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Super-B Vibration Tolerances
J. Seeman SLAC Accelerator Directorate June 16-19, 2009 Perugia Meeting
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Outline Overview June 16-19, 2009 Perugia Meeting
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Super-B Parameter Options
June 16-19, 2009 Perugia Meeting
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New Parameters May-June 2009 (comparison with March 09)
Perugia Meeting
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Arc Lattice Raimondi, Biagini, Wittmer, Wienands Arc cell: flexible solution is based on decreasing the natural emittance by increasing mx/cell, and simultaneously adding weak dipoles in the cell drift spaces to decrease synchrotron radiation All cells have: mx=0.75, my=0.25 about 30% fewer sextupoles Better DA since all sextupoles are at –I in both planes (although x and y sextupoles are nested) Distances between magnets compatible with PEP-II hardware All quads-bends-sextupoles in PEP-II range Arcs & FF June 16-19, 2009 Perugia Meeting
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W. Wittmer June 16-19, 2009 Perugia Meeting
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Quadrupole Alignment Misalignment of quadrupole centers, drive large Closed Orbit Distortion Closed Orbit Amplification Factors (COAF) defined as RMS(cod)/ RMS(error) ~50X in both planes or 100µm RMS Quad. misalignment 5mm offset of COD in lattice Quadrupole and Sextupoles have centers measured to a resolution of 10 and 15 µm with pulsed wire technique Allow 2X for resolution, alignment Tolerance <30µm on girder Girder alignment Tolerance in tunnel <100µm (as achieved elsewhere ) girder amplification factors (3,1.5) in ID are ~7 to 8X less than COAF June 16-19, 2009 Perugia Meeting
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Quadrupole BBA Quadrupoles introduce orbit steering with strength changes if closed orbit is offset by x and y then the steering with strength change K2 is Assuming 1µm BPM resolution and K2 ~2% of weakest quadrupole yields resolution on x and y of ~ 6 and 14µm or better We assume a resolution of 10µm for Dynamic Aperture studies June 16-19, 2009 Perugia Meeting
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Roll Errors and Coupling Correction
Magnetic field error tolerances Girder and Dipole roll tolerance < 0.5 mrad Quadrupole and sextupole roll tolerance < 0.2 mrad BPM roll tolerance < 0.2 mrad Skew correction in the discrete orbit correction magnets Two per super-period Corrects yi << 8pm, introduce a vertical dispersion wave to increase vertical size from diffusion not coupling for increased lifetime or increase roll tolerances June 16-19, 2009 Perugia Meeting
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Orbit Stability and Feedback
Small vertical emittance (~ 8pm) yields small beam size σy ~ 2.8µm and σy’ ~ 3µrad Centroid motion of beam cause effective emittance growth June 16-19, 2009 Perugia Meeting
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Tolerance for Orbit Stability
Many operational LSs have set 10%σ centroid motion tolerances Y < 0.1 σy ~ 0.3 µm and Y’ < 0.1 σy’ ~ 0.3 µradian COAF of ~ 15 to 25 y (quads) < nm random motion Uncorrelated quadrupole motion Xq = 330nm and Yq =23nm adds cm ~1% o to each plane or 10% σx,y June 16-19, 2009 Perugia Meeting
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Correlated Quadrupole Errors
Beta calculates cm for correlated motion from plane wave vibration with velocity of wave, vg ~500 m/sec, amplitude for cm ~20% o shown Later N. Simos measured vg ~285 m/sec so scale frequency by 60% 1μm 1μm June 16-19, 2009 Perugia Meeting
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Tolerance for Quadrupole motion without Feedback
Girder amplification factors need to be included to reference to ground vibration limits Girder design has first resonance (horizontal) > 60 Hz. Reduction of cultural noise. Tolerance Limits dX RMS Quads dY RMS Quads X RMS (εx) Y RMS (εy) Random motion < 0.33 μm < μm 19.4 μm (0.02 nm) 0.5 μm (0.088 pm) Plane wave <3Hz < 20 μm < 2 μm 1 μm (0.4 nm) 0.3 μm (1.6 pm) Plane wave >12Hz ~ 0.5 μm ~ 0.15 μm Additional limits dS RMS Dipole dθ RMS Dipole Dipole Random motion < 10 μm < 0.1 μradians 25 μm (0.036 nm) 0.58 μm (0.12 pm) June 16-19, 2009 Perugia Meeting
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Key SR Parameters Top up > 1 minute Bunch to bunch variation = 20%
Nominal Value Energy 3.0 GeV Stored Beam 500 mA; ΔI/I = 1% RF frequency MHz Circumference 792 m Revolution period, T0 2.642 μs Harmonic number 1320 Number of bunches filled 1056 (~80%) Tunes - Qx, Qy 33.36, 16.28 Emittance Bare Lattice 0 (H/V) 2.0 /0.01 nm-rad Emittance with 8-DWs (H/V) 0.60/0.008 nm-rad Bunch length 15-30 ps 9.3 m & 6.6 m straight sections 15/15 (30 cells) Synchrotron frequency, fs kHz Top up > 1 minute Bunch to bunch variation = 20% 3rd Harmonic bunch length cavity 2 RF & 1 injection in 9.3 m June 16-19, 2009 Perugia Meeting
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High Stability BPM Support
RF Buttons Assembly High stability stand - An array of four 50mm dia invar rods bolted to base Each support mounts one BPM detector assembly Two supports are required for short ID straight to mount RF buttons One or two supports required for XBPM assembly Prototype test in advanced stage 4 Invar rods B. Kosciuk; V. Ravindranath June 16-19, 2009 Perugia Meeting
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Vibration Measurement (4-100 hz) Results
Direction RMS Motion (Test in 902 Building) Natural mode freq Amplification Expected RMS Motion at NSLSII Building Stability Requirement Floor Stand y 75nm 75 nm N/A 1X 25 25 nm 100 nm x 30nm 71 nm 38.7 Hz 2.4X 60 nm 250 nm z 35nm 120 nm 34.5 Hz 3.3X 82 nm 10,000 nm High stability stand meets vibration stability requirements Measurement Set-up V. Ravindarnath, B. Kosciuk, F. Lincoln June 16-19, 2009 Perugia Meeting
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Resonance Modes in Multipole Chamber (3.05m)
# Measurements f, MHz GdfidL Equation 1 447.96 448.81 448.47 2 451.63 456.80 456.49 3 460.04 469.82 469.55 4 472.05 487.46 487.24 5 490.06 509.25 509.09 6 511.67 534.67 534.58 7 536.89 563.24 563.23 8 595.72 594.50 594.56 9 628.97 628.05 628.19 Resonance Modes are too Close to BPM Pass Band Frequency BPM Frequency Pass Band 492 – 508 MHz Resonance Modes could effect BPM performance and requires to be suppressed or moved out of BPM band Transmission of BPM SAW filter Measurement Set-up June 16-19, 2009 Perugia Meeting A. Blendykh, P. Cameron, B. Bacha
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RF Metal Fingers D=160mm D=147mm D=123mm D=160 mm Metal fingers
498 321 315 295 MHz MHz MHz MHz MHz MHz MHz D=160mm MHz MHz MHz MHz MHz MHz MHz D=147mm MHz MHz MHz MHz MHz MHz MHz D=123mm Metal fingers Optimal Solution D=150mm Metal finger configuration – 4 sets; 498 mm long; 315 mm separation Metal finger distance of 150 mm (D) from BPM center provides optimal solution BPM frequency margin > 25 MHz A. Blendykh, H-C Hseuh June 16-19, 2009 Perugia Meeting
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RF BPM System – Performance Requirements - I
Parameters/ Subsystems Conditions *Large Aperture RF BPM Resolution Requirement Vertical Horizontal Single bunch, Single turn resolution 378 kHz) 0.05 nC charge 500 μm rms 5.0 nC charge 20 μm rms Single bunch stored beam resolution ( Hz BW) 0.02 mA current 10 μm rms 2.0 mA current 1 μm rms *Small aperture RF BPM requirements specified to be better by a factor of 2 June 16-19, 2009 Perugia Meeting
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RF BPM System – Performance Requirements - 2
Parameters/ Subsystems Conditions *Large Aperture RF BPM Resolution Requirement Vertical Horizontal 50 mA to 500 mA Stored beam resolution – 20% to 100 % duty cycle BPM Receiver Electronics Assuming no contribution from bunch/ fill pattern effects 0.017 Hz to 200 Hz 0.2 μm rms 0.3 μm rms 200 Hz to Hz 0.4 μm rms 0.6 μm rms 1 min to 8 hr drift 0.2 μm peak 0.5 μm peak Bunch charge/ fill pattern effects only DC to 2000 Hz Mechanical motion limit at Pick-up electrodes assembly (ground & support combined) Vibrations 50 Hz to 2000 Hz 10 nm rms 4 Hz to 50 Hz 25 nm rms 0.5 Hz to 4 Hz 200 nm rms Thermal 1 min to 8 hr 200 nm peak 500 nm peak *Small aperture RF BPM requirements specified to be better by a factor of 2 June 16-19, 2009 Perugia Meeting
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XBPMS B. Kosciuk June 16-19, 2009 Perugia Meeting
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