Research

Dissertation

• Experimental Verification and Time-resolved Bispectral Analysis of Nonlinear Coupling in the Toroidicity-induced Alfven Eigenmode Spectrum (2024)

Honors/awards

Featured Article in Physics of Plasmas (April 2024)
ITPA EP topical group expert member (March 2024)
Sherwood Fusion Theory Student Poster Award (May 2023)
Oleg D. and Valentina P. Jefimenko Physics Fellowship (April 2023)*
Research Trust Fund Seehra Research Award (April 2021 & April 2024)*

Invited talks

1. Wave-wave coupling of fast-ion driven instabilities in the DIII-D tokamak
   WVU Colloquium (Nov. 5, 2025)

Peer-reviewed publications

1. BicAn: An integrated, open-source framework for polyspectral analysis
   Computer Physics Communications (2026)
   G. Riggs, M. Koepke, T. Matheny
2. Instantaneous difference-frequency locking observed in coupled eigenmodes on the DIII-D tokamak
   Nuclear Fusion (2026)
   G. Riggs, M. Koepke, W. Heidbrink, M. Van Zeeland, D. Spong
3. Dependence of ion-cyclotron range of frequencies instabilities on species mix and fast-ion distribution (Part 2: Time evolution)
   Nuclear Fusion (2025)
   W. Heidbrink, G. DeGrandchamp, J. Lestz, K. Thome, S. Vincena, N. Crocker, X. Du, R. Pinsker, G. Riggs, S. Tang, M. Van Zeeland
4. Time-resolved biphase signatures of quadratic nonlinearity observed in coupled Alfven eigenmodes on the DIII-D tokamak
   Physics of Plasmas (2024)
   G. Riggs, M. Koepke, W. Heidbrink, M. Van Zeeland, D. Spong
5. Role of simple spatial gradient in reinforcing the accuracy of temperature determination of HED plasma via spectral line-area ratios
   Atoms (2023)
   G. Riggs, M. Koepke, T. Lane, T. Steinberger, P. Kozlowski, I. Golovkin
6. Establishing an isoelectronic line ratio temperature diagnostic for soft X-ray absorption spectroscopy
   High Energy Density Physics (2022)
   T. Lane, M. Koepke, P. Kozlowski, G. Riggs, T. Steinberger, I. Golovkin
7. Bispectral analysis of broadband turbulence and geodesic acoustic modes in the T-10 tokamak
   Journal of Plasma Physics (2021)
   G. Riggs, S. Nogami, M. Koepke, A. Melnikov, L. Eliseev, S. Lysenko, P. Khabanov, M. Drabinskij, N. Kharchev, A. Kozachek, M. Ufimtsev and HIBP Team

Manuscripts submitted/in preparation

1. Parameterization of the latitudinal dependence of ULF waves in the magnetosphere via long-term statistical observations
   Submitted to Journal of Geophysical Research: Space Physics (2026)
   G. Riggs, W. Tu, T. Sarris
2. Formal power series expansion for infinite exponential of analytic function
   In revision for resubmission to The American Mathematical Monthly (2026)
   G. Riggs

Talks

1. Understanding off-equatorial radiation belt electron radial diffusion via empirical modeling and single particle tracing
   International Space Science Institute Topical Group Meeting (Mar. 17, 2026)
   G. Riggs, W. Tu, T. Sarris
2. BicAn: An integrated, open-source framework for polyspectral analysis
   67th Annual Meeting of the APS Division of Plasma Physics (Nov. 20, 2025)
   G. Riggs, M. Koepke
3. Statistical ULF wave latitude distribution: A key to understanding off-equatorial radiation belt electron radial diffusion
   GEM/CEDAR Workshop (Jun. 25, 2025)
   G. Riggs, W. Tu, T. Sarris
4. Instantaneous difference-frequency locking observed in coupled eigenmodes on the DIII-D tokamak
   ITPA EP Topical Group Meeting (Mar. 21, 2025)
   G. Riggs, M. Koepke, W. Heidbrink, M. Van Zeeland, D. Spong, Y. Ghai
5. Instantaneous difference-frequency locking observed in coupled eigenmodes on the DIII-D tokamak
   DIII-D Energetic Particle Group (Mar. 5, 2023)
   G. Riggs, M. Koepke, W. Heidbrink, M. Van Zeeland, D. Spong, Y. Ghai
6. Time-resolved bispectral signatures of TAE mode-mode coupling observed in the DIII-D tokamak
   ITPA EP Topical Group Meeting (Oct. 2, 2024)
   G. Riggs, M. Koepke, W. Heidbrink, M. Van Zeeland, D. Spong, Y. Ghai
7. Time-resolved biphase signatures of quadratic nonlinearity observed in coupled eigenmodes on the DIII-D tokamak
   KINETIC Center Workshop (Aug. 22, 2024)
   G. Riggs, M. Koepke, W. Heidbrink, M. Van Zeeland, D. Spong, Y. Ghai
8. Time-resolved biphase signatures of quadratic nonlinearity observed in coupled eigenmodes on the DIII-D tokamak [video] [slides]
   Princeton Plasma Physics Laboratory Energetic Particle Seminars (Nov. 29, 2023)
   G. Riggs, M. Koepke, W. Heidbrink, M. Van Zeeland, D. Spong, Y. Ghai
9. Time-resolved biphase signatures of quadratic nonlinearity observed in coupled eigenmodes on the DIII-D tokamak
   DIII-D Energetic Particle Group (Oct. 11, 2023)
   G. Riggs, M. Koepke, W. Heidbrink, M. Van Zeeland, D. Spong

Conference posters

1. Statistical ULF wave latitude distribution: A key to understanding off-equatorial radiation belt electron radial diffusion
   American Geophysical Union Annual Meeting (December 2025)
   G. Riggs, W. Tu, T. Sarris
2. Estimating the radial riffusion coefficient of off-equatorial relativistic electrons in the radiation belts due to geomagnetic latitude-dependent ULF waves
   American Geophysical Union Annual Meeting (December 2025)
   T. Sarris, X. Li, H. Zhao, W. Tu, G. Riggs, S. Tourgaidis, K. Papadakis, W. Liu, L. Yan
3. Comprehensive analysis of beam-driven ion cyclotron range instabilities in mixed species DIII-D plasmas
   67th Annual Meeting of the APS Division of Plasma Physics (November 2025)
   J. Lestz, W. Heidbrink, N. Crocker, G. DeGrandchamp, K. Thome, S. Tong, S. Vincena, K. Barada, X. Du, W. Peebles, R. Pinsker, T. Rhodes, G. Riggs, S. Tang, M. Van Zeeland, L. Zeng
4. Statistical ULF wave latitude distribution: A key to understanding off-equatorial radiation belt electron radial diffusion
   GEM/CEDAR Workshop (June 2025)
   G. Riggs, W. Tu, T. Sarris
5. Time-resolved biphase signatures of quadratic nonlinearity observed in coupled eigenmodes on the DIII-D tokamak
   65th Annual Meeting of the APS Division of Plasma Physics (2023)
   G. Riggs, M. Koepke, W. Heidbrink, M. Van Zeeland, D. Spong
6. Time-resolved biphase signatures of quadratic nonlinearity observed in coupled eigenmodes on the DIII-D tokamak
   Sherwood Fusion Theory Conference (2023)
   G. Riggs, M. Koepke, W. Heidbrink, M. Van Zeeland, D. Spong
7. Preliminary identification and characterization of nonlinear wave-wave, wave-beam, and wave-particle interactions in beam-driven tokamak plasma
   64th Annual Meeting of the APS Division of Plasma Physics (2022) [slides]
   G. Riggs, M. Koepke, W. Heidbrink, M. Van Zeeland, D. Spong
8. TJ-II observations of nonlinear wave-wave coupling in play during Alfven-Eigenmode:Turbulence:Zonal-Flow interactions
   64th Annual Meeting of the APS Division of Plasma Physics (2022)
   M. Koepke, F. Papoušek, M. Ochando, C. Hidalgo, B. van Milligen, G. Riggs
9. Constraining magnitudes of nonzero temperature and density gradients using absorption spectra of radiatively heated target-foil plasma
   Stewardship Science Academic Programs Symposium (2022)
   G. Riggs, T. Lane, P. Kozlowski, M. Koepke
10. Constraining magnitudes of nonzero temperature and density gradients using absorption spectra of radiatively heated target-foil plasma
    63rd Annual Meeting of the APS Division of Plasma Physics (2021)
    G. Riggs, M. Koepke, T. Lane, P. Kozlowski
11. Spectroscopic method to obtain n, T applied to soft x-ray absorption spectra in radiatively heated Z-pinch plasmas
    Stewardship Science Academic Programs Symposium (2021)
    G. Riggs, T. Lane, P. Kozlowski, M. Koepke
12. Bispectral analysis of broadband and quasi-coherent oscillations (geodesic-acoustic modes) to interpret wave-wave interactions in the T-10 Tokamak
    61st Annual Meeting of the APS Division of Plasma Physics (2019)
    M. Koepke, S. Nogami, G. Riggs, A. Melnikov, L. Eliseev, S. Lysenko, P. Khabanov, M. Drabinskij, N. Kharchev, A. Kozachek, M. Ufimtsev
13. Interpretation of bi-coherence in space and lab plasma-wave dynamics
    60th Annual Meeting of the APS Division of Plasma Physics (2018)
    G. Riggs, S. Nogami, M. Koepke, N. Crocker, G. Howes, S. Savin, V. Budaev, L. Zelenyi
14. Alfvén Eigenmode (AE) interactions in Tokamaks: DIII-D Frontier Science Experiments connecting the physics of nonlinear waves and processes in space plasmas
    60th Annual Meeting of the APS Division of Plasma Physics (2018)
    M. Koepke, S. Nogami, G. Riggs, G. Howes, N. Crocker, T. Carter, W. Heidbrink, M. Van Zeeland

Master's thesis

• Interpretations of Bicoherence in Space & Lab Plasma Dynamics (2020)

Technical reports

• Bispectral Analysis: Theory & Implementation (2021)
  
• Extension of Bicoherence Analysis to Multivariate Domains with Application to AstroGK Data (2023)