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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

GEM detectors for the CMS endcap muon system: status of three new detector stations

The High-Luminosity LHC (HL-LHC, or Phase-2 LHC) will deliver proton-proton collisions at 5–7.5 times the nominal LHC luminosity, with an expected number of 140–200 pp-interactions per bunch crossing (Pile-up or PU). To maintain the performance of muon triggering and reconstruction under high background, the forward part of the Muon Spectrometer of the CMS experiment will be upgraded with Gas Electron Multipliers (GEM) and improved Resistive Plate Chambers (iRPC) detectors. A first GEM station (GE1/1) was installed during Long Shutdown 2 (LS2, 2019–2021), a 2 nd station (GE2/1) of Triple-GEM detectors will be installed in winter 2023–24 and 2024–25, while a new 6-layer station (ME0) will be installed in the third Long Shutdown (LS3, 2026–2028). GE11 is considered an early Phase-2 upgrade as it will reduce the p T threshold by combining GEM and Cathode Strip Chamber (CSC) hits in the forward muon system at twice the LHC design luminosity ($\mathcal{L}$ = 2 · 10 34 cm -2 s -1 , 50 PU). After a successful start of Run-3 in 2022, with almost 40 fb -1 collected, the commissioning of the GE1/1 detector is nearly complete. Most chambers are operated stably with an efficiency in excess of 95%, next being the demonstration of the combined CSC-GEM trigger in 2023. The lessons learnt with the first large-area GEM station have lead to improvements in detector and electronics design for the Phase 2 detectors GE2/1 and ME0. This proceeding will discuss the progress made since last MPGD Conference (MPGD 2019), discussing the commissioning and early performance of GE1/1; the design improvements and start of construction of GE2/1; and the R&D currently ongoing for ME0.

47 OTHER INSTRUMENTATION↗
NASA NTRS1976

Improvement in the geopotential derived from satellite and surface data (GEM 7 and 8)

A refinement was obtained in the earth's gravitational field using satellite and surface data. In addition to a more complete treatment of data previously employed on 27 satellites, the new satellite solution (Goddard Earth Model 7) includes 64,000 laser measurements taken on 7 satellites during the international satellite geodesy experiment (ISAGEX) program. The GEM 7, containing 400 harmonic terms, is complete through degree and order 16. The companion solution GEM 8 combines the same satellite data as in GEM 7 with surface gravimetry over 39% of the earth. The GEM 8 is complete to degree and order 25. Extensive tests on data independent of the solution show that the undulation of the geoidal surface computed by GEM 7 has an accuracy of about 3m (rms). The overall accuracy of the geoid estimated by GEM 8 is estimated to be about 4-1/4m (rms), an improvement of almost 1m over previous solutions.

Wagner, C. A.↗
NASA NTRS1984

Verification of the accuracy of GEM-L2 in response to criticism by Lambeck and Coleman

The objective was to evaluate the accuracy of the Goddard Earth Model (GEM)-L2 and its improvement in estimating Lageos orbits in order to provide better baselines for plate tectonics, improved polar motion and Earth rotation. Analyses and comparisons with other models are made to verify accuracy in contrast to the Lambeck and Coleman result which denied the authors' accuracy estimates. The analysis presented completely verifies the accuracy of the GEM-L2 model and disproves the statistical methods of Lambeck and Coleman rejecting the accuracy of GEM-L2 as published in their report. The baselines derived from Lageos with GEM-L2 were estimated to have a 2 cm uncertainty due to the errors in the GEM-L2 gravity model which is supported by the results given. The calibration tests indicate that the errors in GEM-L2 should be reduced by about 30 percent which is in the opposite direction to the result obtained by Lambeck and Coleman.

Lerch, F. J.↗
NASA NTRS1988

A new gravitational model for the earth from satellite tracking data - GEM-T1

A computation of a terrestrial gravitational field model called the Goddard Earth Model GEM-T1 is discussed and compared to previous models, including the GEM-L2. The software tools were redesigned for the model, allowing for the optimization of the technique of relative data weighting and model estimation used in GEM solutions. The GEM-T1 model provides a simultaneous solution for a gravity model in spherical harmonics complete to degree and order 36, a subset of 66 ocean tidal coefficients for the long-wavelength components of 12 major tides, and 5-day averaged earth rotation and polar motion parameters for the 1980 period on. GEM-T1 was derived from satellite tracking data acquired on 17 different satellites whose inclinations ranged from 15 degrees to polar. A simulation of the TOPEX/POSEIDON orbit using the covariances of the GEM-T1 model was made. Estimated radial error for the simulation was reduced to less than 30 cm rms.

Marsh, J. G.↗
NASA NTRS2005

GEMS Revealed: Spectrum Imaging of Aggregate Grains in Interplanetary Dust

Anhydrous interplanetary dust particles (IDPs) of cometary origin contain abundant materials that formed in the early solar nebula. These materials were transported outward and subsequently mixed with molecular cloud materials and presolar grains in the region where comets accreted [1]. GEMS (glass with embedded metal and sulfides) grains are a major component of these primitive anhydrous IDPs, along with crystalline Mg-rich silicates, Fe-Ni sulfides, carbonaceous material, and other trace phases. Some GEMS grains (~5%) are demonstrably presolar based on their oxygen isotopic compositions [2]. However, most GEMS grains are isotopically solar and have bulk chemical compositions that are incompatible with inferred compositions of interstellar dust, suggesting a solar system origin [3]. An alternative hypothesis is that GEMS grains represent highly irradiated interstellar grains whose oxygen isotopic compositions were homogenized through processing in the interstellar medium (ISM) [4]. We have obtained the first quantitative X-ray maps (spectrum images) showing the distribution of major and minor elements in individual GEMS grains. Nanometer-scale chemical maps provide critical data required to evaluate the differing models regarding the origin of GEMS grains.

Keller, L. P.↗
NASA NTRS2009

GEMS

The prime scientific objectives of the Gravity and Extreme Magnetism SMEX, GEMS, are to determine the effects of the spin of black holes, the configurations of the magnetic fields of magnetars, and the structure of the supernova shocks which accelerate cosmic rays. In the cases of both stellar black holes and supermassive black holes, sensitivity to 1% polarization is needed to make diagnostic measurements of the net polarizations predicted for probable disk and corona models. GEMS can reach this goal for several Seyferts and quasars and measure the polarizations of representatives of a variety of other classes of X-ray sources, such as rotation-powered and accretion-powered pulsars. GEMS uses foil mirrors to maximize the collecting area achievable within the SMEX constraints. The polarimeters at the mirror foci are Time Projection Chambers which use the photoelectic effect to measure the polarization of the incident photon. We have built laboratory models with good efficiency and modulation in the 2-10 keV range. An attached small student experiment would add 0.5 keV sensitivity for bright soft sources. The instrument has a point spread function which allows measurement of structures in the brighter nearby supernova remnants. GEMS' Orbital Sciences spacecraft will rotate at a rate of 0.1 revolutions per minute during observations, so that systematic errors due to the detector can be detected and corrected. A program of 35 sources can be observed in 9 months. GEMS is designed for a two year lifetime which will allow a General Observer program that would more than double the number of sources measured. For subsets of black holes, neutron stars and supernova remnants, GEMS will measure the polarization of several sources, solving important questions while establishing the sensitivity required for future missions.

Swank, Jean↗
NASA NTRS2011

Data Analysis And Polarization Measurements With GEMS

The Gravity and Extreme Magnetism SMEX (GEMS) mission was selected by NASA for flight in 2014. GEMS will make the first sensitive survey of X-ray polarization across a wide range of source classes including black hole and neutron star binaries, AGN of different types, rotation and accretion-powered pulsars, magnetars, shell supernova remnants and pulsar wind nebulae. GEMS employs grazing-incidence foil mirrors and novel time-projection chamber (TPC) polarimeters leveraging the photoelectric effect. The GEMS detectors image the charge tracks of photoelectrons produced by 2 - 10 keV X-rays. The initial direction of the photoelectron is determined by the linear polarization of the photon. We present an overview of the data analysis challenges and methods for GEMS, including procedures for producing optimally filtered images of the charge tracks and estimating their initial directions. We illustrate our methods using laboratory measurements of polarized and unpolarized X-rays with flight-like detectors as well as from simulated tracks. We also present detailed simulations exploring the statistics of polarization measurements appropriate for GEMS, and make comparisons with previous work.

Stohmayer, Tod↗
NASA NTRSDate not supplied

Chemical and petrographic characterization of amorphous silicate material in cometary GEMS

Amorphous silicate material (ASM) is found in the matrix of GEMS (glass with embedded metal and sulfides) in chondritic porous interplanetary dust particles (CP-IDPs) and in the matrices of primitive chondritic meteorites. It either formed by irradiation of crystalline precursors in the interstellar medium or by non-equilibrium condensation in the solar nebula. However, the origins of ASM in IDPs and chondrites and their possible relationship are still not well constrained. Here we performed a petrographic and chemical characterization of ASM in five CP-IDPs by Transmission Electron Microscopy (TEM)techniques. We also analyzed carbon and nitrogen isotopic compositions of organic matter by Nano SIMS to constrain the pristine character of analyzed IDPs. ASM in IDPs is depleted in all major element/Si ratios with respect to the solar value. Compared to bulk GEMS analyses, the ASM contains less Fe, because nanophase inclusions of Fe-Ni-metal and FeS are mostly excluded by our approach. In contrast, ASM in meteorites has higher-than-solar Fe/Si ratios, maybe due to aqueous alteration on the meteorite parent bodies. Chemical composition of GEMS ASM indicates a non-equilibrium condensation origin. Silicone oil contamination of particles during collection is excluded, because GEMS collected in dry polyurethane show similar compositions. Magnetite rims around GEMS in our IDP samples indicate heating of some particles during atmospheric entry. However, preserved 15N and13C isotopic anomalies in organic matter around GEMS and in IDP matrix link the IDPs to a cold environment and overall validate their primitiveness.

Birgit Schulz↗
DOE OSTI2022

Reduction of ion backflow using a quadruple GEM detector with various gas mixtures

In gaseous tracking detectors with a large gaseous volume, like Time Projection Chambers (TPC), multiple layers of Gas Electron Multipliers (GEM) can be used to block positive ions from flowing back into the active volume, which is detrimental to the tracking performance. TPCs with multilayer GEM readout are used in the recently upgraded ALICE experiment, and in the upcoming sPHENIX experiment. In both cases, suppression of ion backflow (IBF) is important for achieving the desired detector performance. Here, we report on studies of effective gain, IBF, and energy resolution in quadruple GEM detectors, and on strategies for minimizing IBF by optimizing the operating voltages of the individual GEM layers and the potential differences between different layers. These studies are performed as baseline measurements intended to aid in the optimization of the operating conditions of the GEMs of the sPHENIX TPC.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Notes from the GEM Chair

I hope this letter finds you all safe and healthy. Due to the continuing uncertainties with the COVID-19 pandemic, the GEM Steering Committee (SC) decided, similarly to last year, to once again hold a fully virtual workshop. The GEM 2021 summer workshop will occur from July 26 to July 30, with Sunday July 25 as the Student Day. We will follow the original format of GEM, with plenary sessions in the morning, Focus Group (FG) breakout sessions in the afternoon, and poster sessions in the evening. We encourage you to take this opportunity to share your research, technical efforts, and ideas with the GEM community. Although we realize that the big celebration will happen once we are able to meet in person again, this year is the 30th anniversary of the first GEM meeting and we envision a program that celebrates this significant milestone!

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1991

An improved error assessment for the GEM-T1 gravitational model

Several tests have been designed to estimate the correct error variances for the GEM-T1 gravitational solution that was derived exclusively from satellite tracking data. The basic method uses both independent and dependent subset data solutions and produces a coefficient-by-coefficient estimate of the model uncertainties. The GEM-T1 errors have been further analyzed using a method based on eigenvalue-eigenvector analysis, which calibrates the entire covariance matrix. Dependent satellite data sets and independent altimetric, resonant satellite, and surface gravity data sets all confirm essentially the same error assessment. The calibration test results yield very stable calibration factors, which vary only by approximately 10 percent over the range of tests performed. Based on these calibrated error estimates, GEM-T1 is a significantly improved solution, which to degree and order 8 is twice as accurate as earlier satellite derived models like GEM-L2. Also, by being complete to degree and order 36, GEM-T1 is more complete and has significantly reduced aliasing effects that were present in previous models.

Lerch, F. J.↗
NASA NTRS2004

On the Origin of GEMS

GEMS (glass with embedded metal and sulfides) are a major component of anhydrous interplanetary dust particles (IDPs) their physical and chemical characteristics show marked similarities to contemporary interstellar dust. Recent oxygen isotopic measurements confirm that at least a small fraction (less than 5%) of GEMS are demonstrably presolar, while the remainder have ratios that are indistinguishable from solar values. GEMS with solar oxygen isotopic compositions either (1) had their isotopic compositions homogenized through processing in the interstellar medium (ISM), or (2) formed in the early solar system. Isotopic homogenization necessarily implies chemical homogenization, so (interstellar) GEMS compositions should reflect the average composition of dust in the local ISM. We performed a systematic examination of the bulk chemistry of GEMS in primitive IDPs in order to test this hypothesis.

Keller, L. P.↗
NASA NTRS2007

Does Comet WILD-2 contain Gems?

It is expected that Comet Wild-2 dust should resemble anhydrous carbon-rich, chondritic porous (CP) interplanetary dust particles (IDPs) collected in the stratosphere because some CP IDPs are suspected to be from comets. The rarity of carbonaceous grains and presolar silicates, as well as the presence of high-temperature inner solar nebula minerals in the Wild-2 sample (e.g. osbornite and melilite), appear incompatible with most CP IDPs. However, it is premature to draw firm conclusions about the mineralogy of comet Wild-2 because only approx. 1% of the sample has been examined. The most abundant silicates in CP IDPs are GEMS (glass with embedded metal and sulfides). Nonsolar O isotopic compositions confirm that at least some GEMS in IDPs are presolar amorphous silicates. The presence or absence of GEMS in the Wild-2 sample is important because it addresses, (a) the relationship between CP IDPs and comets, and (b) the hypothesis that other GEMS in IDPs formed in the solar nebula. Here we show that most of the GEMSlike materials so far identified in Stardust aerogel were likely impact generated during collection. At the nanometer scale, they are compositionally and crystallographically distinct from GEMS in IDPs.

Chi, M.↗
NASA NTRS2012

Development of Resistive Electrode Gas Electron Multiplier (RE-GEM)

We successfully produced Resistive-Electrode Gas Electron Multiplier (RE-GEM) which has resistive electrodes instead of the metal ones which are employed for the standard GEM foils. RE-GEM has a resistive electrode of 25 micron-thick and an insulator layer of 100 micron-thick. The hole structure of RE-GEM is a single conical with the wider and narrower hole diameters of 80 micron and 60 micron, respectively. A hole pitch of RE-GEM is 140 micron. We obtained the maximum gain of about 600 and the typical energy resolution of about 20% (FWHM) at an applied voltage between the resistive electrodes of 620 V, using a collimated 8 keV X-rays from a generator in a gas mixture of 70% Ar and 30% CO2 by volume at the atmospheric pressure. We measured the effective gain as a function of the electric field of the drift region and obtained the maximum gain at an drift field of 0.5 kV/cm.

detectors↗
NASA NTRS2016

Possible Gems and Ultra-Fine Grained Polyphase Units in Comet Wild 2.

GEMS and ultrafine grained polyphase units (UFG-PU) in anhydrous IDPs are probably some of the most primitive materials in the solar system. UFG-PUs contain nanocrystalline silicates, oxides, metals and sulfides. GEMS are rounded approximately 100 nm across amorphous silicates containing embedded iron-nickel metal grains and sulfides. GEMS are one of the most abundant constituents in some anhydrous CPIDPs, often accounting for half the material or more. When NASA's Stardust mission returned with samples from comet Wild 2 in 2006, it was thought that UFG-PUs and GEMS would be among the most abundant materials found. However, possibly because of heating during the capture process in aerogel, neither GEMS nor UFG-PUs have been clearly found.

Gainsforth, Z.↗
DOE OSTI2022

Avalanche gain and its effect on energy resolution in GEM-based detectors

Here, we present avalanche gain and associated resolution measurements recorded with a 4 He:CO 2 (70:30) gas mixture and pure SF 6 , a Negative Ion (NI) gas. SF 6 is of particular interest to the directional dark matter detection community, as its low thermal diffusion helps to retain recoil ionization track features over long drift lengths. With the aid of a general form of the reduced first Townsend coefficient (RFTC), multiple GEM-based detector data sets are used to study the high-gain behavior of the 4 He:CO 2 gas mixture. The high-gain data is well described purely in terms of the reduced electric field strength and the number of GEMs, and the robust relationship between the RFTC and the average, reduced, electric field strength across the GEMs is emphasized. The associated (pulse-height) resolution measurements are used to discuss the variance of the avalanche distribution and to describe and estimate the lower limits of energy resolution one should expect to measure using a simple relationship with the RFTC. In the end, a description of avalanche gain, its effect on energy resolution, and the contributing experimental parameters in GEM-based detectors is developed over a broad parameter space for further use.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Effective Gain and Ion Back Flow study of triple and quadruple GEM detector

Abstract Gas electron Multipliers (GEM) are a new generation of gaseous avalanche devices in the Micro Pattern Gaseous Detector (MPGD) category. GEMs are widely used in both nuclear and high energy experiments as well as in medical science. Several parameters define the performance of these types of devices under various experimental conditions. This article focuses on the study of effective gain and Ion Back Flow (IBF) in both triple and quadruple GEM detectors. Effective gain and IBF are two of the most important parameters in determining the performance of GEM detectors.

Instruments & Instrumentation↗
NASA NTRS1972

Gravitational field models for the earth (GEM 1 and 2)

Two models of the earth's gravitational field have been computed at Goddard Space Flight Center. The first, Goddard Earth Model 1 (GEM 1), has been derived from satellite tracking data. The second, Goddard Earth Model 2 (GEM 2), has been derived from a combination of satellite tracking and surface gravimetric data. The geopotential models are represented in spherical harmonics complete to degree and order 16 for the combined solution and complete to degree and order 12 for the satellite solution. Both solutions include zonal terms to degree 21 and related satellite resonant coefficients to degree 22. The satellite data consisted primarily of optical data processed on 300 weekly orbital arcs for 25 close earth satellites. Surface gravity data were employed in the form of 5 deg x 5 deg mean free-air gravity anomalies providing about 70% world coverage. Station locations were obtained for 46 tracking sites by combining electronic, laser, and additional optical tracking data with the above satellite data. Analysis of the radial positions of these stations and a value of mean gravity on the geoid indicated a mean equatorial radius for the earth of about 6378145 meters. Results of geopotential tests on satellite data not used in the solution show that better agreement was obtained with the GEM 1 and GEM 2 models than with the 1969 Smithsonian Standard Earth 2 model.

Lerch, F. J.↗