1D PIC simulations initialization setups. (a) Single-shock case: a hydrogen plasma (n₁ = 2n₀ = 2 × 10¹⁸ cm⁻³, T_e1 = 130 eV and T_i1 = 200 eV) drifts through a background hydrogen plasma (n₁ = n₀ = 1 × 10¹⁸ cm⁻³, T_e2 = 80 eV, and T_i2 = 20 eV) with a drifting velocity of v_d = 350 km s⁻¹ (see Table 2). (b) Double-shock case: a background plasma (n₂ = n₀ = 1 × 10¹⁸ cm⁻³, T_e2 = 80 eV, and T_i2 = 20 eV) is set at rest between two counter-streaming denser plasmas (n₁ = n₃ = 2n₀ = 2 × 10¹⁸ cm⁻³, T_e1 = T_e3 = 130 eV and T_i1 = T_i3 = 200 eV). The drifting velocity v_d = 350 km s⁻¹ imposed to the protons in both configurations leads to a shock velocity of v_s ≈ 640 km s⁻¹. The simulation is initialized ∼11 ns after the lasers start ablating the targets, with a distance of 1.8 mm in between the two shock fronts, while the box has a total length L_x = 11 mm.