Design of a cryogenic photocathode gun with a novel TM02 mode coupler for low emittance

**Dataset Description**  This dataset is constructed based on the research paper *"Low-Emittance Design and Optimization of a Cryogenic TM02-Mode Coupler Photocathode Gun"*, providing comprehensive simulation and design data support for researchers in accelerator physics, free-electron lasers (FELs), and cryogenic engineering. The dataset contains the following key components:  ---1. **Beam Dynamics Simulation Data**  - **ASTRA simulation parameters and outputs**, including critical beam properties:   - Emittance (as low as **0.33 mm·mrad**)   - Bunch length (**0.47 mm**)   - Energy distribution (**103 MeV**)  - Comparative optimization data for **different gun structures** (1.6-cell, 2.6-cell, 3.6-cell), with variables such as:   - Laser pulse width (**5–10 ps**)   - Cathode gradient (**200 MV/m**)   - Performance impacts under varying operational conditions.  ---2. **RF Design and Cryogenic Performance Data**  - **CST Microwave Studio and SUPERFISH simulations**, covering:   - Cavity geometry parameters (elliptical profile ratio, rounding radius)   - Surface electric field distribution   - Quality factor (**Q₀**) and mode separation.  - **Cryogenic material properties** (at **40 K**):   - Residual resistance ratio of copper (**RRR=300**)   - Thermal expansion coefficient   - Conductivity variations   - Frequency shift (**18.1 MHz**).  ---3. **Coupler Design and Multipole Field Suppression Data**  - **J-type and T-type waveguide couplers**:   - S-parameters (**S₁₁ = -35 dB**, **S₂₁ = -3 dB**)   - Electric field distribution   - Multipole field strength (as low as **0.01%**).  - **Panofsky-Wenzel theorem-based calculations**:   - Transverse momentum data   - Quantified multipole field effects on emittance (**0.5 mm·mrad**).  --- 4. **Engineering and Cryogenic System Data**  - **2.6-cell gun engineering designs**:   - Technical drawings (gun structure, cryostat)   - Vacuum parameters (**1×10⁻⁷ Pa**).  - **RF pulse heating performance**:   - Temperature rise (**19.98 K** @ room temperature vs. **4.85 K** @ cryogenic conditions)   - Peak power requirement (**3.761 MW**).  ---**Data Format and Structure**  - **Simulation files**: ASTRA/CST scripts, SUPERFISH input files.  - **Visualizations**: Cavity geometry plots, electric/magnetic field maps.  - **Technical documentation**: Parameter definitions, formula derivations, experimental protocols.  - **Metadata**: Clearly labeled variables, units, and operational conditions.  ---**Applications and Impact**  This dataset serves as a benchmark for **high-brightness electron source design**, supporting:  - Advanced accelerator development  - Cryogenic RF system optimization  - Multi-physics coupling studies  - Major scientific projects like the **Shanghai Soft X-ray Free Electron Laser (SXFEL)** upgrade.  It is the first publicly available dataset detailing the **full design workflow of a TM02-mode photocathode gun**, providing a theoretical foundation for experimental validation and engineering implementation.  ---**Access and Licensing**  - Hosted on open science platforms (e.g., Zenodo, Figshare) under **CC BY 4.0 license** (non-commercial use and derivatives permitted).  - Download links and documentation are accessible via the paper’s supplementary materials or the project homepage.  ---  *For inquiries or collaboration opportunities, please contact the corresponding author.*