Add CFQS experimental data processing toolkit

[Copilot]

Bootstraps the CFQS-Data-Process repository with a full suite of diagnostic data processing tools for the Chinese First Quasi-axisymmetric Stellarator, primarily in MATLAB with Python helpers.

New tools

Diamagnetic loop (diamagnetic/)

• calibrate_diamagnetic.m — eddy-current drift correction via polynomial fit or external vacuum-shot baseline; integrates raw voltage → flux
• calc_stored_energy.m — W(t) from calibrated diamagnetic flux using the Bohm relation; configurable B₀, R₀, a, Λ

Equilibrium geometry (magnetic_axis/, LCFS/)

• plot_magnetic_axis.m — R-Z cross-sections and/or 3-D toroidal curve from equilibrium file
• plot_LCFS.m — LCFS cross-sections at arbitrary φ and 3-D surface rendering with optional magnetic axis overlay

Diagnostics (electrostatic_probe/, magnetic_probe/)

• process_langmuir_probe.m — nonlinear least-squares fit of Langmuir I-V → Tₑ, nₑ, V_f, V_p; ion species configurable via IonMass parameter
• plot_magnetic_probe_spectrum.m — STFT spectrogram, CWT, or time-averaged Welch PSD of Mirnov coil signals

Shared utilities (utils/, python/)

• load_cfqs_data.m — unified loader for MAT/CSV/TXT/HDF5 with optional time-range trimming
• cfqs_colormap.m — custom colour maps (plasma, inferno, diverge, cfqs navy-cyan-gold)
• cfqs_utils.py — Python equivalents: file I/O (MAT v5/v7.3, CSV, HDF5), zero-phase bandpass/lowpass filters, STFT, Bohm density, stored-energy calculation

Usage sketch

% Diamagnetic calibration + stored energy
cal    = calibrate_diamagnetic('shot12345_dia_raw.mat', 'CalFile', 'shot12300_vac.mat');
result = calc_stored_energy(cal, 'B0', 1.0, 'R0', 1.0, 'a', 0.2, 'PlotResult', true);

% Langmuir probe (deuterium plasma)
lp = process_langmuir_probe('shot12345_lp.csv', ...
    'ProbeArea', 1.5e-6, 'IonMass', 2*1.673e-27, 'PlotResult', true);

% Mirnov spectrogram
plot_magnetic_probe_spectrum('shot12345_mirnov.mat', ...
    'FreqRange', [1e3, 300e3], 'Window', 2e-3, 'LogScale', true);

from python.cfqs_utils import load_mat_data, butter_bandpass_filter
data     = load_mat_data('shot12345.mat')
filtered = butter_bandpass_filter(data['signal'], 1e3, 100e3, data['fs'])

Documentation

• docs/data_processing_workflow.md — end-to-end workflow for all six diagnostic paths, shot-file naming conventions, data quality checklist, and export/archiving guidance
• README.md — updated with directory tree, quick-start, and tool reference table

Original prompt

我准备在Github上创建一个代码仓库，命名为CFQS-Data-Process，主要用于存放用于实验数据、模拟数据处理工具。
主要可能包括：处理CFQS逆磁测量系统的标定代码和储能计算代码，CFQS磁轴绘图工具，LCFS绘图工具，静电探针数据处理工具，磁探针频谱绘制工具等等。还会包含一些实验数据处理流程之类的文档。
可能主要是MATLAB，以及少量的Python。

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