1. Interpreting angular divergence measurements Chris Ridgers, Mark Sherlock, Robert Kingham Roger Evans

2. Diagnosing the rear surface Probe rear-surface of the target Large-scale structures on rear - apparent angular divergence larger than actual divergence Target Laser Observer Rear-surface structure Apparent divergence Real divergence

3. Temperature and density profiles Temperature profile wider than beam because… …Ohmic heating saturates TeTe nfnf

4. Rear-surface sheath field Electric field and potential profiles wider than n f Ion spot POOR indicator of angular divergence nfnf EyEy  Sheath:

5. Diagnosing the rear surface Fast-electron number-density (radiation from back) Good – but measure OTR and CTR Background temperature (Planckian spectrum) Over estimate Sheath electric field (ion spot size)? very large overestimate

6. K- measurements Electrons at max K- cross section are nearly isotropic Large K- spots for thin targets implies very large divergence Thicker targets sample electron source at higher energies – more directional K- needs to included in model

7. The initial burst of electrons are the only ones able to escape so the measured energy is lower ( these electrons don’t lose (much) energy in the sheath because they are largely responsible for generating the sheath ). ) Energy distributions from solid targets