Gregory Wallace

Research Scientist

617-252-1802

NW17-123

Biography

Education

BSc, Electrical Engineering, Rensselaer Polytechnic Institute (2003)
PhD, Applied Plasma Physics, Massachusetts Institute of Technology (2010)

Expertise

RF and microwaves; non-inductive current drive; tokamak operation.

Research

In conventional tokamaks, the toroidal current needed to stabilize and confine the plasma is provided by magnetic induction, much like an AC transformer with the plasma as the secondary winding. This is a simple way to drive current in a pulsed device, but cannot be used to sustain the plasma in steady-state. It is possible to drive current in the plasma non-inductively through the application of high power microwaves. These microwaves push electrons preferentially one direction to generate an asymmetric electron distribution function, and thus a net current. Lower Hybrid Current Drive (LHCD) uses waves in the low GHz range of frequency launched by a phased array of waveguides at the plasma edge to drive current in the plasma. Tokamaks have used LHCD with considerable success since the 1980’s, however significant challenges remain in driving current at the high density and building an antenna that will survive the energetic particle fluxes anticipated in fusion reactors. Research at the PSFC is aimed at addressing these challenges, for instance by moving antennas from the conventional location on the low field side (large major radius) to the high field side (small major radius) of the torus.

Publications

G.M. Wallace, S.J. Wukitch, J.C. Wright, C.E. Kessel, A. Davis, T. Rognlien. “Heating and Current Drive Actuators for FNSF in the Ion Cyclotron and Lower Hybrid Range of Frequency.” Fusion Eng. and Design, in press (2017).

G.M. Wallace, F. Poli, M.A. Chilenski, J.W. Hughes, R.T. Mumgaard, S.D. Scott, S. Shiraiwa, and S.J. Wukitch.  “LHCD during current ramp experiments on Alcator C-Mod.”  European Physics Journal Web Conf., Volume 157, 03063, (2017).

G.M. Wallace, S. Shiraiwa, S.G. Baek, P.T. Bonoli, A.D. Kanojia, P. Koert, B.L. LaBombard, R. Leccacorvi, R.R. Parker, D.R. Terry, R. Vieira, S.J. Wukitch. “A scoping study for high field side launch of lower hybrid waves on ADX.”  IEEE Transactions on Plasma Science, vol.PP, no.99, pp.1-6 (2016).

G.M. Wallace, S.G. Baek, P.T. Bonoli, I.C. Faust, B.L. LaBombard, Y. Lin, R.T. Mumgaard, R.R. Parker, S. Shiraiwa, R. Vieira, D.G. Whyte and S.J. Wukitch. “High Field Side Launch of RF Waves: A New Approach to Reactor Actuators.” In Proceedings of the 21st Topical Conference on Radiofrequency Power in Plasmas (RFPPC2015), 2015.

G.M. Wallace, J. Hillairet, P. Koert, Y. Lin, S. Shiraiwa, S.J. Wukitch. “Analysis of double stub tuner control stability in a phased array antenna with strong cross-coupling.” Fusion Engineering and Design, 89, 2748–2754 (2014).

G.M. Wallace, et al. “Advances in lower hybrid current drive technology on Alcator C-Mod.” Nucl. Fusion 53 073012 (2013).

G.M. Wallace, et al. “Lower hybrid current drive in the high density multi-pass regime.” Phys. Plasmas 19, 062505 (2012).

G.M. Wallace, et al. “Lower hybrid current drive at high density in Alcator C-Mod.” Nucl. Fusion 51, 083032 (2011).

G.M. Wallace, et al. “Absorption of lower hybrid waves in the scrape off layer of a diverted tokamak.” Phys. Plasmas 17, 082508 (2010).

Teaching

Invited oral presentation at the 21st Topical Conference on Radiofrequency Power in Plasmas (RFPPC2015). “High Field Side Launch of RF Waves: A New Approach to Reactor Actuators.” April 29, 2015, Lake Arrowhead, California.

Post deadline invited oral presentation at the annual American Physical Society (APS) Division of Plasma Physics meeting. “Lower hybrid current drive in the high density multi-pass regime.” November 18, 2011, Salt Lake City, Utah.