To-Do List For Thesis
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A list of what exactly needs to get done before writing thesis paper, what is required for each item, the estimated completion time, and possible complications that might prolong its completion. This should help prioritize the work and ensure it gets done in a timely manner.
GPT
- Benchmarking SEDCS Routine
- Description: The secondary electron differential cross section (SEDCS) routine has been shown to produce secondary electrons with the "correct looking" energy distribution - i.e. they should follow the theoretical SEDCS curve. However, in order to ensure that it is indeed working correctly, it needs to be benchmarked against a theoretical test case. That is, histograms from a GPT simulation and a theoretical simulation using the same number of test cases can be compared.
- Logistics: Run GPT simulation to produce large number of ionizations. Run test case with external C++ code or make analytical calculations to produce the same number of ionizations. Compare histograms and overlay SEDCS curve. (Compare with IBSimu?)
- Estimated Completion Time: 1-3 days
- Possible Complications: Need good program to produce histograms...Excel and Gnuplot aren't good programs for producing histogram comparison plots. Also need to be able to overlay SEDCS curve on top of histograms. Maybe use Mathematica or SDDS program?
- Benchmarking Ion Energy (Maxwellian) Routine
- Description: The ion energies are set to follow a Maxwellian distribution about 4eV. The routine to do this in GPT is similar to the SEDCS routine above and thus should be benchmarked in the same way: run a test case and compare the resulting ion energy histogram with the histogram from a similar test case from an external C++ code (or make analytical calculation).
- Logistics: Similar to SEDCS routine logistics above, but use Maxwellian curve instead of SEDCS curve.
- Estimated Completion Time: 1-3 days
- Possible Complications: Same as SEDCS routine complications above.
- Benchmarkig Spacecharge3D routine
- Description: The spacecharge3D routine is being benchmarked against an analytical calculation to ensure it correctly works with the ionization routine. Space charge calculations are important in ionization simulations, especially when studying effects like ion trapping within the beam potential and charge neutralization. A derivation is under way to calculate the equations of motion for an ion that is a certain distance away from an electron line current. The ion starts with an initial velocity parallel to the line current and is expected to oscillate about the line current. Based on the equations of motion, one can calculate the positions/times that the ion crosses the line current.
- Logistics: Finish derivation, make analytical predictions for crossing times/positions, run GPT simulation, check results.
- Estimated Completion Time: 1-3 days
- Possible Complications: None that I can think of...
- Secondary Yield Custom Element
- Description: A custom element needs to be built to simulate secondary electrons ejected from the surfaces of the photocathode, anode, and beamline. Given theoretical equations (or at least empirical estimates) for the probability of ejecting a secondary electron from a surface, it should be straightforward to write a GPT custom element based on a similar built-in custom element.
- Logistics: Produce custom element based on existing custom element. My guess is that it will be similar in structure to the ionization custom element, but will be substantially shorter. After production, the custom element needs to be benchmarked against theory and IBSimu to ensure its accuracy.
- Estimated Completion Time: 2-5 days
- Possible Complications: Although unlikely, if no existing custom element is sufficiently similar to what is required for this custom element, it may take a while to create my own custom element based on pieces of several other custom elements. Also, from my experience with the writeremove custom element, I may run into some technical issue with the custom element that may take a while to solve or write a workaround for.
- Vacuum Custom Element
- Description: A custom element needs to be built to allow the user to import 3D vacuum data. This data will be used in conjunction with the ionization routine to calculate the local gas density at a given location in the simulation. This density is then used in the calculation of the ionization probability. Currently, the ionization routine assumes a constant, uniform gas density throughout the ionization region.
- Logistics: Produce custom element based on existing custom element (probably will be based on the 3D electric or magnetic field elements). After production, an option is to make the vacuum custom element time-based (but let's not get ahead of ourselves!).
- Estimated Completion Time: 2-5 days
- Possible Complications: Similar complications as the secondary electron yield custom element.
- Checking possible issue with multi-ionization
- Description: When an electron ionizes a gas molecule, it loses a certain amount of energy. The amount of energy lost is based on the ionization energy of the target gas and the resulting energies of the ion and secondary electron. In theory, an electron can continue to produce ions so long as its kinetic energy exceeds the ionization energy of the target gas. However, because the ionization cross section is extremely small for an electron regardless of its kinetic energy, the probability of a simulated electron producing multiple ions in a given simulation time step is negligible provided the time step is small and thus is not an issue in most simulations. However, this probability can become significant if A.The simulation time step is large, B.The gas density is very high, or C. The simulation uses electron macro-particles and the number of electrons each macro-particle represents is large. The ionization routine handles the case of multiple ionizations by allowing the ionization probability to exceed 1, and then use a Monte Carlo routine to determine if an additional ion is created. If multiple ionizations occur for a given simulation particle in a given time step, all ions are placed within the trajectory of the primary electron. By energy conservation, the electron must lose a certain amount of energy with every ionization. If the kinetic energy of the primary electron drops below the ionization energy of the gas molecule, it can no longer ionizes. The problem occurs when the total amount of energy loss from all ionizations occurring in a given time step for a given electron macro-particle exceeds the difference between the macro-particles kinetic energy and the ionization energy of the target gas (i.e. E_loss > T - Ii). If this condition is met, then it means that the electron macro-particle produced more ions than it should. For example, consider an electron with 20eV of energy ionizing H2 gas, which has an ionization energy of 15.4. Assume the density of the H2 gas is ridiculously high, say, 10^50 m^-3. In a given time step, the ionization probability might be P~20.329, meaning that 20 ions are created and there is a 32.9% chance of creating an additional ion. The GPT ionization routine will place 20 ions within its trajectory. However, because its kinetic energy is only 20eV, only 1 ion is allowed to be created before the electron's kinetic energy drops below the H2 ionization energy. Thus, a check needs to be implemented to ensure this can never happen and the correct number of ions are created for high ionization probabilities.
- Logistics: Implement check (probably a few if-statements within the secondary electron do-while loop) to update the scattered electron's energy with every ionization and check to see if the resulting energy is above the ionization energy before adding an additional ion. Run test GPT simulation with electron macro-particles creating multiple ions per time step to ensure the checks work correctly.
- Estimated Completion Time: 1-3 days
- Possible Complications: With any coding, I might run into some weird technical problem that may take a while to come up with a solution/work-around.