1. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 1 J. Jacob NSLS II Beam Stability Workshop BNL, April 18 th - 20 th, 2007 High Frequency Beam Effects at the ESRF

2. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 2 Outline High Frequency effects affecting beam stability at ESRF (6 GeV) Multibunch  total current, essentially narrow band impedances  Longitudinal:  HOM driven instabilities  Transverse  Dominated by resistive wall instabilities (screening HOM effect)  Ions Single bunch  current per bunch, broad band impedances  Longitudinal:  Microwave instability  Transverse:  Mode coupling instability - TMCI  Head Tail instability  Side effects:  High peak signals  distortion of BPM readings  Heating (bellow shielding, special vessels, …)  Pressure burst, lifetime accidents, beam losses, … RF Phase noise Countermeasures Constructive measures  Minimization of impedances  Vacuum chamber material  Discontinuities, bellow shielding,…  Cavity design  Passive damping (HOMs)  Active damping (Feedbacks)  Reduction of RF Phase noise Operation parameters  Partial filling of the storage ring  Positive chromaticity  RF Voltage,… Effect of Harmonic Cavities  Lifetime increase by bunch lengthening  Landau damping of LCBI  Effect on other beam dynamics 

3. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 3 Multibunch – HOM driven LCBI ESRF–SR: 6 five-cell cavities  lowest LCBI thresholds: 40 mA  stabilized by Landau damping from transient beam loading in fractional SR filling  200 mA in non symmetric 1/3, later 2/3 filling  1998: new cavity temperature regulation to ± 0.05ºC, for precise control of HOM frequencies  stable at 200 mA in uniform and symmetric 2 x 1/3 filling  Not possible to exceed 250 mA  Dec 2006: longitudinal bunch-by-bunch feedback - LFB with  1 ms damping time  300 mA in uniform  Limited   V RF : 9  11 MV against Robinson instability  No further beam increase  Window power at maximum  Robinson  even higher V RF  Maximum 300 mA with existing cavities R/Q = 139  /cellQo = 38500 Rs = 26.8 M  (5 cells)frf = 352.2 MHz V nom = 1.4 … 2.5 MV (Booster: 4 MV pulsed) 2 couplers:  max = 4.4 Max 170 kW/coupler

4. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 4 Multibunch – HOM driven LCBI 1/3 fill 2  s 0.5 ns  bunch Only one part of the bunch train participates to coherent motion Streak camera image of a LCBI Streak camera I threshold [mA] SR Portion filled Increasing gap Landau damping from fractional filling of storage ring [O. Naumann & J. Jacob]

5. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 5 ESRF Cavity Temperature regulation system (cav. 1 & 2) Multibunch – HOM driven LCBI T = T set ± 0.05 ºC  200 mA in uniform filling

6. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 6 Multibunch – HOM driven LCBI QPSK modulator 200 MHz BW low pass FPGA processor ADC in 1.2 GHz to 1.4GHz BW cavity DAC out RF clock  1.4 GHz power amplifier 4 x 50 W = 200 W Phase detection at 1.4 GHz [inspired from PEP II, ALS, DAFNE,…design ] [E. Plouviez, G. Naylor, G. Gautier, J.-M. Koch, F. Epaud, V. Serrière, J.-L. Revol, J. Jacob, …] December 2006: 300 mA reached thanks to LFB (LFB = longitudinal digital bunch-by-bunch feedback) 300 mA delivery to users planned for mid 2008 Bandwidth: f RF /2 = 176 MHz

7. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 7 Multibunch – HOM driven LCBI Phase detector sensitivity [  f(freq) ]  10 mV /° Thermal noise (R = 50 , BW = 176 MHz) Phase detector turn by turn resolution:  5 10 -4 °  4 fs @352 MHz Work at 4 frf = 1.4 GHz   resolution:  1 fs / turn 14 bit ADC, LSB = , usable range ± 8000 LSB  detect-range  ±8 ps  Suppression of spurious signal (RF noise, transients) below ±8 ps ! Dimensioning of LFB: ESRF natural damping time  s = 3.6 ms DSP algorithm  minimum active damping time  damp = 0.5 ms   s /7 (loop delay)  Gain: So, without safety margin:  1 fs / turn  (Kicker provides 500 V)

8. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 8 Multibunch – HOM driven LCBI 0.4ps rms 2.5ps rms 1V/ RF degree 7ps / RF degree Will not saturate the ADC (<8ps), nevertheless: high pass filter in analogue front end LFB Spurious phase signals: mode 0 signals level

9. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 9 Multibunch – HOM driven LCBI 2 x 1/3 filling Would put +/-15 V at the input of the ADC Must be reduced by 30dB in the analog front end:  Beam Transient Suppression (BTS) in front end  Actually simple HP filter suffices LFB Spurious phase signals: beam loading transients

10. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 10 Multibunch – HOM driven LCBI FIR: (a,b,c,1,c,b,a,0,-a,-b,-c,-1,-c,-b,-a,0) Further Mode 0 removal Factor 11 decimation: 11 T 0 = 31  s 16 TAP FIR: 16 x 31  s = 0.5 ms = T synchrotron BP filter at fs Differentiation (V kick  j  ): phase shift by 90° Total averaging 176, sensitivity: 1fs -> 0.08 fs

11. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 11 Improved design Cut off 460 MHz Cut off 749 MHz 4 ridges Multibunch – HOM driven LCBI New 352 MHz Cavities for ESRF Unconditional stability & higher current: 400…500 mA SC cavities (e.g. SOLEIL type): Beam power  2 couplers/cell NC single cell HOM damped cavities / 1 coupler/cell  preferred solution  R&D based one BESSY design with ferrite loaded ridge waveguides for selective HOM damping [E. Weihreter, F. Marhauser] 1 st aluminum prototype at ESRF RF lab Cut off 435 MHz [N. Guillotin, V. Serrière, P. Roussely, J. Jacob]

12. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 12 Multibunch – HOM driven LCBI Tolerated Longitudinal HOM impedance for 18 installed cavities measured on 1 st Al prototype GdfidL simulation of 1 st Al prototype GdfidL simulation of Improved design

13. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 13 Multibunch –TCBI / Resist. Wall & Ions CBI from Transverse HOM impedance never observed: screened by Resistive Wall Instability (RWI) Since commissioning installation of smaller & smaller ID gaps:  8 mm inner height, 5 m long vessels  NEG coated extruded Al  Al: high conductivity  maximize RWI thresholds  NEG: efficient distributed pumping  minimize Bremsstrahlung & ion instabilities  6 mm in-vaccum undulators: Ni-Cu foil Slightly positive normalized chromaticities to damp resistive wall and ion instability  Goal: keep emittances  x = 4 nm rd  z = 25 pm rd  For 200 mA, setting:  x = 0.2  z = 0.6  Vertical Broad Band Resonator (BBR) to be added to RW model to explain thresholds, BBR has a damping effect on narrow band TCBI (f res = 22 GHz, R  /Q = 6.8 M , Q = 1)  First successful tests with transverse bunch-by-bunch feedback - TFB (developed in parallel with LFB) : allows operation with  = 0 for more dynamical aperture & longer lifetime Sytematic conditioning at restart shifts after vacuum opening during shut downs Experience at 300 mA  Successful use of TFB to damp vertical ion instability [P. Kernel, R. Nagaoka, J.-L. Revol]

14. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 14 Multibunch –TCBI / Resist. Wall & Ions 986986 Uniform 124 mA Vertical  x = 0.2  z =0.19 Ion signature around 5 fo 991991 990990 Resistive wall Vertical spectrum near threshold in  v RWI threshold as a function of  v [P. Kernel, R. Nagaoka, J.-L. Revol]

15. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 15 Single Bunch – Bunch Lengthening USM Range Single Hybrid 16 Bunch 4 Bunch Single 7/8 4.5 mA ps rms [J.-L. Revol] I per bunch [mA]

16. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 16 E/EE/E 0.1 % 0.2 % 0.4 % Single Bunch – Microwave instability  E /E I per bunch [mA] keV Energy spread measured at ESRF Tracking simulations  fit of longitudinal BBR: f res = 30 GHz, R s = 42 k , Q=1 (  Z/p = j 0.5 

17. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 17 Single Bunch – Vertical Instabilities [P. Kernel, R. Nagaoka, J.-L. Revol] TMCI threshold Vertical TMCI instability at zero chromaticity Vertical Head Tail Instability Vertical Transverse Mode Coupling Instability at 0.67 mA (TMCI) for  v = 0

18. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 18 Single Bunch – Horizontal Head Tail Increasing difficulties in single bunch mode (also in 16 bunch and hybrid) Injection saturation Overcome by correcting “on line” the half integer resonance and decreasing the zero current tune. The single bunch experiences an increase of the horizontal incoherent tune shift, coming from the asymmetry of the vacuum chamber Decrease of the horizontal instability threshold Overcome by pushing the chromaticity (or reducing the single bunch current in hybrid) October 2002 February 2001 September 2001 Hybrid/16Bunch Working  Single Bunch Working  Zero current tune=0.44 Mode -1 Mode +1 Mode +2 Gap Open [P. Kernel, R. Nagaoka, J.-L. Revol]

19. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 19 RF Phase noise Existing klystron transmitters:  d  /d(HV)  7 ° per % HV  Phase noise up to -50 dBc at multiples of 300 Hz / HVPS ripples  Beam sensitive (f synchrotron = 1.2 to 2 kHz)  Fast phase loop → -70 dBc  Unstable behaviour  Multipactor / input cavity  Mod-Anode breakdowns  Many auxiliaries, trips  Risk of Klystron obsolescence  ESRF RF upgrade project:  Solid State Amplifiers - SSA, based on SOLEIL design  Intrinsicly redundant  Switched power supplies at 100 kHz (far from f synchrotron )  Negligible phase noise  Overall 50 % efficiency 352 MHz 1.3 MW klystron Thales TH 2089 352 MHz –190 kW Solid State Amplifiers (2 units) 682 transistor modules + 42 in standby [P. Marchand, T. Ruan et al.]

20. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 20 Bunch length Harmonic Cavities – theoretical study   [rad] U loss /e V acc [MV] Bunch length U loss /e  [rad] V [MV] V acc (  ) V hc (  ) V m (  ) Harmonic 3  L  4  L  Touschek  4  Touschek   d  /dt

21. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 21 Harmonic Cavities – theoretical study  Interest in a third harmonic RF system for the ESRF ? 200 mA uniform  life = 60 hNO 90 mA in 16 bunch  life = 10 hYES up to 20 mA single bunch  life = 5 hYES  Interaction with BBR, accelerating and higher order modes ?? Single bunch multiparticle model: BESAC: Potential Well and Microwave Instability Multibunch multiparticle model Harmonic cavity, Potential well & Microwave Instability, AC and DC Robinson instabilities, Landau damping of LCBI [J.Byrd, S.De Santis, J.Jacob, V,Serriere] Multibunch single particle model: Transient beam loading effects with a harmonic RF system [G.Besnier, C.Limborg, T.Günzel] [V.Serriere, J. Jacob] ESRF ALS, ESRF  see also [R. Bosch]

22. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 22 Harmonic Cavities – theoretical study Main Results  Potential well distortion (from BBR, i.e. Z/p = j 0.5  ):  e.g. at ESRF in 16 bunch for I/bunch = 5.5 mA LL  wave instab. @ 20 mA  L Harmonic cavity Further factor 3  L LL Potential well @ 5.5 mA LL Harmonic cavity Further factor 4  L EE  wave instab. @ 20 mA  E Harmonic cavity Reduces E-spread  E  Microwave instability (from BBR above 5 mA, 30 GHz, 42 kW, Q=1 ):  e.g. at ESRF in single bunch at 20 mA

23. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 23 Harmonic Cavities – theoretical study Tracking code, confirmed by numerical resolution of Haissinski equation: Total bunch lengthening = Potential well effect X Elongation from harmonic voltage

24. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 24 Harmonic Cavities – theoretical study Microwave Instability & bunch lengthening by harmonic voltage At 25 mA: still bunchlength increase factor of 2.7

25. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 25 Harmonic Cavities – theoretical study Harmonic cavity technology for ESRF ?  low total intensity modes ! Passive NC Cu cavities: Nmin = 150 unrealistic Active NC Cu cavities:Nmin = 12still not practical Passive SC cavity pair:Nmin = 4imposed by AC Robinson Active SC cavity pair:N = 1Only practical solution with 80 … 100 kW generator ESRF :Scaling of Super-3HC to f res,hc = 1056.6 MHz Super-3HC cavity pair: Superconducting Module with a pair of cavities 3 rd harmonic cavity for: SLS & Elettra Scaling of the SC SOLEIL Cavity Construction: CEA & CERN R s /Q= 90 W Quality factor: Q 0 = 2.10 8 f res,hc = 1.5 GHz  Low R/Q of SC cavities  less phase transients  net gain in  life less affected by gap in fill

26. FR NSLS II Beam Stability Workshop, April 2007 High Frequency Beam Effects at the ESRFJ. Jacob, slide 26 Harmonic Cavities – theoretical study HOM driven LCBI at MAX II: Without harmonic cavity: I threshold ≈ 10 mA With harmonic cavity: stable at 250 mA due to Landau damping LCBI Prediction for the ESRF: LCBI thresholds only slightly increased by Landau damping on a higher energy machine like ESRF  E /E  E, nat Harmonic Voltage [kV] measurements [Å. Anderson & al.] Tracking simulation I beam = 250 mA Tracking code Linear model