HF power-ramp experiments at HAARP: experimental determination of threshold power required for the onset of HF-enhanced plasma lines, and onset of artificial ionization in the lower F-Region ionosphere.
Abstract
High-power HF radio waves transmitted from the HAARP facility produce HF-enhanced ion-acoustic and Langmuir waves, and other effects such as artificial optical emissions and ionization. We present data from experiments where the HF power was slowly increased to determine the transmitted power levels for the onset of plasma waves and the onset of artificial ionization.The MUIR UHF radar (446MHz) was used as a diagnostic to detect plasma waves produced by HAARP. Past experiments have shown that power levels as low as 1% of full power can produce enhanced plasma waves. We have therefore used the unique capability of the HAARP phased array to extend the transmitted power to extremely low initial levels. This was accomplished by initially transmitting from only four dipoles from zero power upward in small power increments, and progressively adding more dipole transmitting elements. In this way it was possible to provide upward (or down-ward) power ramps from very low power (with no production of plasma waves) to full power.The HAARP antenna phasing was chosen for transmission in the direction of the earth's magnetic field and the transmitted power was determined at the center of the antenna beam in the direction of the magnetic field. Power densities and electric field values were calculated at 200km altitude, near the altitude of the observed plasma waves. The threshold electric field for the onset of plasma waves is about 50mV/m. However, the HF electric field near the HF reflection height is enhanced by the swelling effect of a factor about 4, thus the actual threshold electric field is about 200mV/m, which is consistent with theory. Because the upper hybrid resonance layer is located below the HF reflection layer, upper hybrid waves may also be excited parametrically by the HF heating wave. Due to the field-aligned nature of the upper hybrid waves, these waves could not be detected directly by the UHF radar. On the other hand, the excitation of these waves may be manifested by the appearance of artificial ionization in the lower region. Short wavelength upper hybrid waves, which have high parametric excitation threshold, effectively energize electrons via finite Larmour radius effect implemented as a Doppler shifted harmonic cyclotron resonance interaction. The onset time of significant artificial ionization was determined from the start of a sharp downward trend in the altitude of the plasma wave production; a threshold electric field value of about 700mV/m was calculated.In addition, spectral analysis of the plasma-line cascade was performed to determine the progressive heating effect on the ion-acoustic wave frequency. The plasma-line cascade results from the parametric decay instability followed by successive Langmuir decay instability events. These spectral lines are separated in the frequency domain by intervals corresponding to the Doppler shifted ion-acoustic frequency appropriate for the wavelength of the diagnostic radar.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E3629W