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:

1. 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. 2.2 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.

3. 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

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with DoRo's Links
(closed down) Chair Experimental Physics III - Physics with Ion Beams EPIII

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