Dr. Andrea Giammanco (UCLouvain) and Sophie Wuyckens (PhD student at UCLouvain) describe the design process of creating a muography detector prototype and discuss details of their involvement with a mission for a recent “UCL to Mars” nonprofit program
Q: What is the “UCL to Mars” program?
“‘UCL to Mars’ is a simulation of a scientific Martian mission. The participants are students who self-organize, passing the baton from one crew to the next, raise funds by themselves (contacting several companies as sponsors), and receive some spontaneous support by professors and researchers of the university. The local infrastructure in the Utah desert, the so-called Mars Desert Research Station (MDRS), is maintained by the Martian Society and accepts crews from all over the world. Since 2001, about 200 crews were hosted at the MDRS. “UCL to Mars” has been among the most regular users, sending one crew per year for a decade.
“UCL to Mars” 2018 was a pilot experience from the point of view of our R&D project (although some of the previous “UCL to Mars” crews had already brought and operated scintillator bars and performed a measurement of the muon flux), so since the start we did not plan to take real muography measurements with our setup, but just to explore the logistical feasibility before getting more ambitious, and of course learning from experience. And we learned a lot!
Our collaborator Eduardo Cortina Gil, a Professor at UCLouvain, already supported previous “UCL to Mars” crews by providing scintillating bars and fully-functional readout systems that previous participants used for muon flux measurements, hence anticipating Sophie Wuyckens’s experiments of 2018; scientifically, what was new last year was that for the first time a “UCL to Mars” mission was used to test a new prototype, instead of just borrowing standard lab material.”
Q: The UCLouvain team developed a new, compact, lightweight, gas tight and robust prototype gas detector with some assistance from the University of Ghent. Could you describe the contributions of the University of Ghent towards the development of this muography detector?
“We would like to acknowledge the crucial role of Michael Tytgat’s team at the University of Ghent, and in particular his graduate students Antoine Pingault and Alexis Fagot.
For several years the Ghent team has had a leading role in RPC developments for large particle physics detectors and started the development of small-area RPCs for a completely different purpose, related to the R&D of the CMS detector towards its Phase-2 upgrade. They were investigating some variants of the current RPC design (such as different electrode materials and eco-friendly gas mixtures), and small-area prototypes were built for these testing purposes. We soon realized that the excellent intrinsic spatial resolution of RPC detectors (easily better than 1 mm), the relative simplicity of construction and low manufacturing cost would make these mini-RPCs a perfect tool for high-resolution muography, and that small size was appealing for several muography applications; that’s how the idea of our collaboration started. Sophie Wuyckens’s personal project for her MSc thesis began at Ghent, where she spent a couple of weeks to learn how to personally build a mini-RPC from A to Z, and then was able to continue at UCLouvain. We also borrowed the front-end electronics from the Ghent group, we filled our detectors with their gas after we realized that we had issues with our own gas mixer, and we resorted to their advice on countless occasions. In the near future we intend to strengthen our link further, and we have already made joint funding applications.”
Q: How did you conduct the gas leakage tests? Did you do these tests on site at the Mars Desert Research Station or later on once the detector was shipped back to the UCL laboratory?
“Before filling the detector casings with the operating gas, tightness tests were performed in the lab by measuring the leakage rate after creating a vacuum inside. We were also able to look for leaking points by using helium. This method revealed several defects in two of the four detectors, and as we had little time before the trip to Utah, we shipped only the other two, taking the time to fix the leakage points after Sophie Wuyckens’s return. For the two detectors that went to Utah and back to our lab, the pressure was measured again after their return, and we could thus verify that they didn’t lose any pressure from the day of sending.”
Q: What are your objectives for this project in the coming year? Do you have plans for further field-testing outside the laboratory setting?
“This was our very first prototype and its main purpose was to gain experience in building and operating these mini-RPCs, but we are already planning our second prototype based on the lessons learned, and we intend this time to improve the spatial resolution, towards real muography applications. We will keep the geometry very modular, and we will perform other out-of-lab tests, in particular to see how fit is this kind of detector for usage in underground tunnels.”
Q: Would it be possible to implement a muography gas detector for an actual mission on a spacecraft for surveying other planets, satellites and asteroids? If so, what would be the biggest challenges you would have to overcome in order to do this?
“Although “UCL to Mars” offers a nice synergy (and our prototype is planned to make a new trip to the Utah desert in the next mission, in April 2019), we are actually skeptical that gas detectors could be a realistic option for actual missions on other planets: the huge pressure involved in landing a spacecraft set very tough requirements in terms of robustness, and probably solid-state detectors would be a safer option. Solid-state detectors are not popular for muography because of their larger cost with respect to gaseous and scintillator detectors, but once compactness and robustness become crucial, they clearly have some advantage over other technologies, and their resolution is excellent. (Incidentally, our UCLouvain team and Dr. Andrea Giammanco have very strong expertise in solid-state detectors for particle physics, so it is not totally inconceivable that this could be a future project!)”
Q: Did you find that there were any advantages to field-testing this detector prior to testing it in the laboratory setting?
“Actually we would have very much preferred to do the other way around, as normally done. Timing was unfortunate, as last year’s “UCL to Mars” happened relatively soon after the start of the project, and so we didn’t have the time to perform a proper testing in the lab before this unconventional test in the field. But we decided to proceed anyway, disregarding a possible “plan B” that was to just recycle the old telescope based on scintillating bars that had been used in a previous mission, because we considered that after all we had nothing to lose and a lot to learn.”
Q: What environments or situations would be particularly suitable for real-world applications of this portable gas detector?
“As mentioned above, what we have in mind is to optimize this detector for usage in underground tunnels; in particular a prominent application would be for archaeological exploration. In that case, gas tightness will be absolutely crucial. The advantage over the scintillator-based detectors (that do not suffer many of the logistic issues of gas detectors, and are therefore more popular for muography in underground settings) is the much better spatial resolution achievable. We chose a very modular design, such that we can change the distance between planes at ease, adapting to the size of the tunnel.”
Q: Could you describe the application process and some of the activities students are involved with in the “UCL to Mars” program?
“After each mission in the Utah desert, the last task for a crew before self-dissolving is to select the members of the next crew. An open call for applications is advertised in the university and competition is fierce as only 7-8 members are allowed per crew. Moreover it is important to maximize its diversity. Selection criteria include: being a student at UCLouvain (at all levels up to PhD), having a meaningful scientific project to propose, strong enthusiasm and a good teamwork attitude.
The “UCL to Mars” crews are multi-disciplinary, so we always also have a large breadth of experiments every year, ranging across several sciences (for example, biology, chemistry, pharmacology, geology, agronomy, and human health), and this work was not the only outcome of last year’s mission to be included in a peer-reviewed scientific publication (see for example http://hdl.handle.net/2078.1/213010 .)
While science and technology are of course at the core of this life-on-Mars simulation, participation is also open to students from the humanities, if they suggest an interesting and relevant project. For example, one of the members of the next crew is enrolled in a Master’s in Law, and he plans to draft a Martian Constitution based on what he will learn from this experience of living together in a realistic simulation of a small segregated colony. It is also customary for the crews to have one member acting as “journalist”. As writing skills are important for the task, that’s typically assigned to a student from the humanities.”
Q: What were the specific logistical conditions that were tested?
“The detectors were completely built and gas-filled in Belgium, and this simplified a lot of things with respect to the option of assembling in situ. Nevertheless we had to face several logistical issues related to sending and manipulating them in a desert. First, the trip to USA in itself was constraining. A solid wood box with polyethylene foam or bubble pack inside was used to contain the detectors and electronics. Secondly, working in the desert means sand and sand is a pain, as it can leak into the detectors while you operate them. The wind had also to be taken into account. In order to offset these effects, our boxes needed to be completely tight, not only to prevent gas leaks but also against sand/dust infiltration. And they had to be heavy enough to not be carried away by the wind, while at the same time light enough to be easily portable. For this purpose, we used solid aluminum boxes closed by means of seals coated with vacuum grease. With all these special precautions, the detectors survived a two-weeks trip to the US. Another issue was the voltage.
In terms of electronics, we chose to design it as portable as possible. The front-end cards, high voltage module, FPGA, CPU, cables etc. were all contained in a single rack, very light and quite small. A WiFi antenna connected with a USB to the CPU allowed us to collect data easily and a fan was mounted on the rack in case of high temperatures. Moreover, in Europe we use 220 V voltage while in North America, sockets allow electricity at a voltage of 120 volts; as a consequence, besides a converter, a transformer was needed in order to produce the 220 V supplying the electronics. No help was needed in order to make the detectors work. Only one person can install everything, which may be excellent for a potential real mission in a complicated setting.”
Q: Do you have plans to return to the Mars Desert Research Station for further testing with a future “UCL to Mars” mission?
“We plan to keep the connection between our muography development project and “UCL to Mars” intact. For example already for the next “UCL to Mars” mission, in April 2019, our prototype will make another trip to Utah, where a new student will profit from what we learned last year, and from all the developments made in the meantime in our lab in Belgium. If everything will go as planned, he might be able to compare the flux from the free sky with the flux passing through one of the elements of the landscape, and therefore do some real muography.”
More information about the UCLouvain “UCL to Mars” Program:
Since its beginnings (the first crew assembled in academic year 2009-2010) until 2017, “UCL to Mars” used to be a rather informal student activity. As years passed, “UCL to Mars” attracted more and more media attention, also thanks to the students’ enthusiasm in organizing outreach seminars and meetings with the general public, not to mention their social media presence (see for example their lively facebook page: https://www.facebook.com/ucltomars/ ). As “UCL to Mars” appeared more and more often on the national press and television, the UCLouvain authorities took note, proud of the achievements of these students. Finally, last year, it was decided to make “UCL to Mars” a registered not-for-profit organization under the official aegis of UCLouvain, which implies the presence of a UCLouvain staff member (as “academic reference person”) in the Board of Directors, whose other members must all be UCLouvain students. Dr. Andrea Giamannco serves in this role since the establishment of the “UCL to Mars” not-for-profit organization.
More information about the UCLouvain (with University of Ghent) prototype Muon Gas Detector:
“CMS Technology Used to Develop A New Prototype Muon Telescope” on the CMS website
“A Portable Muon Telescope Based on Small and Gas-Tight Resistive Plate Chambers”
Published in the Cosmic-Ray Muography issue of the “Philosophical Transactions of the Royal Society A”.
Click the link for information on muography and the EURAXIS program