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 .
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.
2014815
An upgrade proposal of injection bump system for HLS
The current injection bump system in HLS storage ring, which is designed 8 years ago, has been operated 5 years up to the present with acceptable performance. Due to inherent limitation of HLS (Hefei Light Source) storage ring, there are some deficiencies of the design. For the potential of full energy injection, reasonable design objective was summed up. Then, physical design of new bump system was brought forward. Using simple formula, the acceptance to injected beam and perturbation on stored beam were estimated approximately. Finally, the ELEGANT software was used to simulate the injection process with new designed bump system. The simulation results showed that, the injection efficiency would be higher than 90% and perturbation on stored beam would be small enough, which are very essential to full energy injection and top-up operation of HLS.
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.
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.
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.
119207377
Temporal Correlations Between Optical and Gamma-ray Activity in Blazars
We have been using the 0.76-m Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory to optically monitor a sample of 157 blazars that are bright in gamma rays, being detected with high significance (≥10σ) in one year by the Large Area Telescope (LAT) on the {\it Fermi Gamma-ray Space Telescope}. We attempt to observe each source on a 3-day cadence with KAIT, subject to weather and seasonal visibility. The gamma-ray coverage is essentially continuous. KAIT observations extend over much of the 5-year {\it Fermi} mission for several objects, and most have >100 optical measurements spanning the last three years. These blazars (flat-spectrum radio quasars and BL~Lac objects) exhibit a wide range of flaring behavior. Using the discrete correlation function (DCF), here we search for temporal relationships between optical and gamma-ray light curves in the 40 brightest sources in hopes of placing constraints on blazar acceleration and emission zones. We find strong optical--gamma-ray correlation in many of these sources at time delays of ∼1 to ∼10 days, ranging between −40 and +30 days. A stacked average DCF of the 40 sources verifies this correlation trend, with a peak above 99% significance indicating a characteristic time delay consistent with 0 days. These findings strongly support the widely accepted leptonic models of blazar emission. However, we also find examples of apparently uncorrelated flares (optical flares with no gamma-ray counterpart and gamma-ray flares with no optical counterpart) that challenge simple, one-zone models of blazar emission. Moreover, we find that flat-spectrum radio quasars tend to have gamma rays leading the optical, while intermediate and high synchrotron peak blazars with the most significant peaks have smaller lags/leads.
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.
118455588
The lick AGN monitoring project: Reverberation mapping of optical hydrogen and helium recombination lines
We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3 m Shane telescope with the aim of measuring the masses of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~106-107 M ☉ and also the well-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including NGC 5548) showed optical variability of sufficient strength during the monitoring campaign to allow for a time lag to be measured between the continuum fluctuations and the response to these fluctuations in the broad Hβ emission, which we have previously reported. We present here the light curves for the Hα, Hγ, He II λ4686, and He I λ5876 emission lines and the time lags for the emission-line responses relative to changes in the continuum flux. Combining each emission-line time lag with the measured width of the line in the variable part of the spectrum, we determine a virial mass of the central supermassive black hole from several independent emission lines. We find that the masses are generally consistent within the uncertainties. The time-lag response as a function of velocity across the Balmer line profiles is examined for six of the AGNs. We find similar responses across all three Balmer lines for Arp 151, which shows a strongly asymmetric profile, and for SBS 1116+583A and NGC 6814, which show a symmetric response about zero velocity. For the other three AGNs, the data quality is somewhat lower and the velocity-resolved time-lag response is less clear. Finally, we compare several trends seen in the data set against the predictions from photoionization calculations as presented by Korista & Goad. We confirm several of their predictions, including an increase in responsivity and a decrease in the mean time lag as the excitation and ionization level for the species increases. Specifically, we find the time lags of the optical recombination lines to have weighted mean ratios of τ(Hα):τ(Hβ):τ(Hγ):τ(He I):τ(He II) = 1.54:1.00:0.61:0.36:0.25. Further confirmation of photoionization predictions for broad-line gas behavior will require additional monitoring programs for these AGNs while they are in different luminosity states.
14803279
Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. III. Optical Variability and X-Ray/UV/Optical Correlations
We present optical observations of the low-luminosity Seyfert 1 nucleus of NGC 4395, as part of a multiwavelength reverberation-mapping program. Observations were carried out over two nights in 2004 April at Lick, Wise, and Kitt Peak Observatories. We obtained V- and B-band photometry, and spectra over the range 3500-6800 A. Simultaneous Hubble Space Telescope UV and Chandra X-ray observations are presented in companion papers. Even though NGC 4395 was in an extremely low state of activity, we detect significant continuum variability of 2%-10%, increasing toward shorter wavelengths. The continuum light curves, both spectroscopic and photometric, are qualitatively similar to the simultaneous UV and X-ray light curves. Interband cross-correlations suggest that the optical continuum emission lags behind the UV continuum emission by 24 minutes, and that the optical continuum emission lags behind the X-ray continuum emission by 44 ± 13 minutes, consistent with a reprocessing model for active galactic nucleus emission. There are also hints of Balmer emission lines lagging behind the optical continuum by an amount slightly larger than the emission-line lag detected in the UV. These results are all similar to those of other Seyfert 1 nuclei. The emission-line lag yields a mass measurement of the central black hole, which although not very significant, is consistent with the value derived from the simultaneous UV data.
2796912
The Katzman Automatic Imaging Telescope Gamma‐Ray Burst Alert System, and Observations of GRB 020813
We present the technical details of the gamma-ray burst (GRB) alert system of the Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory and the successful observations of the GRB 020813 optical afterglow with this system. KAIT responds to GRB alerts robotically, interrupts its prearranged program, and takes a sequence of images for each GRB alert. A grid-imaging procedure is used to increase the efficiency of the early-time observations. Different sequences of images have been developed for different types of GRB alerts. With relatively fast telescope slew and CCD readout speed, KAIT can typically complete the first observation within 60 s after receiving a GRB alert, reaching a limiting magnitude of ~19. Our reduction of the GRB 020813 data taken with KAIT shows that unfiltered magnitudes can be reliably transformed to a standard passband with a precision of ~5%, given that the color of the object is known. The GRB 020813 optical afterglow has an exceptionally slow early-time power-law decay index, although other light-curve parameters and the optical spectral index are fairly typical of GRBs.