J. A. Jeon

DISCREPANT HARDENING OBSERVED IN COSMIC-RAY ELEMENTAL SPECTRA

The balloon-borne Cosmic Ray Energetics And Mass experiment launched five times from Antarctica has achieved a cumulative flight duration of about 156 days above 99.5% of the atmosphere. The instrument is configured with complementary and redundant particle detectors designed to extend direct measurements of cosmic-ray composition to the highest energies practical with balloon flights. All elements from protons to iron nuclei are separated with excellent charge resolution. Here, we report results from the first two flights of ~70 days, which indicate hardening of the elemental spectra above ~200 GeV/nucleon and a spectral difference between the two most abundant species, protons and helium nuclei. These results challenge the view that cosmic-ray spectra are simple power laws below the so-called knee at ~1015 eV. This discrepant hardening may result from a relatively nearby source, or it could represent spectral concavity caused by interactions of cosmic rays with the accelerating shock. Other possible explanations should also be investigated.

Cosmic-ray Proton and Helium Spectra from the First CREAM Flight

Cosmic-ray proton and helium spectra have been measured with the balloon-borne Cosmic Ray Energetics And Mass experiment flown for 42 days in Antarctica in the 2004–2005 austral summer season. High-energy cosmic-ray data were collected at an average altitude of �38.5 km with an average atmospheric overburden of �3.9 g cm −2 . Individual elements are clearly separated with a charge resolution of �0.15 e (in charge units) and �0.2 e for protons and helium nuclei, respectively. The measured spectra at the top of the atmosphere are represented by power laws with a spectral index of 2.66 ± 0.02 for protons from 2.5 TeV to 250 TeV and –2.58 ± 0.02 for helium nuclei from 630 GeV nucleon −1 to 63 TeV nucleon −1 . They are harder than previous measurements

ENERGY SPECTRA OF COSMIC-RAY NUCLEI AT HIGH ENERGIES

We present new measurements of the energy spectra of cosmic-ray (CR) nuclei from the second flight of the balloon-borne experiment Cosmic-Ray Energetics And Mass (CREAM). The instrument included different particle detectors to provide redundant charge identification and measure the energy of CRs up to several hundred TeV. The measured individual energy spectra of C, O, Ne, Mg, Si, and Fe are presented up to ~1014 eV. The spectral shape looks nearly the same for these primary elements and it can be fitted to an E –2.66 ± 0.04 power law in energy. Moreover, a new measurement of the absolute intensity of nitrogen in the 100-800 GeV/n energy range with smaller errors than previous observations, clearly indicates a hardening of the spectrum at high energy. The relative abundance of N/O at the top of the atmosphere is measured to be 0.080 ± 0.025 (stat.)±0.025 (sys.) at ~800 GeV/n, in good agreement with a recent result from the first CREAM flight.

High fill-factor micromirror array using a self-aligned vertical comb drive actuator with two rotational axes

We present a two-axis micromirror array with high fill-factor, using a new fabrication procedure on the full wafer scale. The micromirror comprises a self-aligned vertical comb drive actuator with a mirror plate mounted on it and electrical lines on a bottom substrate. A high-aspect-ratio vertical comb drive was built using a bulk micromachining technique on a silicon-on-insulator (SOI) wafer. The thickness of the torsion spring was adjusted using multiple silicon etching steps to enhance the static angular deflection of the mirrors. To address the array, electrical lines were fabricated on a glass substrate and combined with the comb actuators using an anodic bonding process. The silicon mirror plate was fabricated together with the actuator using a wafer bonding process and segmented at the final release step. The actuator and addressing lines were hidden behind the mirror plate, resulting in a high fill-factor of 84% in an 8 × 8 array of micromirrors, each 340 µm × 340 µm. The fabricated mirror plate has a high-quality optical surface with an average surface roughness (Ra) of 4 nm and a curvature radius of 0.9 m. The static and dynamic responses of the micromirror were characterized by comparing the measured results with the calculated values. The maximum static optical deflection for the outer axis is 4.32° at 60 V, and the maximum inner axis tilting angle is 2.82° at 96 V bias. The torsion resonance frequencies along the outer and inner axes were 1.94 kHz and 0.95 kHz, respectively.

MEASUREMENTS OF THE RELATIVE ABUNDANCES OF HIGH-ENERGY COSMIC-RAY NUCLEI IN THE TeV/NUCLEON REGION

We present measurements of the relative abundances of cosmic-ray nuclei in the energy range of 500-3980 GeV/nucleon from the second flight of the Cosmic Ray Energetics And Mass balloon-borne experiment. Particle energy was determined using a sampling tungsten/scintillating-fiber calorimeter, while particle charge was identified precisely with a dual-layer silicon charge detector installed for this flight. The resulting element ratios C/O, N/O, Ne/O, Mg/O, Si/O, and Fe/O at the top of atmosphere are 0.919 ? 0.123stat ? 0.030syst, 0.076 ? 0.019stat ? 0.013syst, 0.115 ? 0.031stat ? 0.004syst, 0.153 ? 0.039stat ? 0.005syst, 0.180 ? 0.045stat ? 0.006syst, and 0.139?? 0.043stat ? 0.005syst, respectively, which agree with measurements at lower energies. The source abundance of N/O is found to be 0.054 ? 0.013stat ? 0.009syst+0.010esc ?0.017. The cosmic-ray source abundances are compared to local Galactic (LG) abundances as a function of first ionization potential and as a function of condensation temperature. At high energies the trend that the cosmic-ray source abundances at large ionization potential or low condensation temperature are suppressed compared to their LG abundances continues. Therefore, the injection mechanism must be the same at TeV/nucleon energies as at the lower energies measured by HEAO-3, CRN, and TRACER. Furthermore, the cosmic-ray source abundances are compared to a mixture of 80% solar system abundances and 20% massive stellar outflow (MSO) as a function of atomic mass. The good agreement with TIGER measurements at lower energies confirms the existence of a substantial fraction of MSO material required in the ~TeV per nucleon region.

MEMS micromirror characterization in space environments

This paper describes MEMS micromirror characterization in space environments associated with our space applications in earth observation from the International Space Station and earths orbit satellite. The performance of the micromirror was tested for shock and vibration, stiction, outgassing from depressurization and heating, and electrostatic charging effects. We demonstrated that there is no degradation of the micromirror performance after the space environment tests. A test bed instrument equipped with the micromirrors was delivered and tested in the ISS. The results demonstrate that the proposed micromirrors are suitable for optical space systems.

A New Type of Space Telescope for Observation of Extreme Lightning Phenomena in the Upper Atmosphere

A new type of space telescope with a 3 mm × 3 mm Micro-Electro-Mechanical System (MEMS) micromirror array has been fabricated and launched into space. This telescope has unique features: a wide field of surveillance view, and fast zoom-in and tracking capabilities. Although the micromirror array area is small, the space telescope was capable of observing the space-time development of extreme lightning in the upper atmosphere. It fulfilled its purpose by proving the principles of a space telescope. The concept and technologies used in this telescope can be extended to large MEMS space telescopes for future missions for earth and space science, including gamma ray bursts and ultra high energy cosmic rays. The performance of the space telescope during the ground test before launch as well as its performance in space are here presented to demonstrate the fast zoom-in and tracking capabilities of the telescope.

The CREAM Calorimeter: Performance In Tests And Flights

The Cosmic Ray Energetics And Mass (CREAM) balloon‐borne experiment, designed to directly measure cosmic‐ray particle energies from ∼1011 to ∼1015 eV, had two successful flights since December 2004, with a total duration of 70 days. The CREAM calorimeter is comprised of 20 layers of 1 radiation length (X0) tungsten interleaved with 20 active layers each made up of fifty 1 cm wide scintillating fiber ribbons. The scintillation signals are read out with multi pixel Hybrid Photo Diodes (HPDs), VA32‐HDR2/TA32C ASICs and LTC1400 ADCs. During detector construction, various tests were carried out using radioactive sources, UV‐LEDs, and particle beams. We will present results from these tests and show preliminary results from the two flights.

The Cosmic Ray Energetics and Mass (CREAM) timing charge detector

H. S. AHN , P. ALLISON , M. G. BAGLIESI , J. J. BEATTY , G. BIGONGIARI , P. BOYLE , J. T. CHILDERS , N. B. CONKLIN , S. COUTU , M. A. DUVERNOIS , O. GANEL , J. H. HAN , J. A. JEON , K. C. KIM , J. K. LEE , M. H. LEE , L. LUTZ , P. MAESTRO , A. MALININE , P. S. MARROCCHESI , S. MINNICK , S. I. MOGNET , S. NAM , S. NUTTER , I. H. PARK , N. H. PARK , E. S. SEO , R. SINA , S. SWORDY , S. WAKELY , J. WU , J. YANG , Y. S. YOON , R. ZEI , S. Y. ZINN . Inst. for Phys. Sci. and Tech., University of Maryland, College Park, MD 20742 USA Dept. of Physics, Ohio State University, Columbus, Ohio 43210, USA Dept. of Physics, University of Siena and INFN, Via Roma 56, 53100 Siena, Italy Enrico Fermi Institute and Dept. of Physics, University of Chicago, Chicago, IL 60637, USA School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA Dept. of Physics, Penn State University, University Park, PA 16802, USA Dept. of Physics, Ewha Womans University, Seoul, 120-750, Republic of Korea Dept. of Physics, Kent State University Tuscarawas, New Philadelphia, OH 44663, USA Dept. of Physics and Geology, Northern Kentucky University, Highland Heights, KY 41099, USA Dept. of Physics, University of Maryland, College Park, MD 20742 USA hsahn@umd.edu

UV Radiation from the Night-Time Atmosphere seen from the “Universitetsky-Tatiana” Satellite

Detectors on the “Universitetsky‐Tatiana” satellite measured a smoothly varying intensity of UV radiation from the night‐time atmosphere in the nadir direction and the intensity of the energetic electron flux at the orbit. At high latitudes the UV intensity in the auroral oval is interpreted as being due to electrons penetrating into the atmosphere. At middle latitudes the UV intensity is an order of magnitude less and more data are needed to reveal the origin of this radiation. Millisecond flashes of UV radiation were observed. The flashes’ energy, temporal profile and global distribution are similar to these parameters for Transient Luminous Events (TLEs). These studies will be continued aboard the next satellite “Tatiana‐2”.