Whistler Wave Launch and Diamagnetic Plasma Formation in Laboratory Experiments

Bill H. Quon, Microwave Plasma Applications

252 S. Poplar Ave # 403 Brea, CA 92821

email: bquon1@msn.com

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.

M

n=nc

Whistler Wave Launched from the High Magnetic Field Propagates into Over-Dense Laboratory Plasma

Power dissipation Increases with plasma density increases.

No abrupt changes in reflectivity pattern observed in vicinity of the pe =o boundary.

The maximum plasma density achievable for a given system depends only on power and neutral feed available.

Both power reflection and power transmission became negligibly small at high plasma density.

After J. E. Stevens, “Electron Cyclotron Plasma Sources”In “high Density Plasma Source”, edited by O. A. Povov.

Electrons can be heated by electromagnetic wavesnear the electron cyclotron resonant zone

For whistler waves, the resonance condition requires

- ce - kz vz 0

Strong absorption occurs for those electrons moving backwards kz vz (-ce) < 0.

ECR condition:

ce

in uniform B.

E

EE

E-e

-e

-e

-e

t = 0 t = ¼ t = ½ t = ¼

Phys. Fluids B1 (10), October 1989

0. 40. 80. cm

ce =o

Whistler waves were launched from the maximum B withTeflon filed C-band waveguide horn at 2.45 GHz in AMPED

B=875 G

Exponential increase of energetic electron current was observed when the heating is moved to the flat field region.

Compact Tabletop ECR with Whistler Wave CouplingTokyo Electron Phoenix Laboratories

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Whistler Wave Excitation in Compact ECR

WR430 Coupler

AlN-Wave window

ECR Chamber

Plasma Pump Baffle

Pressure Recovery Baffle

Main Vacuum Chamber

Neodymium Magnet

Iron Pole Piece

Adjustable Magnet

Example of whistler wave absorption in ECR zone

The wavelength of the RHCP wave decreases as the wave approaching resonance.Strong absorption occurs before the wave actually reaching the resonance layer.

Measured waveform in ECR plasma by Quon & Dandl (1989)

L = 20 cmP = 0.1 - 10 m TorrTe = 8.0 - 2.3 eV

P = 6 kW A = 100 cm2

P/A = 60 W/cm2

n = 1 - 2 x1013 cm-3

Over-Dense Plasma Productions in ECR with Whistler Wave

Plasma density 1-2 x 1013 cm-3

are predicted in pressure range0.1 to 10 m Torr from particle and power balance ECRmodel of Dandl and Guest and Lieberman et. Al.

The measured maximum plasma density exceeds 5x1013 cm-3 at the ECR layer.

x12

Electron Run-away in Low Pressure Operation of ECRH Systems

At low neutral gas pressure, p < 10-5 TorrECR plasmas do not achieve very high plasma density, but have relatively higher electron temperature.

The electron energy distribution function usually contain large energetic electron components.In magnetic mirror confinement systems, electrons are runaway to relativistic energy.

The energetic electrons appear to be heated at the relativistic electron cyclotron resonance condition:

= ce = eB/mc

The resonance moves to higher B. Multiple frequencies and upper-off resonance heating were found to have strong effects.

Phys. Fluids,28 (5), May 1985

Diamagnetic field profiles were measured to reconstruct the spatial distribution of diamagnetic plasma

Experimental arrangement

Magnetic field profiles of the diamagnetic current were measured using axial and radial Hall probe arrays.

The 2-D spatial pressure distribution was reconstructed using equilibrium code with the measured diamagnetic field data.

The pressure created a local magnetic minimum in the total magnetic field. The magnetic field contour suggested the hot electrons are trapped in the minimum of the local magnetic mirror.

The majority of the hot population appeared to be heated by the applied frequencies at the localtion where

= 2 ce

The pressure profiles were measured as function of time.

The pressure profiles measured during the build-up time indicated the hot electrons are slashing back-and forth in the flux tube, giving a pressure peak at their turning points in the mirror field.

The ELMO Produced ECRH Plasma with 500 keV Electrons

B=20 kGf = 35 GHzP= 800 W.no ~ 1012 cm-3

nc ~ 1011 cm-3

Tc ~ 100 eVnh ~ 1012 cm-3

Th ~ 500 keV

Estimated RingParamters: 4 cm thick9 cm diameter10 cm long = nT/4B2 ~ 1

After R. A. Dandl et al., Phys. Fluids, 9:1498 (1966)

Summary of Presentation

Effective electron heating can be achieved by launching the Whistler wave into the resonance zone from the high field side of the magnetic system.

At high pressure and high heating power, very high plasma density can be produced. The heating efficiency is higher with higher electron temperature so molecular excitation can be reduced.

At low pressure energetic electrons are generated. When confined by magnetic field mirror, the hot electron population can build up to a plasma pressure that is significant compared with the magnetic field pressure.

The magnetic moment of the localized plasma can be very large: M = IxArea = NT/B.

ELF/VLF Excitation by Pulsed HF Powerat the Electron Cyclotron Resonance

Our goal is to generate a largeplasma magnetic dipole momentbelow or above 100 km above HIPAS.

The ELF/VLF magnetic field produced can be sensed around the world through the earth-ionosphere-waveguide.

Alfven Waves

Whistler Waves

Magnet Dipole

S

N

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Frequency 1.43 MHz dn=0.4 x mode

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Frequency 1.43 MHz dn=0.4 o mode

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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

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y (km)

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<p

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Frequency 1.43 MHz dn=2 o mode

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<p

Electron Heating by Electron Whistler WaveAgainst Electron-Neutral Collisions

Electron heating in single pass of electron Cyclotron Resonance:

E = (Zo/(ck/)*P/A)1/2

= Min (e-n, res, 0 ) v = e/m E

T = ½ e2/mE2 2

e-n = 10-5 sec (collision)res = 10-4 sec (Resonance) 0 = 10-4 sec (Pulse)

The electron-neutral collision time e-n 10-5 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/m2 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 MHzPlasma Parameters ne = 10000 cm-3

Vacuum Electric Field Eo = 4 V/m ( = 128 mW/m2 )Refraction Index n = 3.4Plasma Heating Field E = 4.3 V/mMinimum Collision Time: min 1 x 10-5 sec.Energy Gain (per pass) T = 46.9 eV

The 4 V/m electric field requires a power flux, = 21.3 mW/m2, 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. 10-5 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.

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.

M/m

Bo

•B

Ek •E kB V

156060

300

Insulator

Collector

Fence

7 m

m

8.5

mm

0.6 mm

Grid

Phase 1

Phase 2

Collector/Probe

B

Magnetic field profile

Q-machine

EXPERIMENTAL SET-UP

MPD-1 Schemati

c