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25 //
26 // G4DELPHIMagField implementation
27 //
28 // Created: V.Grichine - 03.02.1997
29 // -------------------------------------------------------------------
30
31 #include "G4DELPHIMagField.hh"
32 #include "globals.hh"
33 #include "G4SystemOfUnits.hh"
34
35 G4DELPHIMagField::G4DELPHIMagField() = default;
36
37 ////////////////////////////////////////////////////////////////////////
38
39 G4DELPHIMagField::~G4DELPHIMagField() = default;
40
41 ///////////////////////////////////////////////////////////////////////
42
43 G4Field* G4DELPHIMagField::Clone() const
44 {
45 return new G4DELPHIMagField;
46 }
47
48 ///////////////////////////////////////////////////////////////////////
49
50 void G4DELPHIMagField::GetFieldValue( const G4double yTrack[], // [7]
51 G4double B[] ) const // [3]
52 {
53 G4int i, n = 8 ;
54 G4double a = 0.001 ; // mm -> m
55 G4double x = a*yTrack[0], y = a*yTrack[1], z = a*yTrack[2] ;
56 G4double x2 = x*x, y2 = y*y, z2 = z*z, r2 = x2 + y2 ;
57 G4double r4 = r2*r2, z4 = z2*z2, r6 = r4*r2, z6 = z4*z2 ;
58 G4double r8 = r4*r4, z8 = z4*z4, r10 = r8*r2, z10 = z8*z2 ;
59 G4double rz = z*std::sqrt(r2), r = std::sqrt(r2+a*a) ;
60 G4double Br ;
61 G4double P[8], Q[8] ;
62 static G4ThreadLocal G4double c[8] =
63 {
64 -9.26e-5, -3.51e-5, 2.94e-6, -1.10e-6,
65 6.25e-8, -1.77e-8, -6.88e-10, -7.52e-11
66 } ;
67 P[0] = 2*rz ;
68 P[1] = 4*rz*(r2 - 4.0*z2/3.0) ;
69 P[2] = 6*rz*(r4 - 4*r2*z2 + 1.6*z4) ;
70 P[3] = 8*rz*(r6 - 8*r4*z2 + 9.6*r2*z4 - 64.0*z6/35.0) ;
71 P[4] = 10*rz*(r8 - 40.0*r6*z2/3.0 + 32*r4*z4
72 - 128.0*r2*z6/7.0 + 128.0*z8/63.0);
73 P[5] = 0 ;
74 P[6] = 0 ;
75 P[7] = 0 ;
76
77 Q[0] = r2 - 2*z2 ;
78 Q[1] = r4 - 8*r2*z2 + 8.0*z4/3.0 ;
79 Q[2] = r6 - 18*r4*z2 + 24*r2*z4 - 3.2*z6 ;
80 Q[3] = r8 - 32*r6*z2 + 96*r4*z4 - 51.2*r2*z6 +128.0*z8/35.0 ;
81 Q[4] = r10 - 50*r8*z2 + 800.0*r6*z4/3.0 - 320*r4*z6
82 + 640.0*r2*z8/7.0 - 256.0*z10/63.0 ;
83 Q[5] = 0 ;
84 Q[6] = 0 ;
85 Q[7] = 0 ;
86
87 Br = 0 ;
88 B[2] = 1.2*tesla ; // the principal Bz value of DELPHI detector
89 for(i=0; i<n; ++i)
90 {
91 Br += c[i]*P[i] ;
92 B[2] += c[i]*Q[i] ;
93 }
94 B[0] = Br*x/r ;
95 B[1] = Br*y/r ;
96 return ;
97 }
98
99 // -----------------------------------------------------------------
100