Value chain · CLM-0694
In plain terms
The scientist who published the threshold formula says a single threshold number does not really exist. Whether the beam becomes unstable depends on the size of the ripples it is making, and as the beam gets stronger, smaller ripples start to grow too. He also warns the threshold drops very low when the beam happens to run almost along the Earth's magnetic field.
The claim as recorded
Duncan attaches an explicit caveat to his own threshold formula that qualifies every single-number threshold comparison built on it: "It is not possible to determine a threshold power in the usual sense for thermal self-focusing because the instability threshold power depends nonlinearly on the excited striation width. As the incident power flux increases, smaller striations can become unstable." He adds that the power flux needed to amplify any particular striation size "becomes very small when the self-focusing beam nearly parallels the geomagnetic field".
Scope and limits
This is a caveat about the physics, not a retraction of the formula. It does not tell you what number to use instead.
What it assumes
No assumptions are recorded against this claim.
Where it comes from
Verbatim from the rendered image of PDF p.7, left column, immediately after equation (11) and its definitions.
Related records
- Answers question
- QST-001 not published in this release
Cite this
energyaperture.com/c/clm-0694
CLM-0694, Energy Aperture, as of 1980-06.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-117
- CLM-0092Duncan's own 1980 paper says the flawed earlier calculation was Holway and Meltz's, and praises Perkins and Roble's as the first thorough...CLM-0093The thousand-fold disagreement between the two published versions was a lost micro prefix in the abstract I was working from. The papers...CLM-0693The formula used here for when a microwave beam starts to focus itself in the ionosphere has now been checked against the original 1980...CLM-0695The 1980 paper says the SPS beam is expected to cause the ionosphere to focus it. It backs this with radar measurements from Arecibo, made...