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    <title id="title">Jules van Irsel</title>
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                        <li><a href="grad-courses.html">Physics Ph.D.</a></li>
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        <div class="section-title"><p>Plasma Vacuum Testing</p></div>

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            <a href="images/vacuum-chamber-plasma.jpg" target="_" class="img">
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                <h2>Generating Space Plasmas</h2>
                <p>
                    Both types of rocket instruments I have worked with measure properties of space plasmas. This requires a
                    laboratory environment that can provide, not just a plasma, but one sustained at an ultra-high vacuum with
                    pressures of around a millipascal.
                    <br><br>
                    To create this vacuum, our lab uses a cryogenic vacuum chamber called
                    <a href="https://sites.dartmouth.edu/lynch-rocket-lab/construction/" target="_"><em>The Elephant</em></a>, which
                    has a base pressure of around a micropascal, and an operating pressure of less than millipascal. Mounted to
                    this chamber is a plasma source which uses a magnetron, like the ones found in everyday microwave ovens, which
                    radiates microwaves through a quartz window, via a waveguide.
                    <br><br>
                    On the other side of the quartz window is a microwave resonant cavity into which various gases, such as helium,
                    nitrogen, or argon, are bled through a needle valve. Once in the cavity, these gases ionize by resonating
                    with the microwaves that are tuned to 2.45 GHz, matching the TE<sub>112</sub> mode resonance design frequency.
                    Interfacing this cavity and the chamber is a backplate with 21 holes that are just large enough to seep the
                    plasma through while fully reflecting the microwaves. This ensures the microwaves do not interfere with the
                    experiments in the same way you can see your food heat up through a microwave oven window! The photo here shows
                    an argon plasma diffusing through the backplate.
                    <br><br>
                    The design of The Elephant was spearheaded by Kristen Frederick-Frost and it became operational in 2005. To
                    learn more, please give her
                    <a href="https://collections.dartmouth.edu/archive/object/dcdis/dcdis-frederick-frost2007" target="_">Ph.D. Thesis</a>
                    a read!
                </p>
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                <h2>Cryogenic Vacuum System</h2>
                <p>
                    Parallel to my research work, an invaluable component of my degree involved operating the vacuum chamber and
                    generating plasmas for the testing of various space-based instruments. This meant pumping down the chamber to
                    ultra-high vacuums many times, which involved more than just vacuum pumps.
                    <br><br>
                    Chambers, like The Elephant, are pumped down to what we call a rough vacuum first. This is done with regular
                    mechanical vacuum pumps, but, since they are mechanical, they require lubrication. This lubrication is oil-based
                    and boils at ultra-high vacuums, hence these pumps stop at around 10 pascal. At this point various valves and
                    oil traps are used to isolate the chamber from these contaminants.
                    <br><br>
                    Once the roughing pump systems are isolated, we turn on the cryogenic compressor, which compresses helium to a
                    liquid and pumps it through what is essentially a radiator. This cools the radiator to just over 4 Kelvin, or
                    −452°F, where, at this temperature, most of the remaining particles left in the chamber condense onto the
                    radiator. This is how we reach up to micropascal pressures.
                    <br><br>
                    Before starting my Ph.D. program, I worked with a very similar vacuum system at the University of Calgary which
                    was originally designed to test the Thermal Ion Imagers aboard the European Space Agency's Swarm mission.
                </p>
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                <h2>Working Inside Vacuum Chambers</h2>
                <p>
                    Besides vacuum pump lubricants, essentially any organic material will boil at ultra-high vacuums and it can
                    contaminate the cryogenic system. This is why, when having to climb into the chamber, one has to suit up
                    head-to-toe. Luckily, I only had to do this a few times!
                </p>
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                    <h5>Transcripts</h5>
                    <ul>
                        <li><a href="documents/transcript-dartmouth.pdf" target="_">Dartmouth College</a></li>
                        <li><a href="documents/transcript-uofc.pdf" target="_">University of Calgary</a></li>
                        <li><a href="documents/transcript-sait.pdf" target="_">SAIT Polytechnic</a></li>
                    </ul>
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                <div>
                    <h5>Selected Publications</h5>
                    <ul>
                        <li><a href="documents/jgr_vanirsel_etal_2025.pdf" target="_">van Irsel et al. (2025), <em>JGR</em></a></li>
                        <li><a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024JA032722" target="_">van Irsel et al. (2024), <em>JGR</em></a></li>
                        <li><a href="documents/arcs-section-d.pdf" target="_">Lynch et al. (2024), <em>NASA</em></a></li>
                    </ul>
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                    <h5>Documents</h5>
                    <ul>
                        <li><a href="documents/cv.pdf" target="_">Curriculum Vitae</a></li>
                        <li><a href="documents/thesis.pdf" target="_">Dissertation</a></li>
                        <li><a href="documents/thesis-proposal.pdf" target="_">Thesis Proposal</a></li>
                        <li><a href="documents/finesst-proposal.pdf" target="_">NASA FINESST Proposal</a></li>
                    </ul>
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                    <h5>In the news</h5>
                    <ul>
                        <li><a href="https://www.bostonglobe.com/2023/10/13/metro/darmouth-professor-kristina-lynch-rockets-eclipse-nasa/" target="_">Rockets Studying the Eclipse</a></li>
                        <li><a href="https://www.astech.ca/archives/indexofpastwinners/space-physics-group-university-of-calgary" target="_">2018 ASTech Special Award</a></li>
                        <li><a href="https://home.dartmouth.edu/news/2020/09/dartmouth-proposal-chosen-possible-space-mission" target="_">ARCS Proposal</a></li>
                        <li><a href="https://www.youtube.com/watch?v=QiX9xL_YhvM" target="_">Surveying the Northern Lights</a></li>
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