15 October 2015 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe...
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Transcript of 15 October 2015 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe...
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26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 1
Single Beam Collective Effects Impedances and Collective Effects for FCC-hhUwe NiedermayerInstitut für Theorie Elektromagnetischer FelderTechnische Universität Darmstadt, [email protected]
With a lot of input from: B.Salvant, X. Buffat, N.Nounet, D. Schulte, CERNT. Egenolf, F. Petrov, O. Boine-Frankenheim, TUD
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Contents
As discussed in Washington:▪Beam pipe impedance▪Other impedance sources▪Coupled bunch instability▪Transverse Mode Coupling Instability (TMCI) threshold
Few new things and issues to be discussed:▪Which components?▪Details on the pipe…▪Plans, codes, outlines, timelinesCollimators!!! Pipe aperture!!!26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 2
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The beam pipe
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 3
Design by R. Kersevan, CERN
So far only this design considered
D. Schulte
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Discretization
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 4
GMSH (Geuzaine et al.) triangular mesh
Thilo Egenolf, TU Darmstadt
Meshing the whole structure is required only for extremely low frequency!
Otherwise: Surface Impedance Boundary Condition (SIBC)
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2D Simulations in the Frequency Domain
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 5
f=100Hz f=1MHz
Horizontal
Vertical
▪ BeamImpedance2D, PYTHON code using FEniCS finite element toolbox(U. Niedermayer et al., PRSTAB 18 032001, 2015)
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Materials
▪ Beam Screen: Titanium▪ Coating: Copper (80um or maybe higher) ▪ Outer pipe, synchr. rad. reflector: Stainless Steel
▪ Conductivities k at room temperature T=293K-Titanium: k0= 1.8 MS/m
-Copper: k0 = 60.0 MS/m
-Stainless steel: k0 = 1.4 MS/m
▪ RRR= k(T=4K)/k(293K) usually RRR ~300▪ Temperatures for the FCC pipe:
-Scenario 1: 40-60 K (roughly… k =100k0 ) -Scenario 2: 120-160 K (roughly… k =10k0)
▪ Magnetoresistance at 16T ?26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 6
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Penetration depth
▪ Surface impedance for coated surface
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 7
Copper
TitaniumVacuum
6.4kHz
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Comparison with round pipe impedance Horizontal
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 8
An artifact, due to numerical cancelation at high gamma
Coating with Copper at 50K, k=6e9 S/m
X2.0
Skindepth=coating thickness 80um
(1 meter pipe)
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Comparison with round pipe impedance Vertical
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 9
An artifact, due to numerical cancelation at high gamma
X1.4
Skindepth=coating thickness 80 um
(1 meter pipe)
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Pumping Holes, Collimators, …
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 10
B. Salvant and X. Buffat, CERN
Collimators scaled from LHC, see also talk by M. Fiascaris(this morning)
Maybe LHC-like carbon collimators are not the best choice…Collimators closed only at top energy!
Pumping holes with resonator model, ... fres=fcutoff ~6GHz Q=1 (Broadband)
S. Kurennoy, Part. Accel., 1995, Vol. 50, pp. 167-175
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Scenario Data
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 11
▪ E=3TeV▪ Qs=0.0028
▪ M=13344 (25ns)▪ rms bunch length 8 cm▪ Nb=1.0e11
▪ Qx=120.31
▪ Qy=120.32▪ Chroma=0
▪ E=50TeV▪ Qs=0.0078
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Coupled bunch resistive instability
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 12
Pipe only, solid Cu 50KE=3TeV
N. Mounet, EPFL Lausanne, formerly CERN
most unstable coupled-bunch mode at lowest frequency=2kHz
Most critical at injection due to less stiff beam!
Growth rate by factor 1.6 higher for 80 umcoating
Required thickness for “thick wall“150 um for 50K450 um for 140K
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TMCI intensity threshold 3TeV
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 13
B. Salvant and X. Buffat, CERN
coherent tune shift of the mode
Pipe +holes Pipe only
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TMCI intensity threshold 50TeV
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 14
B. Salvant and X. Buffat, CERN
More stiff beam, but higher impedance due to closed collimators
Pipe + holes + collimators
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Conclusion
▪ FCC-hh already on the edge of stability only with resistive pipe
▪ 50 turns feedback possible but maybe insufficient▪ 10 turns feedback possible?
▪ Kickers not yet considered▪ Landau damping and Octupoles not yet considered
▪ Impedance should play an important role in collimator design
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 15
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Holes and rips
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 16
3D simulations in the time domain by CST Particle Studio®
Stabilization fins between beam pipe and reflector Vacuum pumping holes
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Wakefield simulation of hole
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 17
Small effect, in the order of the numerical error!
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Updates after Washington Meeting
▪ Holes under investigation: resonator model is justified but probably smaller bandwidth
▪ First simulations show no effect of stabilizing rips…----------------------------------------------------▪ Input from Collimation-Group has to be followed Proper design with few updates required.
▪ Material data: Vacuum group?
▪ We should avoid recalculating the impedance model for every screw that has changed!
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 18
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Electron Cloud effects
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 19
Electron clouds lead to•Tune shift / spread•Synchronous phase shift•Instabilities
• 3D and 2D particle in cell codes for electron cloud simulations• community supported beam tracking codes (e.g. PyOrbit) • working on coupling the electron cloud simulations to the beam tracking including
impedances.
Difference to LHC•Syncr. Rad.•Asymmetry•Small aperture
Pic. by F. PetrovTU-Darmstadt
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Scientific Outlook
▪Asymmetry Quadrupolar impedance
▪Combination of impedance and electron cloud
▪Finally impedance check of all components in the ring?Nooo! Rather exclude some devices a priori and make a simplified model. This is a CDR not a TDR!
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 20
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The End
26 April 2023 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Uwe Niedermayer | 21
Thank you for your attention!