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The analysis line can be used in two different modes.
In the focus mode, the maximum momentum acceptance is achieved (±2%) by making the analysis line achromatic with a maximum dispersion value 1.5 cm/% reached at the intermediate image plane (see figure below). In this mode the coordinates of the fragment at the spectrograph focal plane are sensitive to the momentum of the beam impinging on the target. The momentum of each particle beam must then be tracked, significantly limiting the resolution at the focal plane to about 1 part in 1000 in energy.
In the dispersion-matching mode the whole system (analysis line + spectrograph) is achromatic in the focal plane (see Fig. xxx). The analysis line has a 2D focus (in the dispersive x and non-dispersive y directions ) in the target point and has a high dispersion of about 11 cm/%, limiting the momentum acceptance to ±0.5%. The intermediate image plane has also a 2D focus and a dispersion of 1.5 cm/%. This mode provides the highest possible energy resolution (1 part in 5000 for a 1-mm wide beam spot), since it does not require momentum tracking. Please, be aware that in this configuration, two of the quadrupoles before and after the intermediate image plane (I210TB and 217TB) are strongly focusing, thus requiring unusually higher currents than for a setting in focus mode running at the same rigidity. This may represent a restriction to consider when planning an experiment at high magnetic rigidities (e.g. using a 3H secondary beam).
The monochromatic mode is still in development stage. The motivation is the production of low-energy (5-10 MeV) secondary beams from a high-energy fragmentation beam. The implementation of this mode requires the use of a mono-energetic wedged installed in the intermediate image station. The wedge profile must be built on a case-by-case basis, considering the specific energy and nuclei in the experiment.