This paper presents an explanation for the observation of high-energy protons in PetaWatt experiments. In experiments with solid targets exposed to laser intensities exceeding $10^{20}$ W/cm², high-energy electrons, hard bremsstrahlung, and energetic protons have been observed on the backside of the target. The authors propose that hot electrons generated on the front of the target travel through the target and ionize the hydrogen layer on the backside. These ions are then accelerated by the hot electron cloud to energies of tens of MeV over distances of tens of microns, where they are detected. The paper discusses two possible ion acceleration mechanisms and introduces a new method, Target Normal Sheath Acceleration (TNSA), which is only possible with ultra-intense, short-pulse lasers. The TNSA mechanism involves a "cloud" of hot electrons generated by the laser prepulse interacting with the target, which travel through the target and ionize the proton layer on the back. These protons are then accelerated by the hot electron cloud to high energies. The paper also discusses the physics of the TNSA mechanism, including the scaling of ion energy with electron temperature, and the effects of electron temperature and density on ion acceleration. It presents 1-D and 2-D simulations of the ion acceleration process, showing that the acceleration is strongly dependent on the spatial distribution of the electrons. The simulations show that ions are accelerated in a short time and over a short distance to high energies, and that the directionality of the ions is influenced by the curvature of the target surface. The paper concludes that the ion acceleration mechanism is the result of a population of hot electrons generated in the blow-off plasma created by the laser prepulse interacting with the front of the target. These electrons travel through the target and ionize the proton layer on the back, where they are accelerated by the hot electron cloud. The paper also discusses the potential applications of this mechanism, including the generation of ultra-high brightness ion beams through the use of an ion lens.This paper presents an explanation for the observation of high-energy protons in PetaWatt experiments. In experiments with solid targets exposed to laser intensities exceeding $10^{20}$ W/cm², high-energy electrons, hard bremsstrahlung, and energetic protons have been observed on the backside of the target. The authors propose that hot electrons generated on the front of the target travel through the target and ionize the hydrogen layer on the backside. These ions are then accelerated by the hot electron cloud to energies of tens of MeV over distances of tens of microns, where they are detected. The paper discusses two possible ion acceleration mechanisms and introduces a new method, Target Normal Sheath Acceleration (TNSA), which is only possible with ultra-intense, short-pulse lasers. The TNSA mechanism involves a "cloud" of hot electrons generated by the laser prepulse interacting with the target, which travel through the target and ionize the proton layer on the back. These protons are then accelerated by the hot electron cloud to high energies. The paper also discusses the physics of the TNSA mechanism, including the scaling of ion energy with electron temperature, and the effects of electron temperature and density on ion acceleration. It presents 1-D and 2-D simulations of the ion acceleration process, showing that the acceleration is strongly dependent on the spatial distribution of the electrons. The simulations show that ions are accelerated in a short time and over a short distance to high energies, and that the directionality of the ions is influenced by the curvature of the target surface. The paper concludes that the ion acceleration mechanism is the result of a population of hot electrons generated in the blow-off plasma created by the laser prepulse interacting with the front of the target. These electrons travel through the target and ionize the proton layer on the back, where they are accelerated by the hot electron cloud. The paper also discusses the potential applications of this mechanism, including the generation of ultra-high brightness ion beams through the use of an ion lens.