Electron Hollow Gun Collimation Performance & Simulations - - PowerPoint PPT Presentation

Electron Hollow Gun Collimation Performance & Simulations

Topics:

• Motivation
• Collaboration with CERN
• Electron Gun Charaterization
• Perveance
• Profile Measurements
• Field measurements
• Polar Decomposition
• Electron Beam Dynamics
• WARP simulations

Vince Moens, 11.04.2013

Who am I?

Vince Moens

Master Student @ EPFL Semester Project @ CERN: “A quantitative comparison of the transverse damping and tune resonance crossing lossmap techniques at the LHC” Master Thesis @ Fermilab/CERN via USLARP on Hollow Electron Beam Collimation

• Leonid Rivkin (PSI/EPFL)
• Stefano Redaelli (CERN)
• Giulio Stancari (Fermilab)

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CERN Strategy @ US-LARP CM20

“There are very convincing indications that the LHC could profit from the scraping functionality. The excellent Tevatron results indicate that hollow e-beams could provide this functionality “ - S. Redaelli

• CERN supports studies on hollow e-lens and recommends to focus

available resources towards a possible production of 2 hollow e-lens for the LHC.

• Design of a device optimized for the LHC at 7 TeV
• Actively participate to beam tests worldwide on this topic.
• Start building competence at CERN on the hollow e-beam hardware.
• FNAL will work on optimum conceptual design for the LHC:
• Integral part of Conceptual Design Report for LHC
• Is Hollow Electron Beam Collimation effective?
• Does Hollow Electron Beam Collimation perturb the proton core?
• First specifications in the next 6 months, to be followed by detailed design.
• CERN will establish links to achieve a design report by the end of 2014

3

Classical Collimation System

• Collimation?
• Multi-stage collimation
• LHC primary: 3.4 μrad @

7TeV (RMS value)

• Tevatron Primary: 17 μrad @

980 GeV (RMS value)

LHC Design Report

4

Hollow Electron Beam Lenses

LHC Design Report

• Axial protons unperturbed if

perfectly symmetric

• Off-axis protons obtain tune kick
• Off-axis protons are sent into

secondary collimators

• Tevatron Electron Lens: 0.2 μrad @

980 GEV (RMS value)

0.00001 0.00002 0.00003 0.00004 0.00005 0.00006 0.00007 r @mD 500000 1.0 ¥ 106 1.5 ¥ 106 2.0 ¥ 106 2.5 ¥ 106 EHrL @VêmD

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Why HEBC?

• Tunability!!!! - “Soft Collimator“ or “Diffusion Enhancer
• Close to beam -> 4 sigma
• Ability to pulse the beam
• Resonantly with betatron oscillation
• Remove specific bunch trains
• No nuclear break-up on ion collimation

6

HEBC @ Tevatron

• Tested experimentally at

Tevatron

• 0.6 inch gun in TEL2
• 36 bunches, 3 bunch trains, 3 x

10^11 protons/bunch

• Possibility to control just one train
• Did not affect proton core

immensely if hole big enough

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Electron Gun Characterization

• Perveance
• Profile Measurements
• Field measurements
• Polar Decomposition

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Electron Gun Characterization

• Test Bench & TEL2 -

Tevatron Electron Lens 2 Electron Lens Test Stand

• Development of 1

inch gun

• Difference between

TEL2 and Test Stand: Solenoidal bends

• Components
• Gun
• Gun Solenoid
• Drift/Bend
• Main Solenoid
• Drift/Bend
• Collector
• Collector Solenoid

9

Electron Gun Characterization

• 1 inch Hollow Electron Beam Gun -

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Electron Gun Characterization

• Yield Measurement -
• Yield vs. Energy?
• Space-Charge

Limited Regime

• Child-Langmuir

Law

• Perv ≈ 4.2e-6 perv
• SAM: 6e-6 perv
• Check SAM using

WARP

2012 data by Siqi Li

I = P × V

3 2

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Electron Gun Characterization

• Profile Measurement -
• Deflection using Correctors / BPMs
• Collector with 0.2 mm pinnhole
• ACL code -> 61 x 61 grid @ 1 sec
• R script -> Processing
• 2D & 3D beam profiles
• Current Densities
• Polar Decomposition
• Particle map

Correctors in Main Solenoid

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CATHODE VOLTAGE [kV] MAGNETIC FIELD [T] 0.5 0.9 2.0 3.0 3.6 4.0 5.0 6.0 7.0 8.0 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Electron Gun Characterization

• Measured Profiles -

From Dimensional Analysis: Thus:

 V B2

• =

L2 ∗ e− eM

• L ∝

√ V B

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Electron Gun Characterization

• Current Density Profiles-
• Radial profile of

current density

• Dependent upon:
• Gun Surface profile
• Space-Charge effects
• E x B twist
• Magnetic

confinement

• Tendency to be

higher on inside than outside

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+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 5 10 15 0.0 0.1 0.2 0.3 0.4 Radial distance [mm] Current density [arb. units]

Electron Gun Characterization

• Particle Density Profiles-
• Radial profile of

current density

• Representative of

cathode shape (25.4mm/13.2mm)

• Appears fairly

uniform & symmetric

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10 5 5 10 10 5 5 10 X coord. [mm] Y coord. [mm]

Electron Gun Characterization

• Polar Decomposition -

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−15 −10 −5 5 10 15 −15 −10 −5 5 10 15

Measurement

Xc Yc

HG1b_121219_9p25A_3−3−3kG_4kV_1100mA

−15 −10 −5 5 10 15 −15 −10 −5 5 10 15

Reconstruction

Xc Yc −15 −10 −5 5 10 15 −15 −10 −5 5 10 15

Errors

Xc Yc 5 10 15 20 25 30 5 10 15 20 25 30

Mode amplitudes

Radial mode n Azimuthal mode m

• ●
• ●
• ●
• ●
• ●
• ●
• 5

10 15 20 25 30 0.02 0.05 0.10 0.20

Radial modes

Radial mode n Amplitude

• ●
• ●
• ● ● ●
• ●
• ●
• ● ● ●
• 5

10 15 20 25 30 0.005 0.020 0.100 0.500

Azimuthal modes

Azimuthal mode m Amplitude

Electron Gun Characterization

• Electric Field & Potential -

17

Electron Beam Evolution

• WARP Simulations
• Non-Linear Maps

18

Electron Beam Evolution

• Why simulate? -
• Identify transverse fields throughout beam pipe
• non-linear map for tracking codes (TEL2)
• Compare Simulations to Tbench results
• See effect of bends in TEL2

19

Electron Beam Evolution

• WARP -
• Particle in Cell code
• Developed at Lawrence Berkley

National Laboratory

• Non-neutral plasma beam
• Main components
• Definition of Lattice
• Definition of Source
• Definition of Field Solver

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Electron Beam Evolution

• Problems-
• Package for python
• Difficulties to install:
• Correct versions of python
• Compilation with same compiler
• Super user rights
• Solution:
• Complete install of python & additional

packages in home directory

• Dave Grote (LBL) -> 4 weeks
• Packaged and available as zip file

21

Electron Beam Evolution

• Definition of Lattice -

Test Bench Tevatron Electron Lens 2 Element creation:

• Dedicated Commands
• Surfaces of Revolution

22

Electron Beam Evolution

• Definition of Source-
• Gun
• Cathode and two

Electrodes at negative potential

• Anode at 0 potential
• Inside of big gun

solenoid

23

What now?

• 3 Main tasks:
• Simulation of beam using WARP
• Study of polar decomposition data and strong modes
• Characterization of electric and magnetic field at center of beam
• Remain at Fermilab for 4 more weeks and then

return to CERN

• Work remotely
• Submission deadline: 16 August 2013

24

Acknowledgements

• Giulio Stancari

for his role as supervisor and answering all my questions

• Moses Chung

for aid with WARP and plasma physics

• Alexander Valishev

for support during research and technical issues

• David Grote (LBL)

for support with compatibility issues with WARP and TEV

• Eric Stern

for technical support using TEV and installing WARP

• Valentina Previtali

for technical discussions on Hollow Electron Beams

25

Questions?

26