Difference between revisions of "Outline For Thesis"

From Ciswikidb
Jump to navigation Jump to search
(Created page with "Outline for Thesis Return to Home Page")
 
 
(11 intermediate revisions by the same user not shown)
Line 1: Line 1:
−
Outline for Thesis
+
== Abstract, Intro (obviously) ==
  
 +
===Current Experiments - Motivation for Research===
  
 +
*Current experiments requiring the use of GaAs photo-guns - polarized electron beams
 +
*What is a photo-gun?
 +
*CEBAF Injector - What is it? How do we (currently) model it?
  
 +
===Description of problem - Ionization ===
  
 +
*What is ionization & why is it bad for electron beam production & electron guns?
 +
**Ion Back-Bombardment & QE degradation of the photocathode
 +
***How/where are ions formed in the photogun?
 +
***How many ions reach the photocathode and what are their energies?
 +
***How many of these ions contribute/correlate to QE damage?
 +
**Other ion effects
 +
***Fast-ion instability
 +
***Charge neutralization
 +
***Effect on emittance and tune
 +
***Recombination - can lead to unwanted light incident on the photocathode active area, which may lead to beam halo
  
 +
===Current Solutions ===
  
 +
*Experimental ion mitigation techniques that are currently available:
 +
**Clearing Techniques:
 +
***Clearing electrodes - ion precipitator
 +
***Repelling electrodes - biased anode
 +
***Beam Gaps
 +
***Beam Shaking Techniques
 +
**Damage mitigation techniques:
 +
***Varying laser spot size
 +
***Photocathode elemental makeup (GaAs vs Mb)?
 +
*Theoretical Techniques
 +
**Other ion tracking codes (IBSimu, SIMION, etc.)
  
 +
===The "Thesis" statement ===
 +
*What do **I** bring to the table? Brief description/summary of
 +
**GPT ionization custom element
 +
**Biased anode as ion mitigation technique
 +
**Analysis of how the charge lifetime scales with laser spot size (2017 experiments)
 +
**Ion trapping experiments/simulations
 +
*How all of these help to solve the problem described above?
 +
**Knowing how ions are formed and where they go through measurements and simulations, we can...
 +
***Predict the effectiveness of ion mitigation techniques (such as the biased anode)
 +
***Predict the QE degradation of the photocathode and its charge lifetime under various beam conditions
 +
***Identify the conditions under which ions can cause deleterious effects on the beam (in its creation and its stability) That is, we can identify the sources/causes of damaging ions.
 +
 +
 +
== Ionization Simulations with GPT Custom Element ==
 +
 +
===GPT Description ===
 +
*Purpose - to create particle simulations, often of electron beams, and to track their movement within electromagnetic fields in real-time (as opposed to just getting the trajectory info)
 +
*How does it work? (perhaps with a flow chart?)
 +
**Description of how particle distributions are created and what "macro-particles" are
 +
**Built-in and custom elements with their respective locations (i.e. coordinate systems) are called by the GPT kernel. These elements include:
 +
***E-Field and B-Field maps, usually due to beam line components
 +
***Space charge routines
 +
***Custom elements (like the ionization custom element)
 +
**Equations of motion are derived by solving the Poisson equation using the 5th-order Runge-Kutta Method with an adaptive stepsize control
 +
 +
 +
=== GPT Custom Element Algorithm ===
 +
*Description of how the custom element works and is used to simulate ionization
 +
**Ionization theory - Can be pulled from PSTP proceedings and tech notes
 +
**Secondary Electron Differential Cross Section (SEDCS)
 +
**Ion Energy Distribution (Maxwellian)
 +
**Momentum/Energy Conservation?
 +
*Benchmarking with theory and IBSimu (Can be pulled from future GPT/IBSimu paper)...maybe put in the LIfeSize Runs Section?
 +
 +
== Biased Anode To Mitigate Ion Back-Bombardment ==
 +
*Description of ion back-bombardment
 +
**CEBAF vacuum pressures
 +
**Description of mechanism - electron beam ionizes gas, accelerates towards photocathode, damages it, causing QE decay (describe how this occurs)
 +
*Description of how the biased anode will mitigate it (Can be pulled from PSTP) - compare E-Fields
 +
*Summer 2019 Biased Anode Experiments
 +
**Description of Experiment at CEBAF
 +
**QE Measurements & Charge Lifetime Analysis
 +
**QE Scan Analysis
 +
**GPT Simulations (w/custom element)
 +
**Results/Discussion
 +
*Similar for Winter 2019-2020 Experiments?
 +
 +
== Analyzing 2017 LifeSize Runs with GPT/IBSimu ==
 +
*Description of Experiment - varying laser spot size and calculating photocathode charge lifetime
 +
**QE Scan analysis
 +
**Comparing analysis results with GPT simulations using the ionization custom element
 +
*Comparison & benchmarking with IBSimu
 +
 +
== Ion Trapping at the Gun Test Stand (GTS) ==
 +
*Description of phenomenon & experiments
 +
**Anode bias/Gun solenoid systematic study
 +
**Experiments where ghost beam returns when gun solenoid current is lowered and then raised - perhaps ion trap filling or field emission?
 +
*GPT Simulations (w/custom element)
 +
*Ion Trapping Experiments - Recreating Ghost Beam using Steel Shield. These experiments will help confirm/benchmark the GPT simulations and vice-versa.
 +
*Results/Discussion
 +
 +
== Discussion/Conclusions ==
 +
*What is the most important info that I've learned so that I can pass it on to the next grad student?
 +
**GPT is extensible!
 +
***GPT can accurately simulate and predict the effect of ions on the operation of the photogun, both in the electron beam production (QE decay) and its stability (ion trapping & charge neutralization)
 +
**A biased anode is effective at increasing the charge lifetime of the photocathode by repelling ions downstream of it.
 +
**Ghosts are real! (ion trapping experiments at GTS)
 +
 +
 +
[[To-Do List For Thesis | Go to To-Do List]]
  
 
[[Josh Yoskowitz | Return to Home Page]]
 
[[Josh Yoskowitz | Return to Home Page]]

Latest revision as of 11:30, 29 May 2020

Abstract, Intro (obviously)

Current Experiments - Motivation for Research

  • Current experiments requiring the use of GaAs photo-guns - polarized electron beams
  • What is a photo-gun?
  • CEBAF Injector - What is it? How do we (currently) model it?

Description of problem - Ionization

  • What is ionization & why is it bad for electron beam production & electron guns?
    • Ion Back-Bombardment & QE degradation of the photocathode
      • How/where are ions formed in the photogun?
      • How many ions reach the photocathode and what are their energies?
      • How many of these ions contribute/correlate to QE damage?
    • Other ion effects
      • Fast-ion instability
      • Charge neutralization
      • Effect on emittance and tune
      • Recombination - can lead to unwanted light incident on the photocathode active area, which may lead to beam halo

Current Solutions

  • Experimental ion mitigation techniques that are currently available:
    • Clearing Techniques:
      • Clearing electrodes - ion precipitator
      • Repelling electrodes - biased anode
      • Beam Gaps
      • Beam Shaking Techniques
    • Damage mitigation techniques:
      • Varying laser spot size
      • Photocathode elemental makeup (GaAs vs Mb)?
  • Theoretical Techniques
    • Other ion tracking codes (IBSimu, SIMION, etc.)

The "Thesis" statement

  • What do **I** bring to the table? Brief description/summary of
    • GPT ionization custom element
    • Biased anode as ion mitigation technique
    • Analysis of how the charge lifetime scales with laser spot size (2017 experiments)
    • Ion trapping experiments/simulations
  • How all of these help to solve the problem described above?
    • Knowing how ions are formed and where they go through measurements and simulations, we can...
      • Predict the effectiveness of ion mitigation techniques (such as the biased anode)
      • Predict the QE degradation of the photocathode and its charge lifetime under various beam conditions
      • Identify the conditions under which ions can cause deleterious effects on the beam (in its creation and its stability) That is, we can identify the sources/causes of damaging ions.


Ionization Simulations with GPT Custom Element

GPT Description

  • Purpose - to create particle simulations, often of electron beams, and to track their movement within electromagnetic fields in real-time (as opposed to just getting the trajectory info)
  • How does it work? (perhaps with a flow chart?)
    • Description of how particle distributions are created and what "macro-particles" are
    • Built-in and custom elements with their respective locations (i.e. coordinate systems) are called by the GPT kernel. These elements include:
      • E-Field and B-Field maps, usually due to beam line components
      • Space charge routines
      • Custom elements (like the ionization custom element)
    • Equations of motion are derived by solving the Poisson equation using the 5th-order Runge-Kutta Method with an adaptive stepsize control


GPT Custom Element Algorithm

  • Description of how the custom element works and is used to simulate ionization
    • Ionization theory - Can be pulled from PSTP proceedings and tech notes
    • Secondary Electron Differential Cross Section (SEDCS)
    • Ion Energy Distribution (Maxwellian)
    • Momentum/Energy Conservation?
  • Benchmarking with theory and IBSimu (Can be pulled from future GPT/IBSimu paper)...maybe put in the LIfeSize Runs Section?

Biased Anode To Mitigate Ion Back-Bombardment

  • Description of ion back-bombardment
    • CEBAF vacuum pressures
    • Description of mechanism - electron beam ionizes gas, accelerates towards photocathode, damages it, causing QE decay (describe how this occurs)
  • Description of how the biased anode will mitigate it (Can be pulled from PSTP) - compare E-Fields
  • Summer 2019 Biased Anode Experiments
    • Description of Experiment at CEBAF
    • QE Measurements & Charge Lifetime Analysis
    • QE Scan Analysis
    • GPT Simulations (w/custom element)
    • Results/Discussion
  • Similar for Winter 2019-2020 Experiments?

Analyzing 2017 LifeSize Runs with GPT/IBSimu

  • Description of Experiment - varying laser spot size and calculating photocathode charge lifetime
    • QE Scan analysis
    • Comparing analysis results with GPT simulations using the ionization custom element
  • Comparison & benchmarking with IBSimu

Ion Trapping at the Gun Test Stand (GTS)

  • Description of phenomenon & experiments
    • Anode bias/Gun solenoid systematic study
    • Experiments where ghost beam returns when gun solenoid current is lowered and then raised - perhaps ion trap filling or field emission?
  • GPT Simulations (w/custom element)
  • Ion Trapping Experiments - Recreating Ghost Beam using Steel Shield. These experiments will help confirm/benchmark the GPT simulations and vice-versa.
  • Results/Discussion

Discussion/Conclusions

  • What is the most important info that I've learned so that I can pass it on to the next grad student?
    • GPT is extensible!
      • GPT can accurately simulate and predict the effect of ions on the operation of the photogun, both in the electron beam production (QE decay) and its stability (ion trapping & charge neutralization)
    • A biased anode is effective at increasing the charge lifetime of the photocathode by repelling ions downstream of it.
    • Ghosts are real! (ion trapping experiments at GTS)


Go to To-Do List

Return to Home Page

Retrieved from "https://wiki.jlab.org/ciswiki/index.php?title=Outline_For_Thesis&oldid=20488"