Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 1

Transcription

1 Introduction: bunch length measurements Reminder of optics Non- linear dynamics Low- alpha operation On the user side: THz and X- ray short bunch science CSR measurement and modeling Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 1

2 Introduction: bunch length measurements Picosecond streak camera Hamamatsu C5680 Resolution: 2 ps fwhm RMS bunch length [ps] M. Labat L. Cassinari Bunch current [µa] par paquet Typical bunch lengthening Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 3

3 Reminder of optics Horizontal dispersion function at nominal BETA code x = 3.7 nmrad 1 = Quarter of ring Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 4

4 Reminder of optics Dispersion function at low 1 Control of 2 : High dispersion in the focusing sextupoles BETA code x = 8.6 nm.rad 1 negative values Switch in polarity for one Quad. and one Sext. family Quarter of ring Minimization of x : Control of 1 : x <0 only at the dipole center Exception around the injection section to increase x by varying x in the dipole M. Attal et al., to be published Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 5

5 Reminder of optics Optical functions at nominal BETA code x = z = Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 6

6 Reminder of optics Optical functions at low Control of the chromaticities: High z to compensate for the low x BETA code x = z = 8.40 Optical functions remain unchanged during 1 control But.. Transverse dynamics is strongly affected.. Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 7

7 Non- linear dynamics ON momentum transverse acceptance: Strongly non- linear dynamics at nominal TRACY III code Example with 1 = = = ( nom /25) Linear dynamics Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 8

8 Non- linear dynamics Injection rate is strongly affected by the reduced ON and OFF momentum transverse acceptances ON momentum TRACY III code Example with 1 = = = OFF momentum Amplitude at Injection Injected bunch from the Booster ¼ synchrotron period in ~230 turns Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 9

9 Non- linear dynamics Energy acceptance: at nominal Example with 1 = = = ( nom /25) TRACY III code Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 10

10 CSR and short bunch operation On December th, 2011 the so- called low- alpha mode operation has been delivered to users, which provides: IR beam line Time resolved short X- rays (4.7 ps 1.9 mm RMS bunch length) for 2 beamlines Operation of 2 x 2 days is foreseen for 2012 Hybrid filling mode in order to satisfy both time resolved X-ray and Infrared communities Current per bunch 65 µa/bunch Bunch # 1 value 2 value 1 nominal /25 = = 10-4 Total current, current per bunch 18 ma, 65 µa RMS Bunch length 4.7 ps Horizontal emittance, coupling 8 nm rad, 4 % Lifetime RF voltage 20 hours 3.2 MV 1 and V RF chosen on the basis of THz spectrum optimization Current per bunch is limited by the micro-bunching instabilities threshold: 67 µa per bunch at 1 /25 Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 11

11 CSR and short bunch operation: Stability Beam current stability: o refilling once per hour with 3µA/bunch (tight requirement for THz spectrum stability), o injection with shutters open foreseen for the next operation (April 2012), radiation safety tests in progress. Source point position stability: Slow and Fast orbit feedback systems effective (slightly deteriorated in H plane with respect to the normal mode) H and V long term stability (8 h) nom /25 10 µm Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 12

12 CSR and short bunch operation: Stability Beam current stability: o refilling once per hour with 3µA/bunch (tight requirement for THz spectrum stability), o injection with shutters open foreseen for the next operation (April 2012), radiation safety tests in progress. Source point position stability: Slow and Fast orbit feedback systems effective (slightly deteriorated in H plane with respect to the normal mode) nom 500 Hz: H 10 µm V 700 nm Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 13

13 Science with THz THz spectroscopy using a Fourier Transform interferometer 3 important criteria: Intensity and brilliance AILES beamline: highly collimated beam thanks to dipole edge radiation Confirmed flux gain of ~ with CSR Spectral coverage µwave sources CSR Incoherent SR Frequency (THz) AILES beamline optics dimensioned for long wavelengths (extraction mirror, transport mirrors) Stability Ph.D. project: noise correction system (J. Barros, to be published) Attenuates the effects of microbunching High spectral resolution: more sensitive to intensity fluctuations Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 14

14 Science with THz THz: energy range of (quantified) rotational transitions of molecules in gas phase High- resolution spectroscopy needed to detect the corresponding absorption lines Molecules of astrophysical interest Normal : Too low intensity in this spectral range Low : adapted source Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 15

15 CSR measurement and modeling nom /10 THz measurements on AILES beamline allow to determine the CSR burst current threshold versus / 0 In good agreement with S. Heifest and G. Stupakov analytical threshold [PRST- AB 5 (2002) ] Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 16

16 CSR measurement and modeling Above a current threshold, appearance of microstructures in the longitudinal charge density nom /10 I bunch = 0.22 ma Measurement of a specific frequency nom /10 I bunch = 0.23 ma 35 khz In good agreement with simulation (macro-particle code) C. Evain et al., submitted to EuroPhysics Letters Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 19

17 CSR measurement and modeling Simulation : CSR, Resistive Wall and geometric impedance wakes Bunch current scan over 10 4 turns ( RS ~2800 turns) RW and geometric wakes lengthen further the bunch and slightly shift the burst threshold. + /30 V RF = 3.2 MV CSR power (u.a.) rms E-spread (%) rms bunch length (ps) Bunch current [µa] Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 17

18 CSR measurement and modeling Simulation : CSR, Resistive Wall and geometric impedance wakes Bunch current scan over 10 4 turns ( RS ~2800 turns) Resistive Wall seems to be the driving term of micro- bunching instability - /30 V RF = 3.2 MV CSR power (u.a.) rms E-spread (%) rms bunch length (ps) Bunch current [µa] Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 18

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20 Introduction: Storage Ring main parameters Parameters Design Achieved as of Feb 2012 Energy ( GeV ) RF frequency ( MHz ) Betatron Tunes / / Momentum Compaction x 10-4 / 4.6 x x 10-4 / 4.6 x 10-3 Emittance H ( nm.rad ) Energy spread x x 10-3 Coupling, V / H <1% 0.7% (w/o corr.) 1% (w/ V dispersion) Current Multibunch mode ( ma ) (400 for Users operation) Average Pressure ( mbar ) 1 x x 500 ma Beam Lifetime ( h ) 16 h 400 ma / 500 ma Future Light Sources March 5-9, 2012 Low- alpha mode at SOLEIL 2