RESUMO
In this paper, we present the design and performance of the upgraded University of Florida torsion pendulum facility for testing inertial sensor technology related to space-based gravitational wave observatories and geodesy missions. In particular, much work has been conducted on inertial sensor technology related to the Laser Interferometer Space Antenna (LISA) space gravitational wave observatory mission. A significant upgrade to the facility was the incorporation of a newly designed and fabricated LISA-like gravitational reference sensor (GRS) based on the LISA Pathfinder GRS. Its LISA-like geometry has allowed us to make noise measurements that are more representative of those in LISA and has allowed for the characterization of the mechanisms of noise induced on a LISA GRS and their underlying physics. Noise performance results and experiments exploring the effect of temperature gradients across the sensor will also be discussed. The LISA-like sensor also includes unique UV light injection geometries for UV LED based charge management. Pulsed and DC charge management experiments have been conducted using the University of Florida charge management group's technology readiness level 4 charge management device. These experiments have allowed for the testing of charge management system hardware and techniques as well as characterizations of the dynamics of GRS test mass charging. The work presented here demonstrates the upgraded torsion pendulum's ability to act as an effective testbed for GRS technology.
RESUMO
Various space missions and applications require the charge on isolated test masses to be strictly controlled because any unwanted disturbances will introduce acceleration through the Coulomb interaction between the test masses and their surrounding conducting surfaces. In many space missions, charge control has been realized using ultraviolet (UV) photoemission to generate photoelectrons from metal surfaces. The efficiency of photoelectron emission strongly depends on multiple physical parameters of gold-coated surfaces, such as the work function, reflectivity, and quantum yield. Therefore, to achieve satisfactory charge control performance, these parameters need to be measured accurately. This paper describes a charge control method that achieves self-adaptive charge neutralization while removing the need to measure the above-mentioned physical parameters. First, to explain the principle, a differential illumination model is constructed based on the typical structure of an inertial sensor. A charge management system based on a torsion pendulum system is then introduced along with an UV light emitting diode coupling system. Finally, experimental results are obtained in a vacuum chamber system with a pressure of 10-7 mbar, showing that precise calibration allows the test mass potential to be automatically controlled below 10 mV without considering the physical parameters or measuring the potential of the test mass before or after the control process.
RESUMO
Many applications require charge neutralization of isolated test bodies, and this has been successfully done using photoelectric emission from surfaces which are electrically benign (gold) or superconducting (niobium). Gold surfaces nominally have a high work function (â¼5.1 eV) which should require deep UV photons for photoemission. In practice, it has been found that it can be achieved with somewhat lower energy photons with indicative work functions of (4.1-4.3 eV). A detailed working understanding of the process is lacking, and this work reports on a study of the photoelectric emission properties of 4.6 × 4.6 cm2 gold plated surfaces, representative of those used in typical satellite applications with a film thickness of 800 nm, and measured surface roughnesses between 7 and 340 nm. Various UV sources with photon energies from 4.8 to 6.2 eV and power outputs from 1 nW to 1000 nW illuminated â¼0.3 cm2 of the central surface region at angles of incidence from 0° to 60°. Final extrinsic quantum yields in the range 10 ppm-44 ppm were reliably obtained during 8 campaigns, covering a period of â¼3 years but with intermediate long-term variations lasting several weeks and, in some cases, bake-out procedures at up to 200 °C. Experimental results were obtained in a vacuum system with a baseline pressure of â¼10-7 mbar at room temperature. A working model, designed to allow accurate simulation of any experimental configuration, is proposed.
RESUMO
There is now an enormously rich variety of experimental techniques being brought to bear on experimental searches for dark matter, covering a wide range of suggested forms for it. The existence of "dark matter", in some form or other, is inferred from a number of relatively simple observations and the problem has been known for over half a century. To explain "dark matter" is one of the foremost challenges today - the answer will be of fundamental importance to cosmologists, astrophysicists, particle physicists, and general relativists. In this article, I will give a brief review of the observational evidence (concentrating on areas of current significant activity), followed by anequally brief summary of candidate solutions for the 'dark matter'. I will then discuss experimental searches, both direct and indirect. Finally, I will offer prospects for the future.