Polarization Dependence of the Integrated Bremsstrahlung Cross Section

Gluckstern, R.L.; Hull, M.H.

doi:10.1103/physrev.90.1030

Cited by 167 publications

(76 citation statements)

References 8 publications

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“…III, the bremsstrahlung cross section becomes increasingly peaked in the direction of the velocity of the emitting electron as the energy of the electron increases [13]. Thus, high.energy bremsstrahlung emission in a given direction, relative to a fixed direction (the magnetic axis), tends to be due primarily to electrons whose velocity is also in the given emission direction.…”

Section: Angular X-ray Measurementsmentioning

confidence: 94%

High energy X-ray measurements during lower hybrid current drive on the Alcator C tokamak

et al. 1986

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High energy x-ray emission (E, > 20 keV) from superthermal plasma electrons during lower hybrid current drive on the Alcator C tokamak has been measured using Sodium Iodide (NaI) scintillation spectroscopy. The x-ray spectra are generally linear on a semi-log plot of count rate vs. photon energy and extend out to several hundred keV. For the range of densities (ft, , 0.3-0.8 x 10" cm-3 ) over which current drive was performed on Alcator, there was negligible emission before the injection of radiofrequency (rf) wave power. The radial profiles of the emission were also measured and indicate that the current carrying, high energy electrons exist primarily within the inner half (r/a < 1/2) of the plasma column. Plasma parameter scans produced variations in the x-ray emission profiles that are consistent with changes in the launched Fourier power spectrum, and the conditions imposed by lower hybrid wave accessibility. In addition, the velocity space distribution function of the energetic tail electrons has been determined using the angular variation in the x-ray emission.

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Section: Angular X-ray Measurementsmentioning

confidence: 94%

High energy X-ray measurements during lower hybrid current drive on the Alcator C tokamak

et al. 1986

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“…The bremsstrahlung cross-sections are taken in the relativistic form (see Gluckstern & Hull 1953). Figure 15a shows the time profile of hard X-ray intensity produced by an impulse of length δt e = 1.7 ms.…”

Section: Bursts Of Hard X-ray Emissionmentioning

confidence: 99%

Stationary and impulsive injection of electron beams in converging magnetic field

Siversky¹,

Zharkova²

2009

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Aims. We study time-dependent precipitation of an electron beam injected into a flaring atmosphere with a converging magnetic field by considering collisional and Ohmic losses with anisotropic scattering and pitch angle diffusion. Two injection regimes are investigated: short impulse and stationary injection. The effects of converging magnetic fields with different spatial profiles are compared and the energy deposition produced by the precipitating electrons at different depths and regimes is calculated. Methods. The time dependent Fokker-Planck equation for electron distribution in depth, energy and pitch angle was solved numerically by using the summary approximation method. Results. Steady state injection was found to be established for beam electrons 0.07-0.2 s after the injection onset depending on the initial beam parameters. Energy deposition by a stationary beam is strongly dependent on a self-induced electric field but more weakly dependent on a magnetic field convergence. Energy depositions by short electron impulses are found to be insensitive to the self-induced electric field but are strongly affected by magnetic convergence. Short beam impulses are shown to produce sharp asymmetric hard X-ray bursts on a timescale of the order of tens of milliseconds, often observed in solar flares.

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“…The Q factor and the associated error bars for polarization levels that differ only by 2% is practically indistinguishable, as the polarization region between 88% and 90% illustrates. Both detectors show an excellent potential to distinguish between polarization degrees different by less than 5%, which is an acceptable performance for studying the different physical processes that generate polarized emissions levels (e.g astrophysical synchrotron about 65% to 80%, magnetic photon splitting: about 20% to 30%, Bremsstrahlung radiation up to 80% (Gluckstern and Hull 1953, Baring et al 1995, Skibo et al 1994, Lei et al 1997). …”

Section: Full Experimental Results and Polarimetric Response And Senmentioning

confidence: 99%

Hard X-ray polarimetry with Caliste, a high performance CdTe based imaging spectrometer

et al. 2015

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Since the initial exploration of the X-and soft γ-ray sky in the 60's, high-energy celestial sources have been mainly characterized through imaging, spectroscopy and timing analysis. Despite tremendous progress in the field, the radiation mechanisms at work in sources such as neutrons stars, black holes, and Active Galactic Nuclei are still unclear. The polarization state of the radiation is an observational parameter which brings key additional information about the physical processes in these high energy sources, allowing the discrimination between competing models which may otherwise all be consistent with other types of measurement. This is why most of the projects for the next generation of space missions covering the few tens of keV to the MeV region require a polarization measurement capability. A key element enabling this capability, in this energy range, is a detector system allowing the identification and characterization of Compton interactions as they are the main process at play. The compact hard X-ray imaging spectrometer module, developed in CEA with the generic name of "Caliste" module, is such a detector.In this paper, we present experimental results for two types of Caliste-256 modules, one based on a CdTe crystal, the other one on a CdZnTe crystal, which have been exposed to linearly polarized beams at the European Synchrotron Radiation Facility (ESRF). These results, obtained at 200 and 300 keV, demonstrate the capability of these modules to detect Compton events and to give an accurate determination of the polarization parameters (polarization angle and fraction) of the incoming beam. For example, applying an optimized selection to our data set, equivalent to select 90 degrees Compton scattered interactions in the detector plane, we find a modulation factor Q of 0.78 ± 0.06 in the 200 -300 keV range. The polarization angle and fraction are derived with accuracies of approximately 1° and 5 % respectively for both CdZnTe and CdTe crystals. The modulation factor remains larger than 0.4 when essentially no selection is made at all on the data.We also present in this paper a simple analytical model of the interactions for the detector geometry. We show that the experimental data compare very well with the simulation, and that simple geometrical effects explain some of the observed deviations between the data and the simulation.All of these results, both experimental and from simulations, prove that the Caliste-256 modules have performances allowing them to be excellent candidates as detectors with polarimetric capabilities, in particular for future space missions.

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Polarization Dependence of the Integrated Bremsstrahlung Cross Section

Cited by 167 publications

References 8 publications

High energy X-ray measurements during lower hybrid current drive on the Alcator C tokamak

High energy X-ray measurements during lower hybrid current drive on the Alcator C tokamak

Stationary and impulsive injection of electron beams in converging magnetic field

Hard X-ray polarimetry with Caliste, a high performance CdTe based imaging spectrometer

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