Conceptual design report for the LUXE experiment Abramowicz, H.; Acosta, U.; Altarelli, M. ...
The European physical journal. ST, Special topics,
2021, Letnik:
230, Številka:
11
Journal Article
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This Conceptual Design Report describes LUXE (Laser Und XFEL Experiment), an experimental campaign that aims to combine the high-quality and high-energy electron beam of the European XFEL with a ...powerful laser to explore the uncharted terrain of quantum electrodynamics characterised by both high energy and high intensity. We will reach this hitherto inaccessible regime of quantum physics by analysing high-energy electron-photon and photon-photon interactions in the extreme environment provided by an intense laser focus. The physics background and its relevance are presented in the science case which in turn leads to, and justifies, the ensuing plan for all aspects of the experiment: Our choice of experimental parameters allows (i) field strengths to be probed where the coupling to charges becomes non-perturbative and (ii) a precision to be achieved that permits a detailed comparison of the measured data with calculations. In addition, the high photon flux predicted will enable a sensitive search for new physics beyond the Standard Model. The initial phase of the experiment will employ an existing 40 TW laser, whereas the second phase will utilise an upgraded laser power of 350 TW. All expectations regarding the performance of the experimental set-up as well as the expected physics results are based on detailed numerical simulations throughout.
Purpose
Local specific absorption rate (SAR) cannot be measured and is usually evaluated by offline numerical simulations using generic body models that of course will differ from the patient's ...anatomy. An additional safety margin is needed to include this intersubject variability. In this work, we present a deep learning–based method for image‐based subject‐specific local SAR assessment. We propose to train a convolutional neural network to learn a “surrogate SAR model” to map the relation between subject‐specific B1+ maps and the corresponding local SAR.
Method
Our database of 23 subject‐specific models with an 8–transmit channel body array for prostate imaging at 7 T was used to build 5750 training samples. These synthetic complex B1+ maps and local SAR distributions were used to train a conditional generative adversarial network. Extra penalization for local SAR underestimation errors was included in the loss function. In silico and in vivo validation were performed.
Results
In silico cross‐validation shows a good qualitative and quantitative match between predicted and ground‐truth local SAR distributions. The peak local SAR estimation error distribution shows a mean overestimation error of 15% with 13% probability of underestimation. The higher accuracy of the proposed method allows the use of less conservative safety factors compared with standard procedures. In vivo validation shows that the method is applicable with realistic measurement data with impressively good qualitative and quantitative agreement to simulations.
Conclusion
The proposed deep learning method allows online image‐based subject‐specific local SAR assessment. It greatly reduces the uncertainty in current state‐of‐the‐art SAR assessment methods, reducing the time in the examination protocol by almost 25%.
The LUCID-2 detector Sbrizzi, A.
EPJ Web of Conferences,
01/2018, Letnik:
182
Journal Article, Conference Proceeding
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The LUCID-2 detector is the main online and ofline luminosity monitor of the ATLAS experiment. It is a compact Cherenkov detector made of photomultipliers with a 10 mm diameter quartz window acting ...as the Cherenkov medium. In order to provide a reliable luminosity measurement during years of data-taking, the LUCID-2 detector can use 104 different luminosity algorithms for each of the LHC colliding bunches. The detector stability is kept at a percent level thanks to an innovative monitoring system based on radioactive Bi-207 sources deposited on the photomultipliers quartz window. Combining the LUCID-2 measurement with those of other four ATLAS subdetectors, the luminosity has been estimated with a total uncertainty of 2.1% in 2015 and 2.2% in 2016.
The FAMU experiment aims to measure for the first time the hyperfine splitting of the muonic hydrogen ground state. From this measurement the proton Zemach radius can be derived and this will shed ...light on the determination of the proton charge radius. In this paper, we describe the scientific goal, the method and the detailed preparatory work. This includes the outcome of preliminary measurements, subsequent refined simulations and the evaluation of the expected results. The experimental setup being built for the measurement of the hyperfine splitting to be performed at the RAL laboratory muon facility is also described.
Purpose:
The high precession frequency in ultrahigh field MRI coincides with reduced RF penetration, increased RF power deposition and consequently can lead to reduced scan efficiency. However, the ...shorter wavelength enables the use of efficient antennas rather than loop coils. In fact, ultrathin monopole antennas have been demonstrated at 7 T, which fit in natural cavities like the rectum in the human body. As the RF field generated by the antenna provides an extremely nonuniform B
1 field, the use of conventional RF pulses will lead to severe image distortions and highly nonuniform contrast. However, using the two predominant dimensions (orthogonal to the antenna), 2D RF pulses can be designed that counteract the nonuniform B
1 into uniform flip angles. In this study the authors investigate the use of an ultrathin antenna not only for reception, but also for transmission in 7 T MRI of the rectum.
Methods:
The 2D radially compensating excitation (2D RACE) pulse was designed in matlab. SAR calculations between the 2D RACE pulse and an adiabatic RF pulse (BIR-4) have been obtained, to visualize the gain in decreasing the SAR when using the 2D RACE pulse instead of an adiabatic RF pulse. The authors used the 7 T whole body MR system in combination with an internally placed monopole antenna used for transceiving and obtained 3D gradient echo images with a conventional sinc pulse and with the 2D RACE pulse. For extra clarity, they also reconstructed an image where the receive field of the antenna was removed.
Results:
Comparing the results of the SAR simulations of the 2D RACE pulse with a BIR-4 pulse shows that for low flip angles (θ < 41°) the SAR can be decreased with a factor of 4.8 or even more, when using the 2D RACE pulse. Relative to a conventional sinc excitation, the 2D RACE pulse achieves more uniform flip angle distributions than a BIR-4 pulse with a smaller SAR increase (16 × versus 64 ×).
Conclusions:
The authors have shown that the 2D RACE pulse provides more homogeneous flip angles for gradient echo sequences when compared to a conventional sinc pulse albeit at increased SAR. However, when compared to adiabatic RF pulses, as shown by simulations, the SAR of the 2D RACE pulse can be an order of magnitude less. Phantom and in vivo human rectum images are obtained to demonstrate that the 2D RACE pulse can provide a uniform excitation while transmitting with a single ultrathin endorectal antenna at 7 T. The combination of thin rectal antennas with efficient uniform transmit can open up new possibilities in high resolution imaging of rectal cancer.
The XAFS beamline at Elettra Synchrotron in Trieste combines X-ray absorption spectroscopy and X-ray diffraction to provide chemically specific structural information of materials. It operates in the ...energy range 2.4-27 keV by using a silicon double reflection Bragg monochromator. The fluorescence measurement is performed in place of the absorption spectroscopy when the sample transparency is too low for transmission measurements or the element to study is too diluted in the sample. We report on the development and on the preliminary tests of a new prototype detector based on Silicon Drift Detectors technology and the SIRIO ultra low noise front-end ASIC. The new system will be able to reduce drastically the time needed to perform fluorescence measurements, while keeping a short dead time and maintaining an adequate energy resolution to perform spectroscopy. The custom-made silicon sensor and the electronics are designed specifically for the beamline requirements.
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