1. 1 BROOKHAVEN SCIENCE ASSOCIATES Stability Issues NSLS-II ASAC Meeting April 23, 2007 S. Krinsky

2. 2 BROOKHAVEN SCIENCE ASSOCIATES Stability Task Force / Workshop April 18-20 Visiting Committee M. BogePSI J. ByrdLBL J.R. ChenTaiwan Y. DabinESRF R. Hettel (Chair)SLAC J. JacobESRF J. MaserAPS R. MuellerBESSY-II D. ShuAPS J. SidarousAPS O. SinghAPS C. SteierLBL http://www.bnl.gov/nsls2/workshops/Stability_Wshop_4-18-07.asp

3. 3 BROOKHAVEN SCIENCE ASSOCIATES Electron Beam Sizes and Divergences for Selected NSLS-II Sources Type of source: 5 m straight section 8 m straight section Bending magnet1 T three- pole wiggler σ x [μm]38.599.544.2 (35.4-122)136 σ x' [μrad]14.25.4863.1 (28.9-101)14.0 σ y [μm]3.055.5115.7 σ y' [μrad]3.221.780.630.62

4. 4 BROOKHAVEN SCIENCE ASSOCIATES User Requirements In most cases studied so far, a stability criterion of 10% of the beam size and 10% of the beam opening angle is sufficient, with the exception of the horizontal position for a few techniques Review Committee  Beam size stability also critical A common theme which has been expressed is in stability of beam intensity delivered to the experiment, which affects signal- to-noise directly, and this explains why some cases require beam position stability of <10% of the beam size A “one size fits all” approach may not work for everyone, and tighter stability for a particular experimental program may require local measures

5. 5 BROOKHAVEN SCIENCE ASSOCIATES Need cutting-edge technology in many systems on BL and in accelerator May need mechanical motion/position survey sensors at critical points from source to experiment and in accelerator; ability to include sensors in feedback Need to mechanically model critical beam line set-ups (supports, modes, etc) Find a way to monitor I0 just upstream of sample for all critical systems – normalization on sample-by-sample – but there are limits to quality of I0 detector Recommend phase space acceptance analysis projected to source phase space Use “telescope technology” to maintain relative stability of components (e.g. D. Shu) Need instrumentation infrastructure to verify accelerator vs. beam line stability issues and to help achieve stability goals Committee strongly supports beam designer’s goal to consider source and beam line stability “holistically” Review Committee: Comments on Stability Solutions

6. 6 BROOKHAVEN SCIENCE ASSOCIATES Stability Dependent on Conventional Facilities Stability goals driven by conventional facility design Stability of storage ring tunnel floor Vibration < 25 nm PSD from 4-50hz Stability of experimental floor Vibration level of < 25 nm PSD from 4-50hz for general floor area Vibration level for 1 nm resolution beam lines requires further definition but appears achievable with proper correlation Thermal stability of storage ring tunnel environment +/- 0.1 o C for 1 hour time constant Thermal stability of experimental floor +/- 0.5 o C for 1 hour time constant Review Committee: Accelerator group must confirm that there is no significant thermal load variation during operation

7. 7 BROOKHAVEN SCIENCE ASSOCIATES RMS (2 – 50 Hz): ~ 20 nm

8. 8 BROOKHAVEN SCIENCE ASSOCIATES Ring Building Section Ratchet or Shield Wall Electrical Mezzanine Bldg structure Isolated from tunnel and experimental Floor Earth Shield Berm Experimental Floor Access Corridor Tunnel Floor “ Monolithic Joint ” Isolation Joint Isolation Joint or Void Space Tunnel Roof Isolated Pier for Column Isolated Grade Beam

9. 9 BROOKHAVEN SCIENCE ASSOCIATES Tunnel Design - Ring Building Section Non-vibrating Equipment Need to assure that vibration mitigation measures are carried out at Ring building interfaces with other structures and where systems enter building or tunnel Section at Lab Office Building and Service Building Rotating Machinery Distance determined by modeling & empirical analysis

10. 10 BROOKHAVEN SCIENCE ASSOCIATES Vibration Analysis Finite element calculations used to analyze effect of vibrations on facility 30 ft

11. 11 BROOKHAVEN SCIENCE ASSOCIATES Review Committee: Revisit the project design parameters regarding the infield service buildings. From vibration prospective, it may be better to locate them in the outfield (maybe incorporated into LOBs) A discussion took place, and CFG will pursue that approach from cost/benefit approach. In either case, even with the analysis resulting in acceptable outcome, an attempt should be made to locate rotating equipments as far away from SR as practically feasible.

12. 12 BROOKHAVEN SCIENCE ASSOCIATES Natural modes of vibration for the girder-magnets assembly: (a) rolling mode = 63 Hz, (b) twisting mode = 79 Hz RMS (2-50) Hz Displacements: Floor: 20 nm, Magnets: 21 nm (b) (a) Mode Shapes of the Girder-Magnets Assembly Review Committee: Resonant frequencies often found to be 1.5-2 times lower than calculation. Must prototype magnet-girder assembly

13. 13 BROOKHAVEN SCIENCE ASSOCIATES Tolerance LimitsΔX RMS QuadsΔY RMS Quads Random magnet motion< 0.15 μm< 0.025 μm Random girder motion<0.6 μm< 0.07 μm Tolerances on Magnets’ Motion  ΔX Tolerance limits are easily achievable.  ΔY Tolerance limits:  Thermal: relative thermal displacement between magnets on the same girder: < 0.025 μm. (RMS thermal displacement of girders over a pentant (6 cells) < 0.1 μm)  Vibration: no magnification of ambient floor motion up to 50 Hz. Below 4 Hz girder motions are highly correlated Above 50 Hz the rms floor motion is < 0.001 μm

14. 14 BROOKHAVEN SCIENCE ASSOCIATES Location of BPMs and Correctors BPMs mounted on vacuum chambers: ± 0.2 μm (vertical) User BPMs (upstream and downstream of IDs) : ± 0.1 μm (vertical) X-BPMs: ± 0.1 μm (vertical) There are also fast correctors in straights at both ends of ID Review Committee: Include feed-forward on skew quads to correct for ID changes

15. 15 BROOKHAVEN SCIENCE ASSOCIATES Support of Beam Position Monitors  BPMs on the vacuum chambers need to be located near the fixed or flexible supports.  Thermally insulated, sand-filled steel stands will meet the mechanical stability requirements for the special BPMs. Review Committee: Temperature of insulated supports can change significantly over long shutdowns. Must include method to quickly bring supports to proper temperature at beginning of new run.

16. 16 BROOKHAVEN SCIENCE ASSOCIATES Effect of Feedback Without feedback: If G is a large positive number, with feedback loops on, the error signal is reduced by a factor of 1+G at DC (T(0)=1). At higher frequency, TG is a complex number and has to be designed to avoid oscillation. With feedback: V R U W -1 V  f e f c y PID R W -1 f e f c y  -G T(  ) t

17. 17 BROOKHAVEN SCIENCE ASSOCIATES Review Committee: Consider global system Local systems probably not needed Include maximum flexibility in design for use of correctors and BPMs Make provision for inclusion of x-ray BPMs (2 per ID beamline) There are several proven approaches to incorporating slow and fast correction Digital technology is improving and 15 KHz data rate should be available Carry out real time modeling of feedback system, include errors in response Matrix. Calculations show that 4 BPMs and 4 Correctors per cell is sufficient to meet requirements.

18. 18 BROOKHAVEN SCIENCE ASSOCIATES Corrector magnets & power supplies The system will use 120 corrector magnets with separate horizontal and vertical coils. The magnets will be designed for fast correction of ~ 100 Hz. The dc transfer function of the magnet is 1000 μrad per 19.2 Amps. The magnets will be located over stainless steel bellows and or flanges. The magnets are placed at the ends of each main dipole magnet. There will be 120 horizontal and 120 vertical power supplies. These corrector magnets and power supplies will be also used in slow and alignment corrections. The power supplies will have a high current requirement for slow/alignment corrections and high voltage requirements for fast corrections.

19. 19 BROOKHAVEN SCIENCE ASSOCIATES Corrector magnets & power supplies The power supply requirements from accelerator physics are the following: Frequency Strength - RMS < 5 Hz 800 μrad 20 Hz 100 μrad 100 Hz 10 μrad 1000 Hz 1 μrad Resolution of last bit: 0.01 μrad Noise Level : 0.003 urad ( ~ 4 ppm of 800 μrad ) (Review Committee  1ppm) (These rating are for vertical correction and the horizontal correction is less stringent and they need to be quantified.) Power Supply Description: Four quadrant switch-mode class D amplifier to be incorporated into a bipolar current regulated power supply. Small signal bandwidth of the power supply will be ~ 2 kHz Amplifier has a switching frequency of 81 Hz. which gives a ripple current of ~ 2 ppm. Resolution of 0.01 μrad is planed. Two 16 bit DACs will be used. One will be used for the slow large strength correction and the other for the fast smaller strength correction. Two DACs will have an affective resolution of 18 bits or ~ 0.003 μrad. (Review Committee  20bits)

20. 20 BROOKHAVEN SCIENCE ASSOCIATES Main dipole power supply The power supply is a unipolar, 2-quadrant, current-regulated supply. It will use two 12-pulse SCR converters in series with the center point connected to ground. Each converter will have a two-stage LCRL passive filter and a series pass active filter. Each main dipole magnet bending angle of 0.1047 rad. The CDR has the current ripple spec. ( referred to Imax) of 5 ppm for freq. 60 Hz and greater. This gives a ~ 524 nrad noise in the horizontal direction. CDR has the following power supply parameters: resolution of reference current 18 bit + 1LSB stability (8 h-10 s) – referred to Imax 40 ppm stability (10s-300 ms) – referred to Imax 20 ppm stability (300 ms- 0 ms) – referred to Imax 10 ppm absolute accuracy – referred to Imax100 ppm reproducibility long term – referred to Imax 50 ppm To ensure long-term stability and reproducibility - high-precision DMMs will be used to monitor the power supply current, a redundant current sensor, and the analog current set point. R&D for the main dipole ps is to develop a more thorough electrical circuit model of the system, that will include transmission line effects of the overall circuit.

21. 21 BROOKHAVEN SCIENCE ASSOCIATES Multipole power supplies for quad. & sext. Magnets There is one power supply for each magnet. The power supply is a unipolar, single-quadrant, current-regulated switch-mode design. The power supply will use a DCCT as the current feedback device. To minimize current ripple, an additional output filter will be used. The CDR has the current ripple spec. ( referred to Imax ) of 15 ppm for freq. 60 Hz and greater. CDR has the following: resolution of reference current 16 bit + 1LSB stability (8 h-10 s) – referred to Imax200 ppm stability (10s-300 ms) – referred to Imax200 ppm stability (300 ms- 0 ms) – referred to Imax100 ppm absolute accuracy – referred to Imax200 ppm reproducibility long term – referred to Imax100 ppm To ensure long-term stability and reproducibility - high-precision DMMs will be used to monitor the power supply current, a redundant current sensor, and the analog current set point. The R&D for the multipole power supplies is to build a proto-type and confirm the accuracy, stability, and current ripple of the power supply. (Review Committee  100ppm, 18bit)

22. 22 BROOKHAVEN SCIENCE ASSOCIATES RF BPMs Design similar to one adopted at RHIC 5-mm radius buttons Stray capacitance 1-4 pF (2π×500MHz×50Ω×3pF≈0.5) Signal level -1.1 dBm for 500 mA at 500 MHz Dependence of vacuum chamber shape/size and button capacitance (and hence sensitivity) on fill pattern and circulating current can be significant

23. 23 BROOKHAVEN SCIENCE ASSOCIATES Processing Units Utilized at Elettra, NSSRC, Diamond, Soleil, PLS Fast acquisition 10 kHz sampling rate, 2 kHz BW Slow acquisition: 10 Hz sampling rate, ~4 Hz BW 32 bit data RMS uncertainty (for 10 mm scale in 1 kHz BW) -90.5dB →0.3µm @ Pin = -20 dBm 8-hour stability (ΔT=±1°C) -80dB→1µm Temperature drift (T=10–35°C) -94dB/°C → 0.2µm/°C MTBF ≥ 100,000 hours For 270 units failure rate will be one unit in 17 days Review committee: NSLS-II needs about factor of 2 better performance than available today noise, stability <0.15micron Technology improving, in a few years will be achievable

24. 24 BROOKHAVEN SCIENCE ASSOCIATES Photon Beam Position Monitors Will provide information on photon beam position and angle (to account for errors in the wiggler field) Use of photon BPMs will allow sub-microradian pointing stability Contamination with dipole radiation can be of less concern due to reduced magnetic field in the bending magnet Can be used for orbit feedback and/or control of users optics 2D translation stages will precisely locate the photon BPM Should withstand high power density Review Committee: X-ray BPMs will be essential for NSLS-II Give serious consideration to Decker distortion Hold Workshop on X-Ray BPM Development