Short-pulse Heating: Theory, Experiments and Scaling

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Lizbeth Wilkinson
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1 PARS Workshop November 22 Short-pulse Heating: Theory, Experiments and Scaling Tom Wallace

2 Outline Time domain measurements and impulse responses Very simple way to predict results of conventional heating vs. f Also shows how to optimize scanning Impulse and frequency responses Ionospheric heating Earth-ionosphere waveguide Implications for higher power facilities What will the full HAARP facility produce? Will the optimum heating frequency change?

3 Time-Domain Measurements When we measure an ionospheric signal in the time domain, we see the convolution of the response of the ionosphere to heating with the response of the Earth-ionosphere waveguide With high time resolution measurements of short heating pulses, these two responses can be easily separated and examined Recent time-domain measurements agree very well with theory and simulation

4 Impulse Response of the Ionosphere Short pulse heating allows us to measure the impulse response of the ionosphere directly: Under the heated region, there are ~5 ms before the first echo arrives (~15 km round trip) The impulse response typically lasts about 2 ms

5 Which Impulse Response to Look At? S(t) from a short heating pulse: B(t) from the same pulse: In the past, we ve looked at S(t) as a measure of performance in simulations. Looking at B(t) is generally more useful, and it can be experimentally measured.

6 Why Does B(t) Look Like This? m È rˆ B( x, t) = Ú Í J[ x, t'] ret 2 4p Î r V + t J[ x, t'] ret rˆ cr dv If Ú J dv ª ÓEA, r ^ J and large compared to the size of the source region, and E is constant, B AEm È r x, t) ª Í Ó( t) + Ó( t) 4p r Î c t ( 2 So the magnetic field depends on both S(t) and its time derivative; in fact, the derivative is usually more important even at close range

7 What Determines S(t) and its Time Derivative? Maximum value of S: electron density profile (n e vs. h), heated temperature profile (T e vs. h) Heated temperature profile: electron density profile, nonlinearly on quiver energy (e.g. runaway) Turn-on time constant: quiver energy and temperature profile Turn-off time constant: temperature profile Electron density profile is critical to determining heating altitude; all the following simulations use Barr & Stubbe s profile 2 (normal nighttime polar ionosphere) and give good agreement with measurements.

8 Impulse Response of 3.3 MHz Ionospheric Heating 2.5 Current HAARP FDP 96 kw X-mode

9 Frequency Response of 3.3 MHz Ionospheric Heating 7 Current HAARP FDP 96 kw X-mode

10 Impulse Response of the EIW at km Range Observed values of the reflection coefficient R are h( t) = Â n= R n d ( t -t -( 2n + 1) h / c) r

11 Frequency Response at km Range

12 Combined 3.3 MHz Response at km

13 Experimental 3.3 MHz Frequency Response at 12 km k 2H z 3.3 MHz Heating on 4 March 21 o 1.4 t d e r a p m o C l e v e L d l e i F e g a r e v A Frequency (Hz)

14 Impulse Response of the EIW at a Distance Source Receiver ( ) ( ) ( ) Â = ˆ Á Ë Ê = 2 2 / 1 2 / 1 2 ) ( n r n c n d h n t R t h t d h d

15 Impulse Response of the EIW at 5 km Range

16 Frequency Response of the EIW at 5 km

17 Combined 3.3 MHz Response at 5 km

18 3.3 MHz Temperature Profile for Full HAARP Facility Temperature after 5 ms heating

19 Full HAARP 3.3 MHz Impulse Response

20 Full HAARP 3.3 MHz Frequency Spectrum 35 Full HAARP 3.6 MW X-mode

21 Ratio of Full HAARP to Current FDP Field

22 Full HAARP 3.3 MHz Heating at km Range Predicted Response for Conventional Heating

23 Full HAARP 3.3 MHz Heating at 5 km Range 4 Predicted Response for Conventional Heating

24 Summary Conventional heating is predicted to produce higher fields than the ~3.75x increase expected from a simple power scaling (result of faster heating and runaway) Not yet clear what to expect at higher frequencies with full HAARP Higher frequencies mean higher heating altitudes; this produces higher S(t), but slower changes This result will suggest optimum scanning strategy for the full HAARP

ELF/VLF GENERATION IN THE IONOSPHERE STATE OF THE ART

ELF/VLF GENERATION IN THE IONOSPHERE STATE OF THE ART Dennis Papadopoulos APTI Wih Suppor from Tom Wallace, Gennadi Milikh And Mike McCarrick Presenaion o PARS Workshop November, 4,21 A LITTLE HISTORY