1. Q: Didn't Ron Drever already do Magnetic Suspensions in the 80's ?
A: Yes and no. Ron Drever magnetically levitated both a test mass with mirrors glues on as well as paramagnetic materials (c.f. the Review page). It was mainly soft in the beamline direction. A main goal of that research was to levitate the test mass so as to eliminate any touching of the test mass. The noise of that suspension was not measured at GW sensitivities. The suspension idea we are working on will be soft in all 6 degrees of freedom and is mainly for seismic isolation - not to reduce suspension thermal noise. It will suspend the penultimate mass, not the test mass.
2. Q: How can you glue magnets onto the suspension without screwing up the mirror thermal noise?
- A: We are not proposing to put any magnets on the mirror. We are making a magnetic vibration isolation system for the penultimate mass.
3. Q: Have you thought about the ambient magnetic fields? Doesn't that make magnets a bad idea?
- A: Yes, there is an ambient magnetic field and it fluctuates. The proposed design is designed to be immune to dipole and quadrupole fields.
4. Q: What about Barkhausen noise? Doesn't that make magnets a bad idea?
- A: Barkhausen noise origins from instabilities of magnetic domains. For a permanent magnet, some of the small domains, especially near the edge of the magnet, has a different magnetization direction from the main domain. It is unstable and will relax to the low-energy state if ambient magnetic fields are perturbed. Such relaxation causes pulsing of the magnetic fields and induces noise in the suspension system. Whether this will cause a significant problem depends on the detailed relaxation mechanism and correlations between different pulses (or its noise spectrum). Up to now, we think of using a high-frequency alternating magnetic fields to lift this noise to high frequencies. We will make some measurements to confirm whether it works or not.
5. Q: Will the damping due to hysteresis cause a problem?
- A: We are operating at low frequencies and the magnetic fields produced by the control coils are changing with small amplitudes, order of magnitude smaller than the remanence of the magnets. In this case, the process can be viewed as reversible.