Engineering topics

Fan, C. Y.

Publications and source records attributed to Fan, C. Y..

At least 19 records

NASA NTRS1992

Techniques for the remote sensing of space plasma in the heliosphere via energetic neutral atoms - A review

A survey is conducted for state-of-the-art techniques for detecting energetic neutral atoms (ENAs) in the 100-300 keV range, in regions from the heliospheric boundary to the auroral zones where the solar wind plays a crucial role. While ENA spectrometry allows sampling of the mass and energy distributions of a distant plasma, ENA imaging gives a global view of the structures and dynamics of an extended plasma. The ENA instrument designs discussed share many components which exhibit excellent flight performance as elements in charged-particle analyzers for space missions.

Hsieh, K. C.↗

NASA NTRS1986

Comet Halley neutral gas density profile along the Vega 1 trajectory measured by NGE

Data from the Vega 1 permitted the determination of the total neutral gas density profile along the spacecraft trajectory. Discounting small fluctuations, the field ionization source instrument measured a density profile which varied approximately as the inverse radial distance squared. Data from the electron impact ionization instrument yielded a series of calibration points; e.g., the neutral density at 100,000 km is 10,000/cc. The combined data provide a calibrated total density profile, and imply a neutral production rate of 10 to the 30th power molecules/sec.

Curtis, C. C.↗

NASA NTRS1986

The spatial distribution of energetic ions and electrons in the magnetotail

The spatial distributions of energetic ion and electron bursts on the IMP 7 and 8 satellites in the earth's magnetotail were studied. It was found that the ion bursts were more frequently detected in the dusk than in the dawn quarter of the neutral sheet whereas the electron bursts, more frequently in the dawn than the dusk quarter. The degree of dawn-dusk asymmetry is however energy dependent; the distribution for higher energy particle bursts exhibits higher degree of asymmetry. The morphologies of the distributions manifest themselves as seasonal variations of the most probable solar ecliptic latitudes at which the ion and electron bursts were observed. The amplitudes of the variations are about 25 deg with the seasonal variation for ions leading that for electrons by about 2 months.

Xu, R.-L.↗

NASA NTRS1985

The mean ionic charges of N, Ne, MG, SI and S in solar energetic particle events

The mean ionic charges of nitrogen, neon, magnesium, silicon, and sulfur in solar flare particle events were determined for 12 flares during the time interval from September 1978 to September 1979. The observations were carried out with the MPI/UoMd ULEZEQ Sensor on the ISEE-3 satellite comparing the results with mean charge states established in a hot coronal plasma under equilibrium conditions, different temperatures for different elements are discussed. These range from approx. 2 million K to 7 million K in a single flare. From flare to flare the variation in temperature for each element is less than the variation between different ion species.

Luhn, A.↗

NASA NTRS1985

Scaling from Jupiter to pulsars and the acceleration of cosmic ray particles by pulsars, 3

An expression for the rate of energy generation by a pulsar an estimate of contribution from all the pulsars in our galaxy to the observed cosmic ray intensity was presented. The theory was then developed to an expanded version, and observational facts supporting the theory were cited.

Fan, C. Y.↗

NASA NTRS1985

Solar modulation of cosmic ray intensity and solar flare events inferred from (14)C contents in dated tree rings

The delta 14C values in 42 rings of a white spruce grown in Mackenzie Delta was measured as a continuing effort of tracing the history of solar modulation of cosmic ray intensity. The delta 14C values in six rings were measured, in search of a 14C increase due to two large solar flares that occurred in 1942. The results are presented.

Fan, C. Y.↗

NASA NTRS1984

Direct determination of the ionic charge distribution of helium and iron in He-3-rich solar energetic particle events

The first direct measurement of the ionic charge distribution of the helium isotopes and of iron in (He-3)-Fe-rich solar energetic particle events is reported. No significant contribution of singly ionized helium to the events is found. The two-sigma upper limits for the He-3(+)/He-3(2+) and He-4(+)/He-4(2+) ratios are 0.02 and 0.03, respectively. The mean charge state of iron found by averaging five (He-3)-Fe-rich solar energetic particle events is 19 + or -2, significantly larger than the iron charge state for energetic solar particles in normal composition events. These results appear to favor the resonant heating model proposed by Fisk (1978). It is concluded that temperatures in the source region exceed 5 million K in the events under study.

Klecker, B.↗

NASA NTRS1984

The composition of heavy ions in solar energetic particle events

Recent advances in determining the elemental, charge state, and isotopic composition of or approximate to 1 to or approximate to 20 MeV per nucleon ions in solar energetic particle (SEP) events and outline our current understanding of the nature of solar and interplanetary processes which may explain the observations. Average values of relative abundances measured in a large number of SEP events were found to be roughly energy independent in the approx. 1 to approx. 20 MeV per nucleon range, and showed a systematic deviation from photospheric abundances which seems to be organized in terms of the first ionization potential of the ion. Direct measurements of the charge states of SEPs revealed the surprisingly common presence of energetic He(+) along with heavy ion with typically coronal ionization states. High resolution measurements of isotopic abundance ratios in a small number of SEP events showed these to be consistent with the universal composition except for the puzzling overabundance of the SEP(22)Ne/(20)Ne relative to this isotopes ratio in the solar wind. The broad spectrum of observed elemental abundance variations, which in their extreme result in composition anomalies characteristic of (3)He rich, heavy ion rich and carbon poor SEP events, along with direct measurements of the ionization states of SEPs provided essential information on the physical characteristics of, and conditions in the source regions, as well as important constraints to possible models for SEP production. Previously announced in STAR as N83-20886

Fan, C. Y.↗

NASA NTRS1984

Ionic charge states of N, Ne, Mg, Si and S in solar energetic particle events

The mean ionic charges and source-region temperatures of flare-accelerated N, Ne, Mg, Si and S in three large solar-energetic-particle events during 1978-1979 are determined from ISEE-3 observations, extending the findings of Hovestadt et al. (1981) and Gloeckler et al. (1981) for C, He, O, and Fe. The results are presented in tables and graphs, and the charge states are shown to correspond to different source temperatures even in the same flare, assuming equilibration in the hot plasma. The electron temperatures range from 2 x 10 to the 6th K for C, N, O, Si, and S, 4 x 10 to the 6th K for Ne and Fe, and 7 x 10 to the 6th K for Mg. The possibility that these temperature inconsistencies reflect different stages in the approach to equilibrium is considered.

Luhn, A.↗

NASA NTRS1983

Anisotropies and flows of suprathermal particles in the distant magnetotail - ISEE 3 observations

The ISEE-3 spacecraft has been transferred in 1982 into an earth orbit which brings the satellite close to the tailward Lagrangian point L2 at about 220 R(E) and thus allows exploration of the distant geomagnetic tail. An initial analysis of energetic proton measurements greater than 30 keV from the Max-Planck-Institut/University of Maryland sensor system on ISEE-3 is reported. It has been found that suprathermal protons are a persistent feature of the distant tail. Differential intensitites at 30 keV are essentially constant between the lunar distance and 220 R(E) and about one order of magnitude smaller than in the near earth, or greater than about 20 R(E), plasma sheet. Assuming that these protons are convected with the local plasma flow, it is possible to derive plasma velocities. During time periods where a comparison is possible, these velocities compare favourably well with the velocities derived from the Los Alamos National Laboratory plasma analyzer on board the same spacecraft. The appearance of the plasma sheet, as evidenced by the suprathermal particles, is rather bursty. Anisotropies are large, and predominantly tailward.

Scholer, M.↗

NASA NTRS1983

The composition of heavy ions in solar energetic particle events

Fan, C. Y.↗

NASA NTRS1983

Energy and charge distribution of energetic helium ions in the outer radiation belt of the earth

The first direct measurement of the charge states of helium at energies greater than 0.5 MeV/nucleon in the outer radiation belt, obtained aboard the ISEE-1 spacecraft in 1977, is reported. High abundances of singly ionized helium, with He(+)/He(2+) = 0.4 + or - 0.1 at L = 3.3 was found during one perigee pass, with a sudden decrease of that ratio by a factor of about 10 between L = 3.3 and 3.7. It is shown that nonstationary and/or nonadiabatic processes may play an important role for the distribution of helium ions in the outer radiation belt.

Klecker, B.↗

NASA NTRS1983

11-year cycle solar modulation of cosmic ray intensity inferred from C-14 content variation in dated tree rings

A liquid scintillation-photomultiplier tube counter system was used to measure the Delta-C-14 values of 60 tree rings, dating from 1866 to 1925, that were taken from a white spruce grown in Canada at 68 deg N, 130 deg W. A 10-percent variation is found which is anticorrelated with sunspot numbers, although the amplitude of the variation is 2-3 times higher than expected in trees grown at lower latitudes. A large dip in the data at about 1875 suggests an anomalously large modulation of cosmic ray intensity during the 1867-1878 AD solar cycle, which was the most active of the 19th century.

Fan, C. Y.↗

NASA NTRS1983

Acceleration of particles in the magnetotail

Using data from the Electrostatic Energy-vs-Charge Analyzer of the IMP-7 and -8 satellites for October 1973-October 1974, evidence is adduced for the neutral sheet association of bursts of ions and electrons in the 10 to 500 KeV energy range that have been frequently observed in the earth's magnetotail. It is also noted that the degree of asymmetry for the ion distribution is less for lower energy ions. On the basis of the correlation of the particle bursts with AE indices, two particle acceleration mechanisms are proposed.

Xu, R. L.↗

NASA NTRS1983

Suprathermal H(+) and He(2+) in the distant geomagnetic tail ISEE-3 observations

Preliminary ISEE 3 observations of suprathermal H(+) and He(2+) in the distant geomagnetic tail are summarized, with an emphasis on their energy spectra and composition. Regions found near earth are duplicated in the distant tail, but with various regions more intermixed and less distinct. The H(+) and He(2+) energy spectra in all regions and at all geocentric distances for which observations exist are on average not power laws but are well represented by a given expression. The He(2+)/H(+) ratio of 0.03 to 0.07 in the plasma sheet shows no systematic variation with geocentric distance and is two to three times lower than in the other regions. Well-directed, strong, tailward flows distinguish the near bow-shock/magnetosheath region from the geomagnetic tail and plasma sheet where anisotropies are generally smaller and the flow direction more variable although still tailward, indicating source locations at less than 60 earth radii most of the time.

Gloeckler, G.↗

NASA NTRS1982

Scaling from Jupiter to pulsars and mass spectrum of pulsars

Following the principle of similitude, the energy loss of Jupiter was scaled through the acceleration of high energy particles to that of Crab pulsar. The agreement suggests a classification scheme for all pulsars in which the pulsar angular velocity and its decrease with time are related to the pulsar moment of inertia divided by its radius and its mass is determined according to neutron star models. The mass spectrum of 194 pulsars is found to be approximately 1/sq m.

Fan, C. Y.↗

NASA NTRS1982

Acceleration mechanisms for energetic particles in the earth's magnetosphere

By analyzing data on energetic particle fluxes measured simultaneously with detector systems on several earth satellites, signatures of different acceleration mechanisms for these particles were searched for. One of the samples is an event observed on ATS-6 and IMP-7. IMP-7 was in the dusk quarter at 38 earth radii while ATS-6 was located at local midnight at a distance of 6.6 earth radii. Although the flux variations as observed on the two spacecraft both showed 1.5 min periodicity, there was a 40-second time lag with IMP-7 behind. The results indicate that the particles are accelerated by magnetic field line annihilation, with the x-point located at about 10 earth radii.

Schiferl, S.↗

NASA NTRS1981

Singly charged energetic helium emitted in solar flares

First direct charge state measurements of 0.41-1.05 MeV per nucleon helium accelerated at the sun reveal surprisingly large abundances of singly ionized helium, with typical He(+)/He(++) ratios between 0.04 and 0.21. This unexpected overabundance of He(+) was observed in each of the three large solar-flare particle events which occurred between 1978 August and 1979 October. The data were obtained with the Max-Planck-Institut/University of Maryland Experiment on board the ISEE-3 spacecraft. The observations suggest either strong coronal temperature inhomogeneities including cool regions of approximately 100,000 K or injection of 'cold' chromospheric/photospheric material into the flare acceleration region.

Hovestadt, D.↗