Heatflux power exhaust control in Tokamak Nuclear Fusion Experimental Reactors

I have been working for the past few months on the problem of effectively managing and controlling the heatflux exhaust that comes out of plasma in a Tokamak device. In future Fusion Power Plants, while fusion would be happening inside the core of the plasma, enough high energy particles will leak out of the magnetic bottle and would be diverted towards the so-called target plate where they hit a surface. This flux of particles would carry enough heat to melt all known materials to humans so far. Thus, we plan on using impurity neutral gas seeding near the target plates to “extinguish” the flux by radiating away most of it’s energy. However, if too much impurity is seeded, it can find it’s way to the core of the plasma and cool it internally leading to low efficiency and chances of dramatic disruptions. We don’t want that. I’m working on this control problem to develop a reliable solution.

Multicolor Calibration technique for gravitational wave detectors

We are developing a new calibration method for gravitational wave detectors utilizing the co-resonating frequency doubled green laser in the arms. We’ll demonstrate our method at the 40m prototype at Caltech, where we are aiming to reach 0.1 % uncertainty in detector absolute calibration. This work would allow future LIGO detectors to not be limited by calibration noise even for strong signals.

Cryogenic interferometer lock acquisition and calibration

We are developing a lock acquisition scheme for future cryogenic gravitational wave detectors like LIGO Voyager. Advanced LIGO currently used a frequency-doubled 532 nm green laser to assist in locking five cross-coupled cavities with the main laser at 1064 nm. Since cryogenic Si test mass requires a higher operation wavelength (\(\sim\) 2 \(\mu\)m), we are working on using an optical frequency comb to compare with any arbitrary auxiliary wavelength for lock acquisition. We plan to cancel the intrinsic noise of the frequency comb using a feedforward technique employing a Direct Digital Synthesizer. In the future, the same subsystem can be used for calibrating the detector as well.

Balanced Homodyne Readout at 40m Prototype

We are implementing Balanced Homodyne Readout at the 40m prototype at Caltech to test and characterize this method as a gravitational wave readout scheme. This method has not been implemented on a suspended interferometer before. I led a team of three postdocs, one research scientist, and two graduate students, to upgrade the entire optical layout of 40m, involving adding 7 new suspensions to existing set of 10 suspended optics, and new low noise controls and data acquisition electronics. This is the most major upgrade to the lab in last 12 years.

Direct measurement of Coatings Brownian Noise for Crystalline Coatings

Brownian noise at the high reflectivity Bragg coatings in LIGO mirrors persists to be the dominant noise contributor in 200 Hz to 600 Hz frequency range. Our understanding of the theory of origin of this noise remains untested and incomplete. I worked on a table top optical setup to measure the coatings Brownian noise of thermo-optic optimized GaAs/AlGaAs mirrors down to \(10^{-18}\) m/\(\sqrt{\text{Hz}}\) at 100 Hz. The results of the experiment inform us on our gaps in noise estimation of the coating BRrownian noise using mechanical loss angle which is measured indirectly.