Laboratory Investigation of Nonlinear Whistler Wave Processes* · 2018. 3. 21. · Laboratory...
Transcript of Laboratory Investigation of Nonlinear Whistler Wave Processes* · 2018. 3. 21. · Laboratory...
Laboratory Investigation of Nonlinear Whistler Wave Processes*
Erik Tejero, Chris Crabtree, Lon Enloe, David
Blackwell, Bill Amatucci, Guru Ganguli
[email protected] Physics Division, Naval Research Laboratory
*Work supported by NRL base program and NASA Grant No. NNH17AE70I
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NRL Space Physics Simulation Chamber
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Collaborators
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• Laboratory Experiments
‒ Lon Enloe (NRL)
‒ Bill Amatucci (NRL)
• Theory
‒ Chris Crabtree (NRL)
‒ Guru Ganguli (NRL)
• Space Observations
‒ David Malaspina (UC Boulder)
• Simulations
‒ Dong Lin (VA Tech)
‒ Wayne Scales (VA Tech)
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Studying the Building Blocks of Weak Turbulence
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pump
scatteredwaves
Nonlinear Scattering
Tejero et al., Phys. Plasmas, 22, 091503 (2015)
Parametric Decay
pump
daughterwaves
Verification of Nonlinear Conversion of ES to EM
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B/B0 ~ 510-6 , NL= L
𝑘⊥ Τ𝑐 𝜔𝑝𝑒 > 1
10 MHz 9.96 MHz
Δ𝜔
Δ𝑘∥𝑣𝑡𝑒~1
2
Tejero et al., Sci. Rep., 5, 17852 (2015) and Tejero et al., Phys. Plasmas, 23, 055707 (2016)
gNL
k1®k 2 ~w
pe
2
wk 2
k2
2
1+ k2
2
Wk1
n0T
(k1´ k
2)
||
2
k^1
2 k^2
2k1
å zeIm Z
wk 2
-wk1
k||2
- k||1
vte
æ
è
çç
ö
ø
÷÷
Amplitude Scaling90° turning
Resonance Condition
𝛾𝐿 𝑘,𝜔 = 𝛾𝑁𝐿 𝑘,𝜔,𝑊
Threshold 10 MHz – Pump Wave
9.96 MHz – Scattered Wave
Experiment agrees with theory in detail
Wave Distribution Function Technique Validated
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10 MHz – Pump Wave
9.96 MHz – Scattered Wave
Tejero et al., Phys. Plasmas, 22, 091503 (2015)
Results from WDF and spectral techniques are consistent with laboratory k measurements.
Histogram Results Using Spectral Techniques (SVD)
Triggered Emissions Experimental Setup
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Bz
20 G
mirror point
helical antenna hollow cathode
420 G
SPSC Source Chamber
SPSC Main Chamber
Plasma
Source
Triggered Emission Observed in Laboratory
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𝐸𝑏 = 1.8 𝑘𝑒𝑉 𝐼𝑏 = 20 𝑚𝐴 → Τ𝑛𝑏 𝑛0 = 0.5 − 13% 𝛼 = 40°
Τ𝜔𝑝𝑒 Ω𝑒 = 1.75 − 9.2 Τ𝜔0 Ω𝑒 = 0.425
Nonlinear Scattering in Triggered Emission Data
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23.8 MHz
𝛾 = 860 𝑠−1
Three Wave Decay in Triggered Emission Data
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Chorus-like Emissions Exhibit Subpacket Structure
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Chorus-like emissions observed in laboratory experiments.
Beam Generated Mode
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Laboratory Simulation of
Broadband Noise in Boundary Layers
Dubois
et
al., JG
R, 119,
5624 (
2014)
Broadband Electrostatic Noise
NRL Space Chamber
Scaled PSBL/Lobe Boundary
• Plasma Sheet/Lobe Boundary Layer
simulated by interpenetrating plasmas
• EIH wave generation around the lower
hybrid frequency relaxes boundary layer
• Results in lower frequency shear-driven
waves to form broadband electrostatic noise
KH𝝆𝒊 ≪ 𝑳𝑬𝝎 ≪ 𝜴𝒊
IEDDI𝝆𝒊 ~ 𝑳𝑬𝝎~𝜴𝒊
EIH𝝆𝒊 > 𝑳𝑬
𝜴𝒊 < 𝝎 < 𝜴𝒆
In Situ Observations of Dipolarization Fronts
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[Fu et al. 2012]
~𝛿𝑖 , ~𝜌𝑖
LH waves
Whistler waves
Self-consistent E-field Generation Observed in Lab
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• B = 65 G
• i = 2.2 cm
• e = 0.09 cm
[Divin et al. 2015]
i
Laboratory Experiments Verified EIH Instability
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Comparison of experimental data with theoretical
predictions for the Electron-Ion Hybrid Instability
Sheared transverse flows drive lower hybrid waves
EIH Instability Experimental Verification
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Radiation Belts – Cascais, Portugal Amatucci et al, Phys. Plasmas. (2003)
Amatucci et al, Phys. Plasmas. (2003)
i
lower hybrid eigenmode localized to the shear layer as in DF
Divin et al. Identified Lower Hybrid Drift Instability as Source of Observed Lower Hybrid Waves
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• 𝑘 ො𝑥𝜌𝑒 , 𝑘 ො𝑦𝜌𝑒 ~ −0.6, 0.3
• LHDI modes should be damped
[Divin et al. 2015]
Eigenmode has no single kx to Doppler shift
Reanalysis Shows that Sheared Flows Can Drive Observed Lower Hybrid Waves
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Density 𝑛 = 3.8 × 105 m−3
Magnetic Field 𝐵𝑧 = 26 nT
Ion Diamagnetic Drift 𝑉𝐷𝑖 = 1.9 × 105 m/s
Electric Field 𝐸𝑥 = −20 mV/m
EB Drift 𝑣𝐸 = 1.7 × 106 m/s
Electric Field GradientScale Length
𝐿𝐸 = 54 km
Wave Vector in EB Direction
𝑘𝑦 = 3 × 10−5 m−1
Relevant ParametersAnalysis Results
• LHDI: 𝑘𝑦𝜌𝑒~1
• EIH: 𝑘𝑦𝐿𝐸~1
𝑘𝑦𝜌𝑒 = 0.2 vs 𝑘𝑦𝐿𝐸 = 1.1
∆= −9.3
Conditions above threshold for EIH and wavelength is consistent.
• Propagates in EB direction
Whistler Waves Can Also Be Driven by Sheared Flows
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Whistler Waves Are Bursty, Chirping Waves
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burs
t fr
equency
1/s
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Whistler Waves Exhibit Characteristics Consistent with Particle Trapping
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• f < 0.5 fce
• m = 1
• kz ~ 10 m-1
• Eres ~ 1-10 keV
Velocity Shear-driven Whistler Waves in Lab Are Observed with an Upper and Lower Band
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• Large amplitude bursts
• Chirp both up and down
• Lower band has faster chirp rates
Summary
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• Dipolarization fronts provide a variety of sources of free energy to drive waves
• Laboratory experiments verified EIH instability theory
• Lab and theory results provide quantitative tests to determine source of waves
• Analysis demonstrates that sheared flows are capable of driving the observed lower hybrid waves
• Lab experiments demonstrate that electromagnetic whistler waves can also be driven by sheared flows
• Could observed whistler waves also be due to the EIH instability?
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Begun a coordinated study between lab, theory, modeling, and
space observations to study these waves at dipolarization fronts
Local Approximation Predicts Instability Threshold
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ഥ𝜔3 + 2𝛿2
1 + 𝛿2
ത𝑉0ത𝑘𝑦
− ത𝑘𝑦 ത𝑉0 ഥ𝜔2 − ഥ𝜔 + ത𝑘𝑦 ത𝑉0 = 0
𝑎𝑥3 + 𝑏𝑥2 + 𝑐𝑥 + 𝑑 = 0
∆= 18𝑎𝑏𝑐𝑑 − 4𝑏3𝑑 + 𝑏2𝑐2 − 4𝑎𝑐3 − 27𝑎2𝑑2
If ∆< 0, then 1 real solution and two complex conjugate solutions
Effects of Nonuniform B on EIH• Increased growth rate• No effect on wavelength
Diamagnetic Drift Frequency: 𝜔𝐷𝑒,𝑖 = 𝑘𝑣𝐷𝑒,𝑖
Shear Frequency: 𝜔𝑠 =𝑑𝑣𝐸
𝑑𝑥
ഥ𝜔 =𝜔
𝜔𝐿𝐻, 𝛿 =
𝜔𝑝𝑒
Ω𝑒, ത𝑉0 =
𝑣𝐸
𝜔𝐿𝐻𝐿𝐸, ത𝑘𝑦 = 𝑘𝑦𝐿𝐸
predicted threshold
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