R-3 Repository :: Browsing by Author "Freeman, John W."

Browsing by Author "Freeman, John W."

Now showing 1 - 14 of 14

Acceleration of ambient ions in the Lunar atmosphere
(1981) Bulgher, Debra Lynn; Freeman, John W.; Dufour, Reginald J.; Michel, F. Curtis
The Apollo Suprathermal Ion Detector Experiments (SIDEs) deployed on the lunar surface observe sporadic bursts of positive ions throughout the local lunar night. Evidence exists that the source of these events is most likely the dayside lunar atmosphere. Ionization of the neutral lunar atmosphere by photoionization or chargeexchange produces a population of ions over the sunlit portion of the moon. These ions are accelerated by the interplanetary electric field, executing cycloidal trajectories that may bring them onto the nightside hemisphere of the moon. A nightside surface electric field directed radially inward can then further accelerate these ions onto the lunar surface, altering their energies and trajectories such that they are detected by the SIDE. It is possible to obtain ion trajectories that intersect various positions on the nightside of the moon in this manner. For several nighttime ion events, synthetic particle data have been produced with this model which are in agreement with the observed data. Parameters of the nightside surface potential distribution are determined for the selected events. A profile of the expected surface potential over the nightside hemisphere of the moon indicates a variable surface potential. The height distribution over which the potential is effective becomes increasingly larger, while the magnitude of the surface potential becomes increasingly negative, when approaching local lunar midnight. Assuming an exponential neutral nimber density profile for all atmospheric constituents, indirect observations of the neutral lunar atmosphere can be made by the SIDE. Combined with the effect of the surface potential on the height distribution of these ions, number densities for various species in the lunar atmosphere determined in this manner are in agreement with reported values from various other experiments also deployed on the lunar surface.
An observation of lunar nighttime ions
(1975) Schneider, Henry Emil; Freeman, John W.
The Rice University Suprathermal Ion Detector Experiment deployed on Apollo missions 12, 14, and 15 regularly observes ion events all through the lunar night. The ion events are most often less than 4 hours in duration, and usually less than one hour. The energy spectra of the events vary from mono-energetic at 25 eV/q to 5 eV/q to fairly broad. The energy represented may range from 25 eV/q to 15 eV/q. There is some indication that the peak energy of the events increases from 5 eV/q at local sunset to 75 eV/q at about 3 days before local sunrise and then decreases to 25 eV/q 1 day before the sunrise terminator crossing. The ion energies are generally less than the solar wind and the ion flux (1 ions/cm -sec-ster) is down by 2 orders of magnitude from the solar wind. Ion activity increases in the period 1 to 6 days prior to local sunrise with a peak at 2 to 3 days before sunrise. There is also a weak secondary activity peak 3 to 4 days after local sunset. Data from the Apollo 12 SIDE has not been looked at yet. The Apollo 14 and Apollo 15 SIDE 's both exhibit the same activity profile. This fact suggests a local lunar time dependence rather than a position in orbit for the occurrence of these events.
Argon ion pollution of the magnetosphere
(1983) Lopez, Ramon E.; Freeman, John W.; DuFour, R. J.; Voigt, G. H.
The construction of Solar Power Satellites (SPS) would require the injection of enormous quantities of propellant to transfer cargo from LEO to the construction site at GEO. This propellant, in the form of 2 KeV argon plasma, is expected to considerably modify the space environment since the number of ions injected per SPS (=1^32) is comparable with the total plasmaspheric content above =5 km. In this thesis a model for the dynamics of the ion thruster plasma beam is presented. This model predicts beam travel distances up to a few thousand km, and the transfer of beam momentum to the ionosphere, causing localized heating. Subsequent convection of the argon is investigated using a simple model of the quite-time, and storm-time, magnetosphere. In addition, Ar+ charge exchange lifetimes are calculated and shown to be too large to significantly reduce the amount of Ar+ near the plasmapause between magnetospheric storms.
Calibration of a cycloidal ion mass spectrometer
(1977) Cooke, David Lyttleton; Freeman, John W.
This thesis describes the construction and calibration of a cycloidal type ion mass spectrometer (CIMS) for analysis of space plasmas. Crossed electric and magnetic fields are used to force incoming ions to execute cycloidal trajectories with a net displacement proportional to the mass per unit charge of the ions. The magnetic field is produced by a permanent magnetic while the electric field is varied to select which mass is to be detected. A funnel type channeltron is used as the detector. The main feature of the CIMS is the energy and entrance angle independence of the selection process. In order to determine the real limits of this feature, an Ortec R. F. ion source, capable of producing high fluxes of heavy ions (up to 4 amu) over a wide energy range, was used to calibrate the instrument. The derivation and determination of the mass resolution R=mAm, the energy range, and geometric factor is discussed. The can detect ions in the low keV range with a mass resolution of R = 8, and an •6 9 estimated average geometric factor G = 1x1^-6cm^2sr.
Cusp particle detection and ion injection source oscillations
(1984) Frahm, Rudy Allan; Reiff, Patricia H.; Dunning, F. Barry; Freeman, John W.
The magnetic merging process has been suggested as a means for particle injection into the cusp regions of the earth's magnetosphere. If this process occurs, the injected plasma should reveal a characteristic signature. Electrostatic analyzers are used to detect this plasma. This thesis discusses the design of the electrostatic analyzers which are the central components of the High Altitude Plasma Instrument (HAPI) and Low Altitude Plasma Instrument (LAPI) flown on DE-A and DEHB (Dynamics Explorer satellites) respectively. Also discussed is the calibration of the electrostatic analyzers which I was involved in. This includes the co-authored calibration data acquisition program and my Calibration Data Reduction Routine. Typical satellite instrument output is in spectrogram energy-time format with the particle flux intensity indicated by gray shading. This presentation gives a "visual picture" of how the differential energy flux at each energy changes with time. A presentation of this type using the DE-A HAPI data shows the magnetic merging injection signature: multiple ion "V" structures as the satellite passes through the cusp region when the interplanetary magnetic field has a southward component. An alternative output format which I have helped create produces individual line spectra which allows these "V" structures to be examined in finer detail. If one looks at these "V" structure spectrograms, it is easily noticed that they appear to pulsate with time. I have conducted a harmonic analysis of the peak distribution function per spin from several satellite passes- to determine the periodicity of these pulsations, perhaps related to Kelvin-Helmholtz waves at the magnetopause.
Design and preliminary evaluation of a baloon-borne instrument for measuring atmospheric electrical profiles
(1979) Weinheimer, Andrew John; Few, Arthur A.; Reiff, Patricia H.; Freeman, John W.
A balloon-borne instrument has been developed for the purpose of making fair weather atmospheric electrical measurements. The instrument named Balloon Electrical Environment Profiling System (BEEPS), is similar in principle to balloons flown previously into thunderstorms by our group at Rice. It has the capability of measuring the height profiles of the vector electric field, the vertical component of the conduction current, and the polar conductivities. The balloon is designed to make measurements up through the lower polar stratosphere (14 km), and the first two flights of BEEPS were made from Barrow, Alaska, (71°N, 157°W) in conjunction with a solar magnetic sector boundary crossing, with a flight on either side of the boundary. These flights are part of an effort to measure the electrical response of the atmosphere, as a function of altitude, to the solar sector structure. Knowledge gained from flights such as these may prove valuable to developing an understanding of the role atmospheric electricity may play in those aspects of the sun-weather problem that involve the solar sector structure.
High-speed translunar magnetotail plasma flows
(1979) Shull, Peter Otto; Freeman, John W.
Unusual, high-speed flows of plasma away from the Sun in the translunar magnetotail are discovered to occur persistently. Faster, cooler, and less dense than the plasma flows customarily encountered in the translunar magnetotail, these flows suggest that small-scale magnetic merging occurs regularly in the plasma sheet. Particle and field data from eight and one-half magnetotail crossings are studied, making this the most extensive survey to date. Those crossings are chosen for which there are magnetometer data from Explorer 35 and particle data from the Rice Suprathermal Ion Detector Experiment (SIDE) set up on the Moon by the crew of Apollo 14. This SIDE, like its twins from Apollos 12 and 15, measures plasma energy distributions in the energy/charge range between 1 and 35 eV/q. Computer reduction of these SIDE data yields plasma bulk speeds, temperatures, and densities. With the assumption that the plasma is entirely hydrogen, it is found that the plasma flows are characterized by bulk velocity u = 25 to 7 km/s, ion temperature kT = 5 to 1 eV, and ion density n = .1 to .1 cm. Most of these flows ("bubble" flows) occur within one or two hours of changes in tail magnetic field strength and direction, changes suggesting the passage of the Moon near a magnetic bubble. Two or three flows ("lobe" flows) are associated exclusively with >= 1/y magnetic fields parallel or anti-parallel to the Earth-Sun axis. Neither type of flow is directly related to solar or geomagnetic activity. The transfer of magnetic field energy to mantle plasma in the cislunar magnetotail may cause the bubble flows. Appearances of doubly peaked plasma energy distributions are briefly discussed. The origin of the lobe flows is uncertain. If the field lines associated with them map into a magnetic bubble, the flows are probably bubble flows observed farther than usual from their places of origin. If the field lines map into the polar regions of Earth, then the lobe flows may be ions such as H+, He+, He++, and + escaping from the polar ionospheres.
Magnetosheath phenomena at lunar distances
(1979) Sanders, Gary (Gary D.); Freeman, John W.
Simultaneous data returned by the Apollo Suprathermal Ion Detector Experiments are combined to yield information on the properties of plasmas in the magnetosheath at lunar orbit. Recent analysis of magnetosheath data has shown that the magnetosheath at lunar distances consists of two proton populations having different temperatures. There is evidence that the colder component (kT~1 ev) is unshocked solar wind. The hotter component (kT~1 ev) is characteristic of shocked solar wind. This two temperature structure is observed across the entire magnetosheath at lunar orbit. In addition an interface between the magnetosheath and the plasma sheet is identified. This layer is identified by a systematic change in the magnetosheath flow properties in the vicinity of the magnetopause. The flow is observed to turn inward toward the plasma sheet and become thermalized indicating that the magnetosheath particles can gain access to the plasma sheet at lunar distances. This layer, which we term the injection layer, is believed to be the extension of the entry layer observed on the dayside to lunar orbit.
Observation of bow shock protons at the lunar orbit
(1974) Benson, John Louis; Freeman, John W.
Protons with energies ranging from about 5 eV to 35 eV are observed by the Suprathermal Ion Detector Experiment on both the dusk and dawn sides of the. magnetosphere. On each lunation these particles appear as a rather continuous phenomenon for 3 to 5 days after crossing from the dawn-side magnetosheath into the solar wind and for about 2 days prior to entering the dusk-side magnetosheath. Transverse proton flows of this type have been observed by Asbridge et al., [1968], Scarf et al., [197] and are believed to be deviated solar wind particles that are accelerated at the earth's bow shock and emitted outwardly along interplanetary field lines at greater than solar wind energies. Data from the SIDE and from the Explorer 35 lunar orbiting magnetometer have been analyzed and these data indicate that the transverse ion flows observed by the SIDE in the pre and post bow shock crossing regions of the lunar orbit are due to these deviated solar wind particles. A computer model based on EXB drift trajectories for particles leaving the shock has been developed and synthetic particle data produced by this model are in good agreement with the observed data.
Observation of low energy protons in the geomagnetic tail at lunar distances
(1975) Hardy, David Alfred; Freeman, John W.
Using the three Suprathermal Ion Detectors stationed on the moon, we have detected a region of plasma flowing anti-sunward along the ordered field lines of the geomagnetic tail. This plasma flow is found within the tail, hut exterior to the plasma sheet. It exhibits characteristics uniquely different from the other particle regimes traversed by the moon. The particles display an integral flux of from .1 to 9 x 1^7 ions/cm^2 sec ster, a bulk velocity of from 1 to 25 km/sec, temperatures in the range .4 to 5 x 1^5 degrees Kelvin and number densities between .1 and 5/cm^3. The magnetic field configuration for the times during which the particles were observed exhibits a direction and magnitude that is indicative of the lobes of the geomagnetic tail. In addition, no consistent deviation in the field is seen to correspond with the occurrence of the events. The events have an angular distribution extending over between 5 and 1 degrees. Spatially the events extend over a wide region in both the Y and Z directions. Continuous observations of these particles are seen over distances as great as 17 R in the Y direction and 12 R in the Z direction. The majority of the encounters with this flowing plasma, however, are found in a 12-RQ wide region adjoining the magnetopause. Also there are wide variations between tail passages as to the extent of time over which the particles are seen with an apparent correlation between the number of hours of observation and the Kp index averaged over these times. It is proposed that these particles may have entered through the cusp region. The particles could then be convected down towards the neutral plane by E x B drift and eventually be accelerated by a neutral line to produce the particles in the plasma sheet.
Optical emission measurements during beam plasma interactions
(1985) Mantjoukis, George A.; Haymes, Robert C.; Bernstein, William; Wolf, Richard A.; Freeman, John W.
3914 A light intensity profiles were measured with a geometrically scanning photometer during interations of an energetic electron beam with a weakly ionized plasma. Mass spectrometric measurements indicated N^ to be the dominant neutral constituent. The experiments were carried in the very large SESL vacuum facility at the Johnson Space Center which allowed an interaction length of ~ 2 m. Variable current (1-7 ma) and variable energy (5-16 V) beams were injected over a large pitch angle range ( to ~75°) for several applied magnetic field strengths (.89, 1.52, and 2.22 Gauss) over the pressure range .6-3. x 1“® Torr to allow study of the light intensity dependence on the experiment parameters. The photometer measurements were made at a fixed axial position (midway between the electron gun and the collector); overall measurements of the complete beam emission patterns (total light) were made with several low light level TV cameras. The measured 3914 Â intensity profile gives the radial distribution of the relative ionization rate while its integral gives the (relative) total ionization rate independent of geometry. The following important results were obtained 1) At low beam currents (1^ < Ic, the beam current required for BPD ignition) the relative light intensity and beam geometric configuration were consistent with single particle behavior. 2) For I], > Ic (BPD) the geometry of the illuminated region changes drastically and the 3914 total intensity increases by factors of 1-3 indicating the presence of new ionization sources (suprathermal electrons). (a) For beam injection parallel to the magnetic field (zero pitch angle), the radial width (FWHM) of the illuminated region is approximately twice the maximum (anti-node) width for preBPD conditions; it scales approximately as 1/B and E1/2. (b) For non-zero pitch angle injection, the full width of the illuminated region is approximately equal to the diameter of the single particle helix; at large pitch angle injection, the BPD shows significant limb brightening indicating a somewhat hollow configuation. Significant ionization outside the helical dimensions is not observed. (c) For all conditions the total 3914 light intensity during BPD can be fitted to the parabolic relationship QT ~ K Ic1/2 (Ib - Ic)1/2 Thus the total ionization rate increases nonlinearly with I (the nominal power supply return current) and remains proportional to the square root of the threshold current during BPD although I|j » Ic. The consistency of this scaling over the large injection pitch angle range implies that the important plasma processes are Independent of injection pitch angle. (d) The maximum efficiency of energy transfer from the beam to the plasma (as measured by the total ionization rate) occurs when I|j 2 Ic. Typical estimates of this maximum efficiency range from 3-12Z for the 2 meter path length.
Patterns of soil maturation and mixing at the Apollo 16 landing site: surface soils
(1979) Ray, James R.; Heymann, Dieter; Clayton, Donald W.; Freeman, John W.
An analysis of the Apollo 16 surface soil samples is presented in an effort to distinguish the separate effects due to mixing of unlike fines from those attributable purely to regolithic maturation processes. In establishing a background needed to accomplish this task, aspects of large-scale stratigraphy and geologic sequence in the central highlands are reviewed. Likewise, a comprehensive discussion of the interrelated phenomena associated with a soil's residence in the upper millimeter of the regolith follows. Data for major element chemistry and trapped inert gases are assembled from the literature and used to infer the provenance of archetypical soils and kinship relationships of remaining surface samples. The hypothesis of maturation domination of inert gas variations is considered and its consequences are delineated. It is found that this assumption, while adequate in explaining the gas properties of most soils, fails to account for about one-fifth of the samples, particularly soil 61221. An alternative approach is then presented which views the distinctive soils as remnants of ancient solar wind irradiation. In this context, unambiguous maturation effects are discernible only for the evolution of absolute gas concentrations and the elemental ratio 2^Ne/36^Ar. The unique soil 61221 is found to have excess argon relative to its very low state of maturity by a factor of about ten after correction for outgassing. This anomaly is ascribed to an irradiation between 3.5 and 4. Gy ago by a solar wind with particle flux greater than present by the same factor. A similar gas-rich component occurs in less pure form in other surface samples.
The electric potential of the lunar surface
(1975) Ibrahim, Mohamed Esam; Freeman, John W.
The sunlit lunar surface potential has been determined experimentally using 2 months of data provided by the Apollo Lunar Surface Experiment Package (ALSEP) Suprathermal Ion Detector Experiment (SIDE) deployed at the Apollo 14 and 15 sites. The magnitude of the lunar surface potential was found to vary as the moon passes through the different plasma environments, such as the solar wind, magnetosheath and the earth's geomagnetic tail, in its orbit around the earth. In the dayside solar wind and/or the magnetosheath the potential is approximately +1 volts for the solar zenith angles less than 4°. At higher zenith angles, about 5°, an asymmetry exists where by the potential rises to +18 volts in the dawn side, and drops to +17 volts in the dusk side. In the geomagnetic tail, the data indicate potentials of +1 volts or greater are common in some regions in the tail. This result probably applies to the higher plasma density regions of the plasma sheet and boundary layer. Computation of the dayside surface potential using recently measured values of the magnetosheath parameters and photoelectron flux yield approximately +11 volts potential, which agrees with our observational results. As a result of the positive potential on the dayside of the moon, an electron plasma sheet is formed adjacent to the surface to shield the net positive charge on the lunar surface. The electric field is calculated to be approximately > 1 V/m, directed outward.
The photoklystron
(1980) Simons, Sedgwick Lewis; Freeman, John W.; Dufour, Reginald J.; Few, Arthur A.
The photoklystron is a photoelectric vacuum tube designed to convert broadband light energy directly into monochromatic high frequency AC power. It requires a DC reflecting voltage (which draws no power) and the first model works best with a DC accelerating voltage (which represents an additional input energy) but has been shown to operate with only light energy. With the accelerating voltage, frequencies from 4 to over 2 MHz. have been produced, and electrical efficiencies near 2% have been measured. Computer analysis of the electron trajectories revealed that unlike a reflex klystron the photoklystron works by extracting the kinetic energy of the electrons over a period of several cycles. For net energy output the accelerating and reflecting voltages are adjusted so that the electron trajectories have a period which is a multiple of the period of the RF output desired. Any electrons which are improperly phased are quickly eliminated by collision with the photocathode or repeller. Conditions for optimum interaction of the electrons with the RF field have been investigated both analytically and numerically using a Tektronix 452 computer. Although some aspects of the photoklystron are not fully understood at this time, it has been shown to be a fundamentally new and simple oscillator, offering a wide variety of applications.

Browsing by Author "Freeman, John W."

Results Per Page

Sort Options