intro to electron cloud: an experimental summary
DESCRIPTION
by Jeffrey Eldred Data Analysis Workshop March 13th 2013. Intro to Electron Cloud: An experimental summary. Outline. Electron Cloud Formation Process. Electron Density Measurement Techniques. Secondary Electron Yield Mitigation. Beam Instability and Feedback Damping. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/1.jpg)
by Jeffrey EldredData Analysis Workshop March 13th 2013
Intro to Electron Cloud:An experimental summary
![Page 2: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/2.jpg)
Outline
Electron Cloud Formation Process. Electron Density Measurement Techniques. Secondary Electron Yield Mitigation. Beam Instability and Feedback Damping. Electron Cloud Simulation Software.
![Page 3: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/3.jpg)
Electron Cloud Formation Process
Initial seed electrons are generated. Electrons accelerated by beam bunches. Electrons collide into beampipe and
generate secondary electrons. The cycle repeats until the maximum
concentration of electrons is reached. Simultaneously, instabilities in beam can be
seen coinciding with rising electron density.
![Page 4: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/4.jpg)
Seed Electron Generation
Ionization by high-intensity beam.
– Order of one electron generation per meter, per torr, per particle, per pass.
High-energy beam particle strikes beampipe.
– Especially for grazing incidence, on the order of hundreds per particle lost.
Synchrotron radiation strikes beampipe.
– Electron machines, LHC, muon machines.
![Page 5: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/5.jpg)
Cloud Electron Acceleration Electron crossing on the
trailing edge of a positive bunch receives a net acceleration.
“Resonance” behavior.
secondary electrons
Beam
Net acceleration
e pipe wall
WC41
E-Detector x 4
LANL PSR
![Page 6: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/6.jpg)
Electron Cloud Threshold Effect
Fermilab
![Page 7: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/7.jpg)
Secondary Electron Yield (SEY)
The number, characteristics, and process of electron production from various materials is not completely characterized.
If an electron striking a beampipe generates on average more than one secondary electron than the number of electrons in the cloud is amplified beyond the initial seed.
– This is called multipactoring.
![Page 8: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/8.jpg)
SEY Testing
Fermilab & Cornell
![Page 9: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/9.jpg)
Electron Energy & SEY
Fermilab & Cornell
Fermilab Main Injector steel beampipe material
(eV)
![Page 10: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/10.jpg)
Electron DensityMeasurement Techniques
![Page 11: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/11.jpg)
Retarding Field Analysizer (RFA) Several layers of mesh
at different nonnegative potentials.
Collects electrons and measures current.
Partially sorts the electrons by energy.
Fermilab
![Page 12: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/12.jpg)
Microwave Phase Measurements
A microwave transmitter placed in the beampipe and BPM used as a receiver.
This setup allows measurement over a larger section of the beamline.
The delays in microwave phase proportional to electron-density x path-length.
Microwaves that have anomalous pathlengths are noise, therefore microwave reflectors are used to suppress those.
![Page 13: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/13.jpg)
Secondary Electron Yield Mitigation
![Page 14: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/14.jpg)
Clearing Electrodes Clearing electrodes
can localized or distributed.
Localized: Charged plate in special outlet.
Distributed: Wire hanging in beampipe.
DAFNE INFN ECLOUD Simulation
![Page 15: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/15.jpg)
Solenoidal Fields
Confines keV electrons without affecting MeV or GeV protons.
But need to avoid resonance- when time of flight is equal to the bunch to bunch time. resonance effect
![Page 16: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/16.jpg)
Surface Grooves
Fermilab
![Page 17: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/17.jpg)
Beampipe Conditioning
Fermilab
![Page 18: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/18.jpg)
Surface Coating
TiN conditions faster and better.
Amorphous carbon coating under testing.Fermilab
![Page 19: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/19.jpg)
Beam Instability andFeedback Damping
![Page 20: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/20.jpg)
Characteristics of EC Instability
LANL PSR
![Page 21: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/21.jpg)
Characteristics of EC Instability
Broad-band mode excitation in frequency range of 25-250 MHz.
Rapid instability growth ~50us.
There is also significant variation in instability between pulses.
LANL PSR
BP
M p
ositio
n
![Page 22: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/22.jpg)
Coherent Tune Shift
LANL PSR
![Page 23: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/23.jpg)
Analog Feedback Damping
fiber optic delay
BPM
rf switch
low pass filter
vertical difference
hybridatten
kicker
low-level amp
comb filter
180-deg splitter
power amplifiers
BPM position signal can be filtered, amplified, and delayed.
Apply pi/2 phase shift to signal in order to damp beam frequency with kicker.
LANL PSR
![Page 24: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/24.jpg)
Comb Filtering
Harmonics of revolution frequency damped. Damping at revolution frequency doesn't
seem to affect instability, just wastes power.
Frequency response of a comb filter locked to 1 MHz
0
0.5
1
1.5
2
2.5
0 2 4 6 8 10 12
Frequency(MHz)
Y(w
)
![Page 25: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/25.jpg)
A test of EC damping system
LANL PSR
electron density
Dampening switch
Proton intensity
![Page 26: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/26.jpg)
Why does the instability return after damping?
Problems with electronic implementation?
– Enough power to kickers?
– Dispersion in signal cables? From instability along other axis?
– Horizontal Instability → EC → Vertical Beam accumulation between bunches. Does it drive the betatron oscillation?
![Page 27: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/27.jpg)
Electron Cloud Simulation Software
![Page 28: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/28.jpg)
ORBIT Code
EC module written for ORBIT. ORBIT allows 2D & 3D accelerator sim. Set up for parallel computation.
![Page 29: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/29.jpg)
0 200 4000.01
0.1
1
10
PSR beam line density (scaled) complete SE model (0)=0.5 (Pivi and Furman) ORBIT E-Cloud module =
ini ORBIT E-Cloud module =
ini*0.95
ele
ctro
n's
de
ns
ity
(n
C/m
)
t, nsec
ORBIT EC Simulation results
![Page 30: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/30.jpg)
POSINST & VORPAL
POSINST & VOROAL attempt to model SEY in addition to electron movement in beampipe.
POSINST written exclusively for simulation of electron cloud by CERN. Available for free.
VORPAL new & proprietary, applicable to wider-range of plamsa physics problems.
![Page 31: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/31.jpg)
POSINST & VORPAL results
In this Main Injector simulation, discrepancy traced to a bug in the POSINST code.
Now there is a pretty good agreement between VORPAL and POSINST.
![Page 32: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/32.jpg)
Other Simulation Code
ECLOUD
– Essentially rendered obsolete by more sophisticated codes.
– only simulates 2D electron trajectory. CLOUDLAND
– Another free 3D code developed by CERN, distinct from POSINST.
WARP
– “Particle in Cell” code, lattice approximation.
![Page 33: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/33.jpg)
Active Areas of EC Research
How can we predict the features of electron clouds in the fullest range of accelerator parameters and operating conditions?
What is the most cost effective strategy to mitigate ECs and/or the resulting instability?
How can we measure EC effectively? How much can we trust EC simulation? Can
we improve on the simulation code?
![Page 34: Intro to Electron Cloud: An experimental summary](https://reader035.vdocument.in/reader035/viewer/2022081513/56815874550346895dc5d32e/html5/thumbnails/34.jpg)
Acknowledgements
Much of these plots and information was taken from the IU Electron Cloud Feedback Workshop in 2007.
EC studies conducted at Fermilab Main Injector, Los Alamos Proton Storage Ring.
Acknowledgements