SuperKEKB試運轉期間之BEAST2偵測器中的BGO背景與光度監測器的軟韌體建置、校正與運行

Abstract

SuperKEKB對撞機於2016年開始粒子束的運轉。野獸計畫II是設計用來量測在Belle II實驗中，SuperKEKB對撞機的對撞點附近的粒子束背景。為了即時監控粒子束背景，我們設計了一個系統，利用未摻雜的鍺酸鉍晶體，藉由光纖連接到一個多陽極光電倍增管和一個上插現場可程式邏輯門陣列晶片的讀出板。鍺酸鉍系統的輻射靈敏度在操作於700伏特電壓下、連接額定的10公尺光纖時校正為2.2E-12 ± 11.75% Gy/ADU (analog-to-digital unit)。我們的伽瑪射線輻照研究顯示鍺酸鉍系統遭受到輻射損傷。鍺酸鉍晶體的光輸出在2.5小時內吸收了4.5k雷得劑量之後降了約40%，和以前我們曾經發表過的鍺酸鉍晶體輻射耐受度研究的結果一致。輻照研究也證明了鍺酸鉍系統非常可靠，可以在高輻射環境下運作不會嚴重飽和或有其他問題。除此之外，鍺酸鉍系統在野獸計畫II的運行非常成功，它提供了很多非常有用、關於粒子束背景研究的資料。鍺酸鉍系統提供的資料會促進整個野獸計畫II的發展。我的研究包含了對鍺酸鉍系統的軟韌體設計、系統校正、分析輻照研究結果與統整野獸計畫II中運行的資料。在本論文中，我對鍺酸鉍系統做了全面性的介紹，包含設計、校正、測試、和野獸計畫II中粒子束背景研究的結果。

Beam commissioning of the SuperKEKB collider began in 2016. The Beam Ex-orcism for A STable experiment II (BEAST II) project is particularly designed to measure the beam backgrounds around the interaction point of the SuperKEKB collider for the Belle II experiment. We developed a system using undoped bismuth germanium oxide (BGO) crystals with optical fiber connections to a multianode photomultiplier tube and one field-programmable gate array embedded DAQ (data acquisition) board for real-time beam radiation background monitoring. The radia-tion sensitivity of the BGO system is calibrated as 2.2E−12 ± 11.75% Gy/ADU (analog-to-digital unit) at the 700-V operation voltage with the nominal 10-m-long fibers for transmission. Our γ-ray irradiation study of the BGO system shows that the BGO crystals suffered from radiation damage. The light yields of the BGO crystals dropped by ∼40% after receiving 4.5 krad dose in 2.5 h, which agrees with the results of the radiation hardness study we have reported. The irradiation study also proves that the BGO system is very reliable, being able to function at fairly high radiation conditions without serious saturation or other problems. Besides, the running of the BGO system in BEAST II was very successful. It has provided much useful data for the beam background study. The data that the BGO system provided will facilitate the development of the entire BEAST II project. My study contains the design of the firmware and software, the calibration of the device, the analysis of the results of the irradiation study, and the integration of the data obtained during the running in BEAST II. In this thesis, I make a comprehensive portrait of the BGO system, including the design, calibration, tests, and the results of the beam background study in BEAST II.