Total shadow area s as function of particle energy for dipolar field (8), normalized to the area of the geometrical disk. Two arrows indicate respective energy values of 3 and 12 TeV, for which shadow images are shown in Fig. 4. The respective side length 2 d of the injection window was chosen as 3.0° (1.6°, 1.0°) for E ∈ [1, 10] ([10, 20], [20, 100]) TeV to optimize spatial resolution, while at the same time keeping the field of view large enough to avoid losing any “shadow particles.”