Laurie Burns: Studying Triple-GEM foils by Melis A. '08

In 1997, Fabio Sauli invented the Gas Electron Multiplier (GEM) at CERN, the world’s largest particle accelerator. A triple-GEM consists of thin layer of insulating material called Kapton sandwiched between two sheets of copper, making a grand total of three layers (the “triple” comes from the three separate GEM foils that are stacked to make the final detector.) The composite sheet is then patterned with an array of 600,000 tiny holes (about 70 um in diameter) using a chemical etching process The sheet can be used to detect particles by amplifying ionization patterns by up to ten times. Researchers at the Plasma Science and Fusion Center in the Laboratory for Nuclear Science (LNS) at MIT have developed a prototype detector. Under the guidance of Professor Bernd Surrow and a postdoc, senior Laurie Burns is testing and comparing two types of GEM foils that may be used in future models.

GEMs are able to detect particles using well-known physical principles. When a voltage is applied to the foils, a voltage difference appears because the Kapton is an insulator and does not let current pass. This voltage difference creates an electric field, so if a few electrons were to come near the foil, the charge on the surface would be amplified below. It may be easier to think of the GEM as a sort of microscope for charges, where each foil acts as a lens. Once the “microscope” is hooked up to all the appropriate auxiliary equipment such as an oscilloscope, it can detect, for example, whether a particle is an electron or a positron based on which direction the particle turns in a magnetic field.

Most GEMs currently use foils that were created by the CERN Surface Treatment Service. Since CERN is a research facility and not a foil producing business, MIT’s BatesCenter has begun fabricating its own foils. This is a very delicate process, as a piece of copper stuck in only one of the 600,000 holes can cause the foil to fail. Laurie began her UROP last spring and continued through the summer, where she mostly worked on using scanning software to examine the foils from CERN and Bates. As part of her senior thesis project, she will eventually conduct a comparative study between the two foils by making two model detectors to assess each foil’s properties such as its gain and lifetime. Once the findings of her study are complete, the LNS hopes to develop a triple-GEM that has a surface area nine times larger than the detector currently in use.

Laurie’s research on triple-GEMs has a lot of fascinating applications. The application that I found most impressive was the ability to detect cosmic rays muons. In general, the GEM is better than other detectors because it is safer to use and produces more gain (ratio of signal output to input).

As a physics (course 8) major, Laurie emphasizes that most physics students have the opportunity to conduct experiments in their junior year in the junior lab class. Through the class, students perform eight experiments that provide exposure to various aspects of experimental physics. She says that, in general, physics majors get their first UROPs in their junior year because a lot of background knowledge is necessary to complete meaningful research.

Laurie also discussed some research being done by her fellow physics majors. They include studying:
– Lasers to figure stuff out about gravity (LIGO)
– Computer processes involving physics at the Lincoln Labs
– Computer simulations in a joint project with the Stanford Linear Accelerator Center
– A two-dimensional harmonic oscillator and finding the solutions to it
– Quantum physics
– String theory
– Time travel charge parody (to find out more about this, take Special Relativity (8.20) to find out how to travel into the future!)
– Astrophysics
– Lasers (pulsing, optical physics)

Originally from Massachusetts, Laurie says that her high school physics teacher is one the reasons she decided to be course 8. In her free time, she likes to play the violin and in the past she was in the MIT Chamber Orchestra. She also likes playing intramural sports like ice hockey and is very involved with her sorority. Laurie is currently in the process of applying to graduate schools in applied physics departments and hopes to research optics in the future. She also has a minor in French and is thinking about putting some of her language skills to use while conducting research at CERN.