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8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
1/23
The HelCat Helicon-CathodeDevice at UNM
Bricette Cyrin, with
Christopher Watts, Mark Gilmore, Tiffany Hayes,
Ralph Kelly, Christopher Leach, Andrew Sanchez, Alan Lynn,Jacek Osinski, Shuangwei Xie, Lincan Yan, Yue Zhang
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
2/23
Abstract The HelCat helicon-cathode device is a dual-source linear
plasma device for investigating a wide variety of basic
plasma phenomena. HelCat is 4 m long, 50 cm diameter,
with axial magnetic field < 2.2 kG. An RF helicon source is
at one end of the device, and a thermionic BaO-Ni cathode
is at the other end. Current research topics include the
relationship of turbulence to sheared plasma flows,
deterministic chaos, Alfvn wave propagation and damping,
and merging plasma interaction. We present an overview ofthe ongoing research, and focus on recent results of
merging helicon and cathode plasma. We will present some
really cool movies.
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Summary Studies focus primarily on effects of shear flow covering
a variety of topics Turbulence and chaos generation and suppression
Generation of drift and Kelvin-Helmholtz instabilities
Relative effects of poloidal vs. axial flows
Shear flow effects on injected plasma bubble
New diagnostics: 4m spectrometer and emissive probe
Alfvn wave propagation Damping length studies
Association with bubble injection
Plasma bubble interaction with background plasma Relevant to astrophysical jet formation and coronal mass ejections
New diagnostics Flow and shear measurements
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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HelCat: Helicon-Cathode Device Dual source helicon-cathode
Best of both worlds: high density, steady state helicon with high(er)temperature, broader profile
Vary collisionality over wide parameter range Variable ionization fraction
Pre-ionization of helicon at low pressure Different ionization mechanisms
-> different turbulence Colliding plasmas: way cool!
Science Motivation Drift waves and flow shear Intermittent, convective blobs
Alfvn wave propagation Expanding plasma bubble
into background Helicon physics
1 10000.05 100Collisionality vi /ci
1000
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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HelCat [Helicon-Cathode] Parameters Physical device
4 m long, 50 cm diameter
13 cm diameter helicon; 15 cm diameter thermionic cathode 13 magnetic field coils, 2.2 kGauss max field
Diagnostics Electrostatic and Magnetic Probes Microwave Interferometers (40 GHz, 94 GHz) Visible Spectroscopy
High resolution and survey Fast framing camera
Laser InducedFluorescence
Helicon
Cathode
Magnets
GridBias Rings
Interferometers
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Pretty plasma picturesCathode Source with Ar Plasma
Helicon Source with Ar Plasma [top]and He Plasma [bottom]
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Comparison of helicon & cathode plasma
Helicon Density profiles peaked Temperature profiles Gaussian like (or hollow) Steady-state (typically pulsed 250 ms)
Cathode Density profile varies depending on current & time (note cathode
inhomogeneity) Temperature broad
Pulsed, 10 ms
0
5
10
15
20
1
1.5
2
2.5
3
3.5
0 2 4 6 8 10
Helicon density & temperature profilesCathode density profile
helcion ne
cathode ne
helicon Te
ne(
1018) T
e(eV)
distance (cm)
HeliconB: 400 G
gas fill: 3.00 mTorrpower: 1000.00 W
Cathode
B: 1 kGgas fill: 0.5 mTorr
icath: 500A
0
2 103
4 103
6 103
8 103
1 104
1.2 104
0 50 100 150 200 250 300 350
Helicon ion saturation current
isat
(bits)
time (s)
0
0.5
1
1.5
2
2.5
0 5 10 15 20 25 30 35 40
Cathode ion saturation current
isat
(arb)
time (ms)
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Shear Flow Studies
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Flow and Shear Modification with E
Attempt to actively control turbulence-driven particle transport
Use imposed E to modify Shear flow using bias rings
Changes ExB velocity Independently adjustable
Eventual goal of active feedback control
Manipulation of flow profiles provides control knob for manipulating the
transport
Cathode
AnodeRF Helicon
Source
Magnet CoilsBias Rings
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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0
0.2
0.4
0.6
0.8
1
1.2
-5 0 5 10 15 20 25
Fluctuations under Bias
2.2 mT
Bias Voltage (V)
5000
6000
7000
8000
9000
1 104
5000 6000 7000 8000 9000 1 104
2D phase plot (0V)
Isat (bits)
5000
6000
7000
8000
9000
1 104
1.1 104
1.2 104
5000 6000 7000 8000 9000 1 104
1.1 104
1.2 104
2D phase plot (40V)
Isat (bits)
4000
5000
6000
7000
8000
9000
1 104
1.1 104
4000 5000 6000 7000 8000 9000 1 104 1.1 104
2D phase plot (46V)
Isat (bits)
6400
6600
6800
7000
7200
6400 6600 6800 7000 7200
2D phase plot (50V)
Isat (bits)
4000
5000
6000
7000
8000
9000
1 104
1.1 104
100 1 05 1 10 1 15 120 1 25 1 30 1 35 140
Ion saturation current (0V)
time (ms)
4000
5000
6000
7000
8000
9000
1 104
1.1 104
1 00 10 5 1 10 115 12 0 1 25 130 13 5 1 40
Ion saturation current (50V)
time (ms)
Fluctuation Suppression by Radial Bias Density gradient region show large amplitude, drift wave type
fluctuations
Imposed radial electrical field reduces drift wave fluctuations to a verylow level
Period doubling is observed from phase plot of ion saturation signal
-80
-70
-60
-50
-40
-30
-20
-10
100 1000 104
105
Power spectrum (0V)
freqency (Hz)
Xie: This session GP8.00107
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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-150
-100
-50
0
50
100
150
0 10 20 30 40
Phase Difference between Probes
Bias Voltage (V)
60o
m1
50o
-300
-200
-100
0
100
200
300
400
0 0.02 0.04 0.06 0.08 0.1
Radial Electric Field
Er (0V)
Er (17V)
Er (27V)
Radial Scale
0
1
2
3
4
5
6
7
8
-2 0 2 4 6 8 10
Floating Potential under Different Bias
Vbias=0V
Vbias=17V
Vbias=27V
Radius (cm)
Drift Wave Frequency From power spectrum, it is clear the drift
wave frequency is 600 Hz
This can be verified by plasma movies[see left and laptop]
taken at 1200 frame/sec
rotation period is 2 frames
: so the frequency is 600 Hz
Corroborated by 2-probe correlationmeasurements
Simple theory confirms basic picture See poster GP8.00106 and 107 for more details
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Helicon Source
Mesh GridBias Rings
Mach probeplacement
Controlling and Understanding Flows
(Sheared) flows appear in many plasmas Space Plasmas, such as Solar Wind Laboratory plasmas
(Sheared) flows affect turbulence and transport Create or stabilize instabilities
Using Helicon source, create and control flows Use system of grid (s) and bias ring (group of concentric rings) Bias grid from -40V to 40V
Hayes: This session GP8.00108
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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A
B
D
C
Shearflow yields varied behavior
Control flows with voltage (D) flow with no grid
Create instabilities (A)
Plasma is able to stabilize forlow voltages (B)
Plasma unstable for high voltage(C)
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Cool Movies
Very Cool movies of the m=1 mode in the Ar helicon plasma Shot with a 1200 fps Canon digital camera
Check thenearby laptop
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Model includes:
i) resistive drift modes, ii) Kelvin-Helmholtz modes, and iii) rotation-driven interchange modes
Drift Modes Kelvin-Helmholtz Modes
Radial region of max. instability close toplasma edge, where max. observed
Predicted real + ExB very close tomeasured frequency
m=1 predicted most unstable, asmeasured in experiment
Linear Stability Analysis of Plasmas Under Biasing
Instability predicted with v0z/robserved under biasing.
Radial region of max. instability at radiiof highest observed fluctuations.
Predicted real within 25% of measured
High m (m=8), high kz (z29 cm)
predicted
0/
~nn
Gilmore: This session GP8.00106
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Interchange Modes
Unstable rotation-driven interchangemodes predicted in the edge gradientregion
- where rotation is highest
Predicted real + ExB varies widely acrossunstable region.
Full cylindrical geometry without WKBapprox. is underway.
Linear Stability Analysis cont. Seems to confirm our basic
understanding of the fluctuations But linear analysis cannot describe the
nonlinear physics (such as chaos)
Drift modes are most unstable atthe plasma edge Dominantly m=1 mode
real strongly Doppler downshifted
Kelvin-Helmholtz modes aredestabilized by axial velocity shear(v0z/r ) under biasing
Theory and experiment real agreewithin 25%.
A WKB slab model indicates thatinterchange modes are unstable inplasma edge region More complete analysis needed for
quantitative comparisons.
Conclusions:
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Alfvn Wave Studies Induction coil used to wigglemagnetic field
Exciter circuit 14A @ 100kHz
Second coil measures Alfvn wavedownstream
Experiment Goals1. Do waves travel along field lines?2. Does the wavelength change as theory
predicts?
3. Effects of neutral fraction
5
Funtion Generator
100 kHz
Amp
Helicon plasmaAlfvn wave
exciter detector
Cross correlation
Kelly: Withdrawn
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Black Probe and Emitter aligned verticallyRed -----Emitter rotated 90Blue -----Probe and Emitter both at 90Green ---probe rotated 90
Data near 120kHz with peaks slightly shiftedto emphasize the amplitude differences.
Frequency (kHz)
Power
Tantalizing evidence of Alfvn waves inconclusive
0 50 100 150 200 250
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1 Cross spectral density shows
detected signal at expectedfrequency
Changing probe orientationshould modify signal
However, though some amplitude
variation, no definitive change Conclusion: Variation in magnitude does not
indicate Alfvn waves detected
100 150
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Current Status Of Experiment Density calculated from slope of k vs.
n = 3.40x1019 A little high, but not unreasonable
Emitter works well
Receiver signal noisyWorking onbetter 10MHz filter
Preliminary data indicates Alfven wavesobserved
k vs.
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Magnetic Bubble Expansion Experiments
Radio lobe structure is a fundamental aspect of extra-galactic evolution Coronal Mass Ejections (CMEs) interact with the solar wind, and lead to
severe geomagnetic storms Nonlinear plasma physics issues cannot at present be resolved from
numerical computation or astronomical observations alone Laboratory experiments are needed
Zhang: Thurs. PM; UP8.00133Lynn: Thurs. PM; UP8.00134
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Coaxial Magnetized Plasma Gun
Plasma gun injects bubble intobackground HelCat plasma
Spheromak or other geometry Studies of propagation, evolution andinteraction with background flows
Fast camera verifies plasma injection
Langmuir probe and spectroscopy [next
slides] measure propagation speed.
75 80 85 90 95 100 105 110 115 120 125 130
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
IsatCurre
nt(A)
Time (us)
Tip 1&2Tip 9&10
Jet initiation
Detached jet
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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New optical diagnostics 4m spectrometer
Ion drift velocity and temperaturemeasurements
Survey escelette spectrograph Impurity content
Electron temperature from line ratios
Fast cameras
CCD camera with 600 Hz video Framing camera with 1.2ns gate time
Major new measurements: Azimuthal drift velocity
4m spectrometer used to detect Dopplershifts
Fast, accurate drift measurement via
two-lens/bifilar fiber optic cable setup Mach probe 300-500m/s drifts were not
detectable via our optics
Plasma bubble jet velocities and photos Mach probe 3,100m/s velocity confirmed
optically to be 2,900m/s via Doppler shift
1.2ns 4SpecE camera used to obtain
bubble jet images
Reference Line from
Helicon Plasma
Measured Line from
Plasma Bubble
Leach: This session GP8.00110
8/3/2019 Bricette Cyrin et al- The HelCat Helicon-Cathode Device at UNM
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Emissive Probe Direct measurement of plasma
potential Tungsten filament heated to emissive
temps. Filament swept with high voltage Probe voltage compared to swept voltage
to determine Ion Saturation Current Electron Temperature
Entire circuit is floating Status
Simulations display positive results Real sweep circuit testing well Created 4th plasma source Beam used to map lines of force and
electric field Useful for lining up probes
Basic Emissive Probe Schematic
Floating
Ground
CurrentSupply
HelCat
Beam from emissive probe
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