WDM-Collaboration



The WDM-collaboration has proposed a set of recommended experiments at the future FAIR facility combining intense heavy ion beams with the kilojoule PHELIX laser facility.

The approved experimental proposal [1]

"Radiative Properties of Warm Dense Matter (WDM) produced
by intense heavy ion beams"
or shortly "WDM"

is described in detail in paragraph 5.3 of the Baseline Technical Report [2].

Warm Dense Matter (WDM) [3] refers to high-density finite-temperature regime where free and bound electrons become strongly correlated: the system exhibits long- and short-range order. This intriguing regime takes two broadly distinct manifestations: it occurs when condensed matter reaches temperatures near and above the Fermi temperature and it occurs as plasmas are cooled and/or the density is increased. For example, the plasma can no longer be considered a thermal bath and the behavior of its particles is no longer well described by characteristics of isolated ions. This regime is of importance and an extremely challenging area for scientific inquiry.

The relevance of WDM research arises from a wide occurrence of this state of the matter: it is a subject of investigation in planetary science, cold star physics and all plasma-production devices where the plasma generation starts from cold dense matter (e.g., laser solid matter interaction, heavy ion beam driven plasmas, capillaries, exploding wires, pinch plasmas).

The current knowledge of the plasma behavior is particularly limited in those regions where standard perturbative theoretical approaches are applicable. However, when these methods fail new techniques are needed and this translates directly into the realm of novel experimental science. Indeed, the theoretical difficulties arise from, for example, the importance of density effects (e.g., pressure ionization), as the electrons and ions begin to substantially influence each other. That is, the internal structure of ions becomes a function of the plasma density and temperature while the usually "free" plasma particle exhibit ordering. Experimental problems follow as one must isolate this inherently transient state. This, in brief, is why so little is known about WDM.

In previous laser experiments WDM states have been the subject of investigation but the result have been difficult to obtain for numerous reasons: in-homogeneities, fast time scales (fs) and small spatial dimensions [4]. On the other hand, WDM produced by intense heavy ion beams will have several advantages: large (mm) sample size, long lifetimes (ns), and homogeneity. Typical WDM-temperatures are in the eV range, with temperatures up to the 10 eV range envisaged in future GSI-FAIR experiments for solid density targets [5]. Due to the relatively low temperatures thermally excited X-ray emission from these dense warm samples is not a reasonable diagnostic. However, the use of a powerful optical laser facility (like, e.g. the PHELIX kilojoule laser) that is collocated with the intense heavy ion beams will provide an independent x-ray scattering diagnostic (see Figure 1) yielding on the temperature, density, charge state and ion-ion correlation effects in the WDM [6]. Moreover, different scattering geometries (forward and backward scattering) turn out to be very sensitive to dense plasma effects on the matter and provide therefore critical tests of theory and simulations [7].

In addition, inner-shell  ionization driven by fast ions might induce Kα/Kβ x-ray emission that will have diagnostic potential.

A particular experimental arrangement for the Warm Dense Matter research is based on a dynamic confinement scheme shown in Figure 2 [5] for solid hydrogen. In the traditional static confinement approach the achievement of homogeneity depends on the fact that the massive outer shell (e.g., Pb) will not move over the observation time due to its inertia. A serious disadvantage, however, is that photo-absorption in the outer confining shell is so large that neither X-ray scattered photons (being produced with the PHELIX kJ-pulse) nor inner-shell transitions can pass the dense shell. Simulations for the dynamicconfinement scheme have shown, that a thin plastic tamper allows almost static parameter regimes, see Figure 3, while permitting x-rays (e.g., Kα radiation of mid-Z laser targets at 4 - 10 keV) to pass through [5]. At an ion beam intensity of 8·1010 uranium ions a temperature exceeding 0.5 eV at solid density is expected for the described hydrogen target. The dynamic confinement scheme has also been explored in spherical symmetry which has important technical advantages [7].

The world-wide unique combination of intense heavy ion beams with powerful optical laser-driven x-ray scattering diagnostic will, therefore, allow to perform benchmark experiments in the WDM and dense strongly coupled plasma regime (DSCP) and greatly advance the understanding in this field of research.

The Warm Dense Matter project, denoted the WDM project, proposed in 2004 [8] has successfully passed the scientific evaluation by an international expert committee. In 2005 WDM has then been selected to be one of the recommended experiments in the future FAIR facility at GSI. In 2006 the WDM-technical design report has been approved [1][2].

Since then beam parameters and end-stations of the FAIR facility have been subject to changes. The WDM-collaboration is therefore continuously adapting its scientific program to new possible scenarios to maintain excellence in dense plasma atomic physics within FAIR and also with respect to the world wide emerging light sources of the 4th generation (XUV- and X-FEL’s). An important concern in this respect has therefore been the development of new experiment proposals and target designs that are adapted to the available heavy ion beam parameters [9-11].

Out of these new developments, opacity measurements in the eV regime are of outstanding importance to scientifically access and study the most challenging parameter regimes of Warm Dense Matter and its related fundamental atomic physics in complex environments. Intense heavy ion beams are well suited as isothermal expansion of the irradiated foils allows precise interpretation of the measured data [12].

Next steps are studies of K-alpha and K-beta transitions to explore their use for advanced fundamental studies of atomic physics in dense plasmas. These studies concern also the use of high intensity optical laser experiments and advanced detector developments coupled to high-resolution X-ray spectroscopy.

 

References

  1. FAIR Newsletter, No. 2 (April 2006), p.14, http://www-w2k.gsi.de/FAIR-Newsletter/index.htm.
  2. FAIR Baseline Technical Report 2006, vol. 5, paragraph 5.3:"WDM-Radiative Properties of Warm Dense Matter Produced by Intense Heavy Ion Beams".
  3. R. W. Lee et al., J. Opt. Soc. Am. B 20, 1 (2003).
  4. F.B. Rosmej, R.W. Lee, D. Riley, J. Meyer-ter-Vehn, A. Krenz, T. Tschentscher, An. Tauschwitz, A. Tauschwitz, V.S. Lisitsa, A.Ya. Faenov: "Warm Dense Matter and Strongly Coupled Plasmas Created by Intense Heavy Ion Beam and XUV-Free Electron Laser: An Overview of Spectroscopic Methods", J. Phys. Conf. Ser. 2006, in print.
  5. A. Kozyreva, M. Basko,F.B. Rosmej, T. Schlegel, A. Tauschwitz, D.H.H. Hoffmann: "Dynamic confinement of targets heated quasi-isochorically with heavy ion beam",Phys. Rev. E 68, 056406 (2003).
  6. D. Riley, F.B. Rosmej, GSI-Annual Report 2003-3, 61 (2004), http://www-aix.gsi.de/plasma2003
  7. A. Tauschwitz, J.A. Maruhn, D. Riley, G. Shabbir Naz, F.B. Rosmej, S. Borneis, A. Tauschwitz :Quasi-isochoric ion beam heating using dynamic confinement in spherical geometry for X-ray scattering experiments in WDM regime”, High Energy Density Physics 3, 371 (2007).
  8. F.B. Rosmej et al. 2004: "Radiative Properties of Warm Dense Matter Produced by Intense Heavy Ion Beams", Letter of Intent (LOI) #25.
  9. A. Tauschwitz, J.A. Maruhn, D. Riley, F.B. Rosmej, S. Borneis, A. Tauschwitz and K. Witte:  "Target design for studies of radiative properties in warm dense matter at GSI and FAIR - the WDM collaboration", 5th International Conference on Fusion Science and Applications IFSA (09/09-14/09/2007), Kobe, Japan, J. Phys. Conf. Ser. 112, 032074 (2008).
  10. An. Tauschwitz, V. Efremov, J.A. Maruhn, F.B. Rosmej, A. Tauschwitz : "Quasi-static heating of stack targets with intense ion beams for equation of state measurements“, NIM B267, 2449 (2009).
  11. Anna Tauschwitz, M. Basko, V. Efremov, I. Iosilevskiy, J. Jacoby, J. Maruhn, P. Neumayer, V. Novikov, Andreas Tauschwitz, F. Rosmej: "Outline of experimental schemes for measurements of thermophysical and transport properties in warm dense matter at GSI and FAIR “, Proceedings of the 6th International Conference on Inertial Fusion Sciences and Applications (6-11/09/2009), San Francisco, J. Phys. Conf. Series 244, 042021 (2010).
  12. An. Tauschwitz, V.G. Novikov, A. Tauschwitz, F.B. Rosmej, J. Abdallah, E. Onkels, J. Jacoby, J.A. Maruhn: Intense ion beams as a tool for opacity measurements in warm dense matter, Rapid Communication Applied Physics B 95, 13 (2009).

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Spokesperson
Frank B. Rosmej
frank.rosmej(at)upmc.fr

 

GSI-Representative
Andreas Tauschwitz
a.tauschwitz(at)gsi.de

 

PHELIX-Representative
Stefan Borneis
s.borneis(at)gsi.de

 
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