Physics beyond the Standard Model predicts the possible existence of new particles that can be searched at the low energy frontier in the sub-eV range. The OSQAR photon regeneration experiment looks ...for "Light Shining through a Wall" from the quantum oscillation of optical photons into "Weakly Interacting Sub-eV Particles", such as axion or Axion-Like Particles (ALPs), in a 9 T transverse magnetic field over the unprecedented length of 2 × 14.3 m. In 2014, this experiment has been run with an outstanding sensitivity, using an 18.5 W continuous wave laser emitting in the green at the single wavelength of 532 nm. No regenerated photons have been detected after the wall, pushing the limits for the existence of axions and ALPs down to an unprecedented level for such a type of laboratory experiment. The di-photon couplings of possible pseudoscalar and scalar ALPs can be constrained in the nearly massless limit to be less than 3.5·10 −8 GeV −1 and 3.2·10 −8 GeV −1 , respectively, at 95% Confidence Level.
OSQAR chameleon afterglow search experiment Sulc, M.; Pugnat, P.; Ballou, R. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2019, Letnik:
936
Journal Article
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OSQAR experiment has been extended to the quest of chameleon particles with environment-dependent mass from the search of a magnetic afterglow effect. OSQAR-CHASE (chameleon afterglow search) has ...been run in 2017 using one spare LHC dipole providing a 9 T transverse magnetic field with an 18.5 W laser and state-of-the art CCD detector. Experimental results with and without magnetic field were preliminary analyzed and no clear evidence for a photon-coupled chameleons was confirmed. The very weak false signals was observed with decay time 4300 s. It can be explained by decrease of dark current from initial higher values during CCD cooling in detection phase. Increasing of the sensitivity of the OSQAR-CHASE experiment over the previous GammeV reference experiment assumes that the present coupling constant limit can be reduced around factor of 4.
•OSQAR laser experiment at CERN has been extended to the quest of chameleon particles.•The 18 W laser was shining through a 9 T magnetic field of spare LHC dipole.•The very weak 4.3 Hz false signals was observed after laser switch-off.•There was no difference in afterglow optical signal with and without magnetic field.•The present chameleon–photon coupling constant limit can be reduced by factor of 4.
Recent theoretical and experimental studies highlight the possibility of new fundamental particle physics beyond the Standard Model that can be probed by sub-eV energy experiments. The OSQAR photon ...regeneration experiment looks for “Light Shining through a Wall” from the quantum oscillation of optical photons into “Weakly Interacting Sub-eV Particles”, like axion or axion-like particles (ALPs), in a 9 T transverse magnetic field over the unprecedented length of
2
×
14.3
m. No excess of events has been detected over the background. The di-photon couplings of possible new light scalar and pseudo-scalar particles can be constrained in the massless limit to be less than
8.0
×
10
-
8
GeV
-
1
. These results are very close to the most stringent laboratory constraints obtained for the coupling of ALPs to two photons. Plans for further improving the sensitivity of the OSQAR experiment are presented.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A new method of the quench detection systems (QDS) designed for the LHC 600 A corrector magnet circuits and 6 kA individual powered quadrupole (IPQ) magnet circuits is presented. In order to improve ...the dependability of QDS, a direct measurement of the current derivative is proposed. The quench detection scheme for the 600 A corrector magnet circuits uses the current derivative numerically evaluated from a direct current measurement. In order to make the calculation stable, the current derivative is heavily filtered, thus introducing a significant phase shift, which restricts the operational range of circuit parameters such as the acceleration. For the 6-kA IPQ magnet circuits the main quench detection is based on a classical bridge configuration. The introduction of an additional detection channel for the direct measurement of the current derivative helps to overcome the lack of sensitivity to fully aperture symmetric quenches of the bridge configuration. Transformer-based current derivative sensors are currently under development, using cut cores for easy prototyping, performance control, and installation. Prototypes for the ±600 A current range and ramp rates between 0.1 and 5 A/s were built using different core materials (electrical steel and nanocrystalline cores) and pickup coils with 10 000 and 20 000 windings. In order to characterize the prototypes, the performance was defined in terms of mean sensitivity of the sensor response in V/A/s and the performance quality factor (PQF), defined as a percentage of nonlinearity of the response. An optimization procedure was implemented for finding the best configuration of the sensors, i.e., the air gap in the cut core in order to maximize the mean sensitivity and to minimize the PQF. The tests were carried out at different working points (current ranges and ramp rates) showing promising results (PQF <;0.5% with a sensitivity of 5.5 mV/A/s).
Micrometer-sized dust particles present in the Large Hadron Collider (LHC) beam pipe are believed to have caused many thousands of sporadic beam loss events around the LHC. These so-called ...unidentified falling objects (UFOs) have been under continuous study since the start of high intensity beam operation in the LHC due to their impact on the LHC availability: 139 beam dumps and 12 magnet quenches during Run II (2015–2018) alone. To mitigate the impact of UFOs on future accelerators such as the High Luminosity LHC and the Future Circular Collider, it is fundamental to foster a better understanding of these beam loss events. In this paper, key observations made since the start of LHC operation are summarized and the prevailing UFO hypothesis is confronted by a compilation of observations acquired during Run II. In particular, it is shown that UFOs must carry an initial negative charge before entering the proton beam, or that they are by some other means accelerated toward the beam not only by gravity. A simulation model for the dynamics of the dust particles and their interaction with the beam was developed over the years. This model is improved and validated by measurements. It is however also shown that a subset of observed beam losses, which contain a positive time profile skewness, cannot be explained by it.
The superconducting magnets used in high energy particle accelerators such as CERN's LHC can be impacted by the circulating beam in case of specific failures. This leads to interaction of the beam ...particles with the magnet components, like the superconducting coils, through direct beam impact or via secondary particle showers. The interaction causes energy deposition in the timescale of microseconds and induces large thermal gradients within the superconductors, which are in the order of 100 K/mm. To investigate the effect on the superconductors, an experiment at CERN's HiRadMat facility was designed and executed, exposing short samples of Nb-Ti and Nb3Sn strands in a cryogenic environment to microsecond 440 GeV proton beams. The irradiated samples were extracted and analyzed for their critical transport current Ic. This paper describes the results and analysis of the measurements of Ic as well as thermo-mechanical simulations of the Nb3Sn strands to evaluate the degradation of Ic as a function of the mechanical strain present during and after the beam impact.
Standard Model extensions often predict low‐mass and very weakly interacting particles, such as the axion. A number of small‐scale experiments at the intensity/precision frontier are actively ...searching for these elusive particles, complementing searches for physics beyond the Standard Model at colliders. Whilst a next generation of experiments will give access to a huge unexplored parameter space, a discovery would have a tremendous impact on our understanding of fundamental physics.
Production, assembling and operation of the superconducting (SC) accelerator magnets are substantially different than that of conventional accelerators. A properly designed set of actions addressing ...the electrical integrity at all stages of SC magnet lifecycle i.e. its design, testing, installation and operation are expected to shorten the commissioning phase and to extend the lifetime of the accelerator, also reducing the time for interventions during operation of magnet circuits. A coherent approach to the integrity of electrical circuits is crucial for their lifetime and safe operation. The coherent Electrical Quality Assurance (ELQA) strategy shall span the design, production, testing and operation of the accelerator. The lack of such strategy can cause the investigation and mitigation of electrical faults during final testing of magnet circuits and operation very difficult and ineffective as at this point the possibilities are significantly reduced as compared to the potential of earlier phases. This paper aims to present the main elements of the ELQA from the perspective of the electrical engineering. Presented strategy is based on several years of experience with testing of SC magnets. In the authors' opinion, the implementation of the proposed strategy at the early stage of a project is decisive to protect against and effectively cope with the electrical problems in complex systems like SC accelerator magnet circuits.
During 2016, one-quarter of the LHC main dipoles have has been powered above the 7.7 T operational field, to reach a field of 8.1 T. These tests were done to confirm the extrapolation of the training ...behavior based on a Gaussian tail of the quench distribution. In this paper, it is shown that a modified Gaussian distribution can be used to better model the quench distributions. We then present the data above 6.5 TeV, showing that they are compatible with the previous expectations. We present the data of retraining of sector 12, which was warmed up in 2016 to replace a magnet, and training of individual magnets that went through several thermal cycles: there is an indication that training campaigns during successive warm-ups and cool-downs could become shorter. We finally show that a significant correlation is found between the training of the installed magnet and individual test after a thermal cycle (second cool-down). On the other hand, no correlation is found with individual test under virgin conditions (first cool-down).
The Large Hadron Collider (LHC) contains eight main dipole circuits, each of them with 154 dipole magnets powered in series. These 15-m-long magnets are wound from Nb-Ti superconducting Rutherford ...cables, and have active quench detection triggering heaters to quickly force the transition of the coil to the normal conducting state in case of a quench, and hence reduce the hot spot temperature. During the reception tests in 2002-2007, all these magnets have been trained up to at least 12 kA, corresponding to a beam energy of 7.1 TeV. After installation in the accelerator, the circuits have been operated at reduced currents of up to 6.8 kA, from 2010 to 2013, corresponding to a beam energy of 4 TeV. After the first long shutdown of 2013-2014, the LHC runs at 6.5 TeV, requiring a dipole magnet current of 11.0 kA. A significant number of training quenches were needed to bring the 1232 magnets up to this current. In this paper, the circuit behavior in case of a quench is presented, as well as the quench training as compared to the initial training during the reception tests of the individual magnets.
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