36928210
The nonlinear effects of fringe fields in HLS
The main body of HLS (Hefei Light Source) is an 800 MeV electron storage ring, whose circumference is about 66 m. As a typical small ring, although the sextupole fields for correction of chromaticities are relatively weak, there still exist strong nonlinear fields coming from fringe fields of dipole and quadrupole magnets. In this paper, the effects of fringe fields on chromaticities and tune shifts with amplitude were discussed and calculated for HLS storage ring. Under the low injection energy, the tune shifts with amplitude coming from fringe fields are one of important sources of transverse Landau damping, which is main stabilizing mechanism for HLS ring.
126336869
Low emittance lattice optimization using multiobjective genetic algorithm
Low emittance is a desirable performance for high brightness synchrotron light source and damping ring. The work presented in this paper demonstrates that the lattice of a given electron storage ring, which has fixed circumference and magnet layout, can be optimized to obtain low emittance by using MOGA (Multi-objective Genetic Algorithm). Both dispersion-free and nondispersion-free lattices of HLS (Hefei Light Source) upgrade project are computed as an illustration. Simulation result shows that this method is fast and straightforward. INTRODUCTION Presently, there are many codes for storage ring lattice design, such as MAD, OPA, ELEGANT, etc. The critical problem of designing lattice by these codes is that they will consume the designers lots of time to adjust it repeatedly. Though the designers could get a satisfactory structure, but they couldn’t judge whether the ultimate performance is reached. MOGA is a highly effective randomly searching algorithm, which can globally search a set of solutions over a domain. These solutions are superior to the rest of solutions when considering all of the objectives, which are called Pareto-optimal solutions. This algorithm was introduced into damping ring [1] and storage ring lattice [2] optimization in recent years. It overcomes the above difficulties of the existing codes and converges to a set of Pareto optimal solutions. Also this algorithm settles the high computational complexity. In this paper we will use a nondominated sorting-based multi-objective evolutionary algorithm (NSGA-II) [3] to optimize linear optics of low emittance lattice. NSGA-II AND CONSTRAINT HANDLING APPROACH The Non-dominated Sorting Genetic Algorithm (NSGA) was proposed by Srinivas and Deb in 1994. Later the upgraded algorithm NSGA-II was developed. It overcomes the following difficulties of NSGA: high computational complexity, non-elitist and the need for specifying sharing parameters. The optimization steps of this algorithm are listed as below: First of all, rank and crowding distance of the initial population will be computed. And then sort these individuals based on their non domination. Generate a child population from the initial population, and keep the Pareto optimal solutions .
54892783
APPLICATION OF PCS IN NSRL CONTROL SYSTEM
The upgrade of the National Synchrotron Radiation Laboratory (NSRL) control system is currently being implemented using EPICS (Experimental Physics and Industrial Control System). For cost saving purposes, we use a large number of PCs. PCs play a dominant role as I/O controllers (IOCs) and device controllers in the new control system. In this paper, the application of PCs in the NSRL control system is described.
119213503
Radiation field simulation of C-ADS Injector II
The injector of C-ADS (Chinese Accelerator Driven Sub-critical System) project is a high current, fully super-conducting proton accelerator. Meanwhile, a BLM system is indispensable to this facility, especially in low energy segments. This paper presents some basic simulations for 10MeV proton by Monte Carlo program FLUKA, as well as the distributions on different secondary particles in three aspects: angular, energy spectrum and current. These results are beneficial to selecting the detector type and its location and determining its dynamic range matching different requirements for both fast and slow beam loss. Further, the major impact of the background is analyzed, such as superconducting cavity X radiation and radiation caused by material activation, in this paper as well. This work is meaningful in BLM system research.
119610396
Simultaneous optimization of beam emittance and dynamic aperture for electron storage ring using genetic algorithm
Finding a high quality of lattice that simultaneously meets low beam emittance performance and acceptable dynamic aperture is a challenging task for the storage ring-based light source, especially for the next generation storage ring which is characterized with ultralow beam emittance. This paper presents an alternative method, based on the concept of genetic algorithm, to simultaneously optimize the beam emittance and dynamic aperture for low emittance lattice. Instead of analyzing the nonlinear indicators extracted from the high order nonlinear map, the algorithm can globally optimize the nonlinear performance by the direct dynamic aperture tracking result. So this method is more straightforward and efficient than analyzing the nonlinear driving terms. In order to illustrate this method, the quadrupole and sextupole strengths of a five-bend-achromatic lattice are simultaneously optimized by nondominated sorting genetic algorithm II (NSGA-II). Finally, the optimal linear optics for ultralow emittance lattices with better dynamic aperture are obtained. The result shows that the algorithm is particularly useful for the low emittance lattice design, where the beam emittance and the dynamic aperture always conflict with each other.
118464345
Induced radioactivity analysis for the NSRL Linac in China using Monte Carlo simulations and gamma-spectroscopy
The 200-MeV electron linac of the National Synchrotron Radiation Laboratory (NSRL) located in Hefei is one of the earliest high-energy electron linear accelerators in China. The electrons are accelerated to 200 MeV by five acceleration tubes and are collimated by scrapers. The scraper aperture is smaller than the acceleration tube one, so some electrons hit the materials when passing through them. These lost electrons cause induced radioactivity mainly due to bremsstrahlung and photonuclear reaction. This paper describes a study of induced radioactivity for the NSRL Linac using FLUKA simulations and gamma-spectroscopy. The measurements showed that electrons were lost mainly at the scraper. So the induced radioactivity of the NSRL Linac is mainly produced here. The radionuclide types were simulated using the FLUKA Monte Carlo code and the results were compared against measurements made with a High Purity Germanium (HPGe) gamma spectrometer. The NSRL linac had been retired because of upgrading last year. The removed components were used to study induced radioactivity. The radionuclides confirmed by the measurement are: $^{57}$Ni, $^{52}$Mn, $^{51}$Cr, $^{58}$Co, $^{56}$Co, $^{57}$Co, $^{54}$Mn, $^{60}$Co and $^{22}$Na, the first eight nuclides of which are predicted by FLUKA simulation. The research will provide the theoretical basis for the similar accelerator decommissioning plan, and is significant for accelerator structure design, material selection and radiation protection design.
16622579
IMPROVED STANDARDIZATION OF TYPE II-P SUPERNOVAE: APPLICATION TO AN EXPANDED SAMPLE
In the epoch of precise and accurate cosmology, cross-confirmation using a variety of cosmographic methods is paramount to circumvent systematic uncertainties. Owing to progenitor histories and explosion physics differing from those of Type Ia supernovae (SNe Ia), Type II-plateau supernovae (SNe II-P) are unlikely to be affected by evolution in the same way. Based on a new analysis of 17 SNe II-P, and on an improved methodology, we find that SNe II-P are good standardizable candles, almost comparable to SNe Ia. We derive a tight Hubble diagram with a dispersion of 10% in distance, using the simple correlation between luminosity and photospheric velocity introduced by Hamuy and Pinto. We show that the descendent method of Nugent et al. can be further simplified and that the correction for dust extinction has low statistical impact. We find that our SN sample favors, on average, a very steep dust law with total to selective extinction RV < 2. Such an extinction law has been recently inferred for many SNe Ia. Our results indicate that a distance measurement can be obtained with a single spectrum of a SN II-P during the plateau phase combined with sparse photometric measurements.
119183379
Fourteen months of observations of the possible super-Chandrasekhar mass Type Ia Supernova 2009dc
In this paper, we present and analyse optical photometry and spectra of the extremely luminous and slowly evolving Type Ia supernova (SN Ia) 2009dc, and offer evidence that it is a super-Chandrasekhar mass (SC) SN Ia and thus has a SC white dwarf (WD) progenitor. Optical spectra of SN 2007if, a similar object, are also shown. SN 2009dc had one of the most slowly evolving light curves ever observed for a SN Ia, with a rise time of ~23 d and Δm 15 (B) = 0.72 mag. We calculate a lower limit to the peak bolometric luminosity of ~2.4 x 10 43 erg s -1 , though the actual value is likely almost 40 per cent larger. Optical spectra of SN 2009dc and SN 2007if obtained near maximum brightness exhibit strong C II features (indicative of a significant amount of unburned material), and the post-maximum spectra are dominated by iron-group elements (IGEs). All of our spectra of SN 2009dc and SN 2007if also show low expansion velocities. However, we see no strong evidence in SN 2009dc for a velocity 'plateau' near maximum light like the one seen in SN 2007if. The high luminosity and low expansion velocities of SN 2009dc lead us to derive a possible WD progenitor mass of more than 2 M ⊙ and a 56 Ni mass of about 1.4-1.7 M ⊙ . We propose that the host galaxy of SN 2009dc underwent a gravitational interaction with a neighbouring galaxy in the relatively recent past. This may have led to a sudden burst of star formation which could have produced the SC WD progenitor of SN 2009dc and likely turned the neighbouring galaxy into a 'post-starburst galaxy'. No published model seems to match the extreme values observed in SN 2009dc, but simulations do show that such massive progenitors can exist (likely as a result of the merger of two WDs) and can possibly explode as SC SNe Ia.
14733840
Monte Carlo Simulations of Type Ia Supernova Observations in Supernova Surveys
We have performed Monte Carlo simulations of Type Ia supernova (SN Ia) surveys to quantify their efficiency in discovering peculiar overluminous and underluminous SNe Ia. We determined how the type of survey (magnitude-limited, distance-limited, or a hybrid) and its characteristics (observation frequency and detection limit) affect the discovery of peculiar SNe Ia. We find that there are strong biases against the discovery of peculiar SNe Ia introduced by at least four observational effects: the Malmquist bias, the age of the SN Ia at the time of its discovery, the shape of its light curve, and its degree of extinction. Surveys with low observation frequency (less than once per 10 days) tend to discover SNe Ia that are too old for observers to easily recognize their peculiarity. Subluminous SNe Ia are underrepresented in magnitude-limited surveys because they can only be found within a small volume and they remain above the detection limit for less time. Conversely, overluminous SNe Ia are more easily found in magnitude-limited surveys, although their likely association with dusty regions reduces the volume in which they can be discovered. The unbiased rate of peculiar SNe Ia can be recovered only in distance-limited surveys with high observation frequencies and with detection limits that are fainter than the peak magnitude of a subluminous SN Ia in the farthest potential host.
612176
System size dependence of two-particle angular correlations in p+p, Cu+Cu and Au+Au collisions
We present a systematic study of two-particle angular correlations in p+p, Cu+Cu and Au+Au collisions over a broad range of pseudorapidity and azimuthal angle. The PHOBOS detector has a uniquely large angular coverage for inclusive charged particles, which allows for the study of correlations on both long- and short-range scales. A complex two-dimensional correlation structure emerges which is interpreted in the context of a cluster model. The cluster size and its decay width are extracted from the two-particle pseudorapidity correlation function. The cluster size found in semi-central Cu+Cu and Au+Au collisions is comparable to that found in p+p but a non-trivial increase of cluster size with decreasing centrality is observed. Moreover, the comparison between Cu+Cu and Au+Au systems shows an interesting scaling of the cluster size with the measured fraction of total cross section (which is related to b/2R), suggesting a geometric origin. These results should provide insight into the hadronization stage of the hot and dense medium created in heavy ion collisions.
53121461
Quantum decoherence with holography
A bstractQuantum decoherence is the loss of a system’s purity due to its interaction with the surrounding environment. Via the AdS/CFT correspondence, we study how a system decoheres when its environment is a strongly-coupled theory. In the FeynmanVernon formalism, we compute the influence functional holographically by relating it to the generating function of Schwinger-Keldysh propagators and thereby obtain the dynamics of the system’s density matrix.We present two exactly solvable examples: (1) a straight string in a BTZ black hole and (2) a scalar probe in AdS5. We prepare an initial state that mimics Schrödinger’s cat and identify different stages of its decoherence process using the time-scaling behaviors of Rényi entropy. We also relate decoherence to local quantum quenches, and by comparing the time evolution behaviors of the Wigner function and Rényi entropy we demonstrate that the relaxation of local quantum excitations leads to the collapse of its wave-function.