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NSLS-II Accelerator Systems

NSLS-II Accelerator Systems. Satoshi Ozaki Director, NSLS-II Accelerator Systems Division NSLS-II User Workshop July 17, 2007. Goals for the NSLS-II Accelerator Systems. Requirements for the NSLS-II facility: Ultra-bright and stable synchrotron radiation

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NSLS-II Accelerator Systems

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  1. NSLS-II Accelerator Systems Satoshi Ozaki Director, NSLS-II Accelerator Systems Division NSLS-II User Workshop July 17, 2007

  2. Goals for the NSLS-II Accelerator Systems • Requirements for the NSLS-II facility: • Ultra-bright and stable synchrotron radiation • Spectrum coverage ranging from far IR to hard x-rays • Requirements for the accelerator complex: • Ultra-small horizontal emittanceεx< 1.0 nm•rad (achromatic) • Diffraction limited vertical emittance at 12 keV • Beam stability ~10% of beam size or better (0.3 µm) • Stored current ~ 500 mA 1% with top-off injection • 27 straight sections, each > 6 m for user insertion devices

  3. NSLS-II Concept • NSLS-II Machine Concept • New 3 GeV Electron Storage Ring • Large Circumference (791.5 m), H = 1320 • Low Emittance Booster (~158 m, H = 264) • High Stored Current (500 mA 1%) • Expected Beam Lifetime (~3 hours) • Top-Off Injection (~7 nC every minute) • Superconducting RF (500 MHz) • DBA30 Lattice (15 fold symmetry) • Fifteen 8.6 m and fifteen 6.6 m straights with Hi-Lo β • Small horiz. emittance of bare lattice (~2 nm) • Damping Wigglers (initially 21m  56 m) • Large Dipole Bend Radius (25 m) • Ultra-Low Emittance (1 to 0.5 nm) • Technical Challenges • Lattice design: Sub-nanometer horizontal emittance, large dynamic aperture, wide energy acceptance etc. • Source stability: vibrations, thermal issues, feedback • Insertion Devices: DW, CPMUs, EPUs, and their impact to dynamics of beam

  4. Rendering of the Storage Ring in the Tunnel

  5. Lattice Functions For One Superperiod Goals Bare Emittance: 2.02 nm-rad Dispersion at ID Straight: Zero Beta-Functions: 8.6 m ID Straight (Hi ) (x, y) 18.9/2.9 m 6.6 m ID Straight (Lo ) (x, y) 1.5/0.8 m Twiss parameters for one superperiod of the DBA-30 lattice

  6. Lattice Dynamic Aperture (DA) The DA simulation from 20 randomly seeded sets: alignment tolerances and synchrotron oscillations are included DA is sufficiently robust for high current operation, complex insertion devices, and top-off injection

  7. Damping Wigglers for Emittance Control • Damping wigglers in the dispersion free straight sections enhance the damping of the lattice without significantly increasing the quantum excitation • A novel approach for a light source but is a well established technology for HEP accelerators and colliders • The equilibrium values for the energy spread and the emittance depend not only on the wiggler radiation energy loss but also on the dipole energy loss where nat:equilibrium horizontal emittance o: bare lattice emittance Uw: energy radiated by the wigglers and Uo: energy radiated by bend magnets (7.17 [MeV] / o [m]) • Namely, effectiveness of damping wigglers is enhanced by reducing U0, i.e., increasing the dipole bending radius  (a soft bend)

  8. Emittance and Energy Spread vs. Dipole ρo nat 0 As one increases the damping wigglers, reduction of emittance is limited by increase in energy spread and energy loss (or available RF power)

  9. Limiting Emittance from IBS Effect This reduction of emittance cannot continue forever, when the emittance becomes as small as nm scale, particle diffusion due to intra-beam-scattering (IBS) becomes comparable to the natural emittance. The reduction of total emittance per unit change of the lattice dipole bend radius, taking the IBS emittance growth into account for 500 mA stored current and harmonic bunch lengthening. The optimum range is shown, with the NSLS-II value: 25 m

  10. SR Harmonic Number and Flexible Bunch Patterns • Harmonic Number of the Storage Ring • RF Frequency = 499.68MHz • HSR = 1320 (= 2 x 2 x 2 x 3 x 5 x 11): 791.472 m for SR circumference • Bunch rotation period: 2.64 µsec • Easily factorable H: A wider range of fill patterns, particularly for a mixing of timing bunches in a bunch trains. • H = 1320 is convenient for synchronization with mode-locked lasers • Bunch pattern • Normal with ion clearing gap • Camshaft mode of operation for timing measurements: • 1, 2, 3, 4, 5, 6, 8, 10, - - - bunch train gaps with a higher current (~X2) bunch for timing experiments in the middle are possible • Pulse length • Nominal without lengthening by 1.5 GHz harmonic cavities: ~15 psec • with lengthening by harmonic RF: 30 to 50 psec depending of fill factor

  11. Diverse Beamlines from NSLS-II 3S 6S 4S • Short ID straights (low ): high brightness hard X-rays beamlines • CPMU for ultra-bright hard x-ray beamlines • EPU for polarized x-ray beamlines • Long ID straights: damping wigglers and their high power beamlines and other insertion devices • Study in progress for canted DW’s to generate two beamlines from 1 straight • Three-Pole Wiggler (TPW) in dispersion straights for hard x-ray beamlines, similar in flux as NSLS dipole radiation but ~100 times brighter (< 15) • Soft bend dipoles for soft x-ray and UV beamlines • Three pairs of wide-gap dipoles to provide large aperture beam ports for far IR beamlines B A C D/E

  12. Layout of a 6.6 m Low β Straight CPMU (U19 with 5 mm gap) in a 6.6 m ID straight Two EPU’s in a 6.6 m ID straight

  13. Layout of a 8.6 m High β Straight • Two 3-m long Damping Wigglers in an 8.6-m ID straight • 100 mm period, 1.8 T magnetic field

  14. Advanced Conceptual Design of Insertion Devices Fixed gap damping wiggler 3 m long, 1.8 T peak field With 15 mm gap CPMU in rectangular vacuum box Two 1.5 m long unit with variable gap Maximum field at 150 K: 1.14T Maximum field at room temp.: 1T

  15. Canting of Damping Wigglers Canting Angle = 3.8 mr 0.5 m Crotch Absorber Wiggler Absorber 4.3 mr 9.8 mr Flange Absorber Corrector Magnet • A 7 m long damping wiggler can be divided into two ~3 m long wigglers with canting magnets in between • With special design of the magnets near the front-end, the DW absorber system can be modified to handle the radiation with the total fan angle of 9.8 mrad • This will allow 3.8 mrad canting of two 100 mm period DW’s (~3 m long) with ±3 mrad fan, providing a complete separation of two beams • Impact of 3.8 mrad bend in the achromatic straight on the chromaticity, thus on the emittance control by wigglers must be evaluated, but should be small • ± 0.25 mrad beam deviation from its nominal orbit and an additional ± 1 mm machining and alignment tolerance are allowed

  16. Three-Pole Wigglers • The weak bend of dipoles: good for soft X-ray beamlines • A larger number of hard X-ray beams is desired, particularly with the transfer of the NSLS beamlines in mind • Introduce 3-Pole Wigglers at the upstream end of the second dipoles • The similar radiation power level as the dipole beamline at NSLS, but with a brightness about 2 order of magnitudes higher • However, impact of 3-Pole Wigglers to the storage ring is finite: • 40 cm of space for the wiggler and another 40 cm on the opposite end of the dispersion straight, and repeat it for all sectors to maintain the symmetry added 24 m to the lattice length • Addition of the radiation in the non-achromatic region results in ~10% emittance growth for 15 3-Pole Wigglers • Small but a finite interference between the magnetic field of the dipole and 3-Pole Wigglers (~2/10,000 in dipole field integral), which can be easily compensated with trim current

  17. Extra-long Straight Sections X m X m (6.6 + 2X) m • There have been on-going discussions for extra-long straight sections • Three extra-long straights can be implemented in the current lattice by shortening long straights in adjacent cells in the standard DBA30 configuration and adding the lengths to a short straight • e.g., if 8.6 m long straights are shorten to 2.6 m, leaving a possibility of using a 1 m long warm Insertion device, the extra-long straight can be 16.4 m • While evaluating the option of extra-long straights, we have decided to adopt standard DBA30 as the CD-2 lattice baseline

  18. Beam Stability Requirement • The beam stability required: 10% or less of the beam size (~3 m) over a range of period 20 msec to 30 minute • Settling and vibration (natural and self-inflicting) of the accelerator tunnel and experimental hall floor/beamlines (Tunnel floor <25nm) • Temperature stability (<0.1C) • Mechanical engineering consideration (Resonant frequency: >50Hz) • Magnet power supply and RF noise issue (Higher level of noise filtering) • Closed orbit correction with slow and fast feedback (high precision user BPM’s) • Achievement of good stability must be joint efforts of Conventional Facilities, Accelerator Systems, and Experimental Facilities Groups • Beam Stability Workshop: April 18-20, 2007: Sam Krinsky • Report of the Workshop can be found at http://www.bnl.gov/nsls2/workshops/Stability_Wshop_4-18-07.asp

  19. Summary • Optimized design of the NSLS-II storage ring, based on well proven DBA configuration, has a robust DA with low natural emittance • Combination of damping wigglers and dipoles with a large bending radius provides sub-nm•rad horizontal emittance for ultra-high brightness x-ray beams • With insertion devices, three pole wigglers and soft-bend dipoles including special wide-gap dipoles, NSLS-II can provide synchrotron light in a wide range of spectrum to users • Damping wigglers also make high flux/brilliance hard x-ray beams • With 27 ID straights, 3PW’s and bending magnets, and with possibility of canting ID’s, NSLS-II in its fully developed state can support more than 58 beamlines for the user program • Expected accelerator performances is expected to meet stringent requirements • Further optimization of lattice and beam stability as well as engineering and design, cost estimating, and schedule planning are in progress in preparation of the CD-2 review in November this year

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