Assembly and Commissioning of a New Multi-hit Charged-Particle Detector for Experimental Studies of Laser-Matter Interactions
Taylor McClain
Kansas Wesleyan University
Physics Major
Mentored by Dr. Artem Rudenko and Dr. Daniel Rolles
The main objective of this project is to assemble and commission a new charged-particle detector for the KAMP (Kansas Atomic and Molecular Physics) instrument at the J.R Macdonald Laboratory (JRML). This spectrometer is a novel experimental setup designed for studies of ultrafast light-matter interactions via coincident measurements.
The experiments in question, which are carried out by the Rolles/Rudenko and Ben-Itzhak groups at Kansas State University, involve irradiating gas-phase atoms and molecules with ultrafast light pulses. The KAMP instrument allows for the measuring of all mechanical data for such reactions, such as momenta, emission angles and kinetic energies of all created charged fragments. This allows us to know how a molecule moves, twists, bends, and breaks apart. With a new multi-hit detector (meaning that multiple particles can be detected for each laser shot), more accurate measurements can be taken. This allows us, among other uses, to know more precisely along which channel a molecule dissociates, and to extend such experiments to larger molecules that yield more fragments when they break apart.
This new detector has the ability to detect and analyse more electron and ion hits than the detectors the JRML is employing currently. This is because of their design difference. In the spectrometer used now for the experiments with the PULSAR laser at the JRML, the position-sensitive detectors are quad-anode detectors. This means that the hit position for each particle is measured using two pairs of signal and reference wires crossing the surface of the detector, and depending on where a particle lands in reference to each of the four corners, the position of the particle can be determined mathematically.
Figure 1: Quad-anode
In the new KAMP spectrometer, there is a "hex-anode" detector in addition to a regular quad-anode. In the hex detector, there are three pairs of wires instead of two, and the position is calculated by where the particle lands in reference to each of six corners. The mathematical calculation is slightly more complex, but it offers significant new capabilities, including resolution of particles that cannot be resolved with the quad detector alone.
Figure 2: Hex-anode
This added detectability is what KAMP boasts. Why is it so important for the positions of these particles to be resolved in this way?
Simply put, the drawbacks of the quad detector's incapability to distinguish between two particles that land near the same place at the same time means that researchers are losing data. With the introduction of the hex detector, there may be more redundant data, but there will also be more relevant data than before because of its powerful ability to resolve many similar-landing fragments.
The goal of my time at KSU this summer is to get the chamber and detectors assembled. This requires a knowledge of how this technology works, as well as the proper assemblage procedures. A test chamber has already been assembled, though it is not where the detectors will eventually be placed. Once the assembly of at least one of the detectors is over, tests will hopefully be run to ensure that the detector is working the way it is supposed to. This includes raw dark count data through an oscilloscope, and other such tests before it is used for actual pump-probe femtosecond laser experiments.
Acknowledgments
I would like to thank Artem Rudenko and Daniel Rolles for being my faculty mentors this summer, as well as Shashank Pathak and Javad Robatajazi for teaching me and allowing me to help with this construction. I would also like to give acknowledgment to Kim Coy, Kristan Corwin, and Bret Flanders, for being there for all of the students in this program. Lastly, I give thanks to Drs. David and Kristin Kraemer, my professors at home, who encouraged me to partake in this experience.
Thanks also needs to be given to the JRML technical staff, including Chris Aikens and Justin Millette, for their help with the technical aspects of this project, including design. Additionally, I would like to thank the Physics Department machine shop crew for machining some of the parts needed for this assembly. All of us working on this project are very grateful for your help and expertise.
This project was supported by the National Science Foundation (NSF) and the Air Force Office of Scientific Research (AFOSR) through NSF grant number PHYS-1461251, and by the NSF EPSCoR Track II grant No. IIA-1430493.