The precise regulation of deposition ion energy is a critical frontier in low-temperature plasma physics and surface modification. Bipolar pulse high-power impulse magnetron sputtering (BP-HiPIMS) has emerged as a promising technology that achieves the acceleration of high-density ion fluxes via a reversed positive pulse. However, the basic characteristics and formation process of the double layer (DL) during the positive pulse and its effects on the energy of deposition ions remain incompletely understood. This study aims to systematically investigate the spatial distribution and temporal evolution of the DL and elucidate the underlying correlations between discharge parameters and ion acceleration mechanisms. A home-built emissive probe system (APD-EP3A) and an energy-resolved mass spectrometer (Hiden PSM003) were synchronously employed to diagnose the BP-HiPIMS discharge with a Cu target. The emissive probe, operating in the saturated electron emission regime, provided a high spatial resolution of ~1 mm and a temporal resolution of ~200 ns to capture the transient plasma potential (V_p) evolution from the near-target region (z＜25 mm) to the bulk plasma (z=25~80 mm). Specifically, the evolutionary trajectories of the DL structure and the time-averaged ion energy distribution functions (IEDFs) were comprehensively evaluated under varying positive pulse voltages (U₊=+150 V and U₊=+250 V) and negative pulse widths (τ_-=25~200 µs). The spatiotemporal potential mapping reveals that upon the onset of the positive pulse, the near-target plasma undergoes a dynamic physical reconstruction from a quasi-neutral state to a DL structure. Notably, the physical boundary between the high- and low-potential regions appears near the magnetic null point (z=20~25 mm). This spatial anchoring effect exhibits strong physical robustness governed by the cross-field transport resistance of the magnetic mirror topology. Furthermore, the structural reconstruction of the DL generates a steep local spatial potential drop of ~20 V, serving as the primary axial acceleration source for traversing ions. Varying the discharge parameters demonstrates distinct regulatory mechanisms on the DL and ion energy. Elevating the positive voltage (U₊) not only directly increases the spatial potential drop of the DL boundary but also establishes a clear quantitative correspondence with the high-energy shift of the ion peak in IEDFs. Simultaneously, a higher U₊ shortens the DL formation time, effectively extending the acceleration time window and thereby increasing the overall proportion of high-energy ions. Conversely, prolonging the negative pulse width (τ_-) intensifies the gas rarefaction effect, rendering low-ionization-energy metal atoms the dominant species upon the onset of the positive pulse. While this compositional evolution significantly accelerates the DL formation process, a longer τ_- simultaneously allows a massive flux of unaccelerated initial ions to diffuse to the substrate. This dramatically expands the absolute base of low-energy ions, ultimately leading to a monotonic decrease in the relative proportion of high-energy ions. This study provides direct spatial measurement evidence for the highly transient DL structure and physically elucidates the logical chain from microscopic electric field reconstruction to macroscopic ion kinetic energy gain, offering a theoretical foundation for tailoring energetic ion fluxes to deposit superior-performance advanced thin films.