About me

Plasma/Accelerator Physicist at UCLA • AI and Machine Learning

chaojie.png

Los Angeles, CA

I’m Chaojie Zhang, a plasma and accelerator physicist at UCLA. My research has focused on turning plasma wakefield acceleration from proof-of-principle demonstrations into reliable technology for future colliders and compact light sources, combining experiments, large-scale simulations, and machine-learning-based modeling. The rapid progress of large language models has drawn my interest to AI itself: how the technology is developing, and how it can be applied to frontier scientific research.

I received my B.S. and Ph.D. in Engineering Physics from Tsinghua University. During my Ph.D. I developed femtosecond relativistic electron probing (FREP), which produced the first direct images of plasma wakefields and received the John Dawson Thesis Prize. Since 2017 I have been at UCLA, working on plasma accelerators and kinetic plasma instabilities, and leading experiments at SLAC’s FACET-II and Brookhaven’s Accelerator Test Facility.

More about my work is in my CV, publications, and research projects.

Research Highlights

E304 plasma dual transformer

Plasma Wakefield Transformer

Simultaneous energy boosting and brightness enhancement for next-generation accelerators

As PI of the E304 experiment at FACET-II, I demonstrated a plasma "dual transformer" that decouples energy gain from quality preservation—converting a low-quality drive beam into a new, ultra-bright beam with 2× higher energy (>20 GeV) and 10× higher brightness. This approach achieves sub-0.5% energy spread while maintaining the extreme brightness needed for X-ray free-electron lasers, and enables novel staging architectures that could bypass the quality-preservation challenge plaguing conventional multi-stage designs. Published in Nature Communications (2025).

ML virtual diagnostics

AI/ML-Driven Virtual Diagnostics

Physics-informed machine learning to access the inaccessible

I developed physics-informed "virtual diagnostics" that use machine learning to reconstruct the longitudinal phase space of femtosecond electron bunches from plasma wakefield accelerators—information impossible to measure directly. This ML-driven technique was critical to analyzing E304 results and is now being adopted by collaborators in other PWFA experiments. Beyond diagnostics, it opens the door to ML-enabled optimization and autonomous control of plasma accelerators. Published in Nature Communications (2025).

FREP concept

Femtosecond Relativistic Electron Probing (FREP)

First direct visualization of plasma wakefields at femtosecond resolution

I invented FREP during my Ph.D., using ultrashort relativistic electron bunches from a laser wakefield accelerator to probe plasma wakefields—capturing the first-ever snapshots of these microscopic, transient, near-light-speed structures. This breakthrough enabled the discovery of plasma wake reversal and earned the John Dawson Thesis Prize. FREP has since become an essential diagnostic at the frontier of plasma acceleration. Published in PRL (2017, Editors' Suggestion).

Weibel instability measurement

Probing the Hierarchy of Kinetic Instabilities

First direct laboratory measurement of astrophysical plasma instabilities

As PI of the AE98 experiment at BNL, I led the first direct measurement of the thermal Weibel instability—a fundamental kinetic instability predicted decades ago but with no conclusive experimental validation in laboratories. We mapped the self-generated magnetic fields in laser-ionized plasmas, revealing the growth and saturation of this instability and bridging laboratory and astrophysical plasma physics. Published in PNAS (2022, highlighted by DOE) and PRL (2020).

Let’s Connect

I’m glad to hear from people working on accelerator physics, plasma science, or AI and computing systems. You can reach me through the email link below.

news

Nov 28, 2025 Our plasma "dual transformer" work is published in Nature Communications
Jul 21, 2024 Presented the latest results on plasma wakefield acceleration experiments from FACET-II as a plenary speaker at AAC24 in Naperville, IL.

latest posts

Sep 18, 2026 理解 Transformer
Jul 16, 2026 The Fourth Generation: Where the X-Ray Light Sources Stand in 2026
Jul 11, 2026 Laser-Driven Proton Therapy: Strong Physics, Hard Road to the Clinic

selected publications

  1. Nat. Commun.
    2025
    Plasma-Wakefield Accelerator Simultaneously Boosts Electron Beam Energy and Brightness
    Chaojie Zhang, Douglas Storey, Alexander Knetsch, and 19 more authors
    Summary: Demonstrates that a plasma wakefield accelerator can act as a dual transformer to convert an input electron beam into a new one with much higher energy and brightness.
    DOI Bib PDF Nat. Commun.
  2. Rev. Mod. Plasma Phys.
    2023
    Self-organization of photoionized plasmas via kinetic instabilities
    Chaojie Zhang, Chen-Kang Huang, and Chan Joshi
    Summary: Comprehensive review of self-organization in strong-field photoionized, non-equilibrium plasmas through kinetic instabilities.
    DOI Bib Rev. Mod. Plasma Phys.
  3. PNAS
    2022
    Mapping the self-generated magnetic fields due to thermal Weibel instability
    Chaojie Zhang, Yipeng Wu, Mitchell Sinclair, and 15 more authors
    Summary: First experimental mapping of magnetic fields generated by thermal Weibel instability in laser-ionized plasmas.
    DOI Bib PDF PNAS
  4. Phys. Rev. Lett.
    2020
    Measurements of the growth and saturation of electron Weibel instability in optical-field ionized plasmas
    Chaojie Zhang, Jianfei Hua, Yipeng Wu, and 11 more authors
    Summary: Direct measurements of electron Weibel instability growth and saturation using femtosecond relativistic electron probes.
    DOI Bib PDF Phys. Rev. Lett.
  5. Phys. Rev. Lett.
    2017
    Femtosecond probing of plasma wakefields and observation of the plasma wake reversal using a relativistic electron bunch
    Chaojie Zhang, Jianfei Hua, Yang Wan, and 13 more authors
    Summary: First demonstration of femtosecond relativistic electron microscopy for visualizing plasma wakefields.
    🏆 3 Awards DOI Bib PDF Phys. Rev. Lett.