Atomic Spectroscopy
The Bochum accelerator laboratory
DTL
used to have excellent technical facilities facilities
and operating options for Atomic Physics. Over the years, these have been used most extensively
by the ISS Group (IonenStrahlSpektroskopie - Spectroscopy on Fast Ion Beams)
of P.H. Heckmann, H.H. Bukow and
E. Träbert.
The group enjoyed collaborations with many visitors from abroad, and Bochum people went
to other places for ion beams beyond the range of the Bochum machines.
However, following restructuring and streamlining exercises of the
physics faculty, accelerator-based atomic physics activities have
largely been phased out, as is reflected in the successive shutdown and
removal of key equipment mentioned below.
Particular facilities:
- 2.2 m Grazing-incidence scanning monochromator (McPherson Mod. 247)
with 4 different diffraction gratings (300/600/1200/3600 l/mm) and
regular/coated channeltron detectors. This instrument offers spectral
ranges from 3 to 180 nm, with an optimum range 10 to 60 nm. The highest-
resolution EUV spectra on any fast ion beam have been recorded with
this instrument. The target chamber attached permits foil travels up to
17.5 cm, which renders possible the measurememnt of decay curves which
reach to about 20 or 30 ns after excitation.
Both the foil carriage and the spectrometer exit slit
displacement can be monitored by Heidenhain moiré fringe length gauges
for the measurement of very short lifetimes (down to a few ps) on one hand
and for the linear interpolation of spectra with high (micrometer) precision
on the other, overcoming the periodic errors of the lead screws.
This instrument has meanwhile (1998) been transferred to JiaoTong University, Shanghai (China),
and it has further migrated to Fudan University (EBIT laboratory).
- 2.2 m Grazing-incidence monochromator
(Home-made relative of the above instrument using the 1200 l/mm
grating and an angle of
incidence of 88 deg. This was sufficient to see Mg Kα at a wavelength of λ=1.2 nm.
This instrument is now
on a long term loan to colleagues at the Université
de Liège (Belgium). By early 2002, this instrument has been
completed again by duplicating parts that it had shared with another
spectrometer at Bochum, and by constructing new slits that
will permit narrower settings. Also, local turbopumps are being attached.
- Home-built 30 cm toroidal grating monochromator (based on
Jobin-Yvon's LHT 30 instrument) equipped with a channeltron for fast decays.
A microchannelplate detector for multichannel detection of low-light-level
events has reached testing stage but has since been retired for lack of manpower.
A differentially pumped gas target can be placed on the foil carriage in
place of a foil holder.
This spectrometer is now (2008) in the (slow) process of being converted into another
small, but better resolving VUV spectrometer based on a type IV
holographic grating. Plans for using this instrument include delayed spectra
in the wavelength range 40 - 120 nm, of elements that are abundant in the solar corona.
Presently foreseeable technical problems include:
The control computer is an Apple IIe of (about) 1982 vintage. If it
still runs (as it did until last used in 1998), it won't learn to connect to
the ethernet. Although a (then) modern PC has been obtained from a DTL science grant,
a PC-based control card is beyond budget. An alternative has been offered
by a colleague at Liège who is willing to provide a somewhat less
old Apple "pizza box" as an intermediate unit for web access.
The original turbo pump is beyond salvage, and the replacement then
purchased from faculty/chair funds had to be given back to the chair,
along with all equipment not obtained through outside (DFG,BMBF) funds.
An old-type turbopump on loan from the DTL has been mounted, but the
vacuum system has not yet been completed.
Since the vacuum chamber has been used for a variety of spectrometers
and recoil ion arrangements since it was originally configured, the useage
by several students who had different office spaces that were
consolidated after they left resulted in equipment and parts "disappearing".
Quite possibly the equipment ages faster than the completion procedes.
In early 2005 it looked like a good time to bring the vacuum chamber
with the beam-foil spectroscopy set-up back to the accelerator, using
the only unoccupied beam line position in a pass-through location.
An application stating research plans was duly filed with the lab management.
However, the request for (even temporary) access to this location was
denied, citing "an uncommonly high demand of the machine" in the light
of which my research plans (which offered many breaking points)
were considered as being "too extensive". According to the note by the
lab management, the period of high demand was expected to last as
long as the position of the last remaining physics professor at the lab
and then scientific director, that is, at least till 2007.
In 2007, access was denied again because of uncertainties in laboratory planning
prospects and possible insurance issues with an unemployed researcher.
In 2008, DFG granted a position for the latter, and now refurbishing work
is underway again.
Accelerator facilities:
Two complementary machines have been able to reach the same site
- 450 kV single-stage accelerator
with rf, thermionic and Penning ion sources,
used for fast-beam work with H, He, Li, C, N, O, Ne, Na, Ar
(this machine has meanwhile been retired)
- 4.5 MV Dynamitron tandem accelerator
with He, Duoplasmatron and Middleton-type
high-current sputter ion sources and a gas stripper in the high voltage
terminal.
More than 40 ion beam species produced so far, almost all of which
have also been used for fast beam spectroscopy - which implies that notable
and lasting beam current values have been achieved.
( Beams used for fast-beam spectroscopy:
H, He, Li, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, K, Ca, Sc,
Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, Br, Nb, Mo, Rh, Pd, Ag, I, Eu, Os, Ir, Pt, Au)
Second gas stripper (optional) after the tandem accelerator for
- access to beams of very heavy ions (Os - Au),
- wide-range charge-state vs. energy variation for ion-atom
collision studies (collaboration with U Giessen),
- highly charged primary ion beams to make well-defined secondary
recoil ion beams
Main research areas of the ISS group:
Atomic Structure (Wavelengths) and Dynamics (Lifetimes and Branching ratios)
- Few-electron ions of the 2- to 4- electron isoelectronic sequences,
with measurements at Bochum and at GSI Darmstadt
- Multiply-excited states in few-electron ions
- Intercombination transitions, induced by relativistic effects
- Forbidden lines (at other facilities, like the Heidelberg heavy-ion storage ring TSR,
or on electron beam ion traps (EBIT))
- Excitation and fragmentation of atmospheric gases by ion impact
- Laboratory studies of transitions of solar corona and high-temperature
plasma interest
This astrophysics and plasma physics research continues "off-line", after the removal of the group's
principal equipment and experimental station, on the basis of data
accumulated beforehand, and in cooperation with external collaborators.
- Ion-atom collisions, charge exchange, ionization-cum-excitation
- Development and utilization of new techniques for atomic
Lifetime measurements, like using :
- Slow ion beams of well defined energies for
atomic spectroscopy (microsecond lifetime range)
- The use of heavy ion storage rings for the study of
millisecond to second atomic lifetimes; unprecedented precision has been
reached on intercombination and forbidden transitions in moderately charged ions at
TSR Heidelberg
- Atomic physics with Electron Beam Ion Traps (EBIT), like
SuperEBIT and EBIT II at Lawrence Livermore National Laboratory (California)
(LLNL EBIT) and at the
NIST EBIT,
much of this is aiming at millisecond lifetimes in highly charged ions
National and International Collaborations
with colleagues from Aarhus (Denmark), Argonne (Ill.),
Boone (N.C.), Brookhaven (N.Y.), Cambridge (Mass.),
Daresbury (England), GSI Darmstadt (Hessen), Edmonton (Alberta),
Freiburg (Baden-W.), Gaithersburg (Maryland),
Giessen (Hessen), Guelph (Ont.), Heidelberg (Baden-W.), Kassel (Hessen),
Kiel (Schleswig-Holstein), Laval (Québec), Liège (Belgium),
Livermore (Cal.), Lund (Sweden),
Moscow (Russia), Mumbai/Bombay (India),
Nashville (Tenn.), New Orleans (Louis.),
Notre Dame (Indiana), Oxford (England), Philadelphia (Penn.),
Québec (Québec),
Reno (Nevada), RIKEN (Japan), Shanghai (China),
Stockholm (Sweden), Toledo (Ohio), Troitzk (Russia),
Tucson (Arizona),
for work at Bochum or elsewhere - not even counting a fair number of
splendid continued contacts with colleagues in atomic structure
and collision theory.
Local Home Pages
Accelerator laboratory
DTL
with DoRo's Links
(closed down) Chair Experimental Physics III - Physics with Ion Beams
EPIII
Interested in
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the international
Atomic Physics Home Page ?
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E. Träbert home page.
Page minimally updated (needs more straightening out): 26 Nov 2008