1 BROOKHAVEN SCIENCE ASSOCIATES Stephen Kramer, VUV Ring Manager CSR Emission Studies in VUV/IR Ring NSLS

2 BROOKHAVEN SCIENCE ASSOCIATES Technical Design Parameters NSLS VUV and Xray Light Sources Proposed in 1970’s VUV ops 1982, Xray ops 1984 with >2300 Users/year using >65 beam lines from Far-IR to Hard Xrays VUV /IR Ring Parameters Energy 0.8 GeV Circumference 51m Number of Periods 4 DBA Length ID Straights m Emittance (h,v) 160 nm, >0.4 nm Momentum Compaction.0235 Dipole Bend Radius 1.91 m Energy Loss per Turn 19.8 KeV User Top-off rate hrs. Ports VUV (UND) / IR 16 (2) / 6 IR Energy Spread 0.094% RF Frequency MHz Harmonic Number 9 (7 filled) RF Bucket Height > 1.4% RMS Bunch Length 150ps- 2ns Oper. /Max Current 1/ 1.5 Amp Current per Bunch ma Charge per Bunch 0.5nC Touschek Lifetime > 3 hrs

3 BROOKHAVEN SCIENCE ASSOCIATES VUV Period for Achromatic Optics Peak  x ~ 1.51 m, Doublet makes β x small in dispersion and large in ID making Touschek lifetime small due to septum edge

4 BROOKHAVEN SCIENCE ASSOCIATES IR Developed in 1989  6 in 2004 Mirrors M1 and M2 Mirror M3 Source point e UHV window cone bolometer ( He) lamellar grating interferometer chop

5 BROOKHAVEN SCIENCE ASSOCIATES FIR Port at end of Dipole U11/U12/U12IRU12IR extraction Two VUV ports ahead of FIR, at 7° and 22° into 45° dipole, ρ = 1.91 m dipole chamber shielding cut-off for CSR and ISR f c ~ 24 GHz or 0.8 cm -1

6 BROOKHAVEN SCIENCE ASSOCIATES ~1998 U12IR FIR Beam Saturated Detector

7 BROOKHAVEN SCIENCE ASSOCIATES Threshold Current Microwave Instability Bunch length data showed a threshold of mA for Microwave threshold at MeV with Z bb /n ~ 1.8Ω and Spear scaling

8 BROOKHAVEN SCIENCE ASSOCIATES Energy Dependence Microwave Instability The microwave threshold based on the Keil-Schnell Criterion

9 BROOKHAVEN SCIENCE ASSOCIATES FIR Measurements of Spectra in 2-FIR Interference model for line structure in both ISR and CSR pattern with Δf ~ 1cm -1 spacing in two similar beamlines with different spectra ranges

10 BROOKHAVEN SCIENCE ASSOCIATES Reflection from Dipole Chamber Outer Wall Could give a Sin 2 (2π f Δt) modulation to broadband ISR and CSR spectra ΔL~1cm or frequency spacing ~ 30 GHz Slope =2*sin(  /2) ~ 0.4 Zero at ~30 GHz due to 180 degree phase shift at metal boundary

11 BROOKHAVEN SCIENCE ASSOCIATES FIR Beam Coupler Has Cut Off ~30GHz Optical coupling to FIR port cuts off below ~30 GHz, 4” beam window available 90° Metal paddle to block FIR beam deflects microwaves down to window (ring VC limits) Dipole chamber cut-off waveguide frequency TE 1,0 ~ 2GHz and TM 1,1 ~ 4 GHz Microwave measurements confirm CSR peak ~42GHz ~1.4 cm -1 peak “C”, but see two more “A and B” Microwave horns for deflected light

12 BROOKHAVEN SCIENCE ASSOCIATES Time Dependence of Peak Signals B and C are prompt signals from the bunch limited by RF diode ~1GHz BW Revolution time T o =170nsec A signal ns wide delayed by ~30-50ns from bunch

13 BROOKHAVEN SCIENCE ASSOCIATES Power in Peaks versus Bunch Current C &B signal linear for I o < I th C&B quadratic for I o > I th C&B E y polarization A signal always quadratic or higher beam impedance P~ I 2 * R A signal unpolarized

14 BROOKHAVEN SCIENCE ASSOCIATES A Peak - Wakefield Emission From Bellows Vacuum bellows shield with Cu convolutions 1cm gave calculated beam impedance  RF microwave and charge modulation shows 6.5GHz but ~4GHz at current below  Threshold current

15 BROOKHAVEN SCIENCE ASSOCIATES Micro-bunching measured with SC Triggering the Streak Camera on the A peak signal yielded consistent micro-structure with 150 psec modulation or 6.5 GHz, no other micro-bunch was significant.

16 BROOKHAVEN SCIENCE ASSOCIATES Warnock & Venturini CSR Signal + Interferr. Adding a 0.8cm delay for reflection from outer dipole chamber wall

17 BROOKHAVEN SCIENCE ASSOCIATES Interference Pattern from Different Ports U10IR port has only 20° of bend ahead of port not > 23° for Interference pattern from dipole. However pattern from upstream dipole less clear.

18 BROOKHAVEN SCIENCE ASSOCIATES FIR Beam Port and Detectors Response

19 BROOKHAVEN SCIENCE ASSOCIATES Summary and Status VUV ring CSR emission above Microwave Instability which scales with energy and α 1 CSR and ISR show interference pattern from outer wall broader than WG modes but related Shielded ISR and CSR cut-off frequency appears to be ~ 24 GHz but sharp cutoff, allows the 6 GHz wakefield signal to be observed Wakefield power growth proceeds CSR, shows clear micro-bunching above CSR threshold FIR users not interested in stable CSR emission but maybe hard to achieve without RF upgrade

20 BROOKHAVEN SCIENCE ASSOCIATES