MiniGrail
{{Infobox telescope}}
MiniGRAIL was a third-generation resonant mass antenna,{{cite book | url=https://archive.org/details/firstcourseingen00bern_0/page/214 | title=A First Course in General Relativity | publisher=Cambridge | author=Schutz , Bernard | pages=[https://archive.org/details/firstcourseingen00bern_0/page/214 214–220] | isbn=978-0521887052 | edition=2nd | date=2009-05-14 | url-access=registration }} a massive sphere designed to detect gravitational waves. The MiniGRAIL was the first such detector to use a spherical design. It is located at Leiden University in the Netherlands. The project was managed by the Kamerlingh Onnes Laboratory.{{cite journal
| author=de Waard, A |display-authors=etal
| title=MiniGRAIL, the first spherical detector
| date=2003 | journal=Classical and Quantum Gravity
| volume=20 | issue=10
| pages=S143–S151
| doi=10.1088/0264-9381/20/10/317 |bibcode = 2003CQGra..20S.143D |s2cid=250902916
}} A team from the Department of Theoretical Physics of the University of Geneva, Switzerland, was also heavily involved. The project was terminated in 2005.
Gravitational waves are a type of radiation that is emitted by objects that have mass and are undergoing acceleration. The strongest sources of gravitational waves are suspected to be compact objects such as neutron stars and black holes. This detector may be able to detect certain types of instabilities in rotating single and binary neutron stars, and the merger of small black holes or neutron stars.{{cite web
| first=Jeroen | last=Van Houwelingen | date=2002-06-24
| title=Development of a superconducting thin-film Nb-coil for use in the MiniGRAIL transducers
| publisher=Leiden University | pages=1–17
| url=http://www.minigrail.nl/Student/Jeroen-report.pdf
| accessdate=2009-09-16 }}
Design
A spherical design has the benefit of being able to detect gravitational waves arriving from any direction, and it is sensitive to polarization.{{cite journal
| last1=Gottardi | first1=L. |date=November 2007
| title=Sensitivity of the spherical gravitational wave detector MiniGRAIL operating at 5K
| journal=Physical Review D | volume=76 | issue=10
| pages=102005.1–102005.10
| doi=10.1103/PhysRevD.76.102005
| last2=De Waard
| first2=A.
| last3=Usenko
| first3=O.
| last4=Frossati
| first4=G.
| last5=Podt
| first5=M.
| last6=Flokstra
| first6=J.
| last7=Bassan
| first7=M.
| last8=Fafone
| first8=V.
| last9=Minenkov
| first9=Y. | last10=Rocchi | first10=A. |bibcode = 2007PhRvD..76j2005G |arxiv = 0705.0122 | s2cid=119261963 | display-authors=8 }} When gravitation waves with frequencies around 3,000 Hz pass through the MiniGRAIL ball, it will vibrate with displacements on the order of 10−20 m.{{cite web
| first=Eppo | last=Bruins
| title=Listen, two black holes are clashing!
| date=2004-11-26 | publisher=innovations-report
| url=http://www.innovations-report.com/html/reports/physics_astronomy/report-36884.html
| accessdate=2009-09-16 }} For comparison, the cross-section of a single proton (the nucleus of a hydrogen atom), is 10−15 m (1 fm).{{cite book | first=Kenneth William | last=Ford | date=2005 | title=The quantum world: quantum physics for everyone | page=[https://archive.org/details/quantumworldquan00kenn/page/11 11] | publisher=Harvard University Press | isbn=0-674-01832-X | url=https://archive.org/details/quantumworldquan00kenn/page/11 }}
To improve sensitivity, the detector was intended to operate at a temperature of 20 mK. The original antenna for the MiniGRAIL detector was a 68 cm diameter sphere made of an alloy of copper with 6% aluminium. This sphere had a mass of 1,150 kg and resonated at a frequency of 3,250 Hz. It was isolated from vibration by seven 140 kg masses. The bandwidth of the detector was expected to be ±230 Hz.
During the casting of the sphere, a crack appeared that reduced the quality to unacceptable levels. It was replaced by a 68 cm sphere with a mass of 1,300 kg. This was manufactured by ItalBronze in Brazil. The larger mass lowered the resonant frequencies by about 200 Hz.{{cite journal
| author=de Waard, A.
| display-authors=etal
| title=MiniGRAIL progress report 2004
| journal=Classical and Quantum Gravity | volume=22
| issue=10
| pages=S215–S219 | doi=10.1088/0264-9381/22/10/012
| date=2005 |bibcode = 2005CQGra..22S.215D | s2cid=35852172
| url=https://research.utwente.nl/en/publications/minigrail-progress-report-2004(e2ae42cb-9b18-4d10-84c4-de3c1c77d9dd).html
| url-access=subscription}} The sphere is suspended from stainless steel cables to which springs and masses are attached to dampen vibrations. Cooling is accomplished using a dilution refrigerator.{{cite journal
| author=de Waard, A. |display-authors=etal
| title=Cooling down MiniGRAIL to milli-Kelvin temperatures
| journal=Classical and Quantum Gravity | volume=21
| issue=5 | pages=S465–S471 |date=March 2004
| doi=10.1088/0264-9381/21/5/012 |bibcode = 2004CQGra..21S.465D |s2cid=250811527
|url=https://ris.utwente.nl/ws/files/6702784/Waard004cooling1.pdf
}}
Tests at temperatures of 5 K showed that the detector had a peak strain sensitivity of {{nowrap|1.5 × 10−20 Hz−{{frac|1|2}}}} at a frequency of 2942.9 Hz. Over a bandwidth of 30 Hz, the strain sensitivity was more than {{nowrap|5 × 10−20 Hz−{{frac|1|2}}}}. This sensitivity is expected to improve by an order of magnitude when the instrument is operating at 50 mK.
A similar detector named "Mario Schenberg" is located in São Paulo. The co-operation of the detectors strongly increase the chances of detection by looking at coincidences.{{cite journal
| author=Frajuca, Carlos |display-authors=etal
| title=Resonant transducers for spherical gravitational wave detectors |date=December 2005
| journal=Brazilian Journal of Physics | volume=35
| issue=4b | pages=1201–1203
| doi=10.1590/S0103-97332005000700050 |bibcode = 2005BrJPh..35.1201F |url=http://www.scielo.br/pdf/bjp/v35n4b/a50v354b.pdf| doi-access=free }}
References
{{Reflist|30em}}
External links
- [http://www.minigrail.nl/ MiniGRAIL on the internet]
{{Gravitational wave observatories}}
{{coord missing|Netherlands}}