PARS Workshop on Novel Methods of Excitation of ULF/ELF/VLF to Improve Efficiency and Availability" November 3 - 6, 2002 Sponsored by Air Force Research Laboratory, Office of Naval Research University of Alaska, Fairbanks Institute of Plasma Science and Technology, UCLA Arrowhead Conference Center

Goals and Objectives 1.Review experiments on EM interactions with Ionosphere leading to ULF/ELF/VLF (UEV) 2. Efficient Generation of waves with and without electrojet Examine New Approaches High power EM pulses at HF and Laser frequencies 3. Improved methods of Detection 4. Laboratory experiments and Computer Modeling

UEV Physical Pictures. VLF - Whistler waves Accessibility and electron cyclotron resonance. ELF waves – Ion cyclotron waves. ULF waves – Alfven waves.

Whistler waves are accessible for propagating into and heating the high density plasma The RHCP Whistlers can be excited into both low and high density plasma by launching from high magnetic field (  ce /  > 1). These waves do not go across the R- cutoff layer, and pass the L-cutoff without being affected. The accessibility problem arises in the vicinity of the boundary  pe /  = 1. The CMA diagram shows that the RHCP waves propagation along B will pass this boundary, but those perpendicular to B will be reflected.

The LHCP ion cyclotron waves are similar to the RHCP electron whistler waves. They can be excited using a dipole loop antenna inside the plasma. Excitation LHCP Ion Cyclotron Waves by Modulation of the Diamagnetic Dipole at ELF/VLF with AM HF Power. Densi ty

Electrons can be heated by electromagnetic waves near the electron cyclotron resonant zone For whistler waves, the resonance condition requires  -  ce - k z v z  0 Strong absorption occurs for those electrons moving backwards k z v z  (  -  ce ) < 0. ECR condition:    ce in uniform B.

Alfven Wave B 1, v 1, E 1, J 1

ELF/VLF Excitation by Pulsed HF Power at the Electron Cyclotron Resonance 1.Accelerate electrons to ionizing energy using pulsed HF ECR power. 2.Production of high density plasma by impact ionization. 3.Formation of diamagnetic plasma disk by multiple pulses of HF power. 4.Modulation of diamagnetic plasma by electron heating using CW HF power modulated at ULF/ELF/VLF range. 5.Excitation of Low frequency Whistler modes and ion cyclotron waves to further enhance the ULF/ELF/VLF signals. Our goal is to generate a large plasma magnetic dipole moment below or above 100 km above HIPAS. The ELF/VLF magnetic field produced can be sensed around the world through the earth-ionosphere-waveguide. Alfven Wave

Plasma Diamagnetic Current J  = c BX  p/B 2 I  =  dz  dr J  Magnetic Dipole Moment m =  a 2 I  /c  nT  V/B L A plasma with electron density n=1x m -3 T e = 1 eV and L= 3 km; r=10 km; p= n  T = 1x10 11 eV m -3 Diamagnetic Current Carried by the Plasma: I = 1 A Magnetic Dipole Moment: m =  r 2 I = 3.14 x 10 8 A-m 2 p JJ Localized Plasma produced by HF ECR Carried Magnetic Dipole Moment The objective of an active ionosphere modification is to increase and modulate the diamagnetic dipole moment at the ELF/VLF by HF radiation from ground.

Plasma current produced by HF wave heating can generate significant ELF/VLF radiation signals r  m =  a 2 I/c Magnetic field of magnetic dipole moment: B r = 2 m cos  /r 3 B  = m sin  /r 3 For I = 100A, a = 10 km, the magnetic field induction at 100 km from the dipole ring is about 6.3 pT. Higher ELF/VLF signal levels are expected from collective plasma oscillations and reflection from the ionosphere (the earth-ionosphere waveguide effect). 100 km 3.6 pT 6.3 pT I = 100A a = 10 km

The RHCP wave power is completely absorbed at the ECR zone while the LHCP wave is reflected at the L-Cutoff boundary Ray tracing for the electromagnetic waves satisfying the Appleton Hartree dispersion relation >p>p >p>p <p<p <p<p RHCP LHCP

Whistler wave ducting by a low plasma density trough will effectively increase the HF power flux at the target region Experimental demonstration of the unducted and ducted Whistler waves.

Whistler Wave Propagation and Absorption Index of Refraction (n = ck/  ) n 2 = 1 +  p 2 /  2 / [(  ce /  ) cos  -1] Wave Absorption k i = - D i /(  D/  k) =  p 2 /(2c 2 k 2 v e )  EXP{-[(  -  ce )/kv e ] 2 } P abs = {1- exp [-2⌠k i (x)dx]} P Resonance Length L res : Length of layer with: 1% < P aps /P < 99%

Whistler Wave Propagation and Absorption In the Ionosphere 100 km Index of refraction Imaginary wavenumber Wave Amplitude Waveform The absorption layer for the electron whistler is typically 2-3 kilometer thick.

Electron Heating by Electron Whistler Wave Against Electron-Neutral Collisions Electron heating in single pass of electron Cyclotron Resonance: E = (Z o /(ck/  )*P/A) 1/2  = Min (  e-n,  res,  0 )  v = e/m E  T  = ½ e 2 /mE 2  2  e-n = sec (collision)  res = sec (Resonance)  0 = sec (Pulse) The electron-neutral collision time  e-n  sec at about 100 km altitude in the E-layer where the normal electron temperature is cold, Te = 0.03 eV (300 K). The electrons must gain enough energy (T  > 20 eV) in a time short compared to  e-n such to minimize excitation energy loss. It requires about 20 mW/m 2 of the HF power flux to bring the electrons to the ionizing energy level by electron cyclotron resonance heating in the ECR layer.

Pulsed HF Power Will be Used for Electron Accelerations Frequency: f = 1.4 MHz Plasma Parameters n e = cm -3 Vacuum Electric Field E o = 4 V/m (  = 128 mW/m 2 ) Refraction Index n = 3.4 Plasma Heating Field E = 4.3 V/m Minimum Collision Time:  min  1 x sec. Energy Gain (per pass) T  = 46.9 eV The 4 V/m electric field requires a power flux,  = 21.3 mW/m 2, or 2.7 GW ERP. This power level will be available from pulsed transmitters currently under development at HIPAS Observatory.

Creating High Density Plasma by electron Impact Ionizations The energetic electrons created by HF ECR are capable of ionizing the background neutral particles in a fast time scale, I.e sec. Plasma produced will be localized in the heating region for a time scale of electron-ion recombination time, I.e. ~100 sec. Thus a very high density plasma can be created using multiple HF pulses in a time scale of the recombination time.

Areas of Further Investigation and Preparation for HIPAS Active Ionospheric Modification Experiments 1.Study the wave propagation and wave-particle interactions using realistic 3D PIC simulations 2.Understanding the detailed electron heating and diamagnetic plasma formation process using laboratory modeling experiments with relevant scaling parameters. 3.Detailed power balance including excitation energy losses 4.Develop techniques for charging and discharging the high power pulsed antenna array.

Van Zeeland et al. PRL 2002.