Stopping of Heavy Ions in a Hydrogen Plasma

Experiments are presented which demonstrate, for the first time, the extreme stopping power of fully ionized hydrogen plasma for low-energy (45 keV/u) heavy ions. The plasma was created by an electrical discharge in a 20 cm long quartz tube, producing electron densities up to 7 ×{} 10¹⁶ cm^-3 at plasma temperatures well above 1 eV. In the described experiment a stopping power of 1080 MeV/(mg/cm²) was measured using krypton ions, which exceeds the corresponding value in cold neutral gas by a factor of 35. These measurements provide the first experimental confirmation of theoretical stopping power predictions close to the expected maximum in a fully ionized plasma.