News

CHAOS successfully launched as part of the stratospheric balloon mission BX35 on the 2nd October 2024. At the moment, we are in the middle of the data evaluation and the first results look very promising. In January, we have to submit our final results which will mark the end of CHAOS as part of BEXUS.

But Kiel University is not done yet. Currently, a new team of students is forming to apply to the next BEXUS cycle with the instrument SETH. So, CHAOS is passing on the torch. And fittingly, SETH is the Egyptian god of CHAOS…

You can find some photos from CHAOS’s launch campaign in Kiruna, Sweden below.

The sensor head of our CHAOS experiment contains various different detector types. One of them is the Bismuth-Germanium-Oxide (BGO) scintillator. We want to observe galactic cosmic rays. When the particles travel through the scintillator, photons are created. These mass-less, charge-less and super fast photons are the particle manifestation of light. They propagate through the BGO and are measured at two photodiodes glued to the outside surfaces of the BGO. But how exactly do they propagate through the scintillator? And what factors influence the signal yield at the photodiodes? Investigating this is the subject of my bachelor’s thesis, in which I wrote a Python-based program that simulates the photons’ path through the scintillator. Stay tuned for the results.

The CHAOS particle telescope will be able to differentiate between heavy particles and lighter particles in the Galactic Cosmic Rays (GCRs). The heavier particles are protons and different nuclei while electrons for example are among the lighter particles in the GCRs. To differentiate between those different kinds of high energetic particles the CHAOS telescope is going to use a Cherenkov detector in which particles who are moving faster than the speed of light in the medium are creating so called Cherenkov-radiation. At similar energies the heavier and the lighter particles in the GCRs have vastly different velocities. Therefore only the lighter particles who are moving fast enough will create Cherenkov-radiation in the medium.

In our Cherenkov detector, the material in which the Cherenkov-radiation is created will be aerogel. Aerogels are porous solid bodies whose volume can be made of up to 99.98% pores. Therefore aerogels are among the lightest materials available.

On 22 April, the eagerly awaited blocks of aerogel finally arrived in Kiel. The two custom made blocks from the aerogel factory in japan had to undergo strict inspections to check if they fulfill several quality criteria especially wether or not the deviations in dimension are of a tolerable amount. Because the aerogel is so dust sensitive and brittle the inspection had to be done in our dust free clean room. When we inspected the aerogel we had to undergo several steps to ensure that we don’t carry any dust or electrostatic charge into the clean room. Only in the clean room the aerogel’s packaging was opened and we first saw the sky blue color of the unpacked blocks. The 62mm * 62mm * 40 mm big blocks of aerogel weigh only 26.6 g. While inspecting, the aerogel blocks had to be handled with great caution not to damage or even scratch the material. Afterwards we decided that the aerogel blocks meet our requirements, the deviation in dimension are sufficiently small and. Now we can finally start experimenting with them and getting them ready for flight.

On Thursday 25 April, two schoolgirls visited us as part of Girls’ Day. In the morning we inspected the room in our building and glued one of the photodiodes to the bismuth germanium oxide scintillator. Then we showed and explained two of our current experimental setups. The set-up with the BGO crystal was going to be placed in the vacuum chamber. Together with the students, we took all the necessary precautions and transferred the whole setup to the laboratory with the vacuum chamber. In preparation, several cables were soldered from the test cell to the vacuum feedthrough and further to the readout electronics. These were extensively tested by the girls before commissioning, as were all the other feedthroughs and the power supply. After the lunch break, the measurement setup was put into operation and after successful tests, the vacuum chamber was closed and the air pumped out. As the light output in the BGO is temperature dependent, the next step is temperature calibration. Unfortunately, there is currently a problem with the cooling system, so this test will be delayed. However, with the help of the two students, the test setup in the pump-down vacuum chamber was successfully put into operation.