EVOLUCIÓN DE LA WEB

Directly comparing the spectra of magnesium oxide and aluminum oxide in generated SRIM/TRIM spectra depict the following important details. More scattering occurs in M gO than Al2O3

as evidenced by the increased FWHM of the spectra, and centroid in ToF occurring at longer times. With a larger gain, and less variation due to scattering eects, aluminum oxide layer was chosen over the magnesium oxide to compare against the carbon foil and uncoated MCPs.

(a) SRIM/TRIM predicted residual energy of protons

on all MCP surfaces, energies, and geometries. (b) SRIM/TRIM predicted residual energy of heliumon all MCP surfaces, energies, and geometries.

(c) SRIM/TRIM predicted residual energy of nitrogen

on all MCP surfaces, energies, and geometries. (d) SRIM/TRIM predicted residual energy of argonon all MCP surfaces, energies, and geometries. Figure 5.11: Predicted energy retention of proton, helium, nitrogen, and argon plasma across lead silicate MCPs, aluminum oxide coated MCPs, and magnesium oxide coated MCPs. Geometry eects are accounted for.

Depicted in Figure 5.11 is the direct comparison of SRIM-calculated residual energy for each ion across each MCP under consideration, including geometrical eects. These are the energies that CODIF would register based on energy loss and trajectory after colliding with the MCPs. Three MCP materials are examined between theL_/D 20 andL_/D 40: one without a coating, one with a 60 ˚A layer of M gO, and one with a 60 ˚A layer of Al2O3. Recall the

base MCP lead silicate material is assumed to be 1000 ˚A thick. Additionally, the L_/D ratio governs the maximum angle of grazing incidence that does not exhibit multiple scattering interactions with the MCP channel. For these MCP simulations, that means the L_/D 20 MCP experiences ions grazing at 2.85o _{from normal to the surface, and the} L_/D 40 MCP experiences ions grazing at 1.35o _{from normal to the surface.}

Two trends are immediately apparent. First, there is a schism between residual energy for all ions, between theL_/D20 andL_/D40. TheL_/D 40 retains more of the initial energy than the L_/D 20, causing a separation, with the L_/D 40 being closer to the initial energy. Second, there is a mass dependence: as mass increases, the ion is observed to retain a larger fraction of its initial energy. Next, the Al2O3 coated MCP has slightly better energy retention than

bothM gO and no coatings, with outliers at high energies and low masses.

For the ux data, there is not much dierence between the coatings. From the total spectra-producing ux observed, comparing individual ions in Figures B.1 - B.12. Looking specically at B.1c, B.5c, and B.9c, for example, reveals protons have no signicant dier- ences among the constituent layers. Even the changes in energy only negligibly aected these rates. The driving force in this regard is purely angular. This is also seen in the backscatter and straggler plots, as well as for the remaining ions. The only major dierences occur with mass, and that can be explained by the collision cross section. As the mass of the ion increases, the scattering cross sections for both electronic and nuclear interactions increase. This is partly due to increased atomic nucleus (and by extension electron cloud) size. As a result, more massive particles like argon are exponentially more likely to undergo scattering, which includes classical Rutherford backscatter back out the front of the MCP. Similarly,

the more massive ions also are more likely to be scattered to the point of straggling.

Additionally, M gO is much more reactive than Al2O3, particularly with water. In the

lab, any and all modications to the instrument have to be done on a workbench at atmo- sphere, which allows the water reactions to occur. Then upon reinstallation into a vacuum environment, the water will have to take a substantial amount of time to outgas. Further- more, the now-present water layer becomes the rst few layers of interaction with the MCP, and not the coating, eectively reducing the emissive properties of the M gO layer. As a result, we chose the aluminum oxide coating for the experiment.

6 Results and Discussion

Measured time of ight spectra basics and a baseline comparison with heritage data are discussed in Section 6.1. Following in Section 6.2 which compares the MCP responses to the carbon foils, and contrasts eects caused solely by the diering geometries as well as coatings. Next are the ion ux rate responses to the diering MCPs as well as carbon foil in Section 6.3. Due to the grazing incidence operation of MCPs, the angular dependence is signicant, and discussed within Section 6.4. Finally, sources of error are addressed in Section 6.5.

Appendix A contains the time of ight spectra for all ions and energy ranges used in this thesis. Progression of the changes in time of ight spectra with energy are given in Appendix A.1 while the entrance system normalized comparisons are in Appendix A.2.

6.1 CODIF Spectra Baseline Results

The following Section 6.1.1 establishes a baseline of the instrument, by comparing current spectra taken with the carbon foil to that used to calibrate the ight model of CODIF in 1994. Afterwards, the basics of spectra dependence on initial energy are investigated in Section 6.1.2 in what is called a time of ight progression with energy. Section 6.1.3 goes over the basics of tting all spectra, common among the carbon foil, uncoated MCPs, and coated MCPs. Finally, the energy losses from the time of ight spectra with initial energy are discussed in Section 6.1.4.

6.1.1 Comparison of Current Carbon Foil with Heritage Carbon Foil Spectra