Diagnosing superstrong turbulence in plasma by forbidden line measurements

Observations of satellites of forbidden helium lines yield a new diagnostic of superstrong turbulence in a relativistic beam–plasma system. Comparing the satellite-to-allowed line intensities allows estimates of the volume fraction of atoms that experience high Langmuir fields, i.e., 〈E2〉≥4πnTe. An independent estimate follows from counting the total number of events, and using the calculated optical efficiency of the system, this ratio is estimated independently—agreement is good. This ratio may be the packing fraction of high field cavitons. Its value (∼0.1) implies that collision processes may be important to caviton dynamics.