Magnetic Fields and Magnetic Diagnostics for Tokamak Plasmas

More documents

Recommendations

Info

Magnetic fields and tokamak plasmas Alan Wootton 23. SOME EXPERIMENTAL TECHNIQUES Coils winding The rogowski coil is simply made by obtaining a delay cable, and returning the wire down the center of the delay line (to ensure no net single turn is left). More complicated coils must be made by using variable winding densities (i.e. changing the pitch) or varying the cross sectional area of the former on which the coil is wound. Interference suppression Electrical equipment designed to produced RF energy such as generators, and switching phenomena in electrical circuits, create RF spectra which must be contended with. interference lines dc coupled propagation radiation capacitive coupling (inductive coupling) line attenuation suppression decoupling attenuation components capacitiors inductors filters screening screen devices screen lines line arrangement sensor coil 164
Magnetic fields and tokamak plasmas Alan Wootton Figure 23.1. An illustration of interference paths and suppression techniques. The sources of interference are illustrated in Figure 23.1. The interference propagates either down lines (cables) or by direct radiation. If the wavelength is large compared to the dimensions of the interference source only minor radiation will result, which is mostly found along the lines. This is the case for frequencies up to 30 MHz. When the dimension of the interference source is about that of the wavelength the interference energy will travel by radiation. The dominant frequencies are those where the interference source are l/4 or multiples of it. Favorable radiation conditions imply reduced line propagation (because of increased line attenuation) . Therefore the two propagation paths, comprising direct and capacitive or inductive coupling, suggest two means of suppression, either line attenuation or de-coupling attenuation. Line attenuation is effected by filters. De-coupling attenuation is effected by the construction of the sensor coil and the associated connecting lines. A common problem with probes is capacitive pick-up. To test for this pick up on simple sensor coils, two identical and adjacent coils can be connected in series. Depending on the orientation, the signal obtained should be twice that measured with a single coil, or zero. If the coils connected in opposition do not give a zero signal, then capacitive coupling effects should be considered as a possible source of error. Capacitive coupling can be over using a grounded screen or can around the sensor. Screened rooms The requirement is to screen a room in which a sensitive measurement is being performed from external interference, or to accommodate apparatus which radiate interference in a screened room to keep the surroundings free from interference. The basic method is to use cages of wire mesh, or metal sheet. Both electric and magnetic field components must be considered. Units used for effectiveness are the decibel : ⎛ s = 20log E, B ⎞ noscreen ⎜ ⎟ ⎝ E, B withscreen ⎠ and the Napier ⎛ s = ln E, B ⎞ noscreen ⎜ ⎟ ⎝ E, B withscreen ⎠ 165
Page 1 and 2:
Magnetic fields and tokamak plasmas
Page 3 and 4:
Page 5 and 6:
Page 7 and 8:
Page 9 and 10:
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114: Magnetic fields and tokamak plasmas
Page 163: Magnetic fields and tokamak plasmas
show all

Magnetic Fields and Magnetic Diagnostics for Tokamak Plasmas

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?