研究目的
The aim of the GroundBIRD experiment is to observe the B-mode on large angular scales from the ground, which would provide evidence of cosmic inflation.
研究成果
The GroundBIRD experiment successfully developed a rapid scanning telescope with cold optics and MKIDs, confirming operational readiness through vibration measurements and detector response tests. Magnetic shielding designs are effective, and preparations for observations in the Canary Islands are on track, aiming to detect B-mode polarization as evidence for cosmic inflation.
研究不足
The experiment is limited by potential vibrations from the rotation mechanism, sensitivity to geomagnetic fields requiring effective shielding, and the need for calibration of beam pointing and baseline fluctuations. Observations are constrained to ground-based settings, which may introduce atmospheric noise.
1：Experimental Design and Method Selection:
The experiment uses a telescope with rapid rotational scanning at 20 RPM to mitigate 1/f noise, cold optics at 4 K to reduce instrumental polarization, and microwave kinetic inductance detectors (MKIDs) for fast response times. The design includes a three-axis rotation mechanism (azimuth, elevation, and boresight) and magnetic shielding to handle geomagnetic effects.
2：Sample Selection and Data Sources:
The CMB radiation is the primary data source, observed over large angular scales (multipoles 6 to 300) from the ground at the Teide Observatory.
3：List of Experimental Equipment and Materials:
Includes a telescope mount, cryostat with pulse tube cryorefrigerator and sorption cooler, MKIDs fabricated on 3-inch silicon wafers, magnetic shields (e.g., FINEMET MS-FR, Amumetal 4K), readout system with RHEA analog board and KCU105 FPGA board, and various filters (low-pass, high-pass, IR filters).
4：Experimental Procedures and Operational Workflow:
The telescope rotates at 20 RPM; vibrations are measured at the focal plane. Detector responses to geomagnetism are tested with and without magnetic shielding. The readout system samples MKID responses at up to 1 MSPS. Calibration is done using wire grids and pointing observations.
5：Data Analysis Methods:
Power spectrum density measurements of MKIDs are performed to analyze noise and quasiparticle lifetimes. Simulations using ANSYS Maxwell for magnetic shielding effectiveness are conducted.
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magnetic shield
FINEMET MS-FR
Hitachi Ltd.
Attenuates geomagnetic fields around the radiation shield.
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microwave kinetic inductance detector
MKID
Detects CMB polarization with fast response times for rapid scanning.
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pulse tube cryorefrigerator
Cools the telescope optics to 4 K.
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sorption cooler
Cools the detectors to 250 mK.
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magnetic shield
Amumetal 4K
Provides magnetic shielding at 4 K radiation shield.
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analog-to-digital converter
14-bit ADC
Part of the readout system for converting analog signals from MKIDs.
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digital-to-analog converter
16-bit DAC
Part of the readout system for generating tones for MKID readout.
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field-programmable gate array evaluation board
KCU105
Controls the readout system and processes data from MKIDs.
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RHEA analog board
RHEA
Dedicated analog board for reading out MKIDs with multiple channels.
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