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Guide: Dr. Mayuri S. Rao (Astronomy & Astrophysics, Raman Research Institute), Keerthipriya Sathish (Electronics and Engineering Group, Raman Research Institute)

Project Completed: On-going

Project work done:

1. Hardware and Software Interfacing of APSERa

The software realization for APSERa involved the creation of a GUI-based interface for cryocontroller control and logging. Additionally, a Flask-based web application called APSERa Control Interface (ACI) was developed for overall system monitoring, interactive plotting, and logging, providing real-time control for various devices. ACI includes a Data-logger curve editor application developed Lakeshore curve editing, loading purposes.

2. Standard Run of APSERa

Various iterations of setpoints and KPID values were tested to optimize system performance. Temperature stability was achieved with less than 1K steady state error at 75K, 77K and 120K setpoints by Controller tuning. Pressure variation studies were conducted to investigate leak rates. 

3. PID Modeling

Theoretical modeling of the APSERa cryocooler system was performed using a second-order transfer function, fitted to 280K and 77K setpoint runs, to characterize the plant's behavior. Further analysis was done using MCMC to estimate higher-order plant model parameters, alongside manual parameter inference from graphical analysis of system behavior. The modeling also explored the thermodynamics of a copper plate attached to the cold tip as a passive element, for its transfer function derivation. Which improved our model to be able to capture the temperature fluctuations on the copper plate (which is attached to the cold tip and all electronics for cryo cooling go on top of it), knowing the temperature fluctuations at the cold tip.

4. Shroud Design

A shroud optimized for APSERa was designed with incorporated air passthroughs, improving system efficiency. The design was integrated into the Dewar vessel's CAD file, ensuring compatibility and enhancing the overall thermal management of the experiment. The shroud was fabricated in-house and installed into the system.

5. Antenna and Radome Engineering

The existing antenna for the experiment was simulated with metal structures around it and multi layered soil to understand the effects of the antenna-environment couplings. 

Extensive simulations were conducted to explore spherical and flat Radomes for APSERa, including variations with and without the Dewar vessel. Theoretical analysis of Radome reflections was followed by simulations on the impact of material choices, radome thickness, and buckling pressure. The results led to informed design dimensions for minimizing edge diffraction and optimizing radome performance.

6. Experimental Deployment

A general deployment plan for APSERa to the field was prepared, which included the calculation of dome dimensions and other logistical considerations for setting up the experiment at the designated site.

7. RF Chain Pipeline for APSERa

A significant aspect of my work involved systematics studies, enabling a detailed analysis of non-linearities and non-idealities within the RF chain. I conducted a comprehensive analysis of APSERa's RF chain, focusing on imbalances in microwave devices like amplifiers and couplers etc. To assess these effects, I developed a simulation pipeline to quantify effect of non-linearities on the signal flowing through. Functionality was validated using MATLAB and CST. Various code modules were developed to handle S-parameter algebra, device definitions, and signal manipulation. Journal in preparation

Publications and Conferences:

1. Ghosh, A., Rao, M. S., Sathish, K., Kasturi, S., Narendra, S., & Ibrahim, M., Laboratory Commissioning of a 77 K Cryocooler for the APSERa S-band Telescope, Presented at 43rd Meeting of the Astronomical Society of India (ASI), NIT Rourkela, India, 2025. Accepted.

2. Narendra, S., Sathish, K., Rao, M. S., Srivani, K. S., Girish, B. S., Krishna, D., Shankar, U. N., Kasturi, S., Akshaya, V. G., Kamini, P. A., & Ghosh, A., APSERa – An Upcoming S-Band Cosmology Experiment, Presented at 6th URSI-RCRS, 2024.

3. 'Studying the systematics in RF Chain of APSERa via rigorous modelling of non-idealities', Journal in preparation