Generation and Diagnosis of TW/cm2 Electron Beams

Our experiments have demonstrated reasonably conclusively that electron beams in the 20-30 kA range at approximately 1 MeV can be focused into spots on the order of 1 mm in diameter or smaller to give electron beam densities as high as 2.7 MA/cm2. We have confirmed this measurement by several independent diagnostic techniques. We have also determined that the beam current is space charge limited and appears to follow the parapotential law Ip = R/d Ia¿o ln[¿o+(¿o2-1)1/2] Since the critical current is only proportional to R/d · ¿o, the ratio of Idiode/Icritical (for a given R/d) will become larger at a rate ln[¿o + (¿o - 1)1/2. This strongly suggests that the beam will self focus even more intensely at higher voltages. A limited number of tests at 3.MeV have indicated beam core spots smaller than 1/2 mm, the smallest we have observed to date. Our tests imply that an extension to AURORA-size beams (12 MeV) is feasible and would result in dramatic increases in delivered power together with further reduction in beam area.