Here it is! The
long awaited, much anticipated, never-before seen Final Research Project and
Presentation. If I could figure out how, there would be some nice,
triumphant, dignified music on here, but since I'm not quite that
technologically savvy please start humming Gustav Holst's Jupiter
theme to yourself before you read anything else.
The final report covers my work on the spectrometer characterization (project 1) because I spent most of my time on it and there is a substantial amount of actual results to report. For a final wrap-up on the other two projects, try the research progress page. To see the report and/or presentation, just click on the hyperlinks at the beginning of the next two paragraphs.
The final report itself is pretty technical, designed for those who really want to know all (and I mean all) the details of my project. It is a fairly easy read with lots of graphs and such. If you have any questions after enjoying such an immersion in scientific joy, feel free to e-mail me and ask. If I can tell you the answer, I will. :)
The final presentation (in PowerPoint -- click here to download it in Adobe PDF) was designed to have me speaking along with it. It gives a general overview of the main problems I was trying to solve in my project. For the sake of being friendly and allowing you to know what the heck the pictures on the slides mean, there is a handy slide guide a little further down the page....
Slide 1: This one is pretty self-explanatory. It gives me a chance to say I'm Leah, I'm from Benedictine College, I've been working with Itzik, and my project is characterizing the EBIS-C spectrometer.
Slide 2: Also reasonably obvious: this is the order of my presentation.
Slide 3: Spectrometer Basics. The picture shows a cross-section of my spectrometer. The spectrometer itself is made of 27 metal rings. For basic spectrometer operation, we put a positive voltage on the 5th plate - the extra long one - and the voltage goes down in steps through all the rest of the rings. The detector has a negative charge of 2000 Volts. When I talk about directions in the spectrometer, the X direction is along the spectrometer axis (the pink line goes right along the spectrometer axis). The Y direction is perpendicular to the spectrometer axis. Since the spectrometer is a cylinder with radial symmetry, any direction that or location perpendicular to the spectrometer axis is in the Y direction.
In our experiments, we send two jets through the interaction region. The first jet, the Gas Beam, is not on the picture because it goes straight down into the interaction region. Think of it as going through your computer screen, into the interaction region, and out the back of your computer. The second jet, the Particle Beam, is the pink line following the spectrometer axis. When molecules from these two jets collide, the molecule from the Particle Beam breaks into pieces and the molecule from the Gas Beam is knocked off course. The pieces that pick up or keep a positive charge get pulled into the spectrometer and hit our detector. The main goal of using the spectrometer is to be able to find the initial momentum of all the pieces from the collusion.
Two different types of pieces come from the collusion, and each type has different problems we need to fix before we can find their initial momentum. Pieces from the Gas Beam are called Recoil Ions, and pieces from the Particle Beam (remember, the molecules from this beam break) are called Beam Fragments. We get two pieces of information from the detector: the Time of Flight - how long it takes each piece to get from the interaction region to the detector - and the final position of each piece on the detector.
Slide 4: Recoil Ions Part 1: One problem with our particle breakup experiments is that we can't control exactly where the collusion between two molecules happens. It would be really nice if we could make all the collusions occur at the exact center of the interaction region. Instead, they happen somewhere in about a 2 millimeter square around the center. And even though a millimeter is really small, it can make a big difference. If one recoil ion starts at a particular distance X (i.e. it is along the spectrometer axis ) from the center of the interaction region with one momentum and a different recoil ion starts at a different distance X with a different momentum, it is possible for them to hit the detector at the same time. That means that it is possible for two recoil ions under different conditions to have the same Time of Flight, as demonstrated by the graph on the slide. We use the Time of Flight to find a recoil ion's initial momentum, so if recoil ions with different initial momentum have the same Time of Flight, we have a big problem.
Slide 5: Recoil Ions Part 2: To fix the problem, we use Space and Time Focusing. By placing a second voltage that is a particular percent of the main spectrometer voltage (see slide 1 explanation) on the 11th plate of the spectrometer, we can create a "voltage hill." It works basically like a normal hill. If two skier start going down a slope at the same time, but one skier starts higher up, eventually the one that started higher up (who will have more momentum) will catch up to the other skier, so then for a while they will reach the same place at the same time. When that happens for my recoil ions, it is called Time Focusing. Think about Space Focusing as a big funnel, where things that start out really far away from each other at the top of the funnel all end up really close together at the funnel tip. One of my main goals was to figure out what the best voltage is to create both focusing effects.
Slide 6: Recoil Ions Part 3: The spectrometer has great focusing because there is really a range of a couple percent where the spectrometer will be focused beyond the resolution of our detector. Our detector can only detect distances that are greater then 0.25 mm (about 1/100 of an inch), so as long as the recoil ions hit the detector less than 0.25 mm apart, it will "look" to us experimentally like they hit in the same place. Any focusing voltage (the one on the 11th plate) that results in an difference between the two particles, called error on the graph, that is under the green line will work to give us space focusing. Our detector can only detect time differences greater than 100 picoseconds (1 x 10-10 seconds), so any focusing voltage that causes the recoil ions to hit the detector less than 100 picoseconds apart makes them "hit at the same time" as far as we can tell with our detector. Any focusing voltage that gives an error under the blue line will work to get time focusing.
Slide 7: Beam Fragments Part 1: When we find the initial momentum of beam fragments, we run into a different problem. Having a different X position makes doesn't matter for beam fragments, but having a different Y position or a velocity in the Y direction does. Both situations cause a beam fragment to hit the detector farther away from the spectrometer axis than ordinary physics says it should. This happens because of the electric field in our spectrometer. The two pictures demonstrate how the Y position or Y velocity affect the final position. The dotted pink line shows where a particle should go, and the solid pink line shows where the particle does go in our spectrometer.
Slide 8: Beam Fragments Part 2: We can get around the magnification problem pretty easily as long as we have an equation that gives us a magnification factor. Then we can just divide the magnified distance by the magnification factor and voila! the actual distance from the spectrometer axis to where the beam fragment hits the detector. I found the magnification factor as a function of the energy of the particle beam divided by the main voltage on the spectrometer (we call this quantity Escl). To do that, I made graphs of Escl vs. Magnification for the different kinds of magnification and found an equation to fit the graph.
Slide 9: Beam Fragments Part 3: Most of the beam fragments in a real experiment will have both a Y position and a Y velocity, which means both magnification effects will be influencing the particle at the same time. The equation that tells the total magnified distance from the spectrometer axis to where the beam fragment hits the detector is at the bottom of the slide. Basically it just says that if you add the magnified distance from the Y position plus the magnified distance from the Y velocity, you get the total magnified distance.
Slide 10: Summary: This slide reviews the problems we fix for recoil ions and beam fragments. By fixing these problems, we end up with enough equations and few enough variables that we can solve the equations to get the each recoil ion and beam fragment's initial momentum.
Slide 11: Applications: My spectrometer characterization will be used by my group as a reference when they are doing experiments that use the EBIS-C spectrometer.
Slide 12: Applications: Here are some of the experiments my group is planning on doing with the spectrometer. They will be studying the disassociation (breaking apart) of carbon monoxide 2+, collision induced disassociation and disassociative capture (where the recoil ion looses an electron to the molecule in the particle beam, and then the molecule breaks into two pieces) of HD+ and H2+, and the vibrational state effects of H2+ (how far apart the two H atoms have to be before they will break apart, as well as some other stuff). I wrote about the second experiment in more detail on the left. It is particularly neat because this is the first time we will be able to measure the Ar+. Now with the great focusing of this spectrometer, we will really be able to look at all the pieces from a collision.
