Summary of the Ultimate Storage Ring Workshop R. Bartolini Diamond Light Source and John Adams Institute for Accelerator Science University of Oxford ESLS XX Workshop, Berlin, 22 November 2012

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Chairmans: Bob Hettel (SLAC), Qing Qin (IHEP) Charge survey existing concepts for USRs compare performance goals identify R&D necessary toward a USR prioritise R&D topics and define critical studies to be started asap Ultimate Storage Ring workshop ESLS XX Workshop, Berlin, 22 November 2012

Scientific drivers2 talks Lattice design11 talks Accelerator Physics8 talks Injection schemes6 talks Accelerator engineering10 talks Insertion devices6 talks Feedback systems3 talks Workshop sessions ESLS XX Workshop, Berlin, 22 November 2012

L. Zhang (ESRF)

Scientific drivers ESLS XX Workshop, Berlin, 22 November 2012 Scientific drivers presented by H. Ding (IoP, CAS) and Y. Dong (IHEP, CAS) Brillliance ph/s/mm/mrad/0.1%BW in the range keV Transverse coherence; Photon range up to 300 keV Flagship applications: nanofocus with small spot sizes coherent diffraction imagingwith high transverse coherence weakly diffracting crystal with high brightness/flux non crystallisable proteins with higher coherent flux industrial applicationswith photons up to 300 keV (not so much on time resolved science: ~10 ps quoted)

Survey of ultra-low emittance lattices MAX IV7BA3 GeV320 pm500 mASS length 5mDA 7mm w/errors Sirius5BA w/superbend m & 6m5 mm w/errors Spring-86BA m & 27m3 mm w/errors APS7BA Pep-X7BA m10 mm w/errors ESRF Phase II 7BA m10 mm SOLEILQBA w/longit.. gradient dipole (220) 500Robins. Wiggler + beam adapter Diamondmod. 4BA, 5BA, 7BA m & 7 m2 mm ALS5BA - 7BA m2-3 mm BAPS7BA-15BA m & 7m10 mm w/errors tUSR7BA93100TEV. tunnel0.8 mm

Lattice design: discussion (I) What is the optimal energy for a DLSR? tens keV high brilliance (and some at 300 keV) requires > 3 GeV 5 GeV BAPS – 4.5 PepX – 9 GeV tUSR – 6 GeV Spring8-II What M is optimal? longer cells (larger M) produce smaller emittances trade off between small emittances and straight section length What is the optimal length for straight sections? not much interest for very long undulators (SS 5 – 7 m) Ratio circumference vs lengths of straight section for IDs still a valid figure of merit ESLS XX Workshop, Berlin, 22 November 2012

Lattice design: discussion (II) Dynamic aperture and lifetime minimise sextupoles strength as much as possible use octupoles for correction detuning with amplitude Optimisation techniques FMA (used everywhere) driving term cancellation (MAX IV, Pep-X, …) MOGA (Diamond, …) ESLS XX Workshop, Berlin, 22 November 2012

Lattice design: layouts Lattices layout very similar: classical MBA and MBA with dispersion bump BAPS ring MAX IV ring ESRF Phase II ring DLS modified 4BA

Additional paths to ultra low emittance Adapted from A. Nadji and R. Nagaoka

Lattice design: discussion (III) Matching to photon beam size mandatory to maintain high brightness Coherence definition  < λ/4π or λ/2π? this definition does not yield full coherence yet. What is the target? Beam adapter with solenoid (Chao-Raimondi) same brightness issue with matching to the photon beam phase space nevertheless round photon beams are of interest (BAPS, SOLEIL) ESLS XX Workshop, Berlin, 22 November 2012

Accelerator Physics: current and instabilities Small emittance  short bunches  low instability thresholds Small apertures everywhere arcs & straight sections is worrying for large stored current IBS; Touschek lifetime Coherent Synchrotron Radiation; Resistive Wall Current limited by IBS, especially for very low emittance lattices Effect of CSR also potentially catastrophic especially for those lattices with short natural bunch length Heat load on beamlines optics can be an issue at large current high beam energies (1.5 A Pep-X old design) but IBS is the limiting factor. Unlikely that ultra low emittance will work with current above few 100s mA. ESLS XX Workshop, Berlin, 22 November 2012

Accelerator Physics Countermeasures for CSR: vacuum pipe shielding with small apertures was discussed. Relative impact of RW to be worked out Countermeasures for RW and FII: feedback and fill pattern gaps can help Countermeasures: long bunches Choice Ideal RF frequency HHC factor 5 lengthening for MAX IV 70 mm rms bunches Leave out time resolved studies (to the Linac injector) one ring cannot fit everything ! ESLS XX Workshop, Berlin, 22 November 2012

To reach >200 Apk for lasing:  z = 2 psQ b > 1 nC  z = 0.3 psQ b > 150 pC  z = 0.1 psQ b > 50 pC Lasing happens in by-pass Can the bunch be temporarily compressed for lasing? Transverse gradient undulator concept for large energy spread compressdecompress Adapted from X. Huang, B. Hettel (SSRL) Short pulses for partial FEL lasing However Pep-X wants to operate with short bunches for partial lasing in a by-pass kHz FEL – needs 200 A peak current ; 1.3 GHz high gradient is considered: 200 MW SCRF

Accelerator engineering: magnets R&D ESLS XX Workshop, Berlin, 22 November 2012 Diffraction limited emittance requires magnets with unprecedented strength in storage ring. High gradient and high precision required New designs under consideration foresee magnets whose strength exceed even the most aggressive existing designs and distance is of the order of the gap quadruple gradient MAX IV has 40.0 T/m ESRF – Diamond-II100 T/m Spring8-II 80 T/m BAPS50 T/m  USR90 T/m quadrupoles in dipoles MAX IV has 9 T/m ESRF – Diamond-II 30 T/m sextupoles MAX IV has 2*2200 T/m2 ESRF-Diamond -  USR7000 T/m 2 Spring-8 II T/m 2 BAPS7500 T/m 2 space between magnets (hard edge) 10 cm MAX IV has 7.5 cm Apertures = mm diameter in arcsMAX IV inner diam. 22 mm

Quadrupole magnet design with g > 100 T/m (ESRF) PM quadrupole EM quadrupole

Permanent magnet: SIRIUS will have PM dipoles – ESRF is also looking at this option. Motivated by operational savings and less vibration radiation damage (SmCo) temperature variation field quality and shimming OK appears to be within the present R&D reach quads in dipoles8 T/m quads40 T/m sextupoels1800 T/m 2 Magnetic measurement techniques are adequate Improvement needed but no showstopper here! Accelerator engineering: magnets R&D ESLS XX Workshop, Berlin, 22 November 2012

PM solutions for all type of magnets (ESRF) J. Chavanne ESRF

Accelerator Engineering (III) Components Integration: separate magnets on girders or common blocks a la MAX IV ? blocks integration: alignment left to machining not adjustments and pushes the structure eigenfrequencies up above 50 Hz but complicated vacuum pumping requires NEG e.g. vacuum leak requires opening the whole cell Stability site choice civil engineering construction for stability ESLS XX Workshop, Berlin, 22 November 2012

Accelerator Engineering (III) ESLS XX Workshop, Berlin, 22 November 2012

Accelerator Engineering: Vacuum Small magnets bore (20-26 mm diameter) required to achieve high gradients creates problem with the vacuum system pumping cross section limited insufficient space for pumps, absorbers, antechambers,… MAX IV solution distributed NEG coating Neg coating Cu chamber with external cooling channel Time consuming for NEG coating (~ 10 days for a vacuum chamber) process Limited coating production capability in the world  long procurement time (costs) Activation system to be considered during the vessel design stage ESLS XX Workshop, Berlin, 22 November 2012

Accelerator Engineering: Vacuum ESLS XX Workshop, Berlin, 22 November 2012 E. Al Dmour MAX IV

Injection Crucial aspect for this studies when the low emittance is achieved compromising the DA Traditional 3 or 4 Kicker bump: require 10 mm DA required Top-Up is crucial for sub-um stability Injection transient seems unavoidable; gating needed New scheme emerging are multipole pulsed injection and swap out injection ESLS XX Workshop, Berlin, 22 November 2012

Injection: new schemes Multipole kicker schemes still off-axis: it requires ~5 mm DA (MAX IV data) some R&D still needed but excellent perspective at BESSY-II (O.Dressler’ talk) Swap out injection kick in - on axis - a new bunch and kick out the depleted bunch requires a small emittance injector – can work with 2 mm DA no top up – but fractional replacement of current the injector and the achievable fill pattern limit the total stored current (0.5 nC/bunch) - with a booster or linac ESLS XX Workshop, Berlin, 22 November 2012

Feedback system (I) Stability requirements 10% rules still valid (up to 200 Hz): J.C. Denard’s talk implies no longer submicron stability but nm already achieved (or very close) in the V plane in some machines H plane issues – Amplification factor is higher than in V beamline optics design and stability for diffraction limited e- beams Top-Up mandatory R&D: civil engineering: common slab for ring and experimental hall tunnel temperature control (within 0.1 C) girders’ eigenfrequencies above 50 Hz BPM accuracy: new designs for round pipes; decoupling by bellows; invar supports; better resolution (esp. turn by turn)

SOLEIL’s orbit feedback perfomance Vertical beam motion averaged on all e-BPMs ~300 nm ( Hz ) It means 200 nm RMS in the middle of the straight sections Vertical plane FOFB ON FOFB OFF FOFB ON FOFB OFF J. C. Denard SOLEIL

Feedback systems: discussion Closer integration with the beamlines was unanimously supported including beamlines to the extent of having a feedback of photon at sample back to the beam ? not a popular route: general agreement on the fact that 90% of the time beamline complaints come from beamline equipment itself Improvement of XBPMs in white beam needed (esp for helical IDs) Correction of intensity after monochromator (Diamond) Other feedbacks: Feedback for coupling; Feedback on EPU C. Steier: no revolution is needed (except for EPUs XBPM) but steady mprovement on what already achieved ESLS XX Workshop, Berlin, 22 November 2012

IDs from J. Chavanne’s talk: ID impact with new low emittance lattice Beam dynamics: will need FF tables correction Photon quality: rms phase errors 2-3 degree is adequate Energy spread will become the dominant effect to higher harmonics Heat load: no majpr changes as the size of the photon beam is weakly dependent on emittance (mostly depends on K) from J. Bardth’s talk: comparison CMPUs vs SCUs CPMU mature design; SCU higher field for periods above 10 mm SCU have big potential; CMPU still compatible with users application in the next 5-10 years due to flexibility, fast tuning, reproduclbility

R&D IDs: ESRF ESLS XX Workshop, Berlin, 22 November 2012 J. Chavanne ESRF

R&D IDs: SCU at APS ESLS XX Workshop, Berlin, 22 November 2012  SCU has been built at the APS  Beff = 0.64 T at 500 A  21 periods of 16 mm  Installation is scheduled for December 2012 Completed magnet assembly Fit test of cold mass and current lead assemblies in cryostat M. Jaski APS: Ivanyushenkov et al.. IPAC12,

Conclusions Lots of issues – long to-do list but no show stopper Main issue is probably the optimisation of the nonlinear beam dynamics followed by the choice of the bunch length and whether leaving time- resolved studies on USR 70 mm bunches a la MAX IV vs PepX – partial lasing) but is MAX IV economical? Large community is now undertaking these studies Workshop in December Spring-8 ESLS XX Workshop, Berlin, 22 November 2012

3 rd LOWERING workshop in Oxford 8-10 July 2013 USR Workshop, Beijing, 31 October 2012