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fe4da5cc | 1 | * |
2 | * $Id$ | |
3 | * | |
4 | * $Log$ | |
5 | * Revision 1.1.1.1 1995/10/24 10:21:41 cernlib | |
6 | * Geant | |
7 | * | |
8 | * | |
9 | #include "geant321/pilot.h" | |
10 | *CMZ : 3.21/02 29/03/94 15.41.23 by S.Giani | |
11 | *-- Author : | |
12 | SUBROUTINE GHELIX (CHARGE, STEP, VECT, VOUT) | |
13 | C. | |
14 | C. ****************************************************************** | |
15 | C. * * | |
16 | C. * Performs the tracking of one step in a magnetic field * | |
17 | C. * The trajectory is assumed to be a helix in a constant field * | |
18 | C. * taken at the mid point of the step. * | |
19 | C. * Parameters: * | |
20 | C. * input * | |
21 | C. * STEP =arc length of the step asked * | |
22 | C. * VECT =input vector (position,direction cos and momentum) * | |
23 | C. * CHARGE= electric charge of the particle * | |
24 | C. * output * | |
25 | C. * VOUT = same as VECT after completion of the step * | |
26 | C. * * | |
27 | C. * ==>Called by : <USER>, GUSWIM * | |
28 | C. * Author M.Hansroul ********* * | |
29 | C. * Modified S.Egli, S.V.Levonian * | |
30 | C. * Modified V.Perevoztchikov | |
31 | C. * * | |
32 | C. ****************************************************************** | |
33 | C. | |
34 | DIMENSION VECT(7),VOUT(7) | |
35 | DIMENSION XYZ(3),H(4),HXP(3) | |
36 | PARAMETER (IX=1,IY=2,IZ=3,IPX=4,IPY=5,IPZ=6,IPP=7) | |
37 | PARAMETER (SIXTH = 1./6.) | |
38 | PARAMETER (EC=2.9979251E-4) | |
39 | C. | |
40 | C. ------------------------------------------------------------------ | |
41 | C. | |
42 | C units are kgauss,centimeters,gev/c | |
43 | C | |
44 | VOUT(IPP) = VECT(IPP) | |
45 | IF (CHARGE.EQ.0.) GO TO 10 | |
46 | XYZ(1) = VECT(IX) + 0.5 * STEP * VECT(IPX) | |
47 | XYZ(2) = VECT(IY) + 0.5 * STEP * VECT(IPY) | |
48 | XYZ(3) = VECT(IZ) + 0.5 * STEP * VECT(IPZ) | |
49 | C | |
50 | CALL GUFLD (XYZ, H) | |
51 | ||
52 | H2XY = H(1)**2 + H(2)**2 | |
53 | H(4) = H(3)**2 + H2XY | |
54 | IF (H(4).LE.1.E-12) GO TO 10 | |
55 | IF (H2XY.LE.1.E-12*H(4)) THEN | |
56 | CALL GHELX3 (CHARGE*H(3), STEP, VECT, VOUT) | |
57 | GO TO 999 | |
58 | ENDIF | |
59 | H(4) = SQRT(H(4)) | |
60 | H(1) = H(1)/H(4) | |
61 | H(2) = H(2)/H(4) | |
62 | H(3) = H(3)/H(4) | |
63 | H(4) = H(4)*EC | |
64 | * | |
65 | HXP(1) = H(2)*VECT(IPZ) - H(3)*VECT(IPY) | |
66 | HXP(2) = H(3)*VECT(IPX) - H(1)*VECT(IPZ) | |
67 | HXP(3) = H(1)*VECT(IPY) - H(2)*VECT(IPX) | |
68 | ||
69 | HP = H(1)*VECT(IPX) + H(2)*VECT(IPY) + H(3)*VECT(IPZ) | |
70 | * | |
71 | RHO = -CHARGE*H(4)/VECT(IPP) | |
72 | TET = RHO * STEP | |
73 | IF (ABS(TET).GT.0.15) THEN | |
74 | SINT = SIN(TET) | |
75 | SINTT = (SINT/TET) | |
76 | TSINT = (TET-SINT)/TET | |
77 | COS1T = 2.*(SIN(0.5*TET))**2/TET | |
78 | ELSE | |
79 | TSINT = SIXTH*TET**2 | |
80 | SINTT = (1. - TSINT) | |
81 | SINT = TET*SINTT | |
82 | COS1T = 0.5*TET | |
83 | ENDIF | |
84 | * | |
85 | F1 = STEP * SINTT | |
86 | F2 = STEP * COS1T | |
87 | F3 = STEP * TSINT * HP | |
88 | F4 = -TET*COS1T | |
89 | F5 = SINT | |
90 | F6 = TET * COS1T * HP | |
91 | ||
92 | VOUT(IX) = VECT(IX) + (F1*VECT(IPX) + F2*HXP(1) + F3*H(1)) | |
93 | VOUT(IY) = VECT(IY) + (F1*VECT(IPY) + F2*HXP(2) + F3*H(2)) | |
94 | VOUT(IZ) = VECT(IZ) + (F1*VECT(IPZ) + F2*HXP(3) + F3*H(3)) | |
95 | ||
96 | VOUT(IPX) = VECT(IPX) + (F4*VECT(IPX) + F5*HXP(1) + F6*H(1)) | |
97 | VOUT(IPY) = VECT(IPY) + (F4*VECT(IPY) + F5*HXP(2) + F6*H(2)) | |
98 | VOUT(IPZ) = VECT(IPZ) + (F4*VECT(IPZ) + F5*HXP(3) + F6*H(3)) | |
99 | ||
100 | GO TO 999 | |
101 | ||
102 | 10 CONTINUE | |
103 | DO 20 I = 1,3 | |
104 | VOUT(I) = VECT(I) + STEP * VECT(I+3) | |
105 | VOUT(I+3) = VECT(I+3) | |
106 | 20 CONTINUE | |
107 | C | |
108 | 999 END |