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PB 161649

92c. 148

A WIRE EXPLODER FOR GENERATING

CYLINDRICAL SHOCK WAVES IN A

CONTROLLED ATMOSPHERE

BY D. L. JONES AND K. B. EARNSHAW

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March 3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent

with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials, devices, and structures; advisory services to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; and the development of standard practices, codes, and specifications. The work includes basic

and applied research, development, engineering, instrumentation, testing, evaluation, calibration services,

and various consultation and information services. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau's

unique competence is required. The scope of activities is suggested by the listing of divisions and sections on the inside of the back cover.

Publications

The results of the Bureau's research are published either in the Bureau's own series of publications or

in the journals of professional and scientific societies. The Bureau itself publishes three periodicals avail- able from the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary and pre- liminary reports on work in progress; and Basic Radio Propagation Predictions provides data for determining

the best frequencies to use for radio communications throughout the world. There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series, Handbooks, Miscellaneous Publications,

and Technical Notes. A complete listing of the Bureau's publications can be found in National Bureau of Standards Circular

460, Publications of the National Bureau of Standards, 1901 to June 1947 ($1.25), and the Supplement to National Bureau of Standards Circular 460, July 1947 to June 1957 ($1.50), and Miscellaneous Publication 240,

July 1957 to June 1960 (Includes Titles of Papers Published in Outside Journals 1950 to 1959) ($2.25); avail- able from the Superintendent of Documents, Government Printing Office, Washington 25, D. C.
NATIONAL BUREAU OF STANDARDS

technical jFtete

ikQ

May 1962

A WIRE EXPLODER FOR GENERATING CYLINDRICAL SHOCK WAVES

IN A CONTROLLED ATMOSPHERE

^y

D. L. Jones and K. B. Earnshaw

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature. They are for sale by the Office of Technical Services, U. S. Department of Commerce, Washington 25, D. C.

DISTRIBUTED BY

UNITED STATES DEPARTMENT OF COMMERCE

OFFICE OF TECHNICAL SERVICES

WASHINGTON 25, D. C.

Price $ . 50

February 16, I962

A WIRE EXPLODER FOR GENERATING CYLINDRICAL SHOCK WAVES

IN A CONTROLLED ATMOSPHERE

by

D. L. Jones and K. B- Earnshaw

National Bureau of Standards, Boulder, Colorado

ABSTRACT

A design for a rugged exploding wire device is given. This

device permits the study of strong cylindrical shock waves in

controlled atmospheres using optical and microwave techniques.

Adequate detail and pictures are given to allow construction of

the device.

A WIRE EXPLODER FOR GENERATING CYLINDRICAL SHOCK WAVES

IN A CONTROLLED ATMOSPHERE

hy

D. L- Jones and K. B- Earnshaw

National Bureau of Standards, Boulder, Colorado

Very little information on exploding wire devices is re- ported in the literature. Normally, exploding wire studies are made in air and it is the exploding wire itself that is of

1 2 interest. ' For these studies, the device for exploding the

wire may easily be made to have the necessary low inductanceelectrical connections. In the few instances where the shock

3 h waves from the explosion have been investigated ' relatively

low energy capacitor banks (~ 150 joules) were used. However,

in order to study strong shock waves in a controlled atmosphere

using a capacitor bank of 1500 joules or more a rugged blast

chamber is required. For optical or microwave observations, the

chamber must also be made of a transparent material.

The purpose of this paper is to report a ruggedly designed

exploding wire device which can be used for optical and micro- wave investigations of strong cylindrical shock waves. The

particular advantages of this device are: l) the electrical

connections are designed to have a minimum inductance; 2) the

pressure and type of gas are controllable; 3) "the device is

simple to assemble, and cleaning of the chamber is quite easy;

k) the wire is held in place by gravity; and 5) "the electrodes

for the current return path are removed far enough from the

wire axis to minimize mechanical interference with the expanding

shock wave.

-2-

The assembled wire exploder is shown in Figure 1. The dark

vertical line in the center is the wire which passes through the

lid and the cross arm and makes contact with the bottom electrode.

An exploded view of the device is shown in Fig. 2. Lids A and D are made of plexiglass one inch thick with a diameter of 12-jj- inches. Plexiglass cylinder C is 3 inches long, -^ inch thick,

and has an H§- inch I.D. Vacuum joints between the lids and

the cylinder are obtained by the rubber "0" rings which are

visible in Fig. 2.

The current return path (cross arm B) is ma.de from brass

bar stock which is covered with a sheath of rubber insulation

to avoid arcing. The cross arm is bolted to plate E through the

bottom lid D, securing lid D to the plate. An "0" ring seal

between cross arm B and lid D provides a vacuum seal. Plate E

is fastened to the bottom member G which is attached to ground.

Both plate E and member G are made of ^--inch brass.

The cylindrical insulator J, which encloses a spark gap

switch, is made of teflon with an outer diameter 2.88 inches and

inner diameter of 2.4l inches. This insulator fits into the

machined groove in lid D, through the holes in parts G and E. The top spark gap electrode I is of brass with an outer diameter

of 2.40 inches. It fits into insulator J with the top part (H)

fitting into lid D. The upper 3/8 inch of electrode I (part H)

consists of a -^-inch diameter rod covered with a one inch diameter

teflon cylinder. The "0" ring in the teflon cylinder provides

a vacuum seal for the electrode. The bottom spark gap (electrode

K) which is normally attached directly to the capacitor, is made

of 2.^0 inch outer diameter aluminum. It belongs inside insulator

J near the bottom.

-3-

Triggering is obtained "by means of a high voltage pulse

brought to the top spark gap electrode through a ^--inch hole

in cylinder F. A length of -j^-inch I.D. vacuum tubing outside

the trigger cable insulates the cable from cylinder F. The

trigger cable comes out flush with the center of the top

electrode of the spark gap.

Fittings for gas inlet and vacuum taps may be placed at

any convenient point in either lids A and D or cylinder C. Tests with this device show it to be capable of maintaining a vacuum of 50 microns with a standard fore pump.

Mass spectrometer analyses of argon gas samples taken under

normal operating conditions at 10 cm. Hg. indicate that the

k

gas purity is maintained to better than one part in 10 , or about the standard guaranteed for bottled gases . System inductance depends on the wire size, the pressure and the

voltage, but a typical value (without capacitors) is 48 x 10 '

Henry, including switch inductance. Working voltages have

ranged 3 KV to 20 KV while maximum current at 20 KV is about

150,000 amperes.

This exploding wire device has been used to generate type

III blasts at pressures ranging from atmospheric to five centimeters of mercury. Shock front velocity and distance measurements obtained by the microwave Doppler Method show that detectable shocks travel out as far as seven or eight centimeters

from the wire axis. In fact, measurements of the velocity are made until the electron density in the front falls below the

13 -3

10 cm which is required to reflect the microwaves. Usin,

the measurements the similarity theory for strong cylindrical

7

blast waves has been verified to velocities as low as Mach

number 3 in air.

-kREFERENCES

1) W. G. Chace, "A Bibliography of the Electrically Exploded

Wire Phenomena," GRD-TM-57-5; Air Force Cambridge

Research CenterJ Bedford, Massachusetts (Nov. 1956).

2) W. G. Chace, H. K. Moore, Exploding Wires, Plenum Press

Inc., New York, (1959)"

3) F. D. Bennett, "Flow Fields Produced by Exploding Wires"

in Reference 2, p. 211.

h) K. Oshima, "Experiments on the Cylindrical Blast Waves"

J. Phys. Soc. Japan, 12, 1*4-21, (1957) •

5) W. G. Chace, M. A. Levine, "Classification of Wire Explosions," J. Appl. Phys., 31, 1298, (i960).

6) D. L. Jones, R. M. Gallet, "Microwave Doppler Measurements

of the Ionization Front in Cylindrical Shock Waves

from Exploding Wires," Exploding Wires, Vol. II , Plenum Press Inc., New York, in publication.

7) S. C. Lin, "Cylindrical Shock Waves Produced by Instantaneous Energy Release," J. Appl. Phys., £5, 5*+, (195*0-

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FIGURE 2. EXPLODED VIEW OF CYLINDRICAL SHOCKDRIVER

B- 33684

II. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, U.C., and

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

In general, each section carries out specialized research, development, and engineering in the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the

front cover.

WASHINGTON, D.G.

Electricity. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurements.

Dielectrics. High Voltage.

Metrology. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering Metrology.

Mass and Scale. Volumetry and Densimetry.

Heat. Temperature Physics. Heat Measurements. Cryogenic Physics. Equation of State. Statistical Physics.

Radiation Physics. X-ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.

Nucleonic Instrumentation. Neutron Physics.

Analytical and Inorganic Chemistry. Pure Substances. Spectrochemistry. Solution Chemistry. Standard Refer- ence Materials. Applied Analytical Research.

Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. Combustion

Controls. Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal Physics. Electrolysis and Metal Deposition.

Mineral Products. Engineering Ceramics. Class. Refractories. Enameled Metals. Crystal Growth. Physical

Properties. Constitution and Microstructure. Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials. Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics, Operations Research. Data Processing Systems. Components and Techniques. Computer Technology. Measurements Automation.

Engineering Applications. Systems Analysis.

Atomic Physics. Spectroscopy. Infrared Spectroscopy. Solid State Physics. Electron Physics. Atomic Physics.

Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation. Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Molecular Kinetics. Mass Spectrometry.

Office of Weights and Measures. BOULDER, COLO.

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Cryogenic Technical Services. Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere Research.

Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. Vertical Soundings Research. Radio Propagation Engineering. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements.

Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. Radio and Microwave Materials. Atomic Frequency and Time Interval Standards. Electronic Calibration Center. Millimeter-Wave Research.

Microwave Circuit Standards. Radio Systems. Applied Electromagnetic Theory. High Frequency and Very High Frequency Research. Modulation

Research. Antenna Research. Navigation Systems.

Upper Atmosphere and Space Physics. Upper Atmosphere and Plasma Physics. Ionosphere and Exosphere

Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.

USCMM-N9S-6L
NBS
No. Ih9 cancelled