Value chain · CLM-0072
In plain terms
The 1978 study gives 12 milliwatts per square centimetre for runaway, give or take a factor of two, and says no threshold can be set in the usual way for the self-focusing effect, though its summary repeats an earlier study's figure of 20 for it.
The claim as recorded
Duncan and Gordon give a thermal runaway threshold of 12 mW/cm2 within a factor of two at 2.45 GHz at about 100 km altitude and approximately 67 mW/cm2 at 5.8 GHz, from the relation F_threshold in erg per square centimetre per second equals 2.8e-13 times frequency in hertz squared times neutral temperature in kelvin to the power MINUS one half; they state that a threshold power cannot be determined in the usual sense for thermal self-focusing and use 20 mW/cm2 as the input power density for their Figure 3.2, while their abstract states that "the previous study reaffirmed the predicted threshold for thermal self-focusing at a power density of 20 mW/cm2 (within a factor of two)"; the report does not derive the 20 mW/cm2 figure itself or date the previous study.
Scope and limits
The relation retains only ohmic heating and rotational cooling by nitrogen and oxygen, dropping the solar heat term, vibrational excitation, oxygen fine-structure excitation and thermal conduction. Its authors state the neglected terms mean the calculated thresholds "underestimate the true threshold predictions", so the true value is higher. The 20 mW/cm2 self-focusing figure may be cited only as the abstract's report of an earlier prediction, within a factor of two, which the report's own body says is not a threshold in the usual sense; it may NOT be cited as a threshold this report derived.
What it assumes
No assumptions are recorded against this claim.
Where it comes from
Relation read by rendering the page as an image, because the text layer drops the minus sign. Verified three independent ways: by back-solving from the document's two worked values, by image inspection in one pass, and by image inspection in a second independent pass. Only f in hertz with the negative half-power on temperature reproduces both 12 mW/cm2 at 2.45 GHz and 67 mW/cm2 at 5.8 GHz. Unit conversion: 1 erg/cm2.s = 1e-3 W/m2.
Related records
- Answers question
- QST-009 not published in this releaseQST-010 not published in this release
- Supersedes
- CLM-0064 not published in this release
Cite this
energyaperture.com/c/clm-0072
CLM-0072, Energy Aperture, as of 1978.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-108
- CLM-0043The study the 1978 reference system cites put the level where the beam may start to disturb the ionosphere at about 20 milliwatts per...CLM-0045The apparent conflict between 12 and 23 was not an error. The underlying study gave a range, and the figure adopted sits near the top of it.CLM-0066The figure adopted in 1978 was higher than each of the lower figures in the studies it cited, though those figures were themselves...CLM-0082The formula is the right one for the conditions space solar power would create. It was written for this case, not borrowed from a different...CLM-0083The formula is the right type but nobody has said how far it can be pushed, and at space solar power frequencies the wave is about 200...CLM-0085The 1978 formula does not give a threshold. It relates threshold power to the width of the plasma structures produced, so getting a single...CLM-0101The 1978 contract required the researchers to report fixes if ionospheric disturbance pushed the pilot-beam phase error past 2 to 3...CLM-0132A 1978 NASA-funded study calculated that a beam of about 12 milliwatts per square centimetre at 2.45 GHz would be the point where the...More on the source page.