[情報] PhD position in THz Spectroscopy
Fully-Funded PhD Studentship in
“THz Spectroscopy”
Department of Physical Sciences
Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom
**Open to all Nationalities**
Overview:-
The aim of this PhD is to develop a novel THz spectrometer and apply this
state-of the-art instrument technology to laboratory studies that
investigate the synergy between gas and dust in star-forming environments.
The position is a 3.5 year, fulltime PhD post, starting 1st October 2013
in the in the Department of Physical Sciences, Open University, United
Kingdom (http://www8.open.ac.uk/cepsar/). The successful candidate will be
expected to spend a total of 18 months on secondment at the Rutherford
Appleton Laboratories (RAL) during the PhD period.
To apply, please send a 2-page CV, list of publications (if any), a cover
letter clearly identifying the project to which you are applying,
explaining your enthusiasm and suitability for the post, to Science-
research-degrees@open.ac.uk by 5pm (UT) June 21st 2013. Please arrange for
two letters of recommendation to be emailed directly by your referees to
the same address, by the same date. Interviews will be held on July 9th –
10th 2013 at the OU, Milton Keynes and RAL, Oxfordshire.
Background:-
Since star-formation is intimately linked with galactic evolution,
consuming baryonic matter, and modifying the elemental metalicity of our
universe, understanding the star-formation process is a very key challenge
of modern astronomy. The interstellar medium, in both our own galaxy, and
extra-galactic environments, is the gaseous and dusty material from which
stars from. Prior to the onset of star-formation, atoms and molecules tend
to 'freeze-out' on the dust surfaces, forming interstellar ices - the
largest reservoir of molecular material in interstellar regions. As
star-formation progresses, molecules formed on and in the ice are returned
to the gas phase, via simple heating, or non-thermal (electron or photon
induced) desorption processes. This molecular gas then acts as a vital
coolant during the collapse phase of star formation, as well as providing
the ingredient material (along with the dust and ice) for planet forming
processes. This interplay between the gas and solid phase is a crucial
feedback mechanism that continuously reflects then influences the prevailing
physical conditions (such as density temperature or energy balance) as star
formation progresses.
THz Spectroscopy is a vital tool in observational astronomy offering a
handle on such mechanisms from the sub-mm emission spectra of gases in
star-forming regions.
Modern telescope facilities e.g. Herschel and ALMA have two key findings;
first many typical coolant gases are actually observed in high-abundance
in energetically excited states, i.e. rotationally and vibrationally 'hot',
suggesting many more molecules than previously thought must be non-thermally
ejected from ices; second that a broad plethora of molecules, from water
and methanol (the 'weeds') to complex organics (the 'flowers') are observed
in the spectra, suggesting a rich chemistry emerges from both ice desorption
and subsequent gas-phase processes during star formation. To enable
astronomers to elucidate the underpinning gas-dust-ice interaction mechanisms,
and even to fully understand the wealth of chemical diversity being revealed,
requires detailed laboratory studies of both aspects of these processes.
Development and Exploitation of a THz Spectrometer – this PhD:-
The aim of this PhD is to develop, and then exploit an experiment designed
to study gas-surface interactions, uniquely using the sub-mm spectra as a
probe.
A key part of the research activity will require the candidate to develop
and use a heterodyne spectrometer initially working at the same frequencies
as ALMA band 7(275 – 373 GHz), but using semiconductor diode technology
for the THz mixer detection element. The radiometer front-end will be
initially formed from existing THz technologies developed by the RAL
Millimetre Wave Technology Group (RAL MMTG). It will be integrated with a
high-speed digital spectrometer and tested by using well-known transitions
of CO NO and SO2. Experiments will then follow that involve NO and H2O ices
and ice desorption measurements. This work will be undertaken jointly
between the OU and the RAL MMTG. The frequency range of the spectrometer
will eventually be extended to encompass 200 - 1000 GHz, dependent
upon availability of funding. From a scientific perspective this system
can be used to characterise the sub-mm wave spectra of the 'flower'
molecules - and two key scientific targets to prove the spectrometer
sensitivity will be from the family of PASH (Sulphur bearing poly-aromatic
hydrocarbon molecules) - potential candidates for the 600 GHz 'DIB'
(Diffuse Interstellar Band) discovered by Herschel.
The spectrometer will then be installed at the OU, where interstellar
ice analogues will be grown in situ under low vacuum and temperature
conditions emulating the ISM. Ice desorption, stimulated by thermal
heating, low energy electrons (50 - 500eV) and photons will all be used
sequentially to liberate molecules from the surface, and FT sub-mm emission
spectroscopy of the liberated gases measured against a cold background plate.
The experiments will probe ro-vibrational excitation, orthopara distributions
(in NH3 and H2O) and yields on non-neutral species, such as radicals
(OH, NO) and water clusters, liberated from the surface.
PhD Organisation
The PhD will be jointly supervised by Dr Helen Jane Fraser (OU) and Prof
Brian Ellison (OU / RAL Space). Initially the student will be expected to
work at RAL Space, developing the sub-mm spectrometer, sources and
detectors within the sub-mm and mm astronomy group, utilising existing
technology from ALMA and Earth-Observation instruments. The student will
then relocate to the OU - where the ice chamber will be constructed and
tested in parallel with the spectrometer. Finally the opportunity exists
to exploit the spectrometer for future scientific astronomical and earth
observation missions, or industrial monitoring applications; these
applications will be explored between RAL and the OU in the final year
of the project. RAL and the OU are within a few hours’ drive of each
other, so throughout the PhD day visits are viable from both supervisors
and the student throughout the studentship, likely monthly. Both sites
are commutable from Oxford, Milton Keynes and other nearby towns.
The studentship will cover fees and a maintenance grant of 13,726.00 per
annum, and the PhD will be overseen and awarded by the OU. The position
is open to students of any nationality.
Candidate Requirements:-
Candidates for this PhD should have a Bachelors, or preferably Master’s
degree, (minimum 2:1 or 1st equivalent) in a suitable subject area, i.e.
Physics, Electrical Engineering or Chemistry (with a strong emphasis on
Physical Chemistry). The candidate should have a strong background in
experimental laboratory work, particularly RF engineering or microwave
and sub-mm spectroscopy, and / or instrument design and development, and
experience of instrumental programming is preferable, in languages such
as Labview. The research will involve using vacuum equipment, RF technology,
cryogenics, computing, and quantum mechanical analysis of spectral features.
Some experience of one or all of these areas is therefore advisable. An
interest in the astronomical applications of the project is advisable.
To apply, please send a 2-page CV, list of publications (if any), a cover
letter clearly identifying the project to which you are applying, explaining
your enthusiasm and suitability for the post, to Science-research-degrees
@open.ac.uk by 5pm (UT) June 21st 2013. Please arrange for two letters of
recommendation to be emailed directly by your referees to the same address,
by the same date. Interviews will be held on July 9th – 10th 2013 at the OU,
Milton Keynes and RAL, Oxfordshire.
For additional information or queries please contact:-
helen.fraser@open.ac.uk 0044 1908 322 921
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