Wave and Plasma Simulations: Resonant Effects

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Wave and Plasma SimulationsResonant Effects

• By
• John Lazos

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The Suns Winds

• Hot solar wind blows out.
• The wind is charged particles.
• A Plasma with few collisions.

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MAGNETIZED WIND

• Carries Magnetic Field.
• Magnetized waves travel out.

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Alfven Waves

• MOST IMPORTANT WAVE
• Undamped by the plasma
• So, travels far.

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Resonance

• Singer breaking glass
• Critical phenomenon in physics and engineering

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Space Physics Resonances

• Waves moving at same speed
• Particles moving with the waves
• These are all in resonance

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Resonances We Study

• 1. Alfven Wave Steepening
• 2. Alfven Wave Decay
• 3. Ion Beam Slowdown

• Solar Wind Charged Particles
• Need Technique for Particles

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This is our technique Hybrid Simulations

• Ions Particles
• Electrons Fluid
• Treats a real collisionless solar wind plasma

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1st Simulation Project Wave Steepening

• Alfven wave like string wave
• Propagates down string string magnetic field

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Nonlinear Steepening in Cool Plasma

• Magnetic Intensity varies
• Resonance of two magnetized waves
• Results in steepening

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Prediction by Analysis on Paper
COOL
HOT
VALID HERE
ß

• ß ratio of sound speed squared to the Alfven
  speed squared. (Cool to Hot)

FAILS Triple Resonance
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Scientific Objective 1

• Measure steepening time near ß 1 and higher.
• This can only be done with a numerical simulation.

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Simulation Results
ß
Sound wave Punches Alfven wave ahead
ß 1 4X faster than in cool plasma
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2nd Simulation Project Wave Decay

• Total Intensity Constant
• NO Steepening
• Happens Naturally for wave travel along and
  across magnetic field
• This wave is an Arc-Wave.

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Arc-Wave
Travels OUT of paper
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• Arc-Wave could travel without changing form.
• But the slightest noise kills it.

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Explosion of New Waves
New Growing Wave
Noise
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Arc-Wave Collapses

• Energy for the new waves comes from the original
  Arc-Wave.
• These new waves are resonant and take so much
  from the arc-wave that the arc-wave dies.

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Scientific Objective 2

• Quantify rate of fastest growing new wave.
• Plot as a function of ß.
• ONLY simulations can find these answers.

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Fourier Analysis
Slope gives rate
Finds amplitude for each cycle
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Simulation Results
ß
The colder the plasma, the faster the Arc-Wave
dies.
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3rd Simulation Project Beam Slowdown

• In the Solar Wind, Helium streams faster than
  Protons.
• Wave-Particle resonances have consequences here.

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What we are doing

• Drive a Helium beam through Protons.
• Above a critical speed, waves from noise will
  resonate with Helium.
• Helium slows down as waves steal energy.

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Scientific Objective 3

• Find the critical speed where the beam generates
  new waves.

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Simulation Results
PLOTS OF STREAMING SPEED vs. TIME

• Fast, supercritical beam.
• (U 2.3VA)

• Slower, marginally critical beam. (U 1.8VA)

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Conclusions
1. When ß 1, wave steepens 4 x faster than in
cool plasma. 2. Arc-Wave decays faster in colder
plasma. 3. Beam slowdown occurs above U 1.8VA
(1.8 times the Alfven speed).