Virgo Week January 2003

Slide 1: 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 Measurements of non linear effects between the marionetta arms and the coils Edoardo Bompiani and Paola Puppo Virgo – Rome group Measurements on the marionetta: with AISI304 arms; with Al6063 arms; with steel AISI316LN arms; discussion of the results; Conclusions

Experimental Setup : 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 Experimental Setup We have used a payload prototype similar to the test masses one The mirror displacement was monitored using a camera looking at the markers placed on the mirror, like in the Virgo Payloads. Two kinds of measurements were performed: DC measurements: a costant current I were injected in the coils (same sign) with magnets without magnets AC measurements: a sinusoidal current I at the frequency n were injected in the coils in counter-phase in order to have a traslation along z; with magnets

Slide 3: 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 DC Measurements with the magnets attached on the arms: The measurement of the alinear is performed

Slide 4: 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 alinear = (31.5 ± 0.7) mN/A = (319 ± 3) mrad/A

DC Measurements without magnets : 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 DC Measurements without magnets With steel AISI304 arms: aquadratic = (- 30.3 ± 0.7) mN/A2 With steel AISI316LN arms: aquadratic = (- 180 ± 10) mN/A2 With Al6063 arms: aquadratic = (- 23 ± 3) mN/A2

Slide 6: 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 Force due to magnetization: Fm = = mo cm I2 ∂W (z) ∂z ∂G (z) ∂z where W (z) = mo cm (H (z))2t is the magnetic energy of the arms having a form factor t and (H(z))2 ≈ I2 G(z) is the coil magnetic field squared. cm is the magnetic susceptibility The measured forces are given by a DC effect and are attractive. As a consequence they cannot be due to eddy current effects but to magnetization effects. Force due to magnetization:

Slide 7: 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 AC Measurements with the magnets attached on the arms: I=Io sin(wt) Þ F = Fqyo (w, Io2) + Fqy (w, Io2) (cos(2wt)) Fqyo = Fmagn/2 + Fe.c DC (w) Io2 ; Fmagn/2 + Fe.c. (w) Io2

AC Measurements: steel arms (@1.4 Hz) : 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 AC Measurements: steel arms (@1.4 Hz) With steel AISI304 arms: attractive force aquadratic = (- 10 ± 1) mN/A2 With steel AISI316LN arms: attractive force aquadratic = (- 63 ± 3) mN/A2 mN

Slide 9: 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 With Al6063 arms: repulsive force aquadratic = (31 ± 2) mN/A2 AC Measurements: Al6063 arms (@1.8 Hz)

Slide 10: 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 The measured forces are given by an AC effect. As a consequence they could be due both to eddy current effects and to magnetization effects. Force due to eddy current: Feddy = mo s F (z) w I2 = aeddy w I2 where F (z) is a form factor taking into account the coils and arms geometry and s is electrical conductivity of the arms. The eddy current depends on the driving frequency w. With PVC arms: aquadratic = (- 0.25 ± 0.25) mN/A2

AC Measurements: steel arms : 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 AC Measurements: steel arms mN/A2 AISI 304 AISI316LN

Slide 12: 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 mN/A2 Eddy current residual effect on Steel AISI 316LN arms compared with Al6063 eddy currents effect.

Slide 13: 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 Discussion AISI304 Arms: DC measurements: aquadratic m = (- 30.3 ± 0.7) mN/A2 AC measurements: aquadratic m = (- 20 ± 1) mN/A2 due to unexpected magnetization of the material Al6063 Arms: DC measurements: aquadratic m = (- 23 ± 3) mN/A2 magnetization AC measurements due to a strong eddy currents effect. PVC Arms: aquadratic = (- 0.25 ± 0.25) mN/A2 the marionetta body does not generate any quadratic effect. AISI316LN Arms: DC measurements: aquadratic m = (- 180 ± 10) mN/A2 AC measurements due to eddy currents and magnetization. Eddy current effect » 2 mN/A2/Hz

Slide 14: 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 Conclusions Arms made in the amagnetic steel AIS316LN, with cm = 5 10-3 r = 1/s = 4.5 10-7 W/m. Fmagn. = 1/10 Fcoils @ I=18 A Fe.c. (1 Hz) = 1/10 Fcoils @ I=1600 A

Time and costs : 

Virgo Collaboration Meeting Cascina – January 20-22, 2003 Time and costs 6 series of marionetta arms Needed Time: Material: 2 working weeks; Machining: 1 working month. Costs for both material and machining 1 serie costs 3000 Euro + IVA Total: 18000 Euro + IVA The substitution of the arms can be done without disassembling the payload, by using the new payload safety structure.