Top-off injection will be adopted in NSLS-II. To ensure no injected beam can pass into experimental beamlines with open photon shutters during top-off injection, simulation studies for possible machine fault scenarios are required. We compare two available simulation methods, backward (H. Nishimura-LBL) and forward tracking (A. Terebilo-SLAC). We also discuss the tracking settings, fault scenarios, apertures and interlocks considered in the analysis

Casey, B.

Heese, R.

Hseuh, H.

Job, O.

Krinsky, S.

Li, Y.

Parker, B.

Shaftan, T.

Sharma, S.

UNT Digital Library

   BNL-82318-2009-CP      Top-Off Safety Analysis for NSLS-II   Y. Li, B. Casey, R. Heese, H. Hseuh, P. Job, S. Krinsky, B. Parker, T. Shaftan, S. Sharma  Brookhaven National Laboratory, Upton, NY 11973-5000, USA   Presented at the PAC09 Conference Vancouver, Canada  May 4 – 8, 2009     National Synchrotron Light Source II Project  Brookhaven National Laboratory P.O. Box 5000 Upton, NY 11973-5000 www.bnl.gov    Notice: This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.   This preprint is intended for publication in a journal or proceedings.  Since changes may be made before publication, it may not be cited or reproduced without the author’s permission.    DISCLAIMER  This report was prepared as an account of work sponsored by an agency of the United States Government.  Neither the United States Government nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or any third party’s use or the results of such use of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof or its contractors or subcontractors.  The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.                                      Y. Li#, B. Casey, R. Heese, H. Hse rker, T. Shaftan, S. Sharma, BNL, Upton, NY, 11973, U.S.A.As, apertures and interlocks consven in the presence of magMETHODOLO OFF SAFETY way from magnet calculation result at the maximum lowed vertical offset limited by vacuum chamber transve areas occupied by the unTOP-OFF SAFETY ANALYSIS FOR NSLS-II* uh, P. Job, S. Krinsky, B. Pabstract Top-off injection will be adopted in NSLS-II. To ensure no injected beam can pass into experimental beamlines with open photon shutters during top-off injection, simulation studies for possible machine fault scenarios are required. We compare two available simulation methods, backward (H. Nishimura-LBL) and forward tracking (A. Terebilo-SLAC). We also discuss the tracking settings, fault scenarioidered in our analysis. TOP-OFF SAFETY Like other modern synchrotron radiation light sources, NSLS-II will operate in top-off mode [1]. The top-off injection refers to injecting with photon beamline safety shutters open to maintain a near-constant stored beam current in the ring. In traditional non-top-off mode, photon shutters are closed during injection process to block any injected beam particles from escaping the storage ring enclosure and entering the experiment hall, where they would constitute a radiation hazard. Current plans call for injecting a charge of about 8nC once per minute for NSLS-II. Not even one pulse of injected electron beam can be allowed to escape through the shield wall, because the radiation dose would be unacceptably high. In order to allow top-off injection, it is necessary to carry out comprehensive tracking analysis to show that electrons cannot escape the ring enclosure enet faults or injection errors.  GY OF TOP-ANALYSIS At machine design stage, particle tracking simulations are used to guide us in specifying the location and size of beam collimators, magnet power supply interlock requirements, and other controls needed to avoid unsafe conditions. The simulations required for the top-off safety analysis are quite different from other particle tracking simulations performed for storage rings, which usually concentrate on the stability of long-term motion (dynamical aperture simulations). In top-off safety simulation, we need to track many particles within a specific phase space area for a short distance (fraction of the ring) and change the lattice magnet settings over wide ranges in order to include all possible machine fault scenarios, and consider particle trajectories far acenter, and beyond good-field range. We simplify the analysis and shorten computation time by constraining the tracking simulation to the magnet’s mid-plane. Particles that have an offset in the vertical plane may experience a stronger vertical field in the vicinity of poles, which is simulated by variation of the magnet field. The variation range depends on magnetic field alerse size.   Fig. 1: Forward (a) and backward (b) tracking  There are two options available to do such simulation, backward tracking adopted by APS [2, 3] and ALS [4], and forward tracking by SPEAR 3 [5]. The forward tracking starts from an upstream source, and then tracks particles within a defined phase space area, which is determined by at least two physical apertures in magnet-free section, and checks if any particles can go through the physical apertures at beamline frontends (see Fig. 1 (a)). The backward tracking starts from a physical aperture within the shield wall at which it is safe to have electron scatter, and then tracks particles back into storage ring to check if there are any trajectories that can originate within the storage ring geometric acceptance (see Fig. 1 (b)). In principle these two methods are equivalent.  We have checked this by using these two methods to analyze the same NSLS-II beamline and compared results. In the case of safe situation, forward tracking shows no trajectory originating from the ring acceptance can pass through safety shutter; and backward tracking shows no trajectory within frontend acceptance can track back into the ring acceptance. In the case of unsafe conditions, the phase spacsafe particles given by the two methods overlap at the same longitudinal position. (a) (b)  ___________________________________________  *Work supported by U.S. DOE, Contract No.DE-AC02-98CH10886 #yli@bnl.gov  We chose forward tracking in our simulation for two reasons. First, since our machine is still under design, we have an opportunity to     specify some collimators to stop electron racking can help us dete n to install cow the location where the beam hits the tion. II BEAMLINES b• Beas• LT SCENARIOES tion condition, e-beam and photon-robab ility ven  f mo t with xtrem  our mu gnet n b ort ud rtially sh rte orted.     odels for simulation. All me detailed magnet design and coing her 2% he eventual variation ra ger dipole field is alway for saf nly co  dipole  below normal the setting value, th %~1As we mentioned in previous se nstrain tio e.  of particles with vertical offset in poles and , t s o  vary from 100% to 105%, which cov  maximum f e vi  poles.  of o ection ts is chosen as t um allowed deflection angle ±0.8mard. Tab. 1 lists the onsideration criterion.  close to the ring. Forwarding tct the most effective positiollimators. Second, most of our collimators in the ring and frontends are copper with a thickness of only several centimetres. In order to design the lead shield, we wish to knovacuum chamber or collimators. Forward tracking can provide such informaNSLS-The NSLS-II has several types of beamlines. Each e line has different physical apertures. Wam e catalogue all beamlines into several classes according their source point location: mline with the source point in IDs at long traight section; Beamline with the source point in IDs at short straight section; • Beamline with the source point in Three Pole Wigglers (TPW) and bending magnets. The required apertures and controls to assure safety for each class of beamline is analyzed. MACHINE FAUIn normal operabeam are separated by bending electrons in dipoles, so that no e-beam can enter photon beamline frontends. In defining the tracking scenarios, we referred to other laboratories experience [4] and combined with our practical machine status. The goal of our work is to assure that we design the system such that no faults can lead to unsafe condition. Magnets faults The possible magnet faults were classified by their p ility of occurrence. Two very low probabts, such as simultaneous shorts in th ils of twore magnets, was considered as an evenely low probability and not included inlation. So in each fault scenario, only one mae completely or partially shorted. Partially sh) whole magnet is pad; (2) and just one of poles is compe e cooesicaincl es two cases: (1o letely sh       Fig. 2: Quadrupoles (a) and sextupoles (b) vertical field component profiles on the mid-plane Since particle trajectories may be beyond magnet’s good field range and some coils can be shorted, we can’t use ordinary multipole magnets’ fields are scaled to their settings from the profiles obtained by numerical calculations for each magnet fault. Profiles for quadrupole, sextupole and corrector are represented by a 1-D numerical table (see Fig. 2). Dipole profile is a 2-D table so that it can include the fringe field. Magnets variation range In each scenario, one magnet fault is combined with all other magnets’ possible variation. The variation range depends on thrresponding hardware configuration, such as power supply stability, adjustment range of trim coils, magnet monitoring and interlocks etc. For example, in order to maintain the existence of the closed orbit, none of dipoles can be partially shorted-off by more than 5%, which can be fulfilled by specifying interlock requirement. At the same time, their trim coils can provide an extra maximum ±3% adjustable range. So dipoles can vary between -92~103%. By keepanot for other unpredictable errors, tnge is 90%~105%. In fact, strons good  strengthety, and then we onsiderat is 90 00%.     ction, we coour simula n to mid-plan In order to include the casequadrusextupoles hese two type f magnets vertical field caner theield in thrbit corrcinity of magne The variation rangeheir maximmagnet variation range and c  Table 1: Summary of Magnets Variation Magnet Type Variation Range Consideration Criterion Dipoles 90% ~ 100% Power supply, trim coils, and closed orbit interlock 0.04Quadrpoles 100% ~ 105% Power supply, ofplanfset in vertical e Sextupoles 100% ~ 105% Power supply, offset in vertical plane Correctors -100% ~ 100% Maximum deflect angles  -0.2 -0.1 0 0.1 0.2 0.3-0.04-0.03-0.02-0.0100.010.020.03(a) normalized Byx(m)-0.2 -0.1 0 0.1 0.2 0.3-202468101214x 10-4normalized By(b) x(m) Aperture misalignment All physical apertures, like synchrotron radiation abso  rb cause of m gnment, form s etc, so wed misaligEnerIn rom its no ention of in ergy  will be implemented to  ig. 3 Determination of initial phase space area for forward tracking by  multipole and the dipole ante-chambers can effectively collimate the particles with large horiz ipole (see Fiing parameters. The scan parameters articles energy deviation, magne pletely short or N ge, but we et field specifying t For each scenario included in our scan, the magnet status and the final position where beam is stopped are recorded for further radiation safety analysis. If there are any scenarios which have trajectories travelling through the photon shutter in frontend, we must identify and specify controls to prevent them. Even when the electron beam is stopped by hitting the collimators, as we mentioned before, the 3GeV electron beam can create radiation shower, and we still need to design lead collimators to shield them. Therefore the location where beam is stopped is important information for the design of the lead shielding. ACKNOWLEDGEMENT The authors wish to acknowledge the help and discussion of H. Nishimura (LBL) and A. Terebilo (SLAC), and the continuous support from NSLS-II vacuum and mechanic group’s colleagues: W. Gash, M. Ferreira, L. Doom, and C. Longo. ers, can be deviated from design position beany reasons, such as installation misali distortion due to synchrotron radiation heatwe increase all apertures by the maximum allonment error, specified to be 2mm. gy deviation of Injected beam jected beam could have an energy deviation fminal value because of injector faults. Prevjected beam with certain amount of endeviation to escape from safety shutter must be ensured. In the simulation, controlsassure the maximum energy deviation is ±5%. SAFETY ANALYSIS AND PARAMETERS SCAN Here we use the long straight ID beamline as an example to describe how we implement analysis on its top-off safety. Two stick absorbers within the long straight section are chosen to determine the initial phase space area for tracking by four extreme rays (see Fig. 3).  F four extreme rays   Fig. 4: Beam trajectories (in black) in the normal condition. The central orbit of electron beam (blue dash line) is chosen as the reference, red solid line is the photon beamline centre, and blue solid lines are collimators.             Fig. 5: Two ante-chambers are separated by a billow  We use element-by-element tracking method, the motion through each element is determined by integrating the differential equations of motion driven by the Lorentz force in the mid-plane. Particle’s horizontal offsets are compared with the physical apertures to determine if they can pass through these apertures. The possible machine fault scenarios are simulated by varying magnet’s setting. Fig. 4 shows beam trajectories in normal operation condition, and no beam can go through the crotch absorber. Some detailed study shows the bellow with ±38mm horizontal aperture between theontal offset at the upstream of dg. 4), its geometric design is shown in Fig. 5. As a result no beam can pass the crotch absorber. In order to detect the possible dangerous scenarios as described in previous section, we need to scan the combination of the possible magnet faults, which is established by setting a list of vary include injected pt faults types (compartially short), magnet variation range. ormally the number of scenarios is hucan decrease it by constraining the magnvariation range, which can be realized by some monitoring and interlock requirements on magnepower supply. 0 5 10 15 20 25-0.200.20.40.60.811.21.4s (m)x (m)NSLS-II Long Straight Section IDs Top-off Safety simulation  ante-chamber     bellow  ante-chamber stick absorberstick absorbercrotchabsorberpb fixed maskhoton shuellowtter  7BREFERENCES [1] NSLS-II Preliminary Design Report, HUhttp://www.bnl.gov/nsls2/project/PDR/U [2] M. Borland, et al., PAC’99, p. 2319, 1999 [3] L. Emery, et al., PAC’99, p. 2939, 1999 [4] H. Nishimura, et al., PAC’07, TUPMN112, 2007 [5] J. Safranek, et al., PAC’07, TUPMS055, 2007 

Top-Off Safety Analysis for NSLS-II

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Top-Off Safety Analysis for NSLS-II

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