[1] The SERSIO sounding rocket was launched from Ny-Alesund, Svalbard, into a type 2 ion upflow event simultaneously observed by the European Incoherent Scatter (EISCAT) radar facility in Longyearbyen on 22 January 2004 at 0857 UT. It reached an apogee of 782 km. In situ wave data and thermal particle measurements in the cusp/cleft region clearly show core thermal ion temperature enhancements up to 0.8 eV in association with 0-4 kHz broadband extremely low frequency wave activity (BBELF). The in situ observation of wave heating in the cusp/cleft region at these low altitudes (520-780 km) and high densities (80,000/cm 3 ) is an important measurement and should be included in any model of ion energization. Wave activity in the form of naturally enhanced ion acoustic lines (NEIAL) was seen by the EISCAT radar in the same activity region. Periods of NEIAL were compared with in situ auroral electron data that show no evidence of a bump-on-tail distribution; thus our data do not support using Langmuir turbulence to explain these radar echoes. In contrast, these observations associating NEIAL with BBELF activity suggest that they may be the same phenomenon. During these comparisons, all-sky camera images were used to verify similar environmental conditions between the rocket and radar measurement volumes, while the spatial separation between the volumes was less than 500 km. In situ measurements also confirm the link between soft electron precipitation and thermal electron temperature enhancements in this ion upflow environment.
Full characterization of nighttime ionospheric plasma requires access to both the ion and electron thermal core populations. Efforts to measure particle distributions with rocket and satellite detectors designed to study low energy particles are hindered because the magnitude of spacecraft charging is on the order of or greater than the energy of the bulk of ionospheric particles. This paper presents initial laboratory investigations exploring the formation of plasma sheaths with ionospheric electron energies, densities, and Debye lengths. The goal is to identify the difficulties and solutions to obtaining both thermal electron and ion velocity distributions on one payload. Sheaths around a long cylinder biased with respect to the vacuum vessel wall are studied to verify measurement procedures. An experimental setup in which two conducting spheres, with area ratios in excess of 100, are biased with respect to one another and not referenced to the wall simulates a payload-detector system. Data are compared with simple planar, cylindrical, and spherical sheath models. Ion-rich sheaths conformed with expectations. The criterion for the formation of electron-rich sheaths was found not only to depend on the ratio of ion collector area to electron collector area but also the ratio of the collector area to sheath area. Nonmonotonic electron sheaths obtained by embedding a positively biased electrode within the sheath of a more negative conductor are also explored. It was found that the superposition of two different potential geometries led to the formation of the nonmonotonic potential structures. These initial plasma ion and electron sheath investigations both clarify the behavior of a thermal electron detector previously flown in the ionosphere and explore a low energy parameter regime that is understudied in the laboratory.
We have designed and fabricated a low energy plasma calibration facility for testing and calibration of rocket-borne charged-particle detectors and for the investigation of plasma sheath formation in an environment with ionospheric plasma energies, densities, and Debye lengths. We describe the vacuum system and associated plasma source, which was modified from a Naval Research Laboratory design [Bowles et al. Rev. Sci. Instrum. 67, 455 (1996)]. Mechanical and electrical modifications to this cylindrical microwave resonant source are outlined together with a different method of operating the magnetron that achieves a stable discharge. This facility produces unmagnetized plasmas with densities from 1x10(3)/cm(3) to 6x10(5)/cm(3), electron temperatures from 0.1 to 1.7 eV, and plasma potentials from 0.5 to 8 V depending on varying input microwave power and neutral gas flow. For the range of input microwave power explored (350-600 W), the energy density of the plasma remains constant because of an inverse relationship between density and temperature. This relationship allows a wide range of Debye lengths (0.3-8.4 cm) to be investigated, which is ideal for simulating the ionospheric plasma sheaths we explore.
“Unfortunately the new element for the examination of which he came over, proves shy and will not disclose itself. I cannot imagine what it can be, and seriously doubt its existence. This is disappointing and leaves one more gap in the list of the known elements."
In December 1913 and April 1914, Henry Moseley, a British physicist, published data that is now famed for being the first experimental evidence for the atomic number as a physical property of the nucleus. Shortly after, in June 1914, Moseley used x-ray spectroscopy to analyze several rare earth elements provided by Georges Urbain. Moseley failed to publish his conclusions before his death in the First World War. Despite the efforts of his mother and colleagues, a posthumous publication never materialized. This essay explores the question of why. An in-depth evaluation of extant artifacts and archival materials at the Museum of the History of Science in Oxford related to Moseley’s rare earth research reveals nuances in the process by which he collected and corrected data to form his conclusions. Whereas Moseley was confident his data did not support the claim that Urbain isolated the element with atomic number 72, it failed to inspire Ernest Rutherford to see the work through publication after Moseley’s death. Archival materials reveal some of the pressures that could have prevented publication, including Rutherford’s unfamiliarity with Moseley’s process—but more importantly, the fact that this data would influence the debate over the discovery of element 72. Interestingly, it is likely this controversy led to the retention of relevant archival material. By tracing the actors that created and curated a particular collection of documents and spectra, one can explore how rare earth knowledge was produced and verified in the first few decades of the twentieth century.
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