Transcript
Calhoun: The NPS Institutional Archive Theses and Dissertations
Thesis Collection
1969
An experimental investigation of the mass distribution from the exhaust of a coaxial plasma accelerator. Strouse, Robert Dale Monterey, California. U.S. Naval Postgraduate School http://hdl.handle.net/10945/12169
— NPS ARCHIVE 1969 STROUSE,
R.
>
AN EXPERIMENTAL INVESTIGATION OF THE MASS DISTRIBUTION FROM THE EXHAUST OF A
COAXIAL PLASMA ACCELERATOR
Robert Dale Strouse
DUDLEY KNOX LIBRARY NAVAL POSTGRADUATE SCHOOL MONTEREY, CA 93943-5101
United States
Naval Postgraduate School
THESIS AN EXPERIMENTAL INVESTIGATION OF THE MASS DISTRIBUTION FROM THE EXHAUST OF A COAXIAL PLASMA ACCELERATOR
by
Robert Dale Strouse
June 1969
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DUDLEY KNOX LIBRARY NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA 93943-5002
An Experimental Investigation of the Mass Distribution from the Exhaust of a Coaxial Plasma Accelerator
by Robert Dale Strouse Second Lieutenant, United States Marine Corps 1968 B. S., United States Naval Academy ,
Submitted in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE IN AERONAUTICAL ENGINEERING from the
NAVAL POSTGRADUATE SCHOOL June 1969
ABSTRACT Investigations were conducted on the mass distribution of the
exhaust of
a
coaxial plasma accelerator in order to gain insight into
the manner by which the fuel (gold)
is
ionized and accelerated.
Tests were conducted using both annular sections of gold foil
and single strands of gold wire.
Both types of runs showed a non-
uniform angular distribution with one or more well defined peaks. similarity
between the distributions leads
to the
The
probable conclusion
that the foil, rather than undergoing uniform ionization around the
annulus
,
is
actually ionizing at discreet "spokes" about
Experiments conducted with gold
foil
its
periphery.
involved varying the
distance from the accelerator to the collector.
A
fairly uniform dis-
persion of gold plasma was observed as collector distance increased.
TABLE OF CONTENTS I.
II.
INTRODUCTION
11
A.
BACKGROUND
11
B.
DESCRIPTION OF APPARATUS
13
1
.
Vacuum System
13
2
.
High Voltage System
14
3
.
High Voltage Capacitor and Firing Circuits
14
4
.
Triggering Circuits
15
5
.
Accelerator Electrodes
15
6
.
Photographic Apparatus
15
EXPERIMENTAL PROCEDURE
17
A.
PLASMA ACCELERATOR PROCEDURE
17
B.
RADIOISOTOPE TRACER TECHNIQUE
18
C.
IMAGE CONVERTER CAMERA PROCEDURE
22
III.
RESULTS AND CONCLUSIONS
23
IV.
SUGGESTIONS FOR FURTHER STUDY
2 7
BIBLIOGRAPHY
73
INITIAL DISTRIBUTION LIST
74
FORM DD
75
1473
LIST 1
Tracer Results for Run
2
Tracer Results for Run 13
1
OF TABLES 28 2 9
LIST OF
FIGURES
FIGURE 1
Schematic of Coaxial Plasma Accelerator
30
2
Plasma Accelerator and Vacuum Systems
31
3
Capacitor, Ignitrons
4
Vacuum Control Panel, Pulser Power Supply, and
and Vacuum System
,
32
33
Transformer 5
Vacuum Controls
34
6
High Voltage System
3 5
7
High Voltage Power Supply Control Panel
36
8
Electrode and Ignitron Arrangement
3 7
9
Ignitron Pulser
38
10
Capacitor Discharge Trigger
39
11
Image Converter Camera
4
12
Trigger Box,
13
Triggering Connections for Camera and
Camera Controls and Oscilloscope
41
42
Oscilloscope 14
Sample Disks Arranged
15
Sample Preparation Equipment
44
16
Plasma from .005
Diameter Gold Wire
45
17
Plasma from .00005
Thick Gold Foil
45
18
Plain
19
Deposited Plasma from .005 Wire
in.
in.
for Irradiation
Aluminum Foil Collector in.
43
46
Diameter Gold
46
Figure
Diameter Gold Wire
47
Thick Gold Foil
47
20
Deposited Plasma from .020
21
Deposited Plasma from .00005
22
Capacitor Voltage Calibration
23
Control Factor
-
Runs
1-12
49
24
Control Factor
-
Runs
13 - 17
50
2 5
Normalized Gold Distribution for Collector Accelerator .00005 in. Gold Foil
2
2 6
Normalized Gold Distribution for Collector Accelerator .00005 in. Gold Foil
2 7
in.
in.
48
in. from
51
4 in.
from
52
Normalized Gold Distribution for Collector Accelerator .00005 in. Gold Foil
6 in.
from
53
28
Normalized Gold Distribution for Collector Accelerator .00005 in. Gold Foil
8 in.
from
54
29
Normalized Gold Distribution for Collector 10 in. from Accelerator .00005 in. Gold Foil
55
3
Normalized Gold Distribution for Collector Accelerator .00005 in. Gold Foil
in. from
56
31
Normalized Gold Distribution for Collector 4 in. from Accelerator .00005 in. Gold Foil
57
32
Normalized Gold Distribution for Collector Accelerator .00005 in. Gold Foil
6 in.
from
58
33
Normalized Gold Distribution for Collector Accelerator .00005 in. Gold Foil
8 in.
from
59
34
Normalized Gold Distribution for Collector 10 in. from Accelerator .00005 in. Gold Foil
35
Normalized Gold Distribution Pressure
1
x 10"^mm.
Hg
.
for .02
in.
2
Wire
at
Collector. 5 in. from Accelerator
60
61
Lgurc 36
for .020 Wire at Pressure Collector. 5 in. from Accelerator
62
Normalized Gold Distribution for .020 Wire at Pressure 3.95 x 10"4 mrn Hg. Collector 5 in. from Accelerator
63
Wire at Pressure from Accelerator
64
.020 Wire at Pressure in. from
65
Normalized Gold Distribution 2.4 x 10~^mm.
37
Hg
.
.
3 8
Normalized Gold Distribution 5
39
x 10
1
42
Collector.
_4
mm. Hg
.
x 10
mm. Hg
.
for .02
5 in.
for
Collector. 5
Normalized Gold Distribution 8
4
.
Normalized Gold Distribution 6.5 x 10
40
mm. Hg
Collector
5
for .020
Wire
at Pressure
66
in. from Accelerator
Normalized Gold Distribution for .005 Wire at Pressure 1.4 x 10 mm. Hg. Collector. 5 in. from Accelerator
67
Normalized Gold Distribution
68
3.2 x 10~ 4 mm. Hg
.
for .005 Wire at Pressure Collector. 5 in from Accelerator
Normalized Gold Distribution 4.3 x 10"4mm. Hg. Collector
Wire
Pressure in from Accelerator
69
44
Normalized Gold Distribution for .005 Wire at Pressure 4.9 x 10 "mm. Hg. Collector -5 in. from Accelerator
70
45
Normalized Gold Distribution
.005 Wire at Pressure
71
4 3
6.0 x 10 46
_4
mm. Hg
.
8.0 x 10
mm. Hg
.
5
for
at
Collector. 5 in. from Accelerator
Normalized Gold Distribution -4
for .005
Collector. 5
Wire
Pressure in. from Accelerator
for .005
at
72
ACKNOWLEDGEMENTS The author
is
indebted to Professor D. C. Wooten of the Aero-
nautics Department for his assistance throughout the project.
The
author also wishes to express his appreciation to Messers Theodore
Dunton, Robert Besel, and Dana Maberry, and the remainder of the technical staff of the Department of Aeronautics for their assistance on the
many technical problems encountered
included in this paper.
10
in the
course of the research
.
I.
INTRODUCTION
BACKGROUND
A.
Plasma accelerators provide in
magnetohydrodynamics,
disciplines.
means
a
making detailed studies
for
many diverse
a field of interest in
scientific
Astrophysicists, for example, are interested in the field
from the point of view of explaining the behavior of celestial bodies
and their magnetic and electrical properties perhaps more interested accelerator rather than
phenomena.
in the direct
its
use as
The
a tool in
latter of
.
The engineer
is
applications of the plasma
Among these applications
space propulsion units.
[3]
studying electromagnetic
are shock
wave generators and
these two applications, while
under extensive study, has not yet proven feasible, due to low efficiencies of systems thus far developed [6]
Plasma accelerators depend upon the action of Lorentz forces for their
due
operation [1], as illustrated in Fig.
1.
The magnetic
field
to the current flowing through the electrodes interacts with the
current flowing through the plasma, and produces the familair F=JxB reaction, with the force
accelerator.
(F)
driving the plasma out the barrel of the
Secondary effects due
to current
loops (Hall currents)
within the plasma are relatively small and require sensitive and
sophisticated instrumentation for investigation [7].
These secondary
effects will not be dealt with in the remainder of this paper.
11
The plasma accelerator used in these experiments had previously undergone only two investigations:
velocity measurements
[2]
,
and
determination of environmental pressure effects on gold deposition [91.
The
latter tests
used
a
2.4 inch I.D. cylindrical collector placed con-
centric to the plasma accelerator, and extending to near the top of the bell jar.
These experiments produced two important conclusions:
The
distribution of gold plasma outside the accelerator is not angularly
uniform, and pressure effects were extremely small over the range of -3
pressures, 50 x 10 All previous
mm. Hg
-5 .
to 50
x 10
mm. Hg.,
experiments were done with gold
investigated.
foil.
The non-uniform angular distribution suggested that the gold foil
a
was ionizing only locally
at
one or two places, so that rather than
uniform "doughnut" of plasma, only one or more "spokes" were
produced.
In order to test the
spoke model, gold wire was employed.
Runs made with the wire could be compared to runs made with
foil to
determine the validity of the model. Also of interest accelerator. part
II)
is
the diffusion pattern of the plasma leaving the
By varying the distance of the collector (described in
from the barrel of the accelerator, and noting the pattern of the
deposited plasma at varying distances, diffusion
may be found.
12
a
measurement
of the exhaust
.
DESCRIPTION OF APPARATUS
R.
The coaxial plasma accelerator system used consisted of the following major components:
vacuum system, high voltage power
supply, high voltage capacitor and firing circuits, triggering circuits,
and accelerator electrodes, together with the necessary instrumentation monitoring and controlling the apparatus.
for
1
Vacuum System
.
The vacuum system (Figs. parts.
The
was used of
to
mercury.
first, a
2
and
3)
consisted of two major
Welch 1397B vacuum pump and associated values,
rough the system down to a pressure of about ten microns
The second was
a
Welch 1402B
fore
pump with
Veeco
a
combination diffusion pump, baffle, and nitrogen cold trap.
This high -4
vacuum system was capable
of achieving pressures of
without the liquid nitrogen cold trap. nitude improvement testing with a
was realized with
to
x 10
mm. Hg
Approximately an order of magExtensive
the use of the cold trap.
mass spectrometer type leak detector indicated
leaks were present.
due
1
that no
Vacuum limitations would therefore appear
to be
outgassing of the vacuum system.
Vacuum measurements were made with couple guage at pressures above
1
a
Veeco
DV1M
micron of mercury.
pressures, an ionization guage tube
was used.
thermo-
For lower
The vacuum instru-
mentation was monitored and controlled from a Veeco RG-31X control panel
.
(Figs. 4
and
5)
13
2
High Voltage System
.
The high voltage power supply (rig.
plasma accelerator capacitor was from a control panel (Fig.
through
a
7)
in
charge the
Charging was
on the front of the unit.
series with a 600
to
40KV unit controlled and monitored
a
colenoid operated knife switch and
A microameter
used
6)
megohm
megohm
three
a
resistor
was connected
across the capacitor, so capacitor voltage could be read. curve (Fig. 22) of capacitor voltage as
a
resistor.
A calibration
function of microameter
reading was obtained using a high voltage, Sensitive Research Corp.
1%
full
scale electrostatic voltmeter.
previous calibration
[2]
It
was found
to differ from
by 15%.
The unit was equipped with
a Jennings high voltage relay
which, when opened, grounded the capacitor through high voltage resistor.
The relay could be used
a
one megohm
to abort a shot or bleed
residual capacitor voltage after firing. 3
.
High Voltage Capacitor and Firing Circuits The gold
foil
and wire were ionized
in the
plasma accel-
erator by the discharge of an Axel 6.4 microfarad low inductance
capacitor at 15,000 volts.
100,000
,
Four GE 7703 ignitrons
,
rated at
2
0KV and
amps, peak current provided the switching between the
capacitor and the electrodes of the accelerator.
14
(Fig.
8)
.
4
.
Triggering Circuits
The ignitrons were triggered by circuit (Fig
provided by
9)
.
a
latter circuit
.
202
a 62 68 thyratron in the
The pulser circuit was triggered by 1
120 volt pulse
a
thyratron in a triggering circuit (Fig. 10)
was also used
to trigger
pulser
This
.
an image converter camera and
oscilloscope 5
.
Accelerator Electrodes
The coaxial copper electrodes (Fig. ponents of the plasma accelerator. diameter solid cylinder, as mentioned above.
is
8)
are the basic
The center electrode,
a
1
com-
inch
separated from the capacitor by the ignitrons,
The outer electrode,
tube, is connected directly to ground.
a
Golf
1.5 inch I.D. copper foil or
wire placed across
the gap between the electrodes is ionized upon capacitor discharge.
The electrodes were not perfectly concentric, the axes being approximately .03 inches apart at the extreme end.
In order to
assure reproducible results, scribe marks were made on the electrodes so they could be oriented the same 6
.
way
for
each
firing.
Photographic Apparatus In order to
erator, an Abtronics
The camera
(Fig.
11)
photograph the actual firing of the plasma accel-
Model
1
image converter camera was employed.
was mounted so as
accelerator.
15
to look
down
the barrel of the
The camera has four shutter tubes, each with allowing independent triggering at any desired delay.
its
Due
own
circuit,
to the
camera's
lack of accuracy in the range of small time delays employed (about 2
/-sec. between shots) the camera was monitored on an oscilloscope
(Figs. 12 and 13).
The oscilloscope and camera were both triggered
by the same circuit used to firing circuit.
fire the thyratron in the
The camera was eguipped with
a
main capacitor
monitor output which
provided a signal each time one of the camera circuits fired. put
was used
for the
oscilloscope input.
16
This out-
II.
EXPERIMENTAL PROCEDURE
PLASMA ACCELERATOR PROCEDURE
A.
The basic procedures employed by Brumwell
[2]
and Smith
[9]
in
these experiments were developed
in
previous experiments with the same
These procedures involve the
apparatus.
plasma accelerator
firing of the
and then collecting the discharged plasma on aluminum
foil
collectors
analysis by means of radioisotope tracing.
for
For the firings involving the gold wire (runs 1-12)
were 1.5 inch diameter aluminum
foil
placed over the end of the electrodes. from the end of the accelerator.
disks mounted in
The collector
This point
the collector disk
a
the collectors
plexiglass cap
itself
was
.5
inches
The gold wire was placed across the
.25 inch gap between the electrodes (Fig.
every firing.
,
was used
for
8)
at the
same place
angular reference.
was removed, sprayed with
for
After firing,
clear, acrylic lacquer to
prevent loss or movement of the deposited gold, and then cut into eight,
equal, pie-shaped pieces. to the zero
45
degrees
each
of the
The centerline of the
first
piece corresponded
degree reference, with succeeding pieces being cut every in a
counterclockwise direction.
Six runs were
two sizes of wire, .020-inch diameter and .005-inch -4
diameter.
made with
Pressures were varied from 1.0 to 8.0 x 10
mm. Hg.
For the firings involving gold foil (runs 13-17) the collector (Fig.
was
a
seven inch diameter aluminum
The distance from the collector
foil
to the
17
3)
disk supported on a metal stand.
end of the accelerator was varied
from two to ten inches in two inch increments. lector
was removed and lacquered as before, and samples were cut from The samples were circular, with
the collector with a steel tool (Fig. 15). a
After firing, the col-
diameter of .73 inches.
The
first
sample was cut from the center of
the collector, with subsequent samples cut from concentric circles
inscribed at 3/4 inch intervals from the center of the collector.
sample was placed from which
it
in a paper folder properly
was cut and
its
Each
marked with the circle
angular position from a fixed reference.
For example, the sample cut on circle "O" would be the center sample,
and would be labeled "O-O"
A sample cut from circle "2"
.
(i.e.
,
1-1/2 inches from collector center), 45 degrees from the fixed ref-
erence would be labeled "2-4 5."
This labeling system
over to the data tables used in this report. -4 a pressure of 5 x 10
mm. Hg
.
All runs
was carried
Runs 13-17 were made
were made with
at
a capacitor
voltage of 15KV.
B.
RADIOISOTOPE TRACER TECHNIQUE The tracer technique employed
comparator method determined mass
Assuming
that all
[5],
is
In this
in
method,
these experiments was the a
sample of previously
irradiated together with samples of
unknown mass.
samples receive the same radiation, the unknown
mass may be determined by means
known mass known mass
activity of
of the following equation:
unknown mass unknown mass
= activity of
The activities are determined by means of Irradiation
AGN-201 nuclear Facility. a
was
a scintillation
(1)
counter.
carried out in the Aerojet-General Nucleonics
reactor at the Naval Postgraduate School Reactor
Samples were introduced into the reactor core by means of
hollow plastic tube (Fig.
polyethylene plugs.
14)
with the samples at one end between
Irradiation
was accomplished with
power
a
Gold 197 was
setting of 300 watts for a period of ten minutes. irradiated, undergoing the following reaction:
n + Au
That
is, the
nucleus
(*)
197
Au
198*
. '•
Au
198 ,
(2)
gold nicleus captures a neutron, producing an excited
which decays by emitting
detected by the scintillation counter. detects the
^
+
gamma photons by means
a
gamma photon, which
The scintillation counter
then [4]
of a luninescent material (in this
case sodium iodide) which converts the energy of
a striking
photon into photons at or near the level of visible light. of lights" are detected by a photomultiplier tube, into electrical pulses,
is
gamma
These "flashes
which converts them
which are then amplified and counted.
The
counting unit used provided for the oscilloscope display of the counting process, with the vertical scale
a
measure of the number
of counts
the horizontal scale indicating the channel being counted.
channels could be displayed, each representing
19
a particular
Up
and
to 512
energy
gamma photons being detected. Using an
level of
irradiated gold sample,
pulse height analysis was possible using the oscilloscope, and
a rapid
the proper channels for detecting gold could be easily determined.
Sixteen channels on either side of .411 mev. were found to completely
encompass the gold photopeak. the unit
In
was also eguipped with
each channel, and
addition to the oscilloscope display,
memory, used
a
a selective integrator
to store the
counts
in
which, when the preset
counting time had expired, could be made to sum the total number of
counts
in a
selected band of channels, in this case the 32 channel
Once the integration was
band centered at the .411 mev. energy level.
complete, the total number of counts, together with the counts channel, were printed out by means of a teletype unit.
each
for
The total
counts, summed by the integrator, then divided by counting time, gave the sample activity in counts/min.
Runs 1-13, containing collector foils of firings using gold wire,
were irradiated together.
known gold mass were included. mass
of gold foil,
The small gold sample adhered sprayed with acrylic lacquer.
of
plasma accelerator Four samples of
These samples consisted of
a
known
weighed on an electrical balance, and placed on
plain piece of aluminum foil the
samples,
all
in order to
a
same as the unknown sample pieces.
to the
aluminum
after the former
was
Also included were plain aluminum
accurately determine background count.
aluminum and gold samples were made
?n
foil
Counts
at various times during the
counting process.
Using the control sample data, equation
(1)
may be
slightly altered as follows:
(
activity of
known mass- background known mass
(
activity of
unknown mass- background unknown mass
The ratio on the factor and
left
hand side of equation
was plotted as
a
(3)
activity
=
)
activity
(3)
)
was called by control
function of time (Figs. 23 and 24).
rather than counting the control activities each time an
Thus,
unknown
sample was counted, the control samples were counted only frequencly
enough
to obtain the plots of Figs. 23
and 24, and the control factor
could be taken from the graph at any desired time. It
due
to
was found
that the background count
two factors.
First, about 2/3 of the
due
most
of the nuclides
was
was random noise,
when no aluminum sample was present.
to the short half-life of
This
background activity was
not due to the aluminum control samples, but
recordable even
was random.
Secondly,
aluminum and other impurities
had already decayed, that part
still
in the foil,
active
representing the relatively flat portion of the exponential decay curve,
and not subject to much change over the period of several hours during which counting took place. (164 counts/min.)
was assumed
Therefore, an average value
for the
tracted from the sample activities.
background count and was sub-
The sample activities of the data
tables represent observed activity minus background activity.
21
.
Runs 13-17 were irradiated and counted runs 1-12, with their
own
the
chosen so as
depending upon sample to insure a total of
The number of counts observed
activity is a normally distributed is
to 4 minutes,
1
activity, the length of time being
about 1000 counts.
same manner as
set of control samples.
Counting time varied from
where N
in the
number of counts
given sample
for a
random variable with variance, [5],
C"
=N
With 1000 counts, the variance
31.6 or 3.1 6% of the total count
is
IMAGE CONVERTER CAMERA PROCEDURE
C.
In order to
photograph the plasma moving through the accelerator,
the image converter camera
on the wooden stand, as
was mounted above
in Fig.
11, or directly
the bell jar, either
on the
top.
The advantage of the higher mounting was that
some
of the paralax
was
due
to the fact that
off the axis of the electrodes.
it
flat
plexiglass
would eliminate
each of the four camera lenses
Pictures taken from the higher
position were too small for reproduction (about 1/8 inch in diameter)
and so do not appear appear
to
in this paper.
The effect of paralax does not
have influenced the pictures taken at the lower camera
position (Figs. 16 and 17). Figs. 16 and 17 are photographs of gold foil and .005 in. gold wire, respectively, after ionization. is
2
1/2
The sequence of photographs
upper right, lower right, upper left, lower
/(sec. between photographs.
left,
with approximately
(Camera circuit number
function for the series of photographs of Fig. 17.)
22
3
failed to
III.
RESULTS AND CONCLUSIONS
Results of the radioisotope tracer analyses of the plasma spattered aluminum collectors are presented in graphical form in Figs. 25 -46, with sample data in tables
and
1
2.
Each gold distri-
bution plot has been normalized with respect to the total mass of gold
collected in
its
Figures
respective run.
25-29
are plots of gold distribution as a function of
distance from collector center, where gold
(Fig. 25)
most of the gold
(Fig.
3)
.
in the
to ten
accel-
inches by
At a distance of two inches
is distributed in a
at 3/4 in. from the collector center. to the
was used
was varied from two
erator, and the collector distance
means of an adjustable stand
foil
very narrow band centered
This band corresponds in position
annulus between the accelerator electrodes.
As distance from
the end of the accelerator increases (Figs. 26 - 29) the peak flattens out, indicating diffusion of the plasma inward and outward from the
original annulus
.
Figures 30 - 34 are plots of the same shots mentioned above, with
angular distance from a fixed reference replacing distance from collector center as the abscissa.
Compare these graphs with Figs. 35-46,
the plots of gold distribution for runs using wire.
The similarity
shape between the two sets of curves definitely lends credence
in
to
the spoke model describing the manner in which the gold foil behaves
23
in
the accelerator.
In both
made with wire
For the runs
distribution.
cases, there are notable peaks in the a
peak
at the zero
degree
point, the location of the placement of the wire before firing,
certainly not be unexpected.
However,
for a
number of runs made with
wire, more than one peak occurs, indicating that the wire has
been separated into two or more large plasma slugs. peak phenomenon also appears the foil
in runs
may have only one spoke.
periphery of the gold foil than one peak
is
may be
observed
made with
model total
foil,
(little
indicating that
That is, only one point around the
actually ionized, even though more
in the angular distribution.
and
for foil ionization.
darkness
somehow
This multiple
The similarity between photographs taken of the after ionization (Figs. 16
would
In
17)
foil
and wire
also tend to substantiate the spoke
both cases, there are regions of almost
or no plasma present).
For the foil disk, a total of 15.55 mg. of gold foil (thickness
.00005 in.) were available
for ionization.
For the
.
005-in. diameter
wire, 1.553 mg. were available, and for the .020-in. diameter wire,
24.8 mg
.
were available.
14.98 mg. of
foil
In the runs
were collected
each run.
in
diameter wire, .02065 to .0575 mg
with the foil disks, 6.82 to
.
were collected, and
.020-inch diameter .72 61 to 1.1692 mg to
For the .005 inch
.
for the
Converting these figures
percentages, 44% to 96% of original mass was collected for the
foil,
while 1.2 9% to 3.7% of the .005 -inch wire, and 2.9% to 4.9%
24
.020-inch wire were collected.
of the
A possible explanation of
phenomenon can be found by examining the collectors through scope.
The collectors used
in the runs
this
micro-
a
involving gold foil contained
large numbers of circular gold particles .001 to .003 inches in diameter.
These particles were photographed under 10 power magnification
On
(Fig. 21)
the scale appearing across the photographs, each large division
marked by numerals represents .01 inches.
While too large
to
have
been ionized plasma, these particles were probably "pulled along" by the charged plasma particles.
The gold
foil,
only .00005-inch thick,
could be broken into many tiny particles in a very short period.
The
collectors containing the deposited wire, on the other hand, showed
surface discoloration after a shot (Figs. 19 and 20), with a number of particles smaller than
the .02
.0005-inches across observed in the case of
-inch diameter wire.
It
may be concluded then,
that the
relatively thick wire is unable to disintegrate, as does the foil, and
thus only ionized gold or extremely small non-ionized particles are
accelerated, while the remaining wire breaks up into pieces too large to be pulled
along by the charged plasma.
The relatively high percentages of gold
foil
contrasts sharply to data collected by Smith [9].
collected (44-96%)
Using both the
circular foil collector described previously, together with a horizontal
cap-like collector at
its top,
he was able to collect only about 12-14%
25
of the available
were made cluded
at
in this
No
mass.
It
should be noted however, that
all of his
runs
capacitor voltages of around 7KV, whereas the runs in-
paper were all made at 15KV.
variation in
mass deposition was observed with variation
-4
pressure over the 10
mm. Hg. range
26
for the runs
with gold wire.
in
.
IV.
Among 1
SUGGESTIONS FOR FURTHER STUDY
the possibilities for further study are:
Measure the velocity
.
the electrodes by
means
of
of the
plasma accelerating through
oscilloscope monitored probes inserted
through the walls of the outer electrode, 2
Determine the effect of capacitor voltage on the percent of
.
gold recovered in a shot,
Devise
3.
a
means
of determining the diffusion coefficient
of gold using the accelerator, 4.
By varying the size, shape, or orientation of the center
electrode, study the effects of an asymetrical magnetic field on the
plasma flow, 5.
Analyze the background activity from the aluminum
collectors in order to determine 6.
Conduct
its
foil
sources,
a detailed study of
microscopy
2 7
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