Low-a Operation of the Metrology Light Source

1. Low-a Operation of the Metrology Light Source* J. Feikes, M. Ries, P.O. Schmid, G. Wüstefeld HZB Berlin (Germany) A. Hoehl, R. Klein, R. Müller, G. Ulm PTB Berlin (Germany) * J. Feikes et al., PRSTAB-14, 030705 (2011) ICFA Workshop on Future Light Sources, March 5-9, 2012Thomas Jefferson National Accelerator Facility, Newport News, VA (USA)

2. MLS building of the MLS is owned by: and operated by: Outline - MLS overview - MLS low-a optics - a-buckets -THz measurements - Summary

3. octupole MLS machine MLS: the first machine optimized for coherent THz-radiation main MLS parameter scheme of the ring

4. MLS beam optics optical functions definition of a: L=L0(1+a Dp/p0) a=momentum compaction factor low alpha optics, a=0 user optics, a=0.03 d = Dp/p0 rel. momentum deviation a expansion a=a(d) a = a0 + a1d + a2d2 … control of 3 leading a-terms: quadrupoles sextupoles (3 fam.) octupoles (1 fam.) -> a0 -> a1 -> a2 Disp.=0 crossing of chromatic orbits magnet types: 2-pole 4-pole 8-pole 6-pole

5. fs= fs(Dfrf) MLS measurements a = a(Dp/p0) MAD-8 simulation 2 4 68 10 12 14 1618 20 mom. comp. factor / 10-4 synch.-frequency fs / kHz 2 4 6 8 10 12 14 16 18 20 octupole on fs = 9.5 kHz a0 = 4.6x10-4 octupole off 2 2 3 1 3 2 3 1 2 -4 -2 0 2 4 -2 -1 0 1 2 rel. momentum deviation / % rf-frequency change Dfrf / kHz -> : slope of a= a(d) -> a1=0 , adjusted by sextupoles -> : curvature of a= a(d) -> a2, adjusted by octupoles a-seriesexpansion a = a0 + a1d + a2d2 control of higher order terms of

6. a a d d Low-a operation and octupole control effect of octupole setting on lifetime bucket ‘A’ bucket ‘C’ for |a0| < 2.5x10-4 o - octupoles required !! - life time improves substantially for comparison: MLS user optics a0= 330x10-4 figure parameters: E=250 MeV, Vrf=125kV, IMB=20mA calibration: octupole current=-8A -> a2=35 life time as a function of octupole current

7. a-buckets D. Robin et al., Phys. Rev. E 48, 2149 (1993) rf-buckets: ( , ) a-buckets: ( , ) phase space at transition a0> 0 a0< 0 - simplified Hamiltonian H0=eVrffrev/E0 - FP=fixed points (f,d) at a1=0: - double beam:

8. a-buckets B2 C B1 picture of triple beam at beam profile monitor small amplitude bunch parameters, derived from Hamiltonian: fs02= frevH0a0/2p s0 = 2plrffs0d/H0

9. B2 C B1 B C triple beam a1 = 0 B1 C B2 a-buckets synchrotron side bands of triple beam triple beam a1 = 0 20.7 kHz 14.6 kHz ratio of synchrotron tunes = -> talk M. Ries et al., TUOAB02, IPAC 2011

10. B1-current B1 IB1 / mA Isum / mA d / % B1+B2-current C A C B2 time / h f / prad B1-current (red line) as a function of time, the sum current B1+B2 is indicated by the black line. electron flow from B2 to B1 by master clock manipulation a-buckets topping up with a-buckets the electron flow rate from bucket B2 to bucket B1 is controlled by feedback of the rf-frequency, to keep the bucket B1 current constant within 2 % over 10 h. -> M. Ries et al., ICFA Beam Dynamics Mini Workshop on Low Emittance Rings, 2011

11. Transition a0> 0 a0< 0 quad Q1 current scan, crossing a0 = 0 (Q1 acts on dispersion) - no beam loss at a0=0 crossing! - strong correlation between Q1-current & THz power, THz power shows strong maximum - small dip in beam life time at max. THz power, followed by large dip in lifetime - cross section increase indicates double beam, (spurious dispersion in the vertical plane) DI/I = 0.5%

12. 5 4 THz power /arb. units 3 2 linear fit: PTHz~0.86+0.031*I 1 20 60 100 140 beam current / mA THz CSR measurements CSR power vs. beam current (bursting CSR) at 120 mA an average power of max. 60 mW achieved, measured with a calibrated power meter. linear increase of THz power with bunch current. bursting THz power I**2, -> bunch size changes with current

13. beam line THz detector FTIR spectrometer IR microscope THz CSR measurements THz beam port at the MLS CSR power spectrum corrected gain = 100,000 Example of hardware setup at the THz beam port. Different types of detectors are available. Experiments: detector characterization and development (partly in cooperation with DLR (Berlin) and KIT (Karlsruhe)) and spectroscopy. Spectral range 1.4 1/cm (not shown in fig.) to 50 1/cm. incoherent signal mixed with coherent signals, corrected gain = 100,000

14. bunch length as a function of scaled sb-current: -> MLS data is offset with respect to coasting beam theory CSR bursting measurement CSR in time domain (example) bursting thresholds MLS and BESSY II BESSY II data points theory all other points MLS data zero current bunch length / ps ~ scaled sb-bunch current I CSR bursting threshold detected while increasing rf-Voltage amplitude, (0.5 mA SB-current)

15. Summary - the MLS is the first storage ring optimized for CSR - successful control of 3 orders of a - no beam loss at the a0 = 0 crossing - beam can be stored in 3 types of a-buckets - stable and bursting THz-CSR can be produced - bursting thresholds agree fairly well with theory

17. P. Kuske et al., PAC 2003 1 kHz corresponds to a σ of 1.9 ps.

18. IR/THz Strahlrohre an der MLS X-ray and IR Spectrometry IR IR THz THz Undulator-IR

19. Lifetime / h THz-power s-h / mm Dfrf / Hz s-v / mm bunch current / mA THz CSR measurements beam parameters during low alpha current decay mode

20. arb. unit rf-voltage FWHM-x FWHM-y THz-signal Pos-x current Pos-y time / seconds THz CSR measurements THz-signal & beam parameters versus rf-voltage scan @ 250 MeV & 10 kHz rf-scan: 75 kv - 430 kV current: 0.8 mA THz – signal: THz beam line ~2 mm iris aperture mech. chopper 80 Hz 250MeV, 250kV, 10kHz s0=0.44ps ! suppressed THz signal

21. 150 beam current beam current / mA 100 50 THz power / arb. units 0 -50 -30 -10 time / hours THz CSR measurements reproducibility of the THz / low-a optics 13 beam injections cycles After injection, the decay pattern of the THz signals repeats.

22. starting point, short bunch starting point, short bunch 2 Dp/p long bunch, ½ revolution short bunch, ½ revolution Momentum compaction factor a longitudinal beam dynamics & low-a optics non-isochronous ring momentum dependent revolution time isochronous ring a=0 momentum independent revolution time definition of a: L=L0(1+ a Dp/p0) L = orbit length p = electron momentum crossing of chromatic orbits a = momentum compaction factor a =0 for short bunches

23. CSR bursting measurements BESSY II comparison with theory 10 8 6 4 2 1 before 2003 Nov. 2011 zero current rms bunch length / ps coasting beam theory Jan. 2012 BCS: x=0.5+0.34c+dip 1 10 100 1000 scaled single bunch current mA / MV BESSY II bursting thresholds

24. THz CSR measurements stable and bursting CSR chopped unchopped bursting CSR power stable time InSb time domain signals recorded on an oscilloscope, stable and bursting CSR is detected.

25. History marble run: the revolution frequency is independent of the orbit Figure by courtesy of the Museum of the History of Physics, Padua (Italy) “Isochronous apparatus”, Jean Truchet, 1699 Museum of the History of Physics, Padua (Italy) Museum of the History of Science, Florence (Italy)