9c - experiments in magnetic flux compression...
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University of Alabama in Huntsville
Experiments in Magnetic Flux Compression
Using Plasma Armatures
Matt Turner
Propulsion Research CenterDepartment of Mechanical & Aerospace Engineering
University of Alabama at Huntsville
Academic Advisor: Dr. Clark W. Hawk, PRC/UAH
Research Mentor: Dr. Ron J. Litchford, NASA/MSFC
A Cooperative Research Project betweenUAH/PRC and NASA/MSFC
University of Alabama in Huntsville
Potential Space Thruster Applications
Pulsed Reactor• Microfusion • HEDM
Performance Attributes• improved flux compression • reduced seed field• collimated thrust• power generation
Design Attributes• smaller• more compact• lower weight
detonationtarget
Winterberg / Daedalus ClassMagnetic Compression Reaction Chamber
superconductorcompression wall
exhaust
inductiongenerator
coil
magneticfield
excitationfield coils
electricalpower
structuralshell
University of Alabama in Huntsville
Major Uncertainties
100
>>== uLB
BR i
m σµ
Magnetic Reynolds Number
⇒ low magnetic diffusivitym
m RD
11
0∼=
σµ
micro fusion detonation → Rm >> 1
pulsed plasma jet → Rm > 1
high explosive detonation → Rm > 1
• achieving sufficiently highelectrical conductivity
• suppression of Rayleigh-Taylorsurface instabilities
conductivity → relatively lowtemperature → very highvelocity → very high
Plasma Jet Characteristics
Magnetic Flux Compression with Plasmas
University of Alabama in Huntsville
Fundamental Compression Experiments
Mark 1 Device
… measurement of plasma electricalconductivity is a critical need
Research goal is to investigate scientificand technological feasibility using non-nuclear detonations…
Radial-mode, magnetic flux compression reactor
•Opposing HE charges
•Radially expanding plasmaarmature
•Moderate scale technology demonstrator
•Low cost expendable unit
Hz
r ua
plasmaarmature
shieldingshell
magnetcoil
generatorcoil
shaped chargeexplosive
University of Alabama in Huntsville
Measurement of Plasma Jet Conductivity
Inductive measurement technique provides a low costdirect measurement of plasma jet electrical conductivity …
Lin, S-C., Resler, E. L., and Kantrowitz, A., “Electrical Conductivity of Highly Ionized Argon Produced by Shock Waves,” J. App. Phys., Vol. 26, No. 1, Jan. 1955.
field coil
cavitycharge
jet
search coil
Lin CoilSystem
evacuated tube
time of flightcircuit
University of Alabama in Huntsville
Principle of Inductive Measurement
• magnetic field created by field coil• conductive plasma jet displaces magnetic field lines• magnetic field lines cut across search coil and induce an emf• degree of field displacement (emf) is correlated with electrical conductivity• apparatus calibrated by pre-firing a slug with known conductivity & velocity• electrical conductivity determined by inversion of Fredholm Eqn. of 1st kind
field coil
plasma jet
search coil
Lin CoilSystem
evacuatedshock tube
field lines
University of Alabama in Huntsville
Lin Coil Design
Field CoilField Coil√ 900-turn coil
√ No. 18 enameled wireSearch CoilSearch Coil
√ 50-turn coil
√ No. 28 enameled wire
Design Specifications•• 0.5 −− 1 Tesla excitation field
•• 1-inch diameter working volume
•• 60 A/ 300 V excitation power limit
0.1250
0.1250
0.1250
1.5000
0.1250
0.3125
0.4000
1.3000
1.4250
2.4250
3.8000
all measurements in inches
material: nylon
University of Alabama in Huntsville
Search Coil Parameters
• 50-turns / No. 28 enamelled wire
• L = 8 mm / D = 5.7 cm
• dual 25-turn coil construction
− standard option
− push-pull option
Previous experience using inductive conductivity probes with shock layers has shown thata localized electrostatic charge can generate a signal in a standard configuration searchcoil due to finite capacitance between the coil and the ionized gas inside the tube
PushPush--Pull ConfigurationPull Configuration√ cancels capacitive pick-up
√ Rd is critical damping resistance (≈ 1000 Ω)
Search Coil Design ConsiderationsL
D
standard configuration
L
D
RdRd
push-pull configuration
University of Alabama in Huntsville
Lin Coil Calibration Apparatus
Lin CoilSystem
solenoidactutaed
valve
laser
guide tubeplastic barrel
opticaldetector
breech
glass tubesection
compressedgas cylinder
pressuregage
pressureregulated
helium
manual valve
• light gas gun for slug acceleration (150 psig He)• 1-inch i.d. plastic barrel with 6-inch long glass test section• aluminum slug (D = 1-inch / L = 4-inch / ρ ρ = 3(10)-8 ΩΩ-m)• direct optical measurement of slug velocity• automated solenoid actuation with high speed data capture
University of Alabama in Huntsville
Lin Coil Calibration – Timing Verification
Current
Velocity
Response Function
Velocity
Current
Response Fnc (push)
Response Fnc (pull)
University of Alabama in Huntsville
distance (cm)
indu
ced
volt
age
0 1 2 3 4 5 6 7 80
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
datagaussian fit(σ = 1.8 cm)
distance (cm)
σ/σ
c
-1 0 1 2 3 4 5 60
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
predictedexact
constrained linear inversion
(H = I; γ = 10-3)
Probe Calibration – Algorithm Verification
Probe Response Function Algorithm Performance
University of Alabama in Huntsville
Shape Charge Plasma Jet Conductivity
field coil
cavitycharge
Plasma Jet Conductivity Measurement
jet
search coil
Lin CoilSystem
evacuated tube
time of flightcircuit
University of Alabama in Huntsville
Preliminary HE Testing
• Octol (75% HMX/25% TNT)
• Potassium-Carbonate Seeding- 0%, 1%, 2% by mass
• 15 gram shape charges- 1.25 inch diameter- 44° cone angle
Cast Shape Charges
Control / DAQ Test Article in Chamber
probe
shape charge
detonator
University of Alabama in Huntsville
Preliminary Test Results
Time-of-flight
Response Fnc (push)
Response Fnc (pull)
University of Alabama in Huntsville
HE Testing – Results
Time-of-Flight Output
time (µs)
resi
stor
volt
age
0 10 20 30 40 500
5
10
15
20
25
30test 2-7 (0% seed)BA
11 µµs
10 cm
1
6
109.1 / sec
11(10) sec
dx mu km
dt
−
−= = =Plasma velocity:
cavitycharge
jet
Lin CoilSystem
time of flightcircuit
University of Alabama in Huntsville
time (µs)
resp
onse
(V)
0 10 20 30 40 50-25
-20
-15
-10
-5
0
5
10
15
20
25test 2-10 (0% seed)
push coil
pull coil
time (µs)
resp
onse
(V)
0 10 20 30 40 50-100
-75
-50
-25
0
25
50
75
100test 2-12 (2% seed)
push coil
pull coil
HE Testing – Results
Search Coil Response Function
0% KCO3 2% KCO3
University of Alabama in Huntsville
HE Testing – Analysis
Step Function Gaussian Curve
σ ∗
Vp
Φ
2 2*
1 22 2
c c p c c
c cp c
u I V u I
U IV U I
σ
σ
Φ= Ψ = Ψ
Φ
For a Gaussian function:
1 2 1Ψ = Ψ =
University of Alabama in Huntsville
Integral Method Calculation:
2-122-62-102-4Test
2102284622
18193.61.9
24265.12.5
5658115.9
2200Seed
(%)
51 0c
σ
σ
∗−×
210c c
u
u
σ
σ
∗−×
( / )kS mσ ∗
10 ( )u mµ σ ∗ −
HE Testing – Analysis2*
22c c
c c
u I
U I
σ
σ
Φ= Ψ
Φ
University of Alabama in Huntsville
Fundamental Research on Rayleigh Taylor
Instabilities
u ~ 104 m/s Te ~ 10 eV
vacuumchamber
copperbarrier
HZ
pulseplasmagun
magnetic flux compression wall
excitationcoil
Csparkgap
Tapered Pulse Plasma Gun
Plasma Jet Characteristics
•High speed imaging
•Time-resolved interferometry
•Time-resolved spectroscopy
•dB/dt probes
Diagnostics:
University of Alabama in Huntsville
Development of Pulsed Plasma Experiment
Lin CoilSystem
triggeredsparkgap
C
optical windowpulse plasmagun
vacuumchamber
diffusionpump
high voltagefeedthrough
University of Alabama in Huntsville
Pulsed Plasma Gun Design
University of Alabama in Huntsville
Experimental Set-Up
Design
• four 2-µµF capacitors(ONR surplus)
• configurablepower bus (1, 2, 3, or 4 capacitors in parallel)
• capacitor bank and discharge circuitmounted on cart forportability
University of Alabama in Huntsville
Conclusions• An electrode-less inductive probe for measuring plasma jet
electrical conductivity was designed, calibrated, and tested• Calibrated with slug of known conductivity
Inversion algorithm marginally successfulAssumed conductivity distribution with known solutions
• Laboratory experiments using seeded and unseeded shape charge explosives
Average jet velocity = 9-10 km/secMeasured conductivities: 4 kS/m (unseeded)
26 kS/m (2% seed)• Magnetic Reynolds numbers > 1 (for fractions of a meter scale)
Mark 1 device has a good chance of being sucessful• Inductive probing technique represents a very successful and
reliable tool for investigating plasma jet characteristics• High explosive plasma sources capable of producing high Rem
University of Alabama in Huntsville
Future Plans1.Pulsed plasma gun / discharge
circuit completed- tapered plasma gun designed,
fabricated, and tested- high voltage discharge circuit
operational- vacuum chamber, pump,
feedthroughs assembled- high-purity aluminum magnet
on its way- testing to begin very soon
2.Mark 1 Device, radial-mode magnetic flux compression reactor using high explosive shaped charges
electricalconnector
LN2 Dewarvacuum liner
solenoid
stainless steel
phenolic