7.0 Magnetic Search Coil (MSC)

The Cassini RPWS magnetic sensor (MSC) consists of three search coil magnetometers mounted in a triaxial fixture. The search coil array is mounted on a boom 1 meter from the spacecraft, and is oriented such that the measurement axes of the search coils are aligned with the principle axes of the spacecraft (Bx aligned with the spacecraft x axis, By aligned with the spacecraft y axis, and Bz aligned with the spacecraft z axis). The location and orientation of the search coil magnetometers are shown in Figure 3.1.2. Each sensor axis consists of a mu-metal core 27 cm long wound with 10,000 turns of fine wire, each search coil magnetometer responds to dB/dt over a frequency range of 1 Hz to 12.6 kHz. The search coils were built at the Centre d'Etudes des Environnements Terrestre et Planétaires.

7.1 Amplitude Calibration

The stand-alone calibrations of the RPWS search coil magnetometers were performed A. Meyer at the Centre d'Etudes des Environnements Terrestre et Planétaires using a drive coil in a mu-metal box and verified using a transmitting loop at a low noise location. These calibrations are summarized in the reference in Section 5.1.2, and are reproduced here as Tables 7.1.1, 7.1.2, and 7.1.3, and Figures 7.1.1, 7.1.2, and 7.1.3. Figures and Tables 7.1.1, 7.1.2, and 7.1.3 show the transfer function response for the Bx, By, and Bz search coils.

The End-to-End calibrations for each receiver is given in the individual receiver sections. These End-to-End calibrations were determined by combining the search coil calibration and the receiver calibrations, and verified by a series of tests with the search coils attached to the spacecraft, but in the mu-metal box.

Table 7.1.1

Bx SEARCH COIL

Frequency (Hz)	Output (mV/nT)	Output (dBv/nT)	Output

(Phase °)
0.1

0.2

0.5

0.7

1

2

5

7

10

20

50

70

100

200

500

700

1000

2000

5000

7000

10000

20000	0.21

0.66

2.20

3.22

4.66

9.43

23.85

32.81

46.13

82.51

132.43

142.23

148.08

150.66

149.28

148.42

147.40

146.05

142.56

139.96

133.81

77.45	-73.75

-63.63

-53.16

-49.83

-46.64

-40.51

-32.45

-29.68

-26.72

-21.67

-17.56

-16.94

-16.59

-16.44

-16.52

-16.57

-16.63

-16.71

-16.92

-17.08

-17.47

-22.22	153.6

135.6

111.7

105.2

100.1

92.5

83.7

79.7

74.2

59.0

32.4

23.7

16.1

6.7

0.2

-1.6

-3.4

-8.0

-20.2

-27.9

-40.5

-93.2

Table 7.1.2By

SEARCH COIL

Frequency (Hz)	Output (mV/nT)	Output (dBv/nT)	Output

(Phase °)
0.1

0.2

0.5

0.7

1

2

5

7

10

20

50

70

100

200

500

700

1000

2000

5000

7000

10000

20000	0.21

0.65

2.18

3.19

4.60

9.31

23.55

32.40

45.60

81.56

131.37

141.25

147.06

149.80

148.42

147.74

146.72

144.88

140.93

138.04

131.07

83.37	-73.66

-63.68

-53.25

-49.93

-46.75

-40.62

-32.56

-29.79

-26.82

-21.77

-17.63

-17.00

-16.65

-16.49

-16.57

-16.61

-16.67

-16.78

-17.02

-17.20

-17.65

-21.58	153.4

135.2

111.4

105.0

99.9

92.5

83.7

79.7

74.2

59.2

32.4

23.8

16.2

6.8

0.1

-1.7

-3.6

-8.4

-21.2

-29.4

-42.8

-91.9

Table 7.1.3

Bz SEARCH COIL

Frequency (Hz)	Output (mV/nT)	Output (dBv/nT)	Output

(Phase °)
0.1

0.2

0.5

0.7

1

2

5

7

10

20

50

70

100

200

500

700

1000

2000

5000

7000

10000

20000	0.21

0.65

2.18

3.20

4.62

9.36

23.66

32.55

45.81

81.85

131.22

141.25

147.06

149.62

148.08

147.23

146.55

144.88

140.77

137.40

127.79

76.82	-73.67

-63.71

-53.23

-49.89

-46.71

-40.57

-32.52

-29.75

-26.78

-21.74

-17.64

-17.00

-16.65

-16.50

-16.59

-16.64

-16.68

-16.78

-17.03

-17.24

-17.87

-22.29	153.8

135.4

111.7

105.3

100.1

92.5

83.6

79.7

74.2

59.0

32.3

23.7

16.1

6.6

0.1

-1.7

-3.6

-8.5

-21.7

-30.2

-44.8

-94.3
7.2 Phase Calibration

The stand-alone phase calibrations of the RPWS search coil magnetometers were performed A. Meyer at the Centre d'Etudes des Environnements Terrestre et Planétaires using a drive coil in a mu-metal box and verified using a transmitting loop at a low noise location. These calibrations are reproduced here as Figures 7.2.1, 7.2.2, and 7.2.3, and show the phase response for the Bx, By, and Bz search coils with respect to frequency.

7.3 Magnetic Search Coil Noise Levels

Table 7.3.1 show the measured noise levels for the search coil and preamplifier during bench testing. The in-flight noise level will be discussed in the individual receiver sections.

Table 7.3.1 SEARCH COIL BENCH NOISE LEVELS

Frequency (Hz)	Bx Sensitivity

nT/Hz1/2	By Sensitivity

nT/Hz1/2	Bz Sensitivity

nT/Hz1/2
0.1

0.2

0.5

0.7

1

2

5

7

10

20

50

70

100

200

500

700

1000

2000

5000

7000

10000

20000	2.67E-01

5.95E-02

1.23E-02

6.83E-03

3.98E-03

1.62E-03

6.39E-04

4.65E-04

3.30E-04

1.47E-04

7.01E-05

4.59E-05

3.69E-05

1.95E-05

1.61E-05

1.62E-05

1.63E-05

1.66E-05

1.87E-05

2.21E-05

2.82E-05

8.63E-05	1.98E-01

5.20E-02

1.02E-02

5.94E-03

3.69E-03

1.82E-03

6.62E-04

4.84E-04

3.44E-04

1.55E-04

6.63E-05

4.99E-05

3.82E-05

2.21E-05

1.64E-05

1.60E-05

1.77E-05

1.71E-05

1.87E-05

2.16E-05

2.98E-05

8.18E-05	3.16E-01

8.16E-02

1.39E-02

7.32E-03

4.24E-03

1.74E-03

6.47E-04

4.41E-04

3.18E-04

1.53E-04

6.87E-05

4.94E-05

3.61E-05

2.31E-05

1.76E-05

1.69E-05

1.69E-05

1.71E-05

2.10E-05

2.40E-05

3.44E-05

8.93E-05