- Post Doctoral
MIT Unit Affiliation:
- Electrical Engineering & Computer Science
Post Doc Sponsor / Advisor:
Date PhD Completed:
My research focus is the development of compact x-ray sources by precision control of electron beams and high-gradient accelerators for use in medical imaging and small angle scattering experiments.
I am currently a Postdoctoral Research Associate with a joint appointment in the Nuclear Reactor Lab and the Research Laboratory for Electronics at MIT, where we are working on coherent-ICS x-ray sources. My broader research interests include photonics; high power, high-frequency vacuum electron devices; THz generation via optical rectification; electron-beam dynamics; and advanced accelerator concepts.
From 2008 until 2013 I was a Graduate Research Assistant with the Waves and Beams Division of the Plasma Science and Fusion Center, MIT. My work focused on the development of high-frequency gyrotron traveling-wave amplifiers for short pulse amplification. I also worked on low-loss THz transmission lines and coupling of THz signals in samples for Nuclear Magnetic Resonance-Dynamic Nuclear Polarization experiments. In 2008, I was with the NASA Marshall Space Flight Center developing non-destructive evaluation techniques for applications related to the US space program.
I received a Ph.D. in electrical engineering from the Massachusetts Institute of Technology in 2013, a M.S. degree in electrical engineering from the Massachusetts Institute of Technology in 2010, and B.S. degrees in electrical engineering and in physics from the Missouri University of Science and Technology (formerly University of Missouri - Rolla) in 2007.
Expected End Date of Post Doctoral Position:
Compact THz accelerators, Nano-patterned electron beams via emittance exchange, THz sources
This thesis reports the theoretical and experimental investigation of a novel gyrotron traveling-wave-tube (TWT) amplifier at 250 GHz. The gyrotron amplifier designed and tested in this thesis has achieved a peak small signal gain of 38 dB at 247.7 GHz, with a 32 kV, 0.35 A electron beam and a 8.9 T magnetic field. The instantaneous -3 dB bandwidth of the amplifier at peak gain is 0.4 GHz. A peak output power of 45 W has been measured. The output power is not saturated but is limited by the 7.5 mW of available input power. The amplifier can be tuned for operation from 245- 256 GHz. With a gain of 24 dB and centered at 253.25 GHz the widest instantaneous -3 dB bandwidth of 4.5 GHz was observed for a 19 kV, 0.305 A electron beam. To achieve stable operation at these high frequencies, the amplifier uses a novel photonic band gap (PBG) interaction circuit. The PBG interaction circuit confines the TE₀₃-like mode which couples strongly to the electron beam. The PBG circuit provides stability from oscillations by supporting the propagation of TE modes in a narrow range of frequencies, allowing for the confinement of the operating TE₀₃-like mode while rejecting the excitation of oscillations at lower frequencies. Experimental results taken over a wide range of parameters, 15-30 kV and 0.25-0.5 A, show good agreement with a theoretical model. The theoretical model incorporates cold test measurements for the transmission line, input coupler, PBG waveguide and mode converter. This experiment achieved the highest frequency of operation (250 GHz) for a gyrotron amplifier. At present, there are no other amplifiers in this frequency range that are capable of producing either high gain or high-output power. With 38 dB of gain and 45 W this is also the highest gain observed above 94 GHz and the highest output power achieved above 140 GHz by any conventional-voltage vacuum electron device based amplifier. The output power, output beam pattern, instantaneous bandwidth, spectral purity and shot-to-shot stability of the amplified pulse meet the basic requirements for the implementation of this device on a pulsed dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) spectrometer.
5 Recent Papers:
"Photonic-Band-Gap Traveling-Wave Gyrotron Amplifier."Physical Review Letters 111.23 (2013): 235101
“Linear Electron Acceleration in THz Waveguides,” IPAC 2014.
"THz dynamic nuclear polarization NMR." Terahertz Science and Technology, IEEE Transactions on 1.1 (2011): 145-163.
"Low-loss Transmission Lines for High-power Terahertz Radiation." Journal of Infrared, Millimeter, and Terahertz Waves 33.7 (2012): 695-714.
"Microwave field distribution in a magic angle spinning dynamic nuclear polarization NMR probe." Journal of Magnetic Resonance 210.1 (2011): 16-23.