1 / 26

High Frequency Beam Effects at the ESRF

High Frequency Beam Effects at the ESRF. J. Jacob. NSLS II Beam Stability Workshop BNL, April 18 th - 20 th , 2007. High Frequency effects affecting beam stability at ESRF (6 GeV) Multibunch  total current, essentially narrow band impedances Longitudinal: HOM driven instabilities

dior
Télécharger la présentation

High Frequency Beam Effects at the ESRF

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  2. 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 Outline  High Frequency Beam Effects at the ESRF

  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 b VRF: 9  11 MV against Robinson instability • No further beam increase • Window power at maximum • Robinson  even higher VRF • Maximum 300 mA with existing cavities R/Q = 139 /cell Qo = 38500 Rs = 26.8 M (5 cells) frf = 352.2 MHz Vnom = 1.4 … 2.5 MV (Booster: 4 MV pulsed) 2 couplers: bmax = 4.4 Max 170 kW/coupler High Frequency Beam Effects at the ESRF

  4. Multibunch – HOM driven LCBI 1/3 fill Ithreshold [mA] tbunch Only one part of the bunch train participates to coherent motion 0.5 ns Increasinggap SR Portion filled Streak camera 2 ms Landau damping from fractional filling of storage ring Streak camera image of a LCBI [O. Naumann & J. Jacob] High Frequency Beam Effects at the ESRF

  5. Multibunch – HOM driven LCBI ESRF Cavity Temperature regulation system (cav. 1 & 2) T = Tset± 0.05 ºC  200 mA in uniform filling High Frequency Beam Effects at the ESRF

  6. Multibunch – HOM driven LCBI Phase detection at 1.4 GHz 200 MHz BW low pass FPGA processor S ADC in RF clock DAC out RF clock 1.2 GHz to 1.4GHz BW cavity QPSK modulator 1.4 GHz power amplifier 4 x 50 W = 200 W 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: fRF/2 = 176 MHz [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, …] High Frequency Beam Effects at the ESRF

  7. Multibunch – HOM driven LCBI Dimensioning of LFB: • ESRF natural damping time ts = 3.6 ms • DSP algorithm minimum active damping timetdamp = 0.5 ms ts /7 (loop delay)  Gain: • So, without safety margin: dt  1 fs / turn  (Kicker provides 500 V) High Frequency Beam Effects at the ESRF

  8. Multibunch – HOM driven LCBI 2.5ps rms 0.4ps rms LFB Spurious phase signals: mode 0 signals level 1V/ RF degree 7ps / RFdegree Will not saturate the ADC(<8ps), nevertheless: high pass filter in analogue front end High Frequency Beam Effects at the ESRF

  9. Multibunch – HOM driven LCBI LFB Spurious phase signals: beam loading transients • 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 High Frequency Beam Effects at the ESRF

  10. Multibunch – HOM driven LCBI 16 TAP FIR:16 x 31 ms = 0.5 ms = Tsynchrotron • BP filter at fs • Differentiation (Vkick jt): phase shift by 90° • Total averaging 176, sensitivity: 1fs -> 0.08 fs Factor 11 decimation: 11 T0 = 31 ms FIR: (a,b,c,1,c,b,a,0,-a,-b,-c,-1,-c,-b,-a,0) Further Mode 0 removal High Frequency Beam Effects at the ESRF

  11. Multibunch – HOM driven LCBI 1st aluminum prototype at ESRF RF lab Improved design Cut off 749 MHz 4 ridges Cut off 460 MHz 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] Cut off 435 MHz [N. Guillotin, V. Serrière, P. Roussely, J. Jacob] High Frequency Beam Effects at the ESRF

  12. Multibunch – HOM driven LCBI measured on 1st Al prototype GdfidL simulation of 1st Al prototype GdfidL simulation of Improved design Tolerated Longitudinal HOM impedance for 18 installed cavities High Frequency Beam Effects at the ESRF

  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 ex = 4 nm rd ez = 25 pm rd • For 200 mA, setting: xx = 0.2 xz = 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 (fres = 22 GHz, Rb/Q = 6.8 MW, Q = 1) • First successful tests with transverse bunch-by-bunch feedback - TFB (developed in parallel with LFB) : allows operation with x = 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 TFBto damp vertical ion instability [P. Kernel, R. Nagaoka, J.-L. Revol] High Frequency Beam Effects at the ESRF

  14. Multibunch –TCBI /Resist. Wall & Ions Uniform 124 mA Vertical xx = 0.2 xz =0.19 991 Resistive wall 986 Ion signature around 5 fo 990 RWI threshold as a function of xv Vertical spectrum near threshold in xv [P. Kernel, R. Nagaoka, J.-L. Revol] High Frequency Beam Effects at the ESRF

  15. Single Bunch – Bunch Lengthening 4 Bunch 16 Bunch Single Hybrid Single 7/8 USM Range 4.5 mA ps rms I per bunch [mA] [J.-L. Revol] High Frequency Beam Effects at the ESRF

  16. Single Bunch – Microwave instability 0.1 % sE/E 0.2 % 0.4 % sE/E Energy spread measured at ESRF keV Tracking simulations  fit of longitudinal BBR: fres = 30 GHz, Rs = 42 kW, Q=1 ( Z/p = j 0.5 W) I per bunch [mA] High Frequency Beam Effects at the ESRF

  17. Single Bunch – Vertical Instabilities Vertical TMCI instability at zero chromaticity TMCI threshold Vertical Transverse Mode Coupling Instability at 0.67 mA (TMCI) forxv = 0 Vertical Head Tail Instability [P. Kernel, R. Nagaoka, J.-L. Revol] High Frequency Beam Effects at the ESRF

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

  19. Existing klystron transmitters: dF/d(HV)  7 ° per % HV Phase noise up to -50 dBc at multiples of 300 Hz / HVPS ripples Beam sensitive (fsynchrotron = 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 fsynchrotron) Negligible phase noise Overall 50 % efficiency RF Phase noise 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.] High Frequency Beam Effects at the ESRF

  20. Harmonic Cavities – theoretical study Bunch length Bunch length Vacc [MV] V [MV] Harmonic 3 Vacc (f) Uloss/e Uloss/e Vhc (f) f[rad] f[rad] Vm (f) df/dt df/dt f f sL 4sL tTouschek 4tTouschek High Frequency Beam Effects at the ESRF

  21. Harmonic Cavities – theoretical study • Interest in a third harmonic RF system for the ESRF ? 200 mA uniformtlife = 60 h NO 90 mA in 16 bunchtlife = 10 h YES up to 20 mA single bunchtlife = 5 h YES • Interaction with BBR, accelerating and higher order modes ?? Multibunchsingle particlemodel: Transient beam loading effects with a harmonic RF system Single bunchmultiparticlemodel: BESAC: Potential Well and Microwave Instability [G.Besnier, C.Limborg, T.Günzel] [J.Byrd, S.De Santis, J.Jacob, V,Serriere] ALS, ESRF ESRF Multibunch multiparticlemodel Harmonic cavity, Potential well & Microwave Instability, AC and DC Robinson instabilities, Landau damping of LCBI [V.Serriere, J. Jacob]  see also [R. Bosch] High Frequency Beam Effects at the ESRF

  22. Harmonic Cavities – theoretical study Potential well @ 5.5 mA m-wave instab. @ 20 mA Harmonic cavity Further factor 4 Harmonic cavity Further factor 3 sL sL 3sL 6 sL 12 sL 18 sL m-wave instab. @ 20 mA Harmonic cavity Reduces E-spread sE 2 sE 1.7 sE Main Results • Potential well distortion (from BBR, i.e. Z/p = j 0.5 W): • e.g. at ESRF in 16 bunch for I/bunch = 5.5 mA • Microwave instability (from BBR above 5 mA, 30 GHz, 42 kW, Q=1): • e.g. at ESRF in single bunch at 20 mA High Frequency Beam Effects at the ESRF

  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 High Frequency Beam Effects at the ESRF

  24. Harmonic Cavities – theoretical study • Microwave Instability&bunch lengthening by harmonic voltage At 25 mA: still bunchlength increase factor of 2.7 High Frequency Beam Effects at the ESRF

  25. Harmonic Cavities – theoretical study Super-3HC cavity pair: 3rd harmonic cavity for: SLS & Elettra Scaling of the SC SOLEIL Cavity Construction: CEA & CERN Rs/Q= 90 W Quality factor: Q0= 2.108 fres,hc = 1.5 GHz Superconducting Module with a pair of cavities W ESRF : Scaling of Super-3HC to fres,hc = 1056.6 MHz Harmonic cavity technology for ESRF ?  low total intensity modes ! • Passive NC Cu cavities: Nmin = 150 unrealistic • Active NC Cu cavities: Nmin = 12 still not practical • Passive SC cavity pair: Nmin = 4 imposed by AC Robinson • Active SC cavity pair: N = 1 Only practical solution with 80 … 100 kW generator Low R/Q of SC cavities  less phase transients  net gain in tlife less affected by gap in fill High Frequency Beam Effects at the ESRF

  26. HOM driven LCBI at MAX II: Without harmonic cavity: Ithreshold ≈ 10 mA With harmonic cavity: stable at250 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 Harmonic Cavities – theoretical study Ibeam = 250 mA sE/E measurements [Å. Anderson & al.] Tracking code Tracking simulation Linear model sE, nat Harmonic Voltage [kV] High Frequency Beam Effects at the ESRF

More Related