Fig. 1. Schematic diagram of proton radiography of a two-dimensionally isotropic and stochastic magnetic field.

Fig. 2. (a) Transversal cross-section of the pre-set stochastic magnetic field tubes at $y=2~\text{mm}$. (b) Two-dimensional spectrum of the magnetic field by taking Fourier transforms of the field in (a), which shows an isotropic feature.

Fig. 3. One-dimensional energy spectrum of the magnetic field $E_{B}(k)$. The red line corresponds to the energy spectrum obtained by taking Fourier transforms of the pre-set magnetic field in Figure 2(a), whereas the blue line corresponds to the energy spectrum extracted from proton radiography with Equation (22).

Fig. 4. (a) Proton density perturbation $\unicode[STIX]{x1D6FF}n/n_{0}$ on the detection plane when $L_{D}=5~\text{cm}$. (b) The extracted two-dimensional distribution of $u_{y}$. (c) One-dimensional distributions of $u_{y}$ at $y=2~\text{mm}$ from the extracted results and the pre-settings.