Fields and Waves

Wave-Plasma Interactions in Artificial Modification of the Ionosphere and Magnetosphere by Powerful Radio Waves

Participating Faculty: Spencer Szu-pin Kuo
Collaborators: Drs. James T. Huynh, Paul Kossey, Steven Kuo, and Prof. M. C. Lee
Sponsors: the High Frequency Active Auroral Research Program (HAARP) and the Office of Naval Research (ONR)

Background

A major facility for conducting experiments related to basic radio science research as well as DoD missions is under development in Gakona, Alaska, as part of the High Frequency Active Auroral Research Program (HAARP). The present HAARP HF transmitting system is being expanded from a phased-array antenna of 48 elements to one with 180 elements. After completion of this upgrading, its maximum effective radiated power (ERP) will exceed 1 GW. A backscatter radar (450 MHz) will also be installed soon near the heating site to improve the remote sensing capability of the HAARP. A key objective of the program is to explore physical processes that can be initiated in the ionosphere and magnetosphere via interactions with high power radio waves. Shown in Fig. 1 is a photo of the HAARP HF transmitting system before being upgraded.

Two DoD missions of the HAARP program are 1. an ionospheric virtual antenna for underwater communications and 2. an in-situ array of ELF/VLF transmitters for the population control of radiation belt electrons.

Motivation

Signals in communications with submerged submarines have to penetrate deeply into seawater, which is a conducting dielectric; the relative dielectric constant ε_r ≅ 72 and the conductivity σ ≅ 4 S/m. Thus the attenuation constant α for the high frequency wave is rather high. Fortunately, the attenuation constant decreases with the wave frequency. It has the dependence α = 4×10⁻³√f Np/m for f << 1 GHz. Hence, the wave penetration problem can be resolved by adopting very low frequency carrier. For example, choosing f = 100 Hz leads to α = 4×10⁻² Np/m and the penetration depth δ = 25 m. However, the wavelength of 100Hz wave is 3000 km. To implement a high power and large size antenna (megawatts and hundreds of kilometers) on the ground is costly and has to face environmental impact problems.

In the magnetosphere, very energetic electrons (in MeV level) in the radiation belts have strong impact on space systems, which are designed to survive certain amount of radiation (ionizing) dose accumulated during the lifetimes. Any unexpected radiation flux enhancement can cause satellites to accumulate radiation damage much faster than designed for, which leads to faster degradation of on-board active electronics. 

Objective

To advance the understanding of wave-plasma interaction processes that help for the realization of the future Naval/DoD systems for the missions.

Progress

In the polar region, an electrojet current appears frequently in the lower ionosphere. A dc space charge field drives this current. Thus an amplitude-modulated powerful HF wave modulated at ELF/VLF frequency can be introduced to modulate the electron temperature, which results to the modulation of the electron conductivity in a similar fashion. Consequently, the electrojet current driven by the background dc fields becomes oscillating in time to act virtually as an antenna. The ac part of the current becomes the source current of ELF/VLF radiation. A cartoon showing the antenna and its radiation is presented in Fig. 2. Our research effort is to continuously improve the antenna efficiency and the signal quality,^1-3 which are critical to practical applications.

Our recent work⁴ showed that whistler waves could introduce chaotic scattering on energetic electrons; thus it can be an effective approach for controlling the population of energetic electrons in the radiation belts. This process is elaborated in Fig. 3. The threshold conditions are determined by the transition of the surface of section plots from regular to chaotic and by the decrease of the pitch angle to be less than the loss cone angle. This is demonstrated by the sequence of surface of section plots (a-c) and pitch angle scattering plots (d-f) presented in Fig. 4; the wave magnetic field B₁ is normalized to the background magnetic field B₀, i.e., B₁/B₀; six trajectories corresponding to Ω₀/ω = 3.65-3.9 with 0.05 increment are drawn in the same plot to show the frequency effect and to determine the optimal wave frequency. As shown, the trajectory of Ω₀/ω = 3.9 electron becomes the most chaotic at B₁/B₀ ~ 0.006 and its pitch angle is reduced to about 30⁰ at B₁/B₀ ~ 0.015.

¹S. P. Kuo, M. C. Lee, P. Kossey, K. Groves, and J. Heckscher, Geophys. Res. Lett., 27, 85, 2000.

²S. P. Kuo, S. H. Lee, and P. Kossey, Phys. Plasmas, 9, 315, 2002.

³S. P. Kuo and S. H. Lee, Radio Sci., 39, RS1S32 (1-5), 2004.

⁴S. P. Kuo, P. Kossey, J. T. Huynh, and S. S. Kuo, IEEE Trans. Plasma Sci., 32(2),  362-369, 2004.

Selected recent publications:
[J1] M.C. Lee, R. Pradipta, W. J. Burke, A. Labno, L. M. Burton, J. A. Cohen, S. E. Dorfman, A. J. Coster, and S. P. Kuo, “Did Tsunami-Launched Gravity Waves Trigger Ionospheric Turbulence over Arecibo?”, J. Geophys. Res., 113, A01302, doi:10.1029/2007JA012615, 9 January 2008.                 

[J2] Spencer P. Kuo, Todd Pedersen, and Travis Mills, “Lateral Distribution of Atomic Oxygen Flux Produced by an Array of Three Fan-shaped Plasma Torches”, IEEE Trans. Plasma Sci., 36(3), 1056-1057, doi: 10.1109/TPS.2008.924556, June 2008.

[J3] Lance S. Jacobsen, Campbell D. Carter, Thomas A. Jackson, Skip Williams, Jack Barnett, Chung-Jen Tam, Robert A. Baurle, Daniel Bivolaru, and Spencer Kuo, “Plasma-Assisted Ignition in Scramjets”, J. Propulsion and Power, (doi: 10.2514/1.27358) (0748-4658) vol. 24 no. 4, 641-654, Aug. 2008.

[J4] Spencer P. Kuo, Yen-Liang Wu, R. Pradipta, J. A. Cohen, and M. C. Lee, “VLF wave generation by amplitude-modulated HF heater waves at Gakona, Alaska”, Geophys. Res. Lett., 35, L13101 (1-5), doi:10.1029/2008GL034414, June 2008.

[J5] Spencer P. Kuo, “Plasma Assisted Decontamination of Bacterial Spores”, The Open Biomedical Engineering J., 2, 36-42, doi: 10.2174/1874120700802010036, June 2008.

[J6] Spencer P. Kuo, “Mitigation of energetic electrons in the magnetosphere by amplified whistler wave under double cyclotron resonances”, Nonlinear Processes in Geophysics, 15, 773-782, 2008.

Selected recent patents:
[P1] Spencer Kuo, “Portable Plasma Sterilizer,” US Patent Application # 12/030982, Date of Filing: Feb. 14, 2008.

[P2] Spencer Kuo, “Plasma Assisted Oxygen Decontaminant Generator and Sprayer,” US Patent Application # 12/030962, Date of Filing: Feb. 14, 2008.

[P3] Spencer Kuo, “Plasma Torch Implemented Air Purifier,” US Patent Application # 12/126869, Date of Filing: May 24, 2008.