| 研究課題/領域番号 |
19K23438
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| 研究機関 | 東京大学 |
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研究代表者 |
Stever Samantha 東京大学, カブリ数物連携宇宙研究機構, 特任研究員 (20842991)
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| 研究期間 (年度) |
2019-08-30 – 2021-03-31
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| キーワード | systematic effects / cosmic ray / detectors / cosmology / particle interactions |
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| 研究実績の概要 |
Having purchased the simulation PC through this grant, and obtained a license for the software COMSOL with the Heat Transfer module, I have produced a thermal model for the LiteBIRD detector wafer. This produces pulses of thermal excursions from CR energy injection into the wafer given a starting location and energy. I have used this to produce a pulse library of thermal excursions given the starting conditions of the incoming cosmic ray. I plan to expand this into an automated routine to produce any temperature excursion given its starting location and energy, and the location at which the temperature is read on the wafer.Following this, I have adapted a Python model written by a colleague for producing the current and temperature of a TES giving a varying 'bath temperature' (wafer temperature) and incoming optical power (either from observations or from direct cosmic ray hits).
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
The current status is defined primarily by the ease with which I was able to produce a working thermal model in COMSOL, which was aided by my prior experience working with such models. The current thermal model is also simpler than others I have worked with, as the large silicon wafer comprises only a single layer with the coupling to the thermal bath, and without extra metal layers which would require additional layering from electron-phonon interactions.
The main drawback to the progress of the current project is that it requires some experimental verification on a real LiteBIRD detector, which has not been performed previously by any working group. A radioactive source has been secured, and a sourceholder has been designed, but the cryostat for taking these measurements is at Kavli IPMU, which is closed due to COVID-19. Furthermore, the PI has since moved to a position at Okayama University. The PI plans to travel to Tokyo to complete the experiments as soon as possible.
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| 今後の研究の推進方策 |
The thermal model will be used to test the addition of gold wirebonds at the wafer edge to reduce the time constant of the thermal excursions in the wafer. This will eventually be verified by an experiment at Okayama University after securing a sample wafer from US partners.
Optimising the automated code for utilising the pulse library to produce timelines is ongoing. Given the simple linearity properties of the pulse library, we envisage swift progress.
This model will be used to produce T(t) timelines based on the COMSOL thermal model, and will finally be used to produce simulated time-ordered data of cosmic rays in the LiteBIRD wafer. This TOD will finally be injected into the TOAST-LiteBIRD framework, and its effect on the degradation of the tensor-to-scalar ratio (r) will be used to test mitigation strategies in LiteBIRD using both hardware and software mechanisms. Therefore, the above described framework will soon become an important tool for parameterising the cosmic ray effect and the hardware and software mitigations used to understand and minimise it, ensuring the instrument (and future instruments) protection from this significant systematic effect.
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| 次年度使用額が生じた理由 |
The price of the COMSOL license was not known precisely before the calculation of expenditure, and some balance was required in order to order a computer which would be sufficient for the calculations. Furthermore, the PI incurred less costing for travel expenses during this time as their travel was covered by institutional funding.
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