QED pair cascades in lasers and pulsars

4 problems

• Laboratory pair plasma with measurable collective effects

  Open

  For the pairs from a cascade to act as a true plasma, they must be dense enough to respond together to fields. The question is whether existing lasers and electron beams can produce such a pair plasma and show its collective behavior.

• Does pair cascade absorption cap the attainable laser intensity?

  Contested

  If a few seed electrons start an avalanche, the resulting pair plasma could absorb the laser before it reaches full focus. The question is whether this sets a hard ceiling on how intense a focused laser can get.

• First laboratory observation of a self-sustained avalanche QED cascade

  Open

  In colliding laser beams of enough intensity, the field itself should keep re-accelerating new pairs so their number grows exponentially. No laboratory has yet reached the needed intensity or seen this growth.

• Can pulsar pair cascades supply the pairs inferred in pulsar wind nebulae?

  Contested

  Each charged particle pulled off a pulsar should create many pairs through cascades, and the nebulae around pulsars show how many pairs actually came out. Cascade models may fall short of the number some nebula models need.