scholarly journals The model of the influence of the electron refluxing on the electron transport and Kα emission

2017 ◽  
Vol 35 (3) ◽  
pp. 483-491 ◽  
Author(s):  
J.C. Zhao ◽  
L.H. Cao ◽  
J.H. Zheng ◽  
Z.Q. Zhao ◽  
Z.J. Liu ◽  
...  
Keyword(s):  
Electric Fields ◽  
Critical Thickness ◽  
Energy Conversion Efficiency ◽  
Target Thickness ◽  
Thick Target ◽  
Transport Processes ◽  
Hot Electrons ◽  
Monte Carlo Code ◽  
Photon Yield ◽  
X Ray

AbstractIn our previous research (Zhao et al., 2016), we focus on the transport processes from hot electrons to Kα X-ray emission in a copper foil and nanobrush target when the electron refluxing effect is not taken into account. In this work, considering the refluxing effect, the transport of hot electrons in a solid target is studied by adding the electric fields both at the front and rear surfaces of the target with Monte Carlo code Geant4. Simulation results show that the electron refluxing has an important influence on Kα photon yield and the size of Kα radiation source. Kα yield from the 10-μm-thick target with the electron refluxing effect is 2.7–3.7 times more than that without the refluxing for the electron temperatures from 0.4 to 1.4 MeV. The laser-to-Kα photon energy conversion efficiency ${\rm \eta} _{L \to K_{\rm \alpha}} $ with the refluxing effect is always higher than that without the refluxing, and both of them decrease gradually with laser strength Iλ2. Considering the electron refluxing effect or not, the variations of Kα yield with the target thickness d are very different. A critical thickness of the target dc (~30 μm) is achieved to confirm whether the refluxing effect is valid for the target. For the target with the thickness d less than dc, the refluxing effect can enhance Kα yield with several times, while for the target with the thickness d larger than dc, the refluxing effect is not so effective. The full-width at half-maximum increases from 23 to 56 µm after including the refluxing effect by the electron beam with the radius of 10 µm and the temperature of 400 keV.

scholarly journals Characterization of laser-driven electron and photon beams using the Monte Carlo code FLUKA

2014 ◽  
Vol 32 (2) ◽  
pp. 233-241 ◽  
Author(s):  
F. Fiorini ◽  
D. Neely ◽  
R.J. Clarke ◽  
S. Green
Keyword(s):  
Monte Carlo ◽  
Electron Temperature ◽  
Spectral Characteristics ◽  
Simulation Method ◽  
Target Thickness ◽  
Monte Carlo Code ◽  
X Rays ◽  
Photon Beams ◽  
X Ray ◽  
Plasma Effects

AbstractWe present a new simulation method to predict the maximum possible yield of X-rays produced by electron beams accelerated by petawatt lasers irradiating thick solid targets. The novelty of the method lies in the simulation of the electron refiluxing inside the target implemented with the Monte Carlo code Fluka. The mechanism uses initial theoretical electron spectra, cold targets and refiluxing electrons forced to re-enter the target iteratively. Collective beam plasma effects are not implemented in the simulation. Considering the maximum X-ray yield obtained for a given target thickness and material, the relationship between the irradiated target mass thickness and the initial electron temperature is determined, as well as the effect of the refiluxing on X-ray yield. The presented study helps to understand which electron temperature should be produced in order to generate a particular X-ray beam. Several applications, including medical and security imaging, could benefit from laser generated X-ray beams, so an understanding of the material and the thickness maximizing the yields or producing particular spectral characteristics is necessary. On the other more immediate hand, if this study is experimentally reproduced at the beginning of an experiment in which there is an interest in laser-driven electron and/or photon beams, it can be used to check that the electron temperature is as expected according to the laser parameters.

scholarly journals Acceleration of Runaway Electrons and Joule Heating in Solar Flares

1985 ◽  
Vol 107 ◽  
pp. 191-196
Author(s):  
Gordon D. Holman
Keyword(s):  
Electric Fields ◽  
Joule Heating ◽  
Thermal Plasma ◽  
Solar Flares ◽  
Thick Target ◽  
The Other ◽  
Microwave Emission ◽  
Runaway Electrons ◽  
X Ray ◽  
Flare Model

D.C. electric fields provide the simplest and most direct means of accelerating electrons out of a thermal plasma. Most solar flare models result in the production of D.C. electric fields. On the other hand, microwave and hard X–ray observations of flares provide specific requirements for the number and energy of energetic electrons produced during a flare, and the timescales involved in accelerating them. The microwave emission from flares is understood to be gyrosynchrotron radiation from electrons with energies of 100 keV or greater. The hard X–ray emission (≳ 25 keV) can be interpreted as being either thick–target bremsstrahlung from non–thermal electrons (thin–target radiation may also contribute to the X–ray emission, but the process is less efficient), or thermal bremsstrahlung from hot, impulsively heated plasma. Hence, it is of interest to study the electric field acceleration of “runaway” electrons and the simultaneous Joule heating of the thermal plasma in light of these results from flare observations, without recourse to a specific flare model. Some of the results of such a study are summarized here.

scholarly journals Numerical studies on the ultrashort pulse K-α emission sources based on femtosecond laser–target interactions

2004 ◽  
Vol 22 (2) ◽  
pp. 147-156 ◽  
Author(s):  
J. LIMPOUCH ◽  
O. KLIMO ◽  
V. BÍNA ◽  
S. KAWATA
Keyword(s):  
Electric Fields ◽  
High Efficiency ◽  
Plasma Layer ◽  
Laser Energy ◽  
Short Pulse ◽  
Line Emission ◽  
Target Surface ◽  
Monte Carlo Code ◽  
Laser Target ◽  
X Ray

K-α emission is an intense short-pulse line source well suited for X-ray diagnostic techniques with subpicosecond and micrometer resolution. Numerical simulations are performed here in a search for laser–target interaction regimes where both high efficiency of laser energy transformation to X-ray emission and ultrashort X-ray pulses are achieved. We use the one-dimensional PIC code for the description of the laser interaction with the plasma layer at the target surface. Fast electron transport into the target is treated by our newly developed Monte Carlo code with temporal resolution that is described here in detail. Our simulations reveal extremely short ∼200 fs FWHM bright K-α X-ray pulses emitted from targets heated by 120-fs pulses of a table-top laser. Laser energy conversion efficiency to K-α line emission as high as 6 × 10−5 is noticed. Integration of the emitted energy over the focal spot is carried out to improve the simulation accord with published experimental data. Negligible impact of self-induced electric fields on K-α emission is found for conducting target materials at moderate laser intensities [lsim ]1017 W/cm2.

Connecting solar flare hard X-ray spectra to in-situ electron spectra using RHESSI and STEREO/SEPT observations

2021 ◽  
Author(s):  
Nina Dresing ◽  
Alexander Warmuth ◽  
Frederic Effenberger ◽  
Ludwig Klein ◽  
Lindsay Glesener ◽  
...  
Keyword(s):  
Energetic Electron ◽  
Thick Target ◽  
Transport Processes ◽  
Acceleration Process ◽  
The Sun ◽  
Spectral Indices ◽  
Data Set ◽  
X Ray ◽  
Transport Effects

<p>In-situ observations of solar energetic particle events are determined by a combination of acceleration, injection, and transport processes which are often hard to disentangle. However, the energy spectrum of impulsive electron events is believed to carry the imprint of the flare acceleration process which can be studied by analyzing the hard X-ray (HXR) spectrum of the flare.</p><p>Using STEREO/SEPT electron data of the whole STEREO mission we have identified 64 solar energetic electron event candidates where the HXR solar counterpart of the event was observed by RHESSI. After cleaning of the data set and an independent verification by the timing of associated interplanetary type III radio bursts, we find 17 events which lend themselves for a comparison of the spectral indices observed in situ and at the Sun.</p><p>Special attention is paid to the choice of the in-situ electron spectral index used for comparison as most of the events show spectral transitions (breaks) in the measurement range of SEPT. We find that both the lower and higher spectral indices correlate similarly well with the HXR spectra yielding correlation coefficients of 0.8 but indicating opposite relations with the flare spectrum in terms of the thin- or thick target model. The correlations show no dependence on the electron onset delay, nor on the longitudinal separation between flare and spacecraft magnetic footpoint at the Sun. However, the correlations increase, if only events with significant anisotropy are used indicating that transport effects play a role in shaping the spectra observed in-situ. We will discuss the different transport effects that need to be taken into account and which may even lead to a vanishing imprint of the flare acceleration.</p>

Current Status of Solid-State X-Ray Systems

1985 ◽  
Vol 43 ◽  
pp. 158-161
Author(s):  
Martin Peckerar ◽  
Anastasios Tousimis
Keyword(s):  
Solid State ◽  
Electric Fields ◽  
Spectral Lines ◽  
Current Status ◽  
Mobile Charge ◽  
Electron Hole ◽  
X Ray ◽  
Sensing Systems ◽  
Transmission Electron ◽  
Electron Microscopes

Solid state x-ray sensing systems have been used for many years in conjunction with scanning and transmission electron microscopes. Such systems conveniently provide users with elemental area maps and quantitative chemical analyses of samples. Improvements on these tools are currently sought in the following areas: sensitivity at longer and shorter x-ray wavelengths and minimization of noise-broadening of spectral lines. In this paper, we review basic limitations and recent advances in each of these areas. Throughout the review, we emphasize the systems nature of the problem. That is. limitations exist not only in the sensor elements but also in the preamplifier/amplifier chain and in the interfaces between these components.Solid state x-ray sensors usually function by way of incident photons creating electron-hole pairs in semiconductor material. This radiation-produced mobile charge is swept into external circuitry by electric fields in the semiconductor bulk.

Time-dependent X-ray polarization analysis for anisotropic distribution of hot electrons in ultrahigh intensity laser plasmas

2007 ◽  
Vol 3 (1-2) ◽  
pp. 131-135 ◽  
Author(s):  
T. Kai ◽  
T. Kawamura ◽  
Y. Inubushi ◽  
H. Nishimura ◽  
T. Nakamura ◽  
...  
Keyword(s):  
Time Dependent ◽  
Hot Electrons ◽  
Polarization Analysis ◽  
X Ray ◽  
Laser Plasmas ◽  
Intensity Laser

X‐ray tomography of hot electrons in the barrier region of the tandem mirror GAMMA 10

1990 ◽  
Vol 67 (4) ◽  
pp. 1694-1699 ◽  
Author(s):  
T. Kondoh ◽  
T. Cho ◽  
M. Hirata ◽  
N. Yamaguchi ◽  
T. Saito ◽  
...  
Keyword(s):  
Hot Electrons ◽  
X Ray ◽  
Tandem Mirror ◽  
Barrier Region

A comparison of the thick-target model with stereo data on the height structure of solar hard x-ray bursts

Solar Physics ◽  
1983 ◽  
Vol 88 (1-2) ◽  
Author(s):  
J.C. Brown ◽  
V.A. Carlaw ◽  
D. Cromwell ◽  
S.R. Kane
Keyword(s):  
Thick Target ◽  
X Ray ◽  
Target Model ◽  
Stereo Data

Development of Standard X-Ray Beams for Calibration of Radiobiology Cabinet and Conformal Irradiators

2021 ◽  
Author(s):  
Emily J. King ◽  
Natalie N. Viscariello ◽  
Larry A. DeWerd
Keyword(s):  
Monte Carlo Code ◽  
X Rays ◽  
Energy Agency ◽  
X Ray ◽  
Measurement Models ◽  
Dose Determination ◽  
University Of Wisconsin ◽  
Free Air ◽  
Accurate Dose ◽  
The University

This work seeks to develop standard X-ray beams that are matched to radiobiology X-ray irradiators. The calibration of detectors used for dose determination of these irradiators is performed with a set of standard X rays that are more heavily filtered and/or lower energy, which leads to a higher uncertainty in the dose measurement. Models of the XRad320, SARRP, and the X-ray tube at the University of Wisconsin Medical Radiation Research Center (UWMRRC) were created using the BEAMnrc user code of the EGSnrc Monte Carlo code system. These models were validated against measurements, and the resultant modeled spectra were used to determine the amount of added filtration needed to match the X-ray beams at the UWMRRC to those of the XRad320 and SARRP. The depth profiles and half-value layer (HVL) simulations performed using BEAMnrc agreed to measurements within 3% and 3.6%, respectively. A primary measurement device, a free-air chamber, was developed to measure air kerma in the medium energy range of X rays. The resultant spectra of the matched beams had HVL's that matched the HVL's of the radiobiology irradiators well within the 3% criteria recommended by the International Atomic Energy Agency (IAEA) and the average energies agreed within 2.4%. In conclusion, three standard X-ray beams were developed at the UWMRRC with spectra that more closely match the spectra of the XRad320 and SARRP radiobiology irradiators, which will aid in a more accurate dose determination during calibration of these irradiators.

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