SR90, STRONTIUM SHAPED-CHARGE CRITICAL IONIZATION VELOCITY EXPERIMENT

Eugene M. Wescott, Hans Stenbaek-Nielsen, and Daniel W. Swift

Geophysical Institute, University of Alaska Fairbanks

Arnoldo Valenzuela

Max Planck Institut fiir Extraterrestriche Physik, Garching, Federal Republic of Germany

David Rees

University College, London

Short title: Strontium Critical Velocity Experiment

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PRECEDING PAGE BLANK NOT FILMED

Abstract. In May 1986 we carried out an experiment to test Alfvdn's critical

ionization velocity (CIV) effect in free space, using the first high explosive shaped

charge with a conical liner of strontium metal. The release, made at 540 km altitude

at dawn twilight, was aimed at 48 ° to B. The background electron density was

1.5X 104 cm -3. A faint field-aligned Sr ÷ ion streak with tip velocity of 2.6 km s-! was

observed from two optical sites. Using two calibration methods, we calculate that

between 4.5 X 10 _° and 2 X 102_ ions were visible. We have calculated an ionization

time constant of 1920 s for Sr from the solar UV spectrum and ionization cross section

which combined with a computer simulation of the injection predicts 1.7 X 1021 solar

UV ions in the low-velocity part of the ion streak. Thus all the observed ions are from

solar UV ionization of the slow (less than critical) velocity portion of the neutral jet.

The observed neutral Sr velocity distribution and computer simulations indicate that

2X 102_ solar UV ions would have been created from the fast (greater than critical)

part of the jet. They would have been more diffuse, and were not observed. Using

this fact weestimate that any CIV ions created were less than 102_. We conclude that

future Sr CIV free space experiments should be conducted below the UV shadow

height and in much larger background plasma density.

Introduction

Alfvdn (1954) and later Alfvdn and Arrhenius (1975) proposed a theory of the

formation of the solar system which provided a means of separating the elements

depending upon their ionization potential. As a part of that theory it was proposed

that if a neutral gas streaming through a plasma across a magnetic field exceeds a

critical velocity: Vc = (2WifMa)_, (where Wi and Ma are the ionization potential and
atomic mass of the neutral gas), then the neutral gas would rapidly ionize. For a

central attracting mass, Alfv_n showed that the critical velocity relationship led to a

critical accretion radius for each of four groups of the most abundant elements with

apparently good agreement with the mean distance of several groups of satellites

such as the terrestrial and the giant planets, or the Galilean moons in the Jovian

System (Mobius et. al., 1979).

Laboratory experiments documenting the critical velocity effect have been carried

out for years and were reviewed by Danielsson (1973). Mobius et al., (1979), pointed

out that:

"All the laboratory experiments besides scaling in dimensions are different

from Alfven's cosmogonic scenario in two basic features:

The magnetized plasma is moving with respect to the neutral gas, caused

by the external discharge voltage,

Walls are present, making up the discharge chamber."

Several free space experiments have been made to test the critical ionization

velocity effect with more appropriate scaling factors and without walls. For a review

of theory, laboratory and free space experiments see Newell (1985). The experiments

have used barium and strontium vapor with critical velocities of 2.7 km s-! and

3.5 km s-l, respectively. Haerendel [1982, 1988] observed 16-18% ionization of those

neutrals that exceeded the critical velocity from a conical barium shaped charge

detonated 30 ° to B well below the solar UV horizon in project Porcupine. Deehr et al.

[1982] detected strontium ions in the sunlit detonation of a radial barium shaped

charge. The strontium was present as a 1% impurity in the barium, and the analysis

shows that about 50% of the strontium ionized - at a time when less than 1%

ionization would be produced by solar UV. In 1983 two experiments were carried out
4

from rockets at the magnetic equator in Peru. Star of Lima [Wescott et al., 1986a;

Torbert and Newell, 1986] was a barium conical shaped charge fired perpendicular to

B in partial solar UV illumination. Optical observations indicate that 2.5 to 5 × 1020

Ba ions were produced, which could have been due to the solar UV ionization. Star of

Condor [Wescott et al., 1986b] was a radial shaped charge lined with strontium metal

and detonated such that Sr vapor was produced at all pitch angles to B. The

detonation produced 43% of the neutral gas with velocity component perpendicular to

B greater than the 3.5 km/s critical velocity. Ten minutes after detonation, a fieldaligned ion streak was observed; it was estimated to contain 2.4× 1019 ions, which is

0.004% ionization of the Sr vapor. This amount can be explained by solar UV and

initial Maxwellian temperature tail ionization.

In order to understand the apparent failure of the Alfvdn mechanism to produce a

cascade of ionization in the 1983 Peru experiments, we carried out three additional

CIV experiments from rockets at Wallops Island in May 1986. CRIT I, used two

barium conical shaped charges detonated below the solar UV cutoff altitude at 45 ° to

B at different distances from a well-instrumented mother payload (StenbaekNielsen, et al. 1990; Brenning et al. 1990). There was also a daughter payload

several kilometers up the magnetic field line.

The third experiment, called SR90, consisted of a high-explosive conical shaped

charge with a strontium metal liner on a Taurus-Nike-Tomahawk fired 9 minutes

after the launch of the barium experiment rocket. The Sr release was in full solar UV

radiation. FSppl et al. [1965] estimated the solar UV ionization time constant for Sr

atoms to be 4545 seconds. Based upon this very long ionization time constant, it was

assumed that the solar UV contribution to the ionization processes would be

negligible compared with the Alfvdn mechanism; however, we have found this to be
5

an unwarranted assumption. This paper addresses the optical observations,

computer simulations, and analysis of the SR90 experiment. There were no in situ

diagnostics other than background electron densities from the Millstone Hill radar.

The SR90 Experiment

The Taurus-Nike-Tomahawk, 38.008 UE, was launched from Wallops Island

May 13, 1986, at 0756:00 UT. The payload consisted of an attitude control system,

timers and power supplies to detonate a single high-explosive conical shaped charge

aimed forward and coaxial with the rocket. The shaped charge consisted of 7.4 kg of

75/25 OCTOL high explosive, with a tapered 30-degree conical liner of Sr metal

weighing 0.57 kg. The 2-axis attitude control system was set to nominally align the

shaped charge at 45 ° to B, but the azimuth was undetermined; detonation could occur

anywhere on a 45 ° cone about B.

The detonation occurred at 0801:29 UT, at 539.6 km altitude, 37.72°N lat and

-74.72°E long. By triangulation, the axis of the neutral strontium jet was upwards at

a geodetic elevation angle of 26 ° and azimuth of 212 °, giving an actual angle of 48.2 °

with respect to B. The experiment was observed from three primary optical sites

using low light level imagers: Wallops V25, 37.861°N, -75.457°E, about 2 km from

the launcher; Duck, NC, 36.182°N, -75.751°E; and at Cape May, NJ, 38.945°N,

-74.883°E. NASA film cameras were also operated at Wallops Island near the control

center.

At Duck, NC, observations were made using an intensified film camera and an

intensified silicon intensified target (ISIT) TV system. Figure 1 shows a picture of

the neutral jet taken in white light from the ISIT TV 11.5 seconds after detonation.
6

The detonation azimuth and elevation were very fortunate for analysis of the neutral

velocity distribution, as the viewing angle between Duck and the jet was close to 90 ° ,

allowing the best neutral velocity distribution from a shaped charge that we have

ever obtained. The ISIT image, Figure 1, was digitized and each pixel value was

printed out. The corresponding distances along various angles away from the

detonation point were calculated and plotted on the pixel diagram. We were able to

fit Gaussian curves across the jet at various distances, and to integrate the total

intensity of all neutral Sr gas in velocity intervals hv of 0.875 km s-1. The Gaussian

function for axis intensity, or density dependence, for the fast portion of the jet (v>8

km s-l) has a half amplitude angle of 6.6 ° and is given by:

o21.2

_6.6") 2

I= 10e

where 0 is the angle from the central axis in degrees, and Io is the intensity (or

neutral density) at the center. For velocities between 3.5 and 8 krn/sec the half

amplitude angle is near 10 °, and for the very low velocity material (v<3.5 km s-l) the

half angle is close to 22 °.

Figure 2 shows the differential velocity function derived from integrating the

total pixel counts per 0.875 km s-1 increments. The apparent tip velocity was slightly

over 13 km/sec. The differential velocity distribution was normalized by assuming

that 15% of the 0.556 kg Sr liner was vaporized, based on vacuum chamber

experiments with small Ba and Sr shaped charges (Michel, 1969, 1974).

F0ppl et al. [1965] estimated the ionization time constant for strontium at about

4545 sec and noted "...which is of course highly uncertain." We used this value in

planning the experiment, but after the experiment we were able to calculate a better
number. Using the newer experimental ionization cross section between 1700-2400A

of Ltitjens [1973] which he estimates is good to 30%, convolved with the solar UV

spectrum of Banks and Kockarts [1973] we find an ionization time constant of 1920 s

(+_ 30%). With 5.7 X 1023 Sr atoms available for ionization and a time constant of

1920 sec, in 0.1 s there should be 3×1019 ions, in 1 sec, 3× 102o ions, and in 10 s,

3 × 102t ions produced.

Analysis of the Sr metal chips left over from machining the cone indicates that

there were 2.13% Ba atoms by weight impurity, or 0.012 kg of Ba in the cone.

Assuming 15% vaporization of the Ba, and a solar UV ionization time constant of 28

sec [Hallinan, 1988], the number of Ba ions would equal the number of Sr ions, but

they would not be visible through the Sr ion filters.

Optical Observations

At Duck NC, the Sr injection was also observed with an intensified film camera with

a narrow band 4078£ interference filter on the principal SrII line. A faint fieldaligned streak of Sr _ ions was observed. Figure 3a-f shows a sequence of portions of

six intensified camera frames which were digitized electronically. The bright ovalshaped feature at, Fig. 3a, is the explosive debris cloud with broad band emissions

coming through the 4078£ filter. The field-aligned streak can be seen coming upward

from slightly left of center of the debris cloud at 6.6 s and progressing up the field line

in successive 2-s intervals. The last frame Fig. 3f, at 63 s shows the streak visible

about 85 km along the field line (distances in 20km ticks shown along the field line).

The early time apparent velocity of the tip of the field-aligned Sr ÷ jet is about 2.6

km s-1. With an injection of pitch angle 48.2 ° to B, the corresponding neutral Sr
8

velocity would be 3.9 kms-1. This agrees well with the low-velocity peak in the

differential velocity distribution, Figure 2. The low-velocity peak is estimated to

contain 2.3 × 102_ atoms of Sr.

The ISIT camera at Duck in white light is less sensitive than the intensified film

camera and the bright neutral Sr cloud partially obscured the direction up the

magnetic field line. No ion streak is evident, even with post facto 3-second

integration, but this is consistent with the observed brightness and the sensitivity of

the camera.

A pair of imaging photon detectors (IPD) observing in the ion and neutral

emission lines, respectively, were operated at the Wallops V25 site in the launch

complex. The neutral cloud was very bright, and about 15 seconds after release it

became necessary to stop down the lens aperture to prevent damage to the detector.

Unfortunately, the neutral and the ion detector were both stopped down. As a result

the later ion images are very noisy and are not of as good quality as the images from

Duck. No prompt ions could be identified but a faint trail of Sr ions was detected

along B above the release over a period of 2-3 minutes following the release. No Sr

ions were seen on images at Cape May due to the geometry of the release, the

brightness of the neutrals and the sensitivity of the camera in white light.

Brightness of the Ion Streak and Ion Production Estimate

An estimate of the brightness of the field aligned streak shown in Figure 3f at 63 s

after release can be made using several methods. The most direct is using the IPD

data, but because the lens was stopped down, the signal to noise is low resulting in a

large uncertainty on the result. The streak is not discernible in individual IPD
9

images, but can bebrought out by summing several images. The IPD employs photon

counting technique and thus is absolutely calibrated. The brightness of the ion cloud

near 63 s,as observed in the IPD images, is 100-200 R.

The second method combines the intensified camera data from Duck and the

Wallops Island IPD data. Both data sets are observations filtered on the 4078/_ SrH

line. The intensified film camera is not absolutely calibrated, but an estimate of the

ion cloud brightness can be made using images from the IPD (prior to that

instrument being stopped down) for calibration of corresponding images from the

intensified camera. Assuming the high explosive debris cloud to be broad-band

emissions, the IPD images indicate its brightness at 6.6 s after release to be 40 R/_.

The intensified camera was equipped with a filter of 44A FWHM and 40% peak

transmission.

From densitometry of the original Duck intensifier film frame and the film

development characteristics, we measured the ratio of ion line streak brightness to

center of explosive debris (broad band emissions) brightness at 6.6 seconds after

detonation to be 0.66. Using the IPD basedbrightness of 40 R/_. for the debris cloud,

the ion cloud would have a brightness of 1200 R at 6.6 s. The brightness of the ion

cloud decreasesas 1/time becauseof velocity dispersion. Thus at 63 s the brightness

would be 125 R which is within the brightness range established based on the IPD

data.

Number of ions in cloud:

To obtain the number of ions in the cloud the emission rate is required. For

strontium in full sunlight, F6ppl et. al. (1967) report an emission rate at 4078/_ of

0.087 photons/ions, assuming all ions to be in the ground state. This rate was
10

calculated assuming the depth of the solar Fraunhofer absorption line to be 2%.

Newer solar spectral data (Beckers et al., 1975) of the solar flux at the top of the

atmosphere indicate a brighter solar continuum than that used by FSppl et. al., and

the depth of the absorption line to be closer to 4%. This alone would raise the

emission rate by more than a factor of 2. We have not been able to perform a detailed

calculation of the strontium emission rate as for example has been done for barium by

Stenbaek-Nielsen (1989), but using the newer solar data by Beckers et. al. (1975) we

calculate an emission rate of 0.2 photons/ion -s.

Because of the deep Fraunhofer absorption line in the solar spectrum, a Doppler

shift of the resonance line can change the emission rate drastically. However, the

ions present in the ion cloud discernible at 63 s would all have low velocities, (v < 2.6

km/sec) and the change in the resonance relative to the solar spectrum due to a

velocity component in the direction of the Sun (Doppler effect) is very small and can

be ignored. Therefore, for the estimate of the number of ions in the image, no Doppler

connection is required to the emission rate of 0.2 photons/ion.

We converted the film frame at 63 seconds to a digitized image, subtracted the

background and printed out all the pixel values. The intensity calibration of the

image derived above defines the brightness in all pixels of the cloud. The

triangulated distance from the station to the cloud was 600 km and the field of view of

the image was 4.9 × 5.9 degrees. The total number of ions in the cloud observed in

the image is, by integration over all pixels in the image, found to be 4.5 × 1020 ions.

This value corresponds to 0.17% of the total amount of strontium at velocities less

than 3.5 km/sec.

Model to Calculate Synthetic Images
11

The number of ions observed can be compared with the number of ions expected

from photoionization. In order to estimate how the neutral St jet and field-aligned Sr

ion streak would appear to optical imagers at the various sites used in the

experiment, we made computer simulations of the solar ionization produced effects

using a time constant of 1920 s. The synthetic images were constructed by

calculating brightness at individual points across a 6°X3.6 ° image plane. We

assumed the neutral and ion jets to be optically thin, so that the brightness is simply

the integration of radiation over all particles along the line of sight. For the ionemission rate we used 0.2 photons/ion -s.

The model calculations assumed that the neutral particles followed straight-line

trajectories, traveling radially outward from the site of the shaped-charge explosion.

The neutral density was calculated from the differential velocity distribution

function

d2F

q- dvdO (1)

which is the number of particles with speeds between v and v + dv and with polar

angles 0 and 0 + dO, where 0 is the angle between the burst direction and the radial

vector. Rotational symmetry about the burst direction was assumed. Specifically, we

assumed

--021n2

q=laNF(v)exp((AO) ° ) (2)

where N is the total number of strontium neutrals in the beam, la is a normalizing

constant and the angular width of the beam, hO, was taken to be a function of the
12

velocity. The velocity distribution, F(v), and angular half width were inferred from

TV observations from Duck as shown in Figure 2. The neutral density is given by

q(v,0) -vt l

n ----_e

" (3)

where r is the distance from the burst point, and • is the photoionization lifetime of a

Sr neutral, which we have calculated to be 1920 s.

The calculation of the ion density is based on the assumption that the ion, upon

creation, moves parallel to the magnetic field at a velocity equal to the projection of

the velocity of the parent neutral upon the magnetic field direction. The ions may be

described in terms of the distribution function f= f(x, vs, t), where Vs is the velocity

parallel to the magnetic field. The distribution function satisfies the equation

8f --+v Ib Of -- 1 nn(X,t)8 (X'lb) v--- (4)

Ot _ Ox _0 t

where I b is the unit vector in the direction of the magnetic field. This states that the

total time derivative for ions with velocity vs is given by the rate of decay of the

neutrals present in a given volume element.

The solution to (4) may be evaluated by integrating the right-hand side along the

ion trajectories:

f:-- dt'nn(x',t')6 v t'

_0 0 s

(s)

where

x'(t'): x - IbVs(t--t') (6)
13

The ion number density is obtained by integration of fover the velocity Vs, which is

easily done because of the 8-function in the integral. The result is

n. = --lit dr' t'n, Ix -(1 b x)lb (1 -- t'/t), t'l (7)

' Lt 0

Upon substituting expression (3) for the neutral density

ni= --1 /idt, q(r',0',t]-t'/t e

_t ¢2 (8)

where

and

x_ OxS)'2 + (y_OyS)2+ (Z_OzS) '2 :x, 2 +y,2+z, 2

O'=tan-lI(X'2+y'2)tz'

and s -- (1-t/t')r cos_z, where fi is the angle between the direction of x and the magnetic

field. The os are the direction cosines of the unit vector lb.

The calculation of the image intensities from the volume densities is then a

matter of integrating the volume densities nn and ni along a line of sight. The line-ofsight direction is specified in terms of view angles, a and l], from the observation

point. The picture coordinates are acos_ and asin[_, where a is the angle between the

view direction and the line-of-sight to the burst, and [3 is an azimuthal angle about

the line-of-sight to the burst measured from the projection of the burst direction on

the plane normal to the line-of-sight to the burst. The details of converting the

coordinates in which the density is computed to geocentric coordinates (in which the
14

observer's position, burst location and magnetic field direction are computed) to the

picture coordinates are tedious, and will not be repeated here. The results of the

calculations are synthetic images projected on the image plane as viewed from the

observation point.

Figure 4 shows a contour plot of the brightness of the Sr ions at 4078/_ as viewed

from Duck at t+65.2 seconds. We used the emission rate of 0.2 photons/ion s. The

initiation point is at the lower left corner. The upper right end of the streak would

correspond to 2.6 kms-1 in the neutral velocity distribution, Figure 2. Thus the

streak shown is from neutrals within the low velocity peak, all with velocities less

than the critical velocity.

This simulated view can be compared with the observed streak a 63 s shown in

Figure 3£ The simulation of the ion streak, Figure 4, does not correspond exactly

with the observed streak Figure 3fbecause the actual ions are affected by gravity and

E×B drift. By 63 seconds ions with initial velocities less than 1.5 km/sec will have

reached their maximum altitude and begin to fall back down along B.

The maximum brightness in the simulated image, figure 4, is 175R, which agrees

well with the observed brightness of the streak (100-200R based on the IPD images

from Wallops, and 125R based on the intensified camera images from Duck). Also,

the appearance of the streak in the simulation is very much as that observed in the

Duck image (fig 3f). This is a rather important point. The presence of a field-aligned

streak along the release field line could be taken as evidence of a CIV process present

only in the vicinity of the release, but the simulation clearly shows that the streak

also can be produced by a uniform ionization rate. Thus we must conclude that the

observed ions can all be accounted for by solar UV ionization.
15

Conclusions

We have carried out a free space CIV experiment using the first shaped charge

with a conical strontium metal liner, but no CIV ions were detected. The use of a

conical liner was an improvement over the "Star of Condor" Peru experiment, which

used a radial shaped charge, in that a higher peak velocity and a much more dense jet

were produced. The ambient plasma background density in both experiments was

similar: 2× 104 cm 3. In the Peru experiment we only detected a Sr ion streak 10

minutes after the injection and estimated that we could see 2.4>( 10 _9 ions, or 0.004%

of the vaporized Sr. As the Star of Condor ion streak was first noticed 10 minutes

after the injection, it is likely that many of the ions initially formed by solar UV were

no longer dense enough to be detected, and the ion inventory was low.

In the SR90 experiment we detected a faint SrII field-aligned streak (about 150R)

in 4078A light from the Duck and Wallops V25 optical sites. The tip of the streak had

a velocity of 2.6 km s -1, which corresponds to 3.9 km s _ in the initial 48 ° to B neutral

jet. From several calibrations of the brightness of the ion streak we estimate that the

detectable portion contained about 1021 ions to an uncertainty of a factor of 2. A

computer simulation using a new computation of the solar UV ionization time

constant (1920 s) shows 1.7 × 1021 ions in the slow portion of the ion streak. We note

that the SR90 ion streak detected is from the portion of the neutral jet with velocity

perpendicular to B which is below the Alfv_n critical velocity of 3.5 km s-1 .

Although no high velocity (v>2.6 kin/s) ion jet was observed, the IPD ion images

available combined with model calculations allow an estimate to be made of the

maximum number of CIV ions that could have been present. The release was

observed from Wallops V25 near the edge of the IPD field of view where the ion filter
16

unfortunately rapidly cuts off. Solar UV and CIV ions in a fast (v -_ 9Km/s) field

aligned ion jet would have been clear of the bright explosive debris area about 5

seconds after release and out of the field of view about 9 secondsafter release. We

have an IPD image covering the time interval 4 to 10secondsafter release. There is a

slight increase in the counts in the general area where the jet should be just at the

edge of the passband of the filter. A computer simulation at 10 secondsindicates that

the solar UV produced ions should have a brightness of 30R, which our calibration

indicates is just below the limit of detectability where the fast ion streak should be.

We therefore conclude that if there were CIV ions present in numbers comparable to

the solar UV produced ions we should have seen them. This sets the maximum

number of CIV ions which could have been produced in the fast jet, but not detected,

at less than 2 × 1021to within a factor of two, or less than 0.18% yield of the vaporized

St.

Since this maximum possible CIV yield is a factor of 100 less than the Porcupine

experiment in which the ambient plasma density was 6X 105cm-3, or 30 times

greater, we conjectured that future CIV experiments should have high ambient

background plasma density. This was proven to be true in the CRIT II experiment

carried out on May 4, 1989 from Wallops Island. In this experiment the ambient

background density was 6X105 cm-3, and preliminary analysis indicates about 4%

CIV ionization (Torbert, 1989; Stenbaek-Nielsen et al. 1989).

On the positive side we were able to obtain the best alkali metal shaped charge

neutral velocity distribution as a function of radial angle from the detonation point

and as a differential number of neutrals per unit velocity. We also calculated a solar

UV ionization time constant for Sr of 1920 s (to 30%) which agrees with the observed

ion inventory. If the Sr experiment had been carried out in high ambient electron
17

density and produced 4% CIV ionization, the solar component would be negligible,

but it is clear that future Sr CIV experiments should be carried out below the solar

UV height. Such an experiment is planned for August, 1990 from the CRRES

satellite. On the other hand, Sr vapor releases in the distant magnetosphere or in the

solar wind might have advantages over faster ionizing Ba or Eu to produce larger

volumes of ions.

Acknowledgments. We thank the personnel of NASA Wallops Flight Facility and

in particular, Jay Brown, the payload manager, for payload fabrication and launch

support. DuWayne Bostow was instrumental in managing the high-explosive shaped

charge components and in casting and machining the strontium metal liner. Gale

Weeding of the Denver Research Institute made the high-explosive shaped charge.

Bruce McKibben provided technical optical preparation and optical observations. We

greatly appreciate the assistance of the U.S. Army Corps of Engineers in allowing the

use of the Coastal Environmental Research Station at Duck, NC. Walley Boquist of

Technology International Corporation kindly furnished optical observations of the

neutral Sr jet which were useful in determining the burst position and orientation.

We thank John C. Foster of Millstone Hill Radar for help in providing radar coverage

of the experiment and reduced data on background electron densities. Support for the

University of Alaska Geophysical Institute was provided by grant NAG6-1 and

NAGW-269 from NASA.
18

References

Alfv4n, H., On the Origin of the Solar System, Oxford University Press, New York,

1954.

Alfv4n, H., and G. Arrhenius, Structure and Evolutionary History of the Solar

System,.D. Reidel Publ. Co., Amsterdam, 1975.

Banks, P. M., and G. Kockarts, Aeronomy, Academic Press, New York, 1973.

Beckers, J. M., C. A. Bridges and L. G. Gilliam, A high resolution spectral atlas of the

solar irradiance from 380 to 700 nanometers. Report AFGL-TR-0126, Air Force

Geophysics Laboratory, Bedford, MA, 1976.

Brenning, N., C.-G. F_tulthammar, G. Haerendel, M. Kelley, G. Marklund, R. Pfaff, J.

Providakes, H. C. Stenbaek-Nielsen, C. Swensen, R. Torbert and E. M. Wescott,

Interpretation of the electric fields measured in an ionospheric critical ionization

velocity experiment, J. Geophys. Res., in Press, 1990.

Danielsson, L., Review of the Critical velocity of gas-plasma interactions I:

Experimental observations, Astrophys. Space Sci., 24, 459, 1973.

Deehr, C. S., E. M. Wescott, H. C. Stenbaek-Nielsen, G. J. Romick, T. J. Hallinan, and

H. Foppl, A critical velocity interaction between fast barium and strontium atoms

and the terrestrial ionospheric plasma, Geophys. Res. Lett., 9(3), 195-198, 1982.

F6ppl, H., G. Haerendel, J. Loidl, R. Lt_st, F. Melzner, B. Mayer, H. Neuss, and E.

Rieger, Preliminary experiments for the study of the interplanetary medium by

the release of metal vapor in the upper atmosphere, Planet. Space Sci., 13, 95-114,

1965.

Haerendel, G., Alfv4n's critical velocity effect tested in space, Z. Naturforsch A., 37,

728-735, 1982.
19

Haerendel, G., Hoefner, H. Rieger, E. and Foeppl, H., Re-evaluation of the ion yield in

a critical velocity experiment in the upper ionosphere, COSPAR-XXVII, Plenary

meeting of the Committee on Space Research, Finland, July 1988.

Hallinan, T. J., Observed rate of ionization in barium shaped charge releases in the

ionosphere, J. Geophys. Res., 93, 8705, 1988.

L_tjens, P., Messung des photoionisationsquerschnitts yon BaI und SrI im

Wellenltingenbereich 1700-2400£, Z. Naturforsch, 28____a, 260-263, 1973.

Michel, K. W., Verhalten der Ba-Ionenstrahlen ans Hohlladungen beim NikeTomahawk, MPT-PAF 19 Max-Planck-Institut fur Physik und Astrophysik, 1969.

Michel, K. W., Fluorescent ion jets for studying the ionosphere and magnetosphere,

Acta Astronaut 1, (1-2), 37-69, 1974.

Newell, P.T., Review of critical ionization velocity in space, Revs. Geophys., 23, 93,

1985.

Stenbaek-Nielsen, Calculated emission rates for barium releases in space, Planet.

Space Sci., Vol 37, 11, 1441-1452, 1989.

Stenbaek-Nielsen, It. C., E. M. Wescott, D. Rees, A. Valenzuela, and N. Brenning,

Non-solar UV produced ions observed optically from the "CRIT I" critical velocity

ionization experiment, J. Geophys. Res., in Press, 1990.

Stenbaek-Nielsen, It. C., E. M. Wescott, G. Haerendel, and A. Valenzuela, CRIT II:

Optical observations of critical velocity ionization ions, Abstract SM31A-2, EOS

70 (43), 1277.

Torbert, R. B., and P. T. Newell, A magnetospheric critical velocity experiment:

Particle results, J. Geophys. Res., 91, 9947, 1986.

Torbert, R., An overview of the CRIT II experiment, Abstract EOS 70 (43), 1277,

1989.
2O

Wescott, E. M., H. C. Stenbaek-Nielsen, T. Hallinan, H. FSppl, and A. Valenzuela,

Star of Lima: Overview and optical diagnostics of a barium Alfv6n critical

velocity experiment, J. Geophys. Res., 91(A9), 9923-9931, 1986a.

Wescott, E. M., H. C. Stenbaek-Nielsen, T. Hallinan, H. FSppl, and A. Valenzuela,

Star of Condor: A strontium critical velocity experiment, Peru, 1983, J. Geophys.

Res., 91(A9), 9933-9938, 1986b.
21

Figure Captions

Fig. 1. TV picture of SR90 neutral jet in white light at 11.5 secondsfrom Duck, NC.

Fig. 2. Differential strontium neutral velocity function. The scale is derived from the

assumption that 15%of the liner is vaporized.

Fig. 3a-f. TV frames from portions of digitized intensified film camera at Duck, NC,

showing the development of a slow (v < 2.6 km/s) Sr ion streak. The brightest star

shown with a cross is Cygnus i. The next brightest star is Cygnus 0. The distance

along the magnetic field line from the burst point is shown in 3f.

Fig. 4. Contour plot of computer simulation of Sr ions brightness in 4078/_ at 65.2 s

after detonation as viewed from Duck, NC. The burst point is at lower left hand

corner, and 120 km of field-aligned streak are shown. Tick marks show distance in

km along B. The total ion count in the 6°×3.6 ° field of view is 1.71)< 1021 ions. Only

the brightest portion of the streak would be visible on the Duck intensified camera

frame (Figure 3f).
ORIG_J",I.C,LP,_: ;3

OF POOR QUALIT'_'
dN/dV (atoms/km/sec) X 10 22

O

O

O

._L

t_

0"1

A

O 00

O

Co

----A

<
ORIGIN/_L F/;nE ('_

OF POOR Q,..AL,+"Y
I00 km

6O

4O

I

• I

2O

BRIGHTNESS

T = 65.2 sec.

Z- = 1920 sec.

0

4078 A (R)