Shaped charges pdf

Experiments in Magnetic Flux Compression

Using Plasma Armatures

Matt Turner

Propulsion Research Center

Department 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

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

detonation target

Winterberg / Daedalus Class

Magnetic Compression Reaction Chamber

superconductor compression wall

exhaust induction

generator coil

magnetic field excitation

field coils

electrical power

Major Uncertainties

1

0 0

>> =

= uL

B B

R_m i µ σ

Magnetic Reynolds Number

⇒ low magnetic diffusivity

m m

R

D 1 1

0

∼ =

σµ

micro fusion detonation → R_m >> 1

pulsed plasma jet → R_m > 1

• achieving sufficiently high electrical conductivity

• suppression of Rayleigh-Taylor surface instabilities

conductivity → relatively low temperature → very high

velocity → very high

Plasma Jet Characteristics

Fundamental Compression Experiments

Mark 1 Device

… measurement of plasma electrical conductivity is a

critical need

Research goal is to investigate scientific and technological feasibility using non-nuclear detonations…

Radial-mode, magnetic flux compression reactor

•Opposing HE charges

•Radially expanding plasma

armature

•Moderate scale technology

demonstrator

•Low cost expendable unit

H_z

r u_a

plasma armature shielding

shell

magnet coil

generator coil

Measurement of Plasma Jet Conductivity

Inductive measurement technique provides a low cost

direct measurement of plasma jet electrical conductivity …

Lin, S-C., Resler, E. L., and Kantrowitz, A., “Electrical field coil cavity

charge

jet

search coil

Lin Coil System

{

evacuated tube time of flight

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 Coil System

{

evacuated shock tube

Lin Coil Design

Field Coil

Field Coil √ 900-turn coil

√ No. 18 enameled wire

{

Search Coil

Search 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

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 that a localized electrostatic charge can generate a signal in a standard configuration search coil due to finite capacitance between the coil and the ionized gas inside the tube

Push

Push--Pull ConfigurationPull Configuration √ cancels capacitive pick-up

√ R_d is critical damping resistance (≈ 1000 Ω)

{

Search Coil Design Considerations

L

D

standard configuration

L

D

R_d R_d

Lin Coil Calibration Apparatus

Lin Coil System_{

solenoid actutaed

valve

laser

guide tube plastic bar r el

optical detector br eech

glass tube section

{

compr essed gas cylinder

pressur e gage pressur e

r egulated 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

Lin Coil Calibration – Timing Verification

Current Velocity

Response Function

Velocity

Current

Response Fnc (push)

distance (cm) in d u c e d v o lt a g e

0 1 2 3 4 5 6 7 8 0 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 data gaussian fit

(σ= 1.8 cm)

distance (cm)

σ

/

σc

-1 0 1 2 3 4 5 6 0 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 predicted exact

constrained linear inversion (H = I;γ= 10-3)

Probe Calibration – Algorithm Verification

Shape Charge Plasma Jet Conductivity

field coil cavity

charge

Plasma Jet Conductivity Measurement

jet

search coil

Lin Coil System

{

evacuated tube time of flight

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

Preliminary Test Results

Time-of-flight

Response Fnc (push)

HE Testing – Results

Time-of-Flight Output

0 10 20 30 40 50

0 5 10 15 20 25 30

test 2-7 (0% seed) B

A

11 µµs

10 cm

1 6

10

9.1 / sec

11(10) sec

dx

m

u

km

dt

=

=

=

{

time (µs) re sp o n se (V )

0 10 20 30 40 50 -25 -20 -15 -10 -5 0 5 10 15 20 25

test 2-10 (0% seed) push coil

pull coil

time (µs)

re sp o n se (V )

0 10 20 30 40 50 -100 -75 -50 -25 0 25 50 75 100

test 2-12 (2% seed) push coil

pull coil

HE Testing – Results

Search Coil Response Function

HE Testing – Analysis

Step Function

Gaussian Curve

σ

V

Φ

2 ₂

*

1 2

2 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

1

Integral Method Calculation:

(

kS m

/

)

σ ∗

1 0 u m( )

µ σ ∗ −

Fundamental Research on Rayleigh Taylor

Instabilities

u ~ 104 _{m/s T}

e ~ 10 eV

vacuum chamber

copper barrier

H_Z

pulse plasma gun

magnetic flux compression wall

excitation coil

C spark gap

Tapered Pulse Plasma

Gun

Plasma Jet Characteristics

•High speed imaging

•Time-resolved interferometry

•Time-resolved spectroscopy

•dB/dt probes

Development of Pulsed Plasma Experiment

Lin Coil System tr iggered

spar k gap

C

optical window pulse plasma

gun

vacuum chamber

diffusion pump

Experimental Set-Up

Design

• four 2-µµF

capacitors (ONR surplus)

• configurable power bus (1, 2, 3, or 4

capacitors in parallel)

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 successful

Assumed conductivity distribution with known solutions

• Laboratory experiments using seeded and unseeded shape

charge explosives

Average jet velocity = 9-10 km/sec

Measured 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

Future Plans

1.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

electrical connector

LN₂ Dewar vacuum liner

solenoid stainless steel