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Featured researches published by Knud Thomsen.


Astronomy and Astrophysics | 2001

The Reflection Grating Spectrometer on board XMM-Newton

J. W. den Herder; Graziella Branduardi-Raymont; Knud Thomsen; Marc Audard; A. J. F. den Boggende; Jean Cottam; Luc Dubbeldam; H. Goulooze; P. Guttridge; B. J. van Leeuwen; A. P. Rasmussen; K. Rees; Irini Sakelliou; Takayuki Tamura; J. Tandy; C. P. de Vries; Alex Zehnder

The ESA X-ray Multi Mirror mission, XMM-Newton, carries two identical Reflection Grating Spectrometers (RGS) behind two of its three nested sets of Wolter I type mirrors. The instrument allows high- resolution (E=E = 100 to 500) measurements in the soft X-ray range (6 to 38 A or 2.1 to 0.3 keV) with a maximum eective area of about 140 cm 2 at 15 A. Its design is optimized for the detection of the K-shell tran- sitions of carbon, nitrogen, oxygen, neon, magnesium, and silicon, as well as the L shell transitions of iron. The present paper gives a full description of the design of the RGS and its operational modes. We also review details of the calibrations and in-orbit performance including the line spread function, the wavelength calibration, the eective area, and the instrumental background.


SPIE's International Symposium on Optical Science, Engineering, and Instrumentation | 1998

High-Energy Solar Spectroscopic Imager (HESSI) Small Explorer mission for the next (2000) solar maximum

Robert P. Lin; G. J. Hurford; N. W. Madden; Brian R. Dennis; C. J. Crannell; Gordon D. Holman; R. Ramaty; Tycho T. von Rosenvinge; Alex Zehnder; H. Frank van Beek; Patricia Lee Bornmann; Richard C. Canfield; A. Gordon Emslie; Hugh S. Hudson; Arnold O. Benz; John C. Brown; Shinzo Enome; Takeo Kosugi; N. Vilmer; David M. Smith; J. McTiernan; Isabel Hawkins; Said A. Slassi-Sennou; Andre Csillaghy; George H. Fisher; Christopher M. Johns-Krull; Richard A. Schwartz; Larry E. Orwig; Dominic M. Zarro; Ed Schmahl

The primary scientific objective of the High Energy Solar Spectroscopic Imager (HESSI) Small Explorer mission selected by NASA is to investigate the physics of particle acceleration and energy release in solar flares. Observations will be made of x-rays and (gamma) rays from approximately 3 keV to approximately 20 MeV with an unprecedented combination of high resolution imaging and spectroscopy. The HESSI instrument utilizes Fourier- transform imaging with 9 bi-grid rotating modulation collimators and cooled germanium detectors. The instrument is mounted on a Sun-pointed spin-stabilized spacecraft and placed into a 600 km-altitude, 38 degrees inclination orbit.It will provide the first imaging spectroscopy in hard x-rays, with approximately 2 arcsecond angular resolution, time resolution down to tens of ms, and approximately 1 keV energy resolution; the first solar (gamma) ray line spectroscopy with approximately 1-5 keV energy resolution; and the first solar (gamma) -ray line and continuum imaging,with approximately 36-arcsecond angular resolution. HESSI is planned for launch in July 2000, in time to detect the thousands of flares expected during the next solar maximum.


Astronomical Telescopes and Instrumentation | 2003

RHESSI imager and aspect systems

Alex Zehnder; Jacek Bialkowski; F. Burri; Martin D. Fivian; Reinhold Henneck; A. Mchedlishvili; P. Ming; J. Welte; Knud Thomsen; David Clark; Brian R. Dennis; Gordon J. Hurford; D. W. Curtis; Peter R. Harvey; D. Pankow

RHESSI uses nine Rotating Modulation Collimators (RMCs) for imaging, each consisting of a pair of grids mounted on the rotating spacecraft. The angular resolutions range from 2.3 arcsec to 3arcmin. The relative twist between the two grids of each pair is the most critical parameter. It must be less than 20 arcsec for the finest grid. After precision alignment, it is monitored by the Twist Monitoring System (TMS) to a few arcsec. The Sun-pointing must be known better than 0.4 arcsec for the image reconstruction. This is achieved by the Solar Aspect System (SAS), which consists of a set of three Sun sensors. Each sensor is focusing the filtered Sun light onto a linear CCD. The onboard Aspect Data Processor (ADP) selects the 6 limb positions, which over-define the pointing offset of the Sun center in respect to the imaging axis of the imager. The Roll Angle System (RAS) continuously measures the roll angle of RHESSI within arcmin accuracy. The RAS is a continuously operating CCD star scanner. The time of the passage of a star image over the CCD is recorded and defines the roll angle, comparing its pixel position and amplitude with a star map.


SPIE's International Symposium on Optical Science, Engineering, and Instrumentation | 1999

Solar Aspect System (SAS) for the High-Energy Solar Spectroscopic Imager (HESSI)

Reinhold Henneck; Jacek Bialkowski; F. Burri; Martin D. Fivian; Wojtek Hajdas; A. Mchedlishvili; P. Ming; Knud Thomsen; J. Welte; Alex Zehnder; Brian R. Dennis; G. J. Hurford; D. W. Curtis; D. Pankow

The HESSI SAS is a set of three Sun sensors, which shall provide high bandwidth information on the solar pointing of the rotating spacecraft. The precision of <EQ 0.4 arcsec relative is necessary in order to obtain the HESSI imaging resolution of 2 arcsec; the absolute accuracy of 1 arcsec is required for comparison with other measurements. Each SAS is based on focusing the Sun through a narrow bandwidth filter on to a 2048-element x (13(mu) )2 linear CCD. A digital threshold algorithm is used to select N pixels that span each solar limb for inclusion in the telemetry. Determination of the 6 limb crossing locations provided by the 3 subsystems defines the position offset of the Sun in the rotating frame. In this paper we describe the mechanical and electronic configuration of the SAS FM and the results of the first test measurements.


SPIE's 1996 International Symposium on Optical Science, Engineering, and Instrumentation | 1996

Reflection Grating Spectrometer on board XMM

A. C. Brinkman; H. Aarts; Antonius J. den Boggende; T.M.V. Bootsma; Luc Dubbeldam; Jan-Willem den Herder; Jelle S. Kaastra; Piet A. J. de Korte; Boris van Leeuwen; R. Mewe; E.J. van Zwet; Todd A. Decker; Charles J. Hailey; Steven M. Kahn; Frits Paerels; Steven M. Pratuch; Andrew P. A Rasmussen; Graziella Branduardi-Raymont; Phil R. Guttridge; Jay V. Bixler; Knud Thomsen; Alex Zehnder; Christian Erd

The x-ray multi-mirror (XMM) mission is the second of four cornerstone projects of the ESA long-term program for space science, Horizon 2000. The payload comprises three co- aligned high-throughput, imaging telescopes with a FOV of 30 arcmin and spatial resolution less than 20 arcsec. Imaging CCD-detectors (EPIC) are placed in the focus of each telescope. Behind two of the three telescopes, about half the x-ray light is utilized by the reflection grating spectrometer (RGS). The x-ray instruments are co-aligned and measure simultaneously with an optical monitor (OM). The RGS instruments achieve high spectral resolution and high efficiency in the combined first and second order of diffraction in the wavelength range between 5 and 35 angstrom. The design incorporates an array of reflection gratings placed in the converging beam at the exit from the x-ray telescope. The grating stack diffracts the x-rays to an array of dedicated charge-coupled device (CCD) detectors offset from the telescope focal plane. The cooling of the CCDs is provided through a passive radiator. The design and performance of the instrument are described below.


Astronomical Telescopes and Instrumentation | 2000

Description and performance of the reflection grating spectrometer on board of XMM-Newton

Jan-Willem den Herder; Antonius J. den Boggende; Graziella Branduardi-Raymont; A. C. Brinkman; Jean Cottam; Luc Dubbeldam; Christian Erd; Manuel Guedel; Jelle S. Kaastra; Steven M. Kahn; R. Mewe; Frits Paerels; Andrew P. A Rasmussen; Irini Sakelliou; Joshua David Spodek; Knud Thomsen; Cor P. de Vries

The ESA X-ray Multi Mirror mission, XMM-Newton, carries two identical Reflection Grating Spectrometers behind two of its three nested sets of Wolter I type mirrors. The instrument allows high-resolution (E/(Delta) E equals 100 to 500) measurements in the soft X-ray range (6 to 38 A or 2.1 to 0.3 keV) with a maximum effective area of about 150 cm2 at 15 A. The satellite was successfully launched on December 10, 1999, from Guyana Space Center. Following the launch the instrument commissioning was started early in 2000. First results for the Reflection Grating Spectrometers are presented concentrating on instrumental parameters such as resolution, instrument background and CCD performance. The instrument performance is illustrated by first results from HR 1099, a non-eclipsing RS CVn binary.


EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy | 1990

Extreme UV imaging telescope array on the spectrum X-G satellite

Alex Zehnder; Joerg Bialkowski; P. Buehler; E. Morenzoni; N. Schlumpf; W. Schoeps; Knud Thomsen; T. Courvoisier; A. Orr; L. Chesalin; V. Dremin; D. K. Stepanov; Rashid Sunyaev; Oswald H. W. Siegmund; John V. Vallerga; Peter William Vedder; Supriya Chakrabarti; John Kennedy Warren; Giovanni Bonanno; G. A. H. Walker; K. Lund

EUVITA, an array of eight extreme UV imaging telescopes with normal incidence reflection multilayer coated mirrors with central wavelengths of the individual telescopes between 50 and 250 A, is discussed. The scientific objectives of the EUVITA program are summarized and the instrument configuration and sensitivity are described. The detector electrons and command and the data handling system are briefly addressed.


VIII International Scientific Colloquium "Modelling for Materials Processing" | 2017

Modelling of Rotating Permanent Magnet Induced Liquid Metal Stirring

Valters Dzelme; Andris Jakovics; Mārtiņš Sarma; Knud Thomsen

In this work, we investigate numerically liquid metal stirring induced by rotating permanent magnets. We investigate the characteristic velocity dependence on the permanent magnet rotation rate and compare it to data from neutron radiography experiments. In addition to several recognized imperfections in the experimental results, we further improve the numerical model, investigating numerically the impact of using transient instead of timeaveraged force.


Radiochimica Acta | 2013

A comparison between the chemical behaviour of lead-gold and lead-bismuth eutectics towards 316L stainless steel

Stephan Heinitz; D. Schumann; Jörg Neuhausen; S. Köchli; Knud Thomsen; Ernests Platacis; O. Lielausis; Imants Bucenieks; A. Zik; A. Romancuks; Kalvis Kravalis; L. Buligins; A. Türler

Summary Lead-gold eutectic (LGE) has been recently proposed as an alternative target material for high power spallation sources. In order to compare the corrosive properties of LGE to the better-studied eutectic of lead-bismuth (LBE), an isothermal twin-loop made of SS 316L was built and operated at the Institute of Physics of the University of Latvia. We have measured the concentration of steel alloying elements dissolved in both alloys at the end of two test campaigns via ICP-OES. In case of LGE, a pronounced concentration increase of Fe, Ni, Mn and Cr is found in the liquid metal, which is significantly higher compared to LBE. Similar results were obtained during complementary investigations on material samples exposed to both alloys in this twin-loop at 400 ◦C and 450 ◦C. These findings indicate that in contact with LGE, SS 316L steel suffers from substantial chemical attack. Detailed investigations using structure materials other than SS 316L have to be undertaken before qualifying LGE as a serious alternative to LBE.


In: Flanagan, KA and Siegmund, OHW, (eds.) X-RAY AND GAMMA-RAY INSTRUMENTATION FOR ASTRONOMY XI. (pp. 13 - 21). SPIE-INT SOC OPTICAL ENGINEERING (2000) | 2000

In-flight calibration of the XMM-Newton reflection grating spectrometers

Christian Erd; Marc Audard; Antonius J. den Boggende; Graziella Branduardi-Raymont; A. C. Brinkman; Jean Cottam; Luc Dubbeldam; Manuel Guedel; Jan-Willem den Herder; Jelle S. Kaastra; Steven M. Kahn; R. Mewe; Frits Paerels; J. R. Peterson; Andrew P. A Rasmussen; Irini Sakelliou; Joshua David Spodek; Knud Thomsen; Cor de Vries; Alex Zehnder

The activities during the instrument calibrations are summarized and first data are presented. The main instrument features, the line-spread function and the effective area, are discussed and the status of the in-flight calibrations is summarized.

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Alex Zehnder

Paul Scherrer Institute

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Luc Dubbeldam

National Institute for Space Research

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R. Mewe

National Institute for Space Research

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Brian R. Dennis

Goddard Space Flight Center

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G. J. Hurford

University of California

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