High Frequency Beam Effects at the ESRFJ. Jacob

NSLS II Beam Stability Workshop BNL, April 18th - 20th, 2007

OutlineHigh Frequency effects affecting beam stability at ESRF (6 GeV)Multibunch total current, essentially narrow band impedancesLongitudinal: HOM driven instabilitiesTransverseDominated by resistive wall instabilities (screening HOM effect)IonsSingle bunch current per bunch, broad band impedancesLongitudinal:Microwave instabilityTransverse:Mode coupling instability - TMCIHead Tail instabilitySide effects:High peak signals distortion of BPM readingsHeating (bellow shielding, special vessels, )Pressure burst, lifetime accidents, beam losses, RF Phase noise

Countermeasures

Constructive measures Minimization of impedancesVacuum chamber materialDiscontinuities, bellow shielding,Cavity designPassive damping (HOMs)Active damping (Feedbacks)Reduction of RF Phase noise

Operation parametersPartial filling of the storage ringPositive chromaticityRF Voltage,

Effect of Harmonic CavitiesLifetime increase by bunch lengtheningLandau damping of LCBIEffect on other beam dynamics

Multibunch HOM driven LCBI ESRFSR: 6 five-cell cavitieslowest LCBI thresholds: 40 mAstabilized by Landau damping from transient beam loading in fractional SR filling 200 mA in non symmetric 1/3, later 2/3 filling1998: new cavity temperature regulation to 0.05C, for precise control of HOM frequencies stable at 200 mA in uniform and symmetric 2 x 1/3 filling Not possible to exceed 250 mADec 2006: longitudinal bunch-by-bunch feedback - LFB with 1 ms damping time 300 mA in uniform Limited b VRF: 9 11 MV against Robinson instabilityNo further beam increaseWindow power at maximumRobinson even higher VRFMaximum 300 mA with existing cavitiesR/Q = 139 /cellQo = 38500Rs = 26.8 M (5 cells)frf = 352.2 MHz Vnom = 1.4 2.5 MV (Booster: 4 MV pulsed)2 couplers: bmax = 4.4Max 170 kW/coupler

Multibunch HOM driven LCBIStreak camera image of a LCBILandau damping from fractional filling of storage ring[O. Naumann & J. Jacob]

Multibunch HOM driven LCBIESRF Cavity Temperature regulation system (cav. 1 & 2)T = Tset 0.05 C 200 mA in uniform filling

Multibunch HOM driven LCBI[inspired from PEP II, ALS, DAFNE,design ][E. Plouviez, G. Naylor, G. Gautier, J.-M. Koch, F. Epaud, V. Serrire, 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 2008Bandwidth: fRF/2 = 176 MHz

Multibunch HOM driven LCBIDimensioning of LFB:ESRF natural damping time ts = 3.6 ms DSP algorithm minimum active damping time tdamp = 0.5 ms ts /7 (loop delay)

Gain:

So, without safety margin: dt 1 fs / turn (Kicker provides 500 V)

Multibunch HOM driven LCBI1V/ RF degree7ps / RF degreeWill not saturate the ADC (

Multibunch HOM driven LCBI2 x 1/3 fillingWould put +/-15 V at the input of the ADCMust 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

Multibunch HOM driven LCBIFIR: (a,b,c,1,c,b,a,0,-a,-b,-c,-1,-c,-b,-a,0)Further Mode 0 removalFactor 11 decimation: 11 T0 = 31 ms16 TAP FIR: 16 x 31 ms = 0.5 ms = TsynchrotronBP filter at fs Differentiation (Vkick jt): phase shift by 90Total averaging 176, sensitivity: 1fs -> 0.08 fs

Multibunch HOM driven LCBINew 352 MHz Cavities for ESRF

Unconditional stability & higher current: 400500 mASC cavities (e.g. SOLEIL type): Beam power 2 couplers/cellNC 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. Serrire, P. Roussely, J. Jacob]

Multibunch HOM driven LCBITolerated Longitudinal HOM impedance for 18 installed cavitiesmeasured on 1st Al prototypeGdfidL simulation of 1st Al prototypeGdfidL simulation of Improved design

Multibunch TCBI / Resist. Wall & IonsCBI 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 AlAl: high conductivity maximize RWI thresholdsNEG: efficient distributed pumping minimize Bremsstrahlung & ion instabilities6 mm in-vaccum undulators: Ni-Cu foilSlightly positive normalized chromaticities to damp resistive wall and ion instabilityGoal: keep emittances ex = 4 nm rdez = 25 pm rdFor 200 mA, setting: xx = 0.2xz = 0.6Vertical 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 lifetimeSytematic conditioning at restart shifts after vacuum opening during shut downsExperience at 300 mASuccessful use of TFB to damp vertical ion instability[P. Kernel, R. Nagaoka, J.-L. Revol]

Multibunch TCBI / Resist. Wall & Ions[P. Kernel, R. Nagaoka, J.-L. Revol]

Single Bunch Bunch Lengtheningps rms[J.-L. Revol]I per bunch [mA]

Single Bunch Microwave instabilitysE/EI per bunch [mA]keVEnergy spread measured at ESRF Tracking simulations fit of longitudinal BBR: fres = 30 GHz, Rs = 42 kW, Q=1 ( Z/p = j 0.5 W)

Single Bunch Vertical Instabilities[P. Kernel, R. Nagaoka, J.-L. Revol]Vertical Head Tail InstabilityVertical Transverse Mode Coupling Instability at 0.67 mA (TMCI) for xv = 0

Chart1

0.631.642

0.672.53.54

23.85.25

4.65.77.3

12.38.512.92

13.4

17.8

'98

04 Dec 01

Dec_01

98

Nov_02

Vertical chromaticity

Current threshold [mA]

Ith vs xV at 8 MV

Sheet1

vertical mode 0 detuning

Vrf = 8 MVVrf = 8 MV

gxiV = 0.0482 (measured)20-Oct-01gziH = 0.132, GziV = 0.084 (meas)

Vrf=8 MV

chromaV = 0.11, chromaH = 0.15i [mA]QV (m=0)i [mA]QV (m=-1)

0.190.38810.170.38250.170.38660.170.39280.070.38890.07

0.430.38610.480.38170.480.38430.480.39120.160.38810.160.3835

0.550.3850.330.38210.330.38550.330.39190.260.38710.260.3831

0.630.3830.610.38150.40.38590.40.3829

0.490.38530.490.3829

0.550.38510.550.3828

0.60.60.3826

0.660.660.3826

0.720.720.382

Vrf = 8 MVWith all openReduction due to closure to 3.5 mm8MV8 MV

xVIth [mA]xVDI [mA]xVITh2002xVIth '98

0.0480.630.0480.238620.151.64

0.14780.670.14780.42293.540.252.5

0.247620.24760.250.56495.250.353.8

0.5184.60.5180.430.65197.30.465.7

0.735612.30.73561.50.758912.920.568.5

0.6513.4

0.7517.8

Sheet1

0.38810.38660.38890.38350.3825

0.38610.38430.38810.38310.3817

0.3850.38550.38710.38290.3821

0.3830.38590.38290.3815

0.38530.3828

0.38510.3826

0.3826

0.382

04-Dec-01xV=0.048

16-Aug-99xV=0.084

20-Oct-01xV=0.11

Current [mA]

Tune

Vertical TMCI at 8 MV

'98

04 Dec 01

Dec_01

98

Nov_02

Vertical chromaticity

Current threshold [mA]

Ith vs xV at 8 MV

0.25

0.43

1.5

Vertical Chromaticity

DI [mA]

Reduction of current due to gap closure to 3.5 mm

Single Bunch Horizontal Head TailIncreasing difficulties in single bunch mode (also in 16 bunch and hybrid)[P. Kernel, R. Nagaoka, J.-L. Revol]

RF Phase noiseExisting 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 dBcUnstable behaviourMultipactor / input cavityMod-Anode breakdownsMany auxiliaries, tripsRisk of Klystron obsolescence

ESRF RF upgrade project: Solid State Amplifiers - SSA, based on SOLEIL designIntrinsicly redundantSwitched power supplies at 100 kHz (far from fsynchrotron)Negligible phase noiseOverall 50 % efficiency

352 MHz 190 kW Solid State Amplifiers (2 units)682 transistor modules + 42 in standby[P. Marchand, T. Ruan et al.]

Harmonic Cavities theoretical studyf [rad]Uloss/eVacc [MV]Uloss/ef [rad]V [MV]Vacc (f)Vhc (f)Vm (f)Harmonic 3sL4sLtTouschek4tTouschekffdf/dtdf/dt

Harmonic Cavities theoretical studyInterest in a third harmonic RF system for the ESRF ?200 mA uniformtlife = 60 hNO90 mA in 16 bunchtlife = 10 hYESup to 20 mA single bunchtlife = 5 hYES

Interaction with BBR, accelerating and higher order modes ?? Single bunch multiparticle model: BESAC: Potential Well and Microwave Instability Multibunch multiparticle modelHarmonic 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.Gnzel][V.Serriere, J. Jacob]ESRFALS, ESRF see also [R. Bosch]

Harmonic Cavities theoretical studyMain ResultsPotential well distortion (from BBR, i.e. Z/p = j 0.5 W): e.g. at ESRF in 16 bunch for I/bunch = 5.5 mAMicrowave instability (from BBR above 5 mA, 30 GHz, 42 kW, Q=1): e.g. at ESRF in single bunch at 20 mA

Harmonic Cavities theoretical studyTracking code, confirmed by numerical resolution of Haissinski equation:Total bunch lengthening = Potential well effect X Elongation from harmonic voltage

Harmonic Cavities theoretical studyMicrowave Instability & bunch lengthening by harmonic voltageAt 25 mA: still bunchlength increase factor of 2.7

Chart3

9466842270885522

1101010976682996544

137131312255105778166

185101016566143101011622

255202024010102205520011

25 mA

20 mA

15 mA

10 mA

Harmonic Voltage [MV]

rms bunch length [ps]

Sheet1

Vh=0 MV

Ibeam [mA]bl [ps]deltabl [ps]sigmae [10-3]dsigmae [10-3]Vhbl (10mA)deltabl (10mA)bl(15ma)deltabl (10mA)bl(20mA)deltabl (20mA)bl(25mA)deltabl (10mA)

105521.450.10552702848946

157021.660.10.565482697911010

2084820.218161055122713713

259462.150.51.5116214361651018510

2200122010240525520

Vh=0.5 MV

Ibeam [mA]bl [ps]deltabl [ps]sigmae [10-3]dsigmae [10-3]bunch length increase factor

106541.40.11.1818181818

158261.650.151.1714285714

209791.80.21.1547619048

251101020.251.170212766

Vh=1 MV

Ibeam [mA]bl [ps]deltabl [ps]sigmae [10-3]dsigmae [10-3]

108161.30.11.4727272727

1510551.50.051.5

2012271.70.11.4523809524

25137131.80.21.4574468085

Vh=1.5 MV

Ibeam [mA]bl [ps]deltabl [ps]sigmae [10-3]dsigmae [10-3]

1011621.220.12.1090909091

1514361.380.052.0428571429

20165101.550.151.9642857143

25185101.70.21.9680851064

Vh=2 MV

Ibeam [mA]bl [ps]deltabl [ps]sigmae [10-3]dsigmae [10-3]

1020011.20.23.6363636364

15220101.450.083.1428571429

2024051.682.8571428571

25255201.750.22.7127659574

Sheet1

000000.10.1

000000.10.1

000000.20.2

000000.50.5

Vh=0 MV

Vh=0.5 MV

Vh=1 MV

Vh=1.5 MV

Vh=2 MV

Sheet2

066022088022

01010066099044

01313055077066

0101006601010022

0202001010055011

25 mA

20 mA

15 mA

10 mA

Harmonic Voltage [MV]

rms bunch length [ps]

Sheet3

Vh [MV]

ibeam [mA]sigmae [10-3]

901.06

1001.06

Vh[MV]ibeam [mA]sigmae [10-3]

2901.06

21001.06

1.8901.06

Sheet3

5522654481116200662211

7022826610514322055661010

8488979912216524077101055

94661101010137185255131310102020

Vh=0 MV

Vh=0.5 MV

Vh=1 MV

Vh=1.5 MV

Vh=2 MV

beam intensity [mA]

rms bunch length [ps]

single bunch length vs beam intensity

Harmonic Cavities theoretical studyHarmonic cavity technology for ESRF ? low total intensity modes !Passive NC Cu cavities: Nmin = 150 unrealisticActive NC Cu cavities:Nmin = 12still not practicalPassive SC cavity pair:Nmin = 4imposed by AC RobinsonActive SC cavity pair:N = 1Only practical solution with 80 100 kW generatorLow R/Q of SC cavities less phase transients net gain in tlife less affected by gap in fill

Harmonic Cavities theoretical studyHOM driven LCBI at MAX II:Without harmonic cavity: Ithreshold 10 mAWith harmonic cavity: stable at 250 mA due to Landau dampingLCBI Prediction for the ESRF: LCBI thresholds only slightly increased by Landau damping on a higher energy machine like ESRF