First Collective Effects Measurements in NSLS-II A. Blednykh Accelerator Physicist, BNL/NSLS-II Sep , 2014

Transcription

1 First Collective Effects Measurements in NSLS-II A. Blednykh Accelerator Physicist, BNL/NSLS-II Sep , 2014 (LOWεRING 2014) 1 BROOKHAVEN SCIENCE ASSOCIATES

2 Outline Phase 1 (25mA / PETRA-III) and Phase 2 (50mA / CESR-B) Commissioning w/o ID s Local Beam Impedance Measurements First Collective Effects and Beam Impedance Measurements Summary 2 BROOKHAVEN SCIENCE ASSOCIATES

3 Energy 3.0 GeV Circumference 792 m Number of Periods 30DBA Length Long Straights 6.6 & 9.3m Emittance (h,v) <1nm, 0.008nm Momentum Compaction Dipole Bend Radius 25m Energy Loss per Turn <2MeV NSLS-II Parameters NSLS-II Machine Concept Superconducting RF Top-Off Operation DBA30 Lattice Ultra-Low Emittance (<1 nm) Damping Wigglers Large Dipole Bend Radius (25 m) Provision for IR Source Three-pole wiggler x-ray sources Energy Spread 0.094% RF Frequency 500 MHz Harmonic Number 1320 RF Bucket Height 3% RMS Bunch Length 15ps Average Current 500mA Current per Bunch 0.5mA Charge per Bunch 1.2nC 3 BROOKHAVEN SCIENCE ASSOCIATES

4 ReZy, M /m RF Straight Section (PETRA-III, Cell24) W y, V/m σ s = 14. 4mm σ s = 3mm s, mm Vertical Dipole Short-Range Wakepotential ReZ, Frequency, GHz Real Part of the Longitudinal Impedance 15 yd, V/pC/m E 110 E , mm Frequency, GHz Real Part of the Transverse Impedance Vertical Kick Factor vs. Bunch Length 4 BROOKHAVEN SCIENCE ASSOCIATES

5 Longitudinal Coupled-Bunch Instability Measured CB Instability driven by PETRA-III HOM s Frequency MHz Bunch Mode Average Current ma Cavity Temperature C Calculated PETRA-III Higher-Oder Longitudinal Modes Shunt Impedance, R sh, Frequency, f, MHz Quality Factor, Q Growth rates for 1320 bunches uniformly filling the ring: 1 = I + 0η (pmω τ μ 4πE 0 ν 0 + μω 0 + ω s )e pmω 0+μω 0 +ω 2 s σ 2 ReZ (pmω 0 + μω 0 + ω s ) s p= Worst Case Scenario Frequency Set to : f r = MHz ReZ 2Mω ω 0 + ω s = R sh, = 0.6MΩ Matching To Measured Growth Time Frequency Set to : f r = MHz Growth Time: τ gr = 6.7 ms Growth Time: τ gr = 8.2 ms Damp. Time : τ rad = 27 ms 5 BROOKHAVEN SCIENCE ASSOCIATES

6 NEG Coated DW Chamber (Cell 8) BPM (SA) BPM (SA) BPM (LA) BPM (LA) NEG coating long. surface roughness: < 1μm Table 1: Numerically Obtained Data (σ s = 3mm) k yrw, V/pC/m Straight Section (Cell08): k yd, V/pC/m k yt = 170 V/pC/m DW Chamber Profile k yq, V/pC/m Fast Corr BLW SA BPM 1.36 TBD TBD DW Chamber 114 (Al) SA BPM 1.36 TBD TBD BLW Fast Corr V. Kiselev and V. Smaluk, Measurement of Local Impedance by an Orbit Bump Method, NIMA 525 (2004), q ( s ) ( s) y ) y 0 y ( s) k y0 cos ( s) ( s0 E e 2sin y Measured Vertical Kick Factor: k y = 235V/pC/m 6 BROOKHAVEN SCIENCE ASSOCIATES y (1), ν y = 0.239

7 Odd Cell (Standard Arc) BPM (LA) BPM (LA) BPM (LA) BPM (LA) C. Hetzel 7 BROOKHAVEN SCIENCE ASSOCIATES

8 Transverse Mode Coupling Instability Average Transverse Coherent Tune Shift (Vanishing Chromaticity) ν y ν s av = e2 N e β y 4π γ mc 2 ν s k y = 0.7 Vertical Kick Factor (Geometric) k y = c π 0 dk ImZ y (k)e k2 σ 2 Broad-Band Resonator k y BBR = c R 2 πσ s Q (k r σ s > 1) Resistive Wall (Normal Conducting) k y rw = 0.58 cz 0 4π s 2 b Z 1/ / 0 cond 2s 0 L b 4 s 0 σ s k y = 425 V/ pc m 20 ID s with 2.5mm radius Bunch Length, σ s = 3mm 70m of Cu & β y = 3m Bunch Charge, Ne = 1.25nC k y β y = 49kV/pC Energy, E = 3GeV I Synchrotron Tune, ν s = th = 1.8mA per bunch TMCI Threshold, k y β y < 180 kv/pc A. Blednykh et al., Transverse Impedance Of Small-Gap, EPAC06 S. Krinsky, Simulation of Transverse Instabilities, BNL IR 8 BROOKHAVEN SCIENCE ASSOCIATES

9 Phase 1, Vertical Plane (Vanishing Chrom.) On-Line Plot (CSS-Panel) of the Spectra ξ x,y = 0 Vertical Tune and Spectra of BPM41 vertical TBT data Accumulated Single Bunch Current: I 0 = 0.7mA Measured Vertical Kick Factor G. Bassi k y = ν y ΔI 0 2E 0 ω 0 β y = 14 kv/pc m Energy, E 0 = 3GeV RF Voltage, V RF = 1.86MV Bunch Length, σ s = 3.3mm Beta Function, β y = 7.7m Rev. Frequency, ω 0 = 2π 378.6kHz A. Blednykh et al., NSLS-II Commissioning with 500MHz, IPAC14 9 BROOKHAVEN SCIENCE ASSOCIATES

10 Resistive Wall Evaluation (σ s =3mm) Length, mm k loss, V/pC k y, kv/pc/m k y β y, kv/pc Long Straight Sections (3.3) 0.52 (1.2) 3 (6.7) Short Straight Sections Even Arcs Odd Arcs Total: (11.6) 1.48 (2.15) 18.4 (22.1) Loss Factor k loss = 1.2 cz 0 4π L 2πb 2 s 0 σ s 3/2 Kick Factor k y = 0.58 cz 0 4π 2s 0 L b 4 s 0 σ s NSLS-II Circumference: m 10 BROOKHAVEN SCIENCE ASSOCIATES

11 Vertical Plane (Positive Chromaticity) High intensity due to lowering and ramping up V RF Transverse bunch-by-bunch feedback system OFF 2.1mA ξ x,y +2/+2 Synchrotron Light Monitor ξ x,y = +4.6/+4.6 Synchrotron Tune ν s = hη 2πβ s 2 E 0 V RF cosφ s Vertical tune as a function of current ξ x,y = +1/+1 ξ x,y = +2/+2 I 0 = 0.96mA I 0 = 0.7mA Bunch Length σ s = 2πc ω 0 ηe 0 hev RF cosφ s σ ε E 0 Spectra of BPM41 vertical TBT data. 11 BROOKHAVEN SCIENCE ASSOCIATES

12 Horizontal Plane (Single Bunch) Horizontal Tune vs. Current for high Resolution FFT Method Measured horizontal TBT data at chromaticity ξ x,y = +1/+1, BPM 6 (I 0 = 0.85 ma). Horizontal Tune vs. Current for Interpolated FFT Method for all 180 BPMs Y. Hidaka Broad-Band Resonator ω r = 2π 30GHz Q = 1 R sh,x = 0.4MΩ/m G. Bassi Absolute value of the measured horizontal growth rate as a function of current at ξ x,y = +1/+1 and ξ x,y = +2/+2 with the fitted slope. 12 BROOKHAVEN SCIENCE ASSOCIATES

13 Phase 2, Achieved a Stored Current of 50 ma Screenshot of the CSS-Panels (BLW C08, C18 & Septum) Surface Temperature Increases about 0.3 degrees Celsius 13 BROOKHAVEN SCIENCE ASSOCIATES

14 Summary NSLS-II storage ring commissioning continue Phase 3, ID s commissioning in under way Repeat local impedance measurements with modified local bump model for 4 straight sections occupied with NEG coated chambers, 3DW s and 1 EPU, and for several variable-gap IVU s Orbit Response Matrix Fit Method for Local Transverse Impedance Measurements is going to be applied Single bunch (0.5 ma) and average current (500 ma) goals are achievable 14 BROOKHAVEN SCIENCE ASSOCIATES

15 Acknowledgments NSLS-II/BNL/US: B. Kosciuk, C. Hetzel, H.-C. Hseuh, B. Bacha, W. Cheng, F. Willeke, T. Shaftan, G. Bassi, G. Wang, S. Ozaki, B. Podobedov, Y. Li, L.-H. Yu, Y. Hidaka, J. Choi, L. Yang DIAMOND/UK V. Smaluk 15 BROOKHAVEN SCIENCE ASSOCIATES

16 Back-Up Slides 16 BROOKHAVEN SCIENCE ASSOCIATES

17 RF Spring Aperture Limitation Phase 1 (Cell10) After Phase 1, 25mA (Cell08) Difficulties in Orbit Correction The assembly method needs to revised! The fan burned through the spring 17 BROOKHAVEN SCIENCE ASSOCIATES

18 Commissioning Phase 1: Longitudinal Coupled-Bunch Instability Analysis Observed longitudinal instability in multi-bunch mode (~1000 bunches) by HOM with frequency f r = 728MHz (bunch mode 603) with growth time τ gr = 6.7ms, much smaller than the longitudinal radiation damping time τ s = 27ms, at an average current I 0 = 11.64mA mA. Courtesy of D. Teytelman 18 BROOKHAVEN SCIENCE ASSOCIATES

19 Transverse Coupled-Bunch Stability Analysis (I av =25mA) (Analysis performed prior to the commissioning) Transversely unstable at zero chromaticity (ξ=0): growth time τ gr = 0.74ms τ x = 54ms Cure: 1) Run at positive chromaticity to provide damping via slow head tail effect 2) Frequency shift (ΔΩ) of HOM s 1 Im( Fastest growing mode μ=74 IbMc ) 4 ( E / e) 0 x p Re Z τ gr vs. Ω at ξ = 0 ( pm ). 0 0 Slow head-tail effect: damping at ξ=2 Self consistent simulations of head-tail effect + coupled-bunch interaction with the OASIS code M=132, N=3.1x10 9, R BB =1MΩ/m: (1,60KHz), (2,40KHz) Working Points (ξ,δω) M=132, N=3.1x10 9, R BB =0.5MΩ/m : (1,110KHz), (2,70KHz) M=66, N=6.2x10 9, R BB =0.5MΩ/m : (1,60KHz), (2,40KHz) ΔΩ, khz 19 BROOKHAVEN SCIENCE ASSOCIATES

20 Phase 2, Vertical TbT Data (+2/+2, V RF =1.2MV) 0.2mA 0.75mA 1.16mA 0.43mA 0.8mA 1.27mA 0.55mA 0.85mA 1.87mA 0.6mA 0.9mA 1.98mA 0.65mA 0.96mA 0.7mA 1mA 20 BROOKHAVEN SCIENCE ASSOCIATES