Fourier analysis of 3D error fields in tokamaks

Statistical analysis of expected error fields in tokamaks and their correction

“…The ITER magnet system is assumed to have 228 degrees of freedom (DOF), defined by the possible deviations of the coils from their nominal positions and shape [1][2][3][4]. There are four DOF for each of the six CS sections and the six PF coils, and ten DOF for each of the 18 TF coils.…”

“…The expected (m,n) error fields are determined in two steps [2]. First, the normal component B ⊥ of an error field is calculated on a rational magnetic surface ψ = const with the safety factor q = 2 for the given plasma equilibrium configurations [15][16][17][18][19][20][21][22][23].…”

“…(m,n) = (1,1), (2,1), (3,1) Here l is the poloidal length of a field line along the rational magnetic surface q = 2. The poloidal angle θ(l) is defined by the equation:…”

“…To assess the asymmetric error fields anticipated in tokamak magnet systems, a statistical approach is applicable [1][2][3][4][5][6][7][8]. The main contributors to error fields in existing tokamaks are deviations of the toroidal field (TF) and poloidal field (PF) coils and the central solenoid (CS) sections from their design positions.…”

“…The start-of-flattop (SOF) conditions of the plasma current scenario have been used for analysis as they are the least tolerant of the growing of locked modes (1,1), (2,1), (3,1), because of the low plasma density and lack of rotation induced by neutral beams [9][10][11][12][13][14]. The study performed suggests that the resultant (m,n) error field in ITER can be expected to be several times higher than the locked mode threshold (LMT).…”