Thuong Hoang research

Keywords: Inflation, Cosmic Microwaves Background (CMB), superconducting Transision Edge Sensor (TES), Half-wave plate, Cryogenics system, Magnetic fields and star formation, Dust polarization

Research topics are classified into Simulation, Data analysis, and Instrumentation

I have been contributing to several Cosmic Microwave Background (CMB) projects such as LiteBIRD, QUBIC, simons Observatory (SO), CMB-S4, and BICEP. Future CMB projects aim to measure polarization signal that imprint primordial gravitational waves from the Early Universe in the context of the Big Bang theory. I am curious in roles magnetic fields and star formation processes.
Summary of my experiences:

Experimental (LiteBIRD): Desmonstration of a small prototype polarization modulator unit (PMU) for LiteBIRD low-frequency telescope.

Data analysis: Measurement of magnetic fields in the plane-of-sky toward M17 cloud using SOFIA/HAWC+ thermal dust polarization at 154 micromets.

Experimental (SO): Calibrated Transition Edge Sensor (TES) focal plane for Simons Observatory.

Simulation (LiteBIRD): Study systematic effects for LiteBIRD CMB satellite.

Experimental and data analysis (QUBIC): Testbed Transition Edge Sensor (TES) array with a radioactive source for ground-based QUBIC experiment.

Simulation (CMB-S4): Study survey strategy at Atacama-Chile for CMB-S4 project.

Simulation (Planck): Cosmic ray interaction with detectors of the Planck satellite and the future mission LiteBIRD.

7. LiteBIRD: Desmonstration of a small prototype polarization modulator for LiteBIRD low-frequency telescope.

Figure: The experimental setup.

LiteBIRD telescopes employ polarization modulation units (PMU) using continuously rotating achromatic half-wave plates (AHWP). The PMU is a crucial component to reach unprecedented sensitivity by mitigating systematic effects, including 1/f noise. We have developed a 1/10 scale prototype PMU of the LiteBIRD LFT, which has a 5-layer achromatic HWP and a diameter of 50 mm, spanning the observational frequency range of 34-161 GHz. The HWP is mounted on a superconducting magnetic bearing (SMB) as a rotor and levitated by a high-temperature superconductor (YBCO) as a stator.

In this study, the entire PMU system was cooled to 10 K in a cryostat chamber using a 4-K Gifford-McMahon cooler. A coherent millimeter-wave polarized signal was passed through the rotating HWP and the resulting modulated signal was detected. The AHWP modulated optical signal and rotational synchronous signals from the rotational mechanism were analyzed . The testbed was built to integrate the broadband HWP PMU and assess potential systematic effects in the optical data, paving the way for a full-scale model.
This study is published in the SPIE proceeding [ SPIE ]. I recored a video of the full prototype PMU system testbed in Liquid Nitrogen (77 K), the PMU is levitated and spun [ HWP levitation]

6. SOFIA: Magnetic fields toward M17 cloud.

Figure: An RGB image of M17 (the Omega Nebula or Swan Nebbula also known as Horseshoe Nebula in the constellation Sagittarius at a distance of 1.98 kpc) Photodissociation Region (PDR).

Star formation is influenced by self-gravity, turbulence, and magnetic fields (B-fields), but the precise role of B-fields in the evolution of dense clouds and the star formation process is not fully understood. One way to study B-fields is through the measurement of dust polarization induced by aligned grains. The strength of B-fields can be estimated using the Davis-Chandrasekhar-Fermi (DCF) method through thermal dust polarization.

This study presents the measurement of the component of magnetic fields in the plane- of-sky of the M17 region using thermal dust polarization data obtained with SOFIA/HAWC+ at 154 μm wavelength. The DCF method was used to determine the presence of strong magnetic fields of approximately 327 ± 34 μG and 839 ± 80 μG in lower- and higher-density regions, respectively. The gravitational mass-to-magnetic flux ratio was also calculated, and the relative contributions of B-fields and turbulence in the M17 region were examined. In addition, the alignment of dust grains in this region was investigated using the radiative torque paradigm.

The study is published in the ApJ journal [ arxiv:2108.10045 ]

5. Simons Observatory (SO): Testbed focal plane.

Figure: Testbed focal plane module of thousands Transistion Edge Sensors and readout system at Mike Niemack's Cosmology group - Cornell University.

The Simons Observatory (SO) is a Cosmic Microwave Background (CMB) project located at the Atacama desert in Chile that aims to study the early universe, its content, and its evolution. The SO experiment will use a 6-meter Cross-Dragone Large Aperture Telescope (LAT) and three 42-centimeter Small Aperture Telescopes (SATs) equipped with thousands of Tran-sition Edge Sensors (TES) in a Universal Focal plane Module (UFM; see Figure). The LAT is designed to measure CMB anisotropies at arcminute scales, while the SATs will observe low foreground regions in search of B-mode signals. The UFM is a 4-centimeter tall by 15-centimeter hexagonal module with two main components: a Universal Microwave Mul-tiplexing module (UMM) and a TES detector stack array. The UMM consists of 100-mK cold components (μmux chips, an RF-wafer, and a DC-wafer), including microwave Superconducting Quantum Interference Devices (SQUID) and a frequency domain multiplexing system, which drive and read out TES bolometers.

I have been working on the testbed system for the readout chain and UMM of the UFM:

focusing on performance, screening, and design requirements. Specifically, I have mea- sured lumped shunt resistance on a 500 micromets thickness DC wafer using both a warm microscope method and a cold four-wire measurement approach readout by our electronic system, from 100 mK to room temperature.

I have also embedded the UMM inside an external magnetic field (generated by a Helmholtz coil) to observe shifts in resonators when the magnetic field is varied, as SQUIDs are sensitive to external magnetic fields

Additionally, I have used a system called the coldload to optically characterize the UFM by setting up a black-body radiation emission at the 4 K stage inside a dilution refrigerator.

A study of external magnetic fields and the SO's readout system SQUID is published in [ arXiv:2012.04532 ]

4. LiteBIRD: Systematic effects.

Figure: LiteBIRD: A Lite satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection.

The future Cosmic Microwave Background (CMB) satellite LiteBird have been selected to probe B mode polarization to measure the tensor-to-scalar r ratio with a sensitivity σr ≤ 0.001, which is almost two orders of magnitude beyond the Planck sensitivity. Several important systematic effects could contribute to final observation as 1/f noise, asymmetric beams, bandpass mismatches, the interaction of cosmic rays withthe focal plane.

Bandpass mismatch error is one of the important systematic effects that can affect thecurrent and next-generation measurements of the polarization of the Cosmic Micro wave Background radiation (CMB). The slightly different frequency bandpasses among detectorsintroduce leakage from intensity into CMB polarization.

Using full focal plane simulations, I evaluated the level of this effect for future CMB satellite missions and estimated of its possible impact on the final determination of the tensor-to-scalar ratio r . I have simulated thetime streams with filter variations as observed in the Planck HFI. I assumed nominal scanning strategies and detector parameters for LiteBIRD. I projected data using the simplest map-making coaddition method. Power spectra of residual EE and BB coming from the leakage maps are computed for 80 % sky fraction excluding the galactic plane. The amplitude of leakage depends on the scanning strategy of the satellite parameterized with precession angle, spin angle, precession spin and rotating spin. The conclusion of this work is that the spurious angular power spectrum could potentially bias r for measurements of the reionization bump, and of the recombination bump. The bandpass mismatch effect is negligible in case of an ideal HWP.

The study is published in JCAP [ arXiv:1706.09486 ]

3. QUBIC: Calibrated Transition Edge Sensor (TES) array with a radioactive source.

A set up of radioactive source in front of an 256-TES arrays inside a cryostat at AstroParticles and Cosmology laboratory - Paris University.

I have studied the interaction of particles with a 256 TESs array of the ground-based QUBIC(Q&U bolometric interferometer for cosmology) experiment. In order to test the sensitivity of detectors to cosmic rays, the behaviour of TES array will be similarily as study of collecting CMB photons from the sky.

An 241 Americium radioactive source is set up in front of the 256-TES array in the mixing chamber inside the cryostat cooling down to background temperature Tb=300 mK. When particles hit a TES pixel, the deposited energy could be transformed to temperature elevation of the TES components (eg: Thermometer, absorbing grid, substrate) and also affect the neighbor pixels that provides a possible measurement of the cross-talk among pixels.

This study allows us to understand the thermal time constant (30-60 ms) of a TES and the readout system time constant (10-20ms) .

The study is published in [ https://doi.org/10.1117/12.2312080 ], and [ arXiv:2101.06787 ]

2. CMB-S4: Survey strategy at Atacama-Chile.

Figure: The hitcount map of a single detector fo one year observaton of a Large Aperture Telescope (LAT) at Atacama.

Current and next ground-based CMB experiments will mainly deploy at two major sites, the Simons Observatory at the Atacama Desert in Chile and the South Pole Observatory. The observation strategy of an instrument plays an essential role in the ability to increasingly sensitive maps of the CMB polarization anisotropies.

I have been studying the optimization strategies for telescopes located at the Atacama Desert site (SO, CMB-S4, CCAT: Cerro Chajnantor Atacama Telescope) using the Time Ordered Astrophysics Scalable Tools ( TOAST T) installed at the National Energy Research Scientific Computing Center (NERSC). In my study, TOAST is used to simulate a hardware configuration of a typical telescope then create a sky observation. The resulted observational schedule and hit count maps of detectors can be used to evaluate the depth, efficiency, and uniformity of the survey strategy.

The detail study of CMB-S4 Large Aperture Tescope (LAT) at Chile is written in CMB-S4 website [ Modulate scan high cadence LAT ].

1. Planck: Bolometer and Cosmic Rays.

Figure: The agreement between analytical approach and MCMC simulation for number of events per deposit energy for Proton and Helium primary Cosmic Rays.

In my master thesis (2015), I worked on the topic: Cosmic rays (CRs) interaction with Planck satellite detectors for the measurement of the CMB radiation polarization. The galactic particle of energy ∼1 GeV hit the silicon die of polarization sensitive bolometers (PSB) and spider wed bolometers (SWB). The interaction produces long glitches (τ≈500 ms)on the scientific data. Therefore the modeling, analysis, and simulation play a vital role tounderstand and characterize of the long glitches. This understanding allows us to better remove the impact of the long glitches in polarization sensitive bolometers data.

I developed a simple model of the interaction of galactic particles with the silicon die of the Planck bolometers. I predicted the number of events per deposit energyd due to primary cosmic rays particles. I have observed good agreements between the analytical approach and the Monte Carlo simulation method.

Basing on this experienced study with Planck, I had been studying the interaction of cosmic rays with the focal plane of the LiteBIRD mission.

Master thesis [ pdf ].