Using Tune Shifts to Evaluate Electron Cloud Effects on Beam Dynamics at CesrTA Jennifer Chu Mentors: Dr. David Kreinick and Dr. Gerry Dugan 8/11/2011REU.

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Presentation transcript:

Using Tune Shifts to Evaluate Electron Cloud Effects on Beam Dynamics at CesrTA Jennifer Chu Mentors: Dr. David Kreinick and Dr. Gerry Dugan 8/11/2011REU Final Presentation1

Outline Review of Electron Clouds and Tune Shifts Simulations of New Data Varying the Simulation Parameters 8/11/2011REU Final Presentation2

Electron Clouds ILC will collide electrons and positrons Accelerating charges radiate Photons knock electrons off walls of beampipe Photoelectrons are accelerated by beam and knock off more electrons, forming a cloud Electrons in the cloud are attracted to positive beams 8/11/2011REU Final Presentation3

Tune Shifts Beams are displaced from nominal path Tune (Q): number of oscillations of a particle about nominal path, per turn around the ring Tune shift (ΔQ): difference in tune caused by electric field of electron cloud Q y = /11/2011REU Final Presentation4

CesrTA is used to measure tune shifts Beams are set into oscillation BPMs measure the position for 2048 turns Fourier transform is used to calculate tune shifts Taking Data 8/11/2011REU Final Presentation5

POSINST POSINST is a simulation code used to model the electron cloud effects Simulations are run for different values for each of five parameters which describe the physics of electron cloud generation Simulations are compared to data to test accuracy of the model 8/11/2011REU Final Presentation6

Comparing Data to Simulations 8/11/2011REU Final Presentation7

Goals We want to find the optimal set of parameters that most accurately models electron clouds The simulation can then be used to predict the behavior of electron clouds in damping rings of future linear colliders 8/11/2011REU Final Presentation8

Submitting Jobs to the Queue Simulations were run on Cornell’s batch nodes Each job is only allowed 48 hours of CPU time I wrote code to parallel process the simulations to get more statistics I monopolized the queues for the summer: 87 data sets x 5 simulation parameters x 2 for x, y tune shifts x 6 jobs per submission > 5000 total jobs 8/11/2011REU Final Presentation9

Calculating Tune Shifts I used Mathematica to post-process the results of POSINST to calculate the tune shifts I superimposed the tune shifts from multiple simulations onto plots of the data for comparison 8/11/2011REU Final Presentation10

June 2011 Coherent Tune Shift Data GeV e+: 20 x 0.5 mA GeV e+: 45 x 0.5, 1.0, 1.5, 2.0 mA 4.00 GeV e+: 20 x 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0 mA 4.00 GeV e+: 45 x 0.2, 0.4, 0.6, 0.8, 1.0, 1.2 mA 5.3 GeV e+: 20 x 0.5, 1.0, 2.0 mA 5.3 GeV e-: 20 x 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0 mA 5.3 GeV e+: 45 x 0.2, 0.4, 0.6, 0.8, 1.0, 1.2 mA 5.3 GeV e-: 45 x 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6 mA Bunch spacing studies: GeV e-: 30 x 0.2, 0.4, 0.6, 0.8, 1.0, 1.2 mA for 12, 16, 20 ns spacing GeV e-: 45 x 0.2, 0.4, 0.6, 0.8, 1.0, 1.2 mA for 4, 8, 12 ns spacing 8/11/201111REU Final Presentation

2.1 GeV4.0 GeV5.3 GeV 8/11/2011REU Final Presentation mA/bunch 1.00 mA/bunch 0.40 mA/bunch 1.00 mA/bunch

Simulation Parameters Parameters describe the physics of electron cloud generation When a radiated photon from the beam knocks into the wall of the beampipe, photoelectrons are generated (1) Quantum Efficiency: number of electrons generated for every photon 8/11/2011REU Final Presentation13

Secondary Emission Photoelectrons are accelerated by the electric field of the beam and continue to produce more electrons (2) Secondary Emission Yield (SEY): number of secondary electrons generated for every primary electron (3) Energy at the SEY Peak 8/11/2011REU Final Presentation14

Types of Secondary Electrons When a photoelectron hits a wall of the vacuum chamber, it can: 1.Bounce off (elastic) 2.Interact with material (rediffused) 3.Knock off electrons in material (true) (4) Fraction of Secondaries that are Rediffused (5) Fraction of Secondaries that are Elastic Sketch of the currents that are used to define the different components of secondary emission. Figure taken from M. Furman and G. Lambertson, “The electron-cloud instability in the arcs of the PEP-II positron ring” 8/11/2011REU Final Presentation15

Varying the Simulation Parameters 8/11/2011REU Final Presentation16

Summary Tune shifts are used to study electron clouds Simulations were run and compared to data for all five parameters and all 77 new data sets Model seems to work reasonably well for a variety of beam energies and bunch currents Finding the optimal parameters will allow the model to be used for future linear colliders 8/11/2011REU Final Presentation17