CONCLUSIONES Y RECOMENDACIONES

SRIM/TRIM calculated the scattering of each individual ion, and output the ion's nal energy and trajectory after interacting, as well as ux data. Both these parameters are then subsequently used to generate a simulated ToF spectra within the CODIF instrument by enforcing a 3.00cm ight path in the direction parallel to the surface. By varying just

Figure 5.10: SRIM simulations of 15keV N+ over a range of incident angles onto a 60

Angstrom layer of aluminum oxide over a traditional lead silicate MCP.

the angle over the range of energies used in the experiments, the angular eects can be investigated. Raw SRIM calculations of a select few angles for a steady, monoenergetic beam of nitrogen is given in Figure 5.10. A monoenergetic 15 keV beam of N+ impinges

onto the inner wall of a MCP pore. This has a 60 ˚A Al2O3 layer coated on top of the base

MCP lead silicate material, which is 1000 ˚A thick. As mentioned previously, incident angle of the oxygen ion varied from 0.1o −4.85o in 0.25o steps, and each step collected data of

50000 separate ions. Section 5.3.2 talks about the assumptions as well as accounting for the eects of geometry. Flux results have been adjusted according to the geometrical eects and split into an L_/D 20 and L_/D 40 set, using Equation 5.22.

Plotted in Figure 5.10 are only a select few angular data sets for clarity. However, what can be seen are two major, important trends:

1. Centroid of the spectra increases as the angle of incidence increases 2. FWHM of the spectra increases as the angle of incidence increases

of the MCP plus coating, if present. First, the incoming angle highly constrains the scattering processes acting on the ion. More oblique angles cause more dispersion of the ions spatially, and cause the ions to lose more energy in the collisions which increase the transit time. The larger angle also causes the ensemble average exit angle to increase as well; this o-axis trajectory means the ions will take longer to reach the end of the 3 cm ight path and increase the transit time accordingly. The net result of both of these impose a larger FWHM and long decay tail of the spectra.

These following paragraphs and gures in Appendix B depict a wide array of salient de- tails concerning the spectra for ions in SRIM/TRIM. These are investigated and separated by coating of MCP. Inuence of the incident angle on the spectra parameters were inves- tigated, iterating over all the energies that are used experimentally in this work. Spectra details include the resulting centroid of the time of ight spectra (residual energy retained by the ion), the FWHM imposed, and numerous important ux rates. Of these ux rates, particular attention was given to the successful grazing ions, the backscatter ux back the way it came and out of the MCP, and the rate of particles that are scattered beyond the CODIF detection limits of 300 ns ToF. From these we can also calculate the number of implanted ions.

Uncoated Standard MCP Figures B.1 - B.4 depict the net trends of the ions impinging on an uncoated lead silicate MCP, covering protons, helium, nitrogen, and argon, respec- tively. These trends include position of ToF centroid, spectra FWHM, throughput ux, backscattered ux, and the ux of particles scattered beyond recognition, or the straggling ions. These straggling ions are plasma that have been scattered to the point where the residual energy they retain causes the ToF to be longer 300 ns, which is the cuto for the electronics of CODIF.

What can be seen are the following trends. First, for all ions simulated, total initial energy does not aect the total number of ions successfully grazing o the surface. All

energies are within 1% or less of each other in terms of specularly reected ion ux. L_/D ratio as well as angle of incidence is much more signicant. Second, backscatter and straggler ux rates observe a mass dependence. Heavier ions are more susceptible to straggling as well as backscattering back out the way the ions entered than light ions. Finally, the FWHM for all ions are relatively static, variances of about 10% are seen across dierent masses. Energy slightly changes these values as well, with an increase in energy typically reducing FWHM by a marginal amount. The major contributor is the angle of incidence. Finally, the centroid of the distribution has a slight angular dependence. Increasing obliqueness of the angle of impact shifts the centroids to longer ToF values. Energy is more signicant for centroid energy due to the relationship of the ToF to the energy.

M gO Coating Figures B.5 - B.8 depict the trends of the magnesium oxide simulations for protons, helium, nitrogen, and argon, respectively. Similar to the above no-coating results, these ions closely mimic the observed trends of the uncoated MCP. Distinct angular dependence aects all ion's centroid values, FWHM, total grazing particles, backscatter, and straggling ions. For each ion, there is a noticeable split between the eects of geometry of the L_/D 20 and L_/D 40. The narrower MCP of L_/D 40 trends towards a larger change over all the parameters listed above over a smaller change of angle of incidence, making it more sensitive to angular changes.

Compared against the standard, uncoated MCP, the addition of magnesium oxide subtly changes the observed tendencies listed above. First, the centroids in time of ions scattering o theM gO coating are marginally slower than that of the uncoated MCP, for the majority of ion masses and energies. Only a few low energy, high mass ions are sporadically better performance than either the aluminum oxide or uncoated MCP. Additionally, the FWHM suers as a result of the scattering. This response in energy, mass, and angle makes this coating perform the worst of the MCPs in general. Flux rates are relatively consistent between the coatings; there is no signicant dierence in rates of any particular ion and are

all within 1% of each other regardless of coating. This, again, lends support to a purely angular driving force behind the scattering eects.

Al2O3 Coating Figure B.9-B.12 shows the simulated ToF spectra of protons, helium, ni-

trogen, and argon, respectively, over the typical ranges used in CODIF. Simulations show the following trends in the ToF spectra.

These gures depict the trends of the spectra in time. SRIM oers the ability to look at the ensemble averaged energy deposition per depth. Energy transferred to the electron cloud and exchanged in a nuclear recoil collision both as a function of depth are obtained and plot- ted in the following gures (Figures B.9-B.12). These gures illustrate again just how similar all the MCP coatings behave. Addition of aluminum oxide inuences the observed energy and FWHM tendencies, contrasting against the uncoated and magnesium oxide MCPs. Most importantly, the centroids in time of ions scattering o the alumina coating are marginally faster than that of any other MCP for all ion masses and energies, barring a select few out- liers at high energies and low mass. Consequently, the particles scattered o the alumina coating retain marginally more energy after the collision. Additionally, the FWHM resulting from the scattering is on the order of a nanosecond in favor of the alumina coating compared to that of the magnesia coating. However, the uncoated MCP FWHM is superior to that of the aluminum oxide, making this coating fair as a middle-of-the-road choice for scattering eects. In general, in terms of energy, mass, and angle, this coating's scattering performance is the best of the MCPs. Flux rates are relatively consistent between the coatings; there is no signicant dierence in rates of any particular ion and are all within 1% of each other regardless of coating. Again, this evidence is indicative of a purely angular driving force behind the scattering.