Electron Hollow Gun Collimation Performance & Simulations - PowerPoint PPT Presentation

Electron Hollow Gun Collimation Performance & Simulations Topics: Vince Moens, 11.04.2013 Motivation • Collaboration with CERN • Electron Gun Charaterization • Perveance • Profile Measurements • Field measurements • Polar Decomposition • Electron Beam Dynamics • WARP simulations •

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) • 2

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 μ rad @ 7TeV (RMS value) • Tevatron Primary: 17 μ rad @ 980 GeV (RMS value) LHC Design Report 4

Hollow Electron Beam Lenses E H r L @ V ê m D • Axial protons unperturbed if 2.5 ¥ 10 6 perfectly symmetric 2.0 ¥ 10 6 1.5 ¥ 10 6 • Off-axis protons obtain tune kick 1.0 ¥ 10 6 500000 • Off-axis protons are sent into r @ m D secondary collimators 0.00001 0.00002 0.00003 0.00004 0.00005 0.00006 0.00007 Tevatron Electron Lens: 0.2 μ rad @ • LHC Design Report 980 GEV (RMS value) 5

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 7

Electron Gun Characterization • Perveance • Profile Measurements • Field measurements • Polar Decomposition 8

Electron Gun Characterization - Test Bench & TEL2 - • Development of 1 inch gun • Difference between TEL2 and Test Stand: Solenoidal bends • Components Tevatron Electron Lens 2 Gun • Gun Solenoid • Drift/Bend • Main Solenoid • Drift/Bend • Collector • Collector Solenoid • Electron Lens Test Stand 9

Electron Gun Characterization - 1 inch Hollow Electron Beam Gun - 10

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 3 I = P × V 2 2012 data by Siqi Li 11

Electron Gun Characterization - Profile Measurement - Correctors in Main Solenoid 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 • 12

Electron Gun Characterization - Measured Profiles - 0.35 0.30 0.25 MAGNETIC FIELD [T] 0.20 From Dimensional Analysis:  V  L 2 ∗ e − � � 0.15 = B 2 e M 0.10 √ V Thus: L ∝ B 0.05 0.5 0.9 2.0 3.0 3.6 4.0 5.0 6.0 7.0 8.0 CATHODE VOLTAGE [kV] 13

Electron Gun Characterization - Current Density Profiles- 0.4 + + + + + • Radial profile of + + + + + current density + + + + + + + + + + + + + + + Current density [arb. units] 0.3 • Dependent upon: + + + + Gun Surface profile • + + + + Space-Charge effects • + + + E x B twist • + 0.2 + + + + Magnetic • + + confinement + + • Tendency to be 0.1 + higher on inside + + + than outside + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 0.0 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 0 5 10 15 Radial distance [mm] 14

Electron Gun Characterization - Particle Density Profiles- • Radial profile of current density 10 • Representative of cathode shape 5 Y coord. [mm] (25.4mm/13.2mm) • Appears fairly 0 uniform & symmetric � 5 � 10 � 10 � 5 0 5 10 X coord. [mm] 15

Electron Gun Characterization - Polar Decomposition - HG1b_121219_9p25A_3 − 3 − 3kG_4kV_1100mA Measurement Reconstruction Errors 15 15 15 10 10 10 5 5 5 Yc Yc Yc 0 0 0 − 5 − 5 − 5 − 10 − 10 − 10 − 15 − 15 − 15 − 15 − 10 − 5 0 5 10 15 − 15 − 10 − 5 0 5 10 15 − 15 − 10 − 5 0 5 10 15 Xc Xc Xc Mode amplitudes Radial modes Azimuthal modes ● ● 30 ● ● 0.500 0.20 25 ● ● ● ● ● Azimuthal mode m 20 Amplitude 0.10 ● Amplitude ● 0.100 ● ● 15 ● ● ● ● ● ● ● 0.05 ● 10 0.020 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 5 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 0.005 ● ● ● ● 0.02 ● ● 0 5 10 15 20 25 30 0 5 10 15 20 25 30 0 5 10 15 20 25 30 Radial mode n Radial mode n Azimuthal mode m 16

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 20

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 - Element creation: • Dedicated Commands • Surfaces of Revolution Test Bench Tevatron Electron Lens 2 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