AIDT 온디바이스 STEM 뮤온 스핀 회전(μSR) 아브리코소프 소용돌이 격자 및 런던 침투 깊이 서보 엔진

using System;
using System.Runtime.CompilerServices;

namespace ZeliDesk.Stem.Muon
{
    public readonly ref struct MusrLatticeState
    {
        public readonly double MeanFieldTesla;       // 평균 국소 자기장  (Tesla)
        public readonly double DepolarizationRateUs; // 스핀 감쇠율 sigma (us^-1)
        public readonly double LondonDepthNm;        // 런던 침투 깊이 lambda_L (nm)
        public readonly double SuperfluidDensityNs;  // 유효 초유체 밀도 지표 (10^28 m^-3)
        public readonly double AsymmetryPeak;        // 초기 비대칭도 A0
        public readonly double LarmorFreqMhz;        // 라모어 세차 주파수 (MHz)

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public MusrLatticeState(double meanB, double sigma, double lambdaNm, double ns, double a0, double freq)
        {
            MeanFieldTesla = meanB;
            DepolarizationRateUs = sigma;
            LondonDepthNm = lambdaNm;
            SuperfluidDensityNs = ns;
            AsymmetryPeak = a0;
            LarmorFreqMhz = freq;
        }
    }

    public ref struct MusrSpectroscopyEngine
    {
        private const double GammaMuRadPerTesla = 851.616e6; // rad/(s*T)
        private const double GammaMuMhzPerTesla = 135.5388;  // MHz/T
        private const double FluxQuantum = 2.067833848e-15;  // Wb (h/2e)
        private const double Me = 9.10938356e-31;           // kg
        private const double ECharge = 1.602176634e-19;     // C
        private const double Mu0 = 1.25663706212e-6;        // H/m

        private readonly double _upperCriticalFieldTesla;   // Bc2 (Tesla)
        private double _appliedFieldTesla;                  // 인가 횡자기장 (Tesla)
        private double _sampleTempK;                        // 시료 온도 (K)

        public MusrSpectroscopyEngine(double bc2Tesla = 20.0, double initFieldTesla = 0.5, double initTempK = 4.2)
        {
            _upperCriticalFieldTesla = bc2Tesla;
            _appliedFieldTesla = initFieldTesla;
            _sampleTempK = initTempK;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public MusrLatticeState StepServo(double measuredDepolarizationUs, double fieldAdjustmentTesla, double dtSec)
        {
            _appliedFieldTesla = Math.Clamp(_appliedFieldTesla + fieldAdjustmentTesla, 0.01, 10.0);

            // 1. 라모어 세차 주파수 계산
            double larmorFreqMhz = GammaMuMhzPerTesla * _appliedFieldTesla;

            // 2. 가우시안 감쇠율 sigma(us^-1)로부터 자속 격자 분산 역산
            double sigmaUs = Math.Max(measuredDepolarizationUs, 0.01);
            double sigmaRadPerSec = sigmaUs * 1e6;

            // 3. 브란트(Brandt) 공식에 따른 런던 침투 깊이 lambda_L (m) 계산
            // sigma = 0.06091 * gamma_mu * Phi0 / lambda_L^2 * (1 - b)
            double bReduced = _appliedFieldTesla / _upperCriticalFieldTesla;
            double fieldFactor = Math.Max(1.0 - bReduced, 0.05);

            double numerator = 0.06091 * GammaMuRadPerTesla * FluxQuantum * fieldFactor;
            double lambdaSquared = numerator / sigmaRadPerSec;
            double lambdaMeters = Math.Sqrt(Math.Max(lambdaSquared, 1e-16));

            // 4. 런던 공식 n_s = m* / (mu0 * e^2 * lambda_L^2) 초유체 전자 밀도 계산
            double ns = Me / (Mu0 * ECharge * ECharge * lambdaMeters * lambdaMeters);

            return new MusrLatticeState(
                meanB: _appliedFieldTesla,
                sigma: sigmaUs,
                lambdaNm: lambdaMeters * 1e9,
                ns: ns * 1e-28,
                a0: 0.285, // 표준 뮤온 분광 초기 비대칭도
                freq: larmorFreqMhz
            );
        }
    }
}