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Picture of a hemisphere of the LOM - IceCube's new detector design. It is an elongated half-sphere with eight photomultiplier tubes placed within, secured with gels.

The Ice and Its Many Cables – or, what I learned about instrumentation physics

SURF is an awesome summer research opportunity — though perhaps you have already had a good glimpse of that from our blogs year after year. It is not only a chance to research new science but also learn about yourself as a scientist: Is computation your thing, or can you not stand staring at a screen for hours on end at mysterious errors? Do you really like experimental physics, or is this next cable going to be your last straw? (sometimes, the answer to all questions posed above is yes, and in the end, yes, you still want to pursue this most annoying science ever, whatever that is to you. Such is the nature of knowledge, and the passion for it). There is an uglier truth: sometimes, you found the project, or even the work demanded by the field, wanting. If that happens to be the case, it is okay: you need to know both what you like and what you despise, (and also the weight of responsibility) but it’s better that you know it now than later. 

For this SURF, the task bestowed upon me is to design a functionality-and-basic-stress testing procedure for the photomultiplier tubes (PMTs) and their accompanying electrical bases, called the wuBase, before they are to be included in the Long Optical Module (LOMs), a new design for the IceCube detector. Simulations predicted that the LOMs will increase IceCube’s sensitivity four-fold! As always, testing and calibrating your equipment before beginning an experimental search is one of the utmost important tasks!

Here is what I learned about instrumentation, or experimental physics in general, through this epic journey of five fortnights:

  1. The topic might sound simple, but the work is not

Oftentimes, you will soon learn that science is labor-intensive, for a reason. Before I get into thinking about what the task might involve, it has sounded like a one-and-done deal — how many functionalities do you even need to test the PMTs on? They just need to be able to catch the light, right? (Turns out, there are a lot.) As I soon realize — and perhaps this is applicable to all scientific projects, not just experimental physics — there is always complication, consideration, and sometimes the-lesser-of-the-trouble design decisions waiting for me down the road. The key, I learned, is to be patient with myself, with my equipment, and with the process; it will take more time than one thought, but such is the nature of poking around with the laws of nature and seeing what it will do — sometimes it surprises you! 

(And sometimes, the surprise is so small, so subtle— that it takes me a week and several hundred hours of nonsensical data to realize what exactly is going wrong. That, too, is a part of the road.)

Picture of a hemisphere of the LOM - IceCube's new detector design. It is an elongated half-sphere with eight photomultiplier tubes placed within, secured with gels.

Several PMTs are placed in a glass hemisphere of the LOM, to test the snugness of the design. The PMTs are adhered to the glass using specifically formulated gel pads, with additional support structure inside.

  1. You must understand your equipment well

Perhaps this goes without saying, but yes, you must understand what your equipment is designed for, what parameters it is designed for (is it designed for high voltage? low voltage? high charge? or low charge?), and how it works. My first days at SURF were spent understanding how the PMT works, where it works, and what its pitfalls are. Turns out, there are a lot of things that could produce “ghost” data – sparks in the graphs that are not from real signals, but instead an artifact of the designs. No equipment is perfect, and all equipment has its blindspots, so it became very important that I am aware of what those imperfections and blindspots are, especially when I must collect precise data.

As a fun example — my equipment has a certain range of data acceptance, after which is exceeded, all the signals will return zero as if there has been nothing going through the detector in the first place. Well, I forgot that, even if my fiber optic is pointing down on the table, the light from the room would still enter the cable and overwhelm my equipment. There went half a day trying to figure out why my equipment acted up and not detecting anything!

  1. You most likely will not escape coding

Believe me, I tried (no offense, coding). 

The thing is, I don’t mind the work, but I have always believed that there should be something out there that is hands-on that is worth my time more than sitting in a stuffy room and coding. Turns out, I was approaching it in all the wrong ways. Coding is not a wholly separate task from the hands-on experiment – rather, it is there as a tool to complement it. You won’t need to write a hundred lines of code for each experiment you are doing, but if one were to repeat the same three tasks one has to do for tens, maybe hundreds, of PMTs— it’s time to open up that text editor and write some Python. 

Besides, another big and unavoidable part of experiments is analyzing data. Why are we doing experiments if nobody checks that the data produced makes sense, is usable, and then uses them? This is where the computation strength of the machine comes into play – I fit trends, I eliminate points, and I visualize the data with graphs, all using computers!

And as it is with all things experimental — it takes time, especially if you haven’t had a lot of chances to practice. But it is, in the end, a learned and incredibly useful skill. Take your time, be patient with yourself, and build up your experience!

  1. Communication, communication, and more communication is the key

Working at a large collaboration like IceCube very much instilled in me the idea that science is all about collaboration, and collaboration requires communication. Eventually, it set in that my task is much a bigger deal than I have thought it is: both the US and Japan teams will be testing and assembling the same designs, which includes hundreds of PMTs for tens of LOMs, and possibly a lot more in the future. Everyone will want to make sure that this testing procedure is reasonable and covers all functionality needed. 

In between developing the overall goal of the testing procedures and setting up components of the test setup, I also have to present my plan to the LOM development group, composed of my SURF mentor, several grad students, post-docs, and scientists — from both UW Madison and Chiba University in Japan. Somehow it feels much more monumental, and intimidating, to present your work to a panel of international collaborators, who have years and decades of experience with the PMTs and similar IceCube detectors. It also means waking up before 8am local time (which is 10pm in Japan) so that I can share my work. 

All the trepidation aside, the point is to learn from each other. These are the people with expertise, and they are sharing it with me to ensure that my procedure will work, will accurately reflect the operations of the PMTs, and will be relevant to what the PMT will experience and expected to be able to do in the ice. This procedure might even be adapted by other teams for their set-ups. And I am taking suggestions and learning from these experts — including using the data structure proposed by the Japan team to store my data.

  1. Stay versatile and open-minded:

The fun thing about experimental research is that there are so many venues for exploration. I have learned things about solid states physics, optics, microelectronics, and many skills that people would associate with the arts of engineering. I have soldered chips from boards, desoldered chips from boards, and designed specific parts to be 3D printed for my setups (which did involve me spending some time reviewing how to use Solidworks… Thanks Caltech!) The thing is, you do not need to know everything to be able to do experimental research, but being flexible definitely helps you! What I found is more important, though, is the open-mindedness to learning these skills, which requires the confidence that I can learn and the patience to understand that it is okay not to succeed or understand how to do things right off the bat. That versatility and persistence is perhaps the most important skill I have learned as an experimentalist. 

A Photomuliplier tube placed in a 3D-printed holder, customed to fit its shape

I got to design custom 3D-printed part! This PMT holder is specifically designed to hold the 4-inch PMT, with a slightly wider (measured!) radius to fit the holder collars and all other accessories the PMT will eventually be attached with.

Checking my watch and counting down – I am now on week 7 of SURF. It is not over yet, but the scale of time is tipped beyond the halfway point, and soon enough this journey would come to a close. Nonetheless, I have learned a lot – both about myself and about physics. Perhaps one day, nearly graduating, I should review and update this “skill sheet” (knock on wood).

Good luck, fellow experimentalists out there— and have fun tinkering!

Chi Cap ’25

I flitter around here and there — from the coast of Vietnam, all the way to the scorching heat of Texas, and now to Pasadena! When I’m not daydreaming about the sea or the stars, I like to write fictions and poetry, watch movies, or swimming. I’m also a member of the TechLIT club and the Totem Literary Magazine on campus, and I’m very active in Dabney House, where I am currently the Vice-President and Health Advocate.

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