Light Ion High Voltage Repeller & High Harmonic Generation using Two Color Driving Fields

by Sean Buczek

supervisorItzik Ben-Itzhak, Distinguished Professor of Physics

Kansas State University Physics Department  REU Program

 This program is funded by the National Science Foundation through grant number PHYS-1461251.  Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Project Overview:  I was involved in two projects this summer. The first, and the one that I spent most of my time working on, was developing an apparatus that will allow for more reliable imaging of ion momentums within a vacuum. The problem that my group has been running into is that when using the lasers to dissociate an ion beam, many background gases are also ionized. These background ions are much lighter than the ion beam we are curious about, and thus hit the detector before the interesting ions. This can lead to dead times on the detector, effectively blinding it for a small portion of time. The Light Ion High Voltage Repeller, more often referred to simply as the repeller, will stop these background ions by creating a large, very temporary potential “wall,” so to speak. Since we have the ability to turn this “wall” on and off very quickly, we can have it stop the unwanted ions while having it not hinder the important ones. This will allow us to take higher resolution imaging as well as waste less time worrying about losing data.

The other project I have had the privilege of working on is an experiment to generate ultra-fast x-ray laser pulses. Specifically, we used a technique called high harmonic generation using a two color driving laser in order to make these very short lived (roughly 10-18 seconds long) x-ray pulses. Unfortunately, this project takes more time to complete than how long I was here. Given that, I was only involved in the setup and initial data taking for the experiment, helping the group of graduate students (lead by Travis Severt) to find the high harmonics. My assistance helped to confirm that we are able to generate the high harmonics in our lab, and helped with a few other steps that will save them time in the future.

Research Description:  In this section I will give a brief description of how I conducted the research for both of my projects. A more detailed description of both of my projects can be found in my final presentations, which I have made available below. 

For the repeller, a lot of the work was done using a simulation software called SimIon, which is an industry standard for this sort of task. After discussing with my advisor, Dr. Ben-Itzhak, about a basic design for the repeller, I simulated the environment that it would go into and found an arrangement that would do what we wanted. This eventually turned out to be a series of rings with specific voltages applied to each of them. I conducted a series of simulations within the software to see what affects the inclusion of this repeller would have on the other parts of an experiment being ran while it was in use. Once we were satisfied with the results from the simulation, schematics were made and sent to a manufacturer. After a short amount of time, we had the parts needed for construction. This is what took up a good portion of my last few weeks here. Constructing the repeller, wiring it properly and then testing it turned out to be a significant chore. As of the time of this writing, tests are still ongoing to see how well the setup functions. Currently, we believe we have an issue with how quickly we can ramp off the voltage on the repeller with the power supplies that we have available. A paper will likely be written about this apparatus once enough tests have been ran an it is used in an actual experimental setup.

My participation in the other project was more hands on from the start, though it was more sporadic on when I was working on it. Mainly, I was helping place and align optics that we used during testing. I also did a significant portion of work towards optimizing the various nonlinear processes that are needed in order to generate high harmonics. We could not get too much progress done on the project, as we were riddled with small issues we continually ran into. Despite this, we still got through much of the necessary early work in order for the experiment to go more smoothly in the future. More details about what we were looking for is available in the full presentation.

Final PresentationClick to view the presentations I made for the repeller and the two color HHG (pdf form for both). Neither one is absolutely complete, but the details they are missing do not pertain to the projects and understanding them.

About Me:  At the time of this writing, I am going into my senior year at Drake University, where I study Physics and Mathematics. I also compete in Track and Field for my university and I am an active member of my fraternity, Phi Delta Theta. I enjoy a large variety of activities, ranging from drawing (I am pursuing a minor in graphic design) to video and tabletop gaming. All of this I somehow find time to enjoy in between study sessions for classes and my various commitments to my team and fraternity. In my time in the REU here at Kansas State, I was recovering from a pretty serious ankle injury I sustained at the end of the previous track season, which made getting around campus slightly annoying, but also gave me a sort of celebrity status around the dorms we stayed in and started many conversations with people that I otherwise wouldn’t have talked to. In short, I’m glad I got to meet more people around here, if only temporarily.

Useful Links

I have found the following links particularly informative or useful:

American Physical Society Statements on Ethics

American Institute of Physics

James R. Macdonald Lab