, thus effectively mapping those two variables on the cartesian coordinates of the focal plane. In this way it is possible to calculate the momentum and the scattering angle from an accurate, and potentially simpler, position measurement.
The magnetic system of the MAGIX's spectrometers is composed of a quadrupole followed by a dipole in each of the two arms. The former forces all the particles within its acceptance, which enters at different angles from the interaction point, to travel in a plane parallel to the faces of the dipole magnets. In an ideal case, assuming a point-like source, the distance of that plane from the medial plane of the system depends only on the scattering angle at the origin. Thus a measurement of such a distance can be converted to a measurement of the scattering angle which is the quantity of physical interest
For each of the above defined scattering planes, the dipole magnets, will bend the trajectory of the particles entering between their faces, the bending radius being proportional to the momentum of the travelling particle. Assuming the same azimuthal angle, after a fixed bending angle the particles will be dispersed along the radial direction so that a measurement of the exit position of the particle along that direction will provide an accurate measurement of the particle momentum.
If the edges of the dipoles are specifically designed, it is possible to define a single angle for which all particles of the same momentum, scattered to any azimuthal angle, will be focused on the same point. The locus of all focusing points for all scattering planes defines the focal plane of the magnetic spectrometers
Alternatively a magnetic system can be represented as an optical system with each magnet replaced by a corresponding optical element. In this representation, the magnetic system of the MAGIX's spectrometers are optically equivalent to a convex, focusing lens, followed by a prism which separates the different colours of the light.
Each spectrometer is housed in a single mechanical structure, pivoting around the centre of the target system. Because several of the most interesting processes we wish to study require the collection of scattered particles as forward as possible, in the direction of the incoming beam, the spectrometer housing is designed to rotate up to about 14 degrees from the beam line
Moreover many interesting process can benefit from the measurement of the scattered particles on different scattering plane which can reduce the systematic background of those analysis. This can be done rotating the spectrometers in the azimuthal direction.
Due to the low energy of the beam electrons is extremely important to minimize any material that the scattered particles need to cross before being detected. For this reason the spectrometers will have a windowless interface with the scattering chamber, that is they will share the same vacuum as the target so that the only window that must be crossed by those particle is that which separate the magnets from the detector chamber.