This workshop provides the opportunity for the CHESS community to make the scientific case for a dedicated beamlines optimized for the study of nanosecond dynamics at CHESS.
Organizers: Todd Hufnagel (JHU), Brian Schuster (ARL)
The recent upgrade of the storage ring has positioned CHESS as one of two U.S. synchrotrons that are well-suited for in situ studies of bulk structural materials with sub-microsecond temporal resolution. The purpose of this workshop is to explore opportunities for x-ray diffraction, imaging, and spectroscopy on this time scale, with a particular emphasis on defense and national security applications. The workshop talks and discussions will form the basis of a white paper outlining the science case for building one or more new beamlines to enable these capabilities.
The context for the workshop is that other synchrotron user facilities such as APS and ESRF are pursuing upgrades to maximize the spatial coherence of their x-ray beams, which is accomplished by reducing the emittance (effectively, the cross-sectional area in phase space) of the electron beam in the storage ring. While undoubtedly useful for techniques that require high coherence (such as phase contrast imaging and coherent diffractive imaging), this approach requires strong focusing magnets, which in turn requires small apertures. Because the maximum possible current in a bunch scales as the cube of the aperture size, the maximum bunch current in these next-generation machines will be significantly limited compared to their present-day storage rings.
These observations suggest that CHESS can position itself as a premier facility for time-resolved experiments that do not require high spatial coherence of the x-rays, including x-ray imaging, x-ray diffraction, and x-ray spectroscopy. The relatively large emittance of the electron (or positron) beam at CHESS means that the charge per electron bunch can be much larger than at other high-energy synchrotrons. Furthermore, the larger emittance and (on a practical level) the smaller number of beamlines at CHESS provide the opportunity to use a wider variety of bunch (timing) structures, including timing sequences designed for specific classes of experiments.
With these considerations in mind, the workshop is intended to explore in depth the possibilities for timing experiments at CHESS to explore sub-microsecond dynamics of materials. The first session of the workshop will provide an overview of the field, including drivers for dynamic experiments (Jensen). This will be followed by a presentation of the upgraded storage ring and insertion device characteristics (Shanks), including a discussion of potential novel timing modes. Equally important are the capabilities of existing and prospective detectors, particularly for x-rays with energies above 30 keV (Becker). The goal of this first session is to familiarize prospective users of these capabilities of what is, and is not, expected to be possible.
The next four talks will focus on the primary techniques of x-ray imaging (Schuster, Branch), diffraction (Bernier), and spectroscopy (Coppari). The primary goal here is to assess the alignment of the experimental requirements — which are driven by specific application needs — with the potential capabilities provided by CHESS.
The last five talks emphasize specific application areas: Spall (Mallick), high explosives (Smilowitz), reactive materials (Hooper), deformation and fracture of metals (Cerreta), and heterogeneous materials (Kumar). The goal for this part of the workshop is to identify specific experiments in a few key areas that might lead to important scientific and engineering advances. An important part of this will be to make sure that capabilities of the experiments, enabled by the characteristics of the source and detectors, will be sufficient to achieve the desired scientific outcomes.
As a guideline to the speakers and workshop participants, the table below provides an overview of some of the key characteristics of the upgraded CHESS source, in comparison to the source characteristics of the Dynamic Compression Sector (DCS) at the Advanced Photon Source).
DCS (current APS, 24 bunch mode) |
DCS (APS-U 48 bunch mode) |
CHESS-U timing mode |
|
Charge per bunch (nC) |
15 nC |
15 nC |
50 nC (9 bunches) |
Interval between bunches (ns) |
153.4 ns |
76.7 ns |
280 ns (9 bunches) |
Pulse width (ps) |
30 ps |
? |
~60 ps (depends on mode) |
Energy range (keV) |
7-35 keV (pink, focused) |
5-50+ keV (CCU) |
|
Max spot size (µm) |
2.5 mm (V) x 3.7 mm (H) (white beam) |
~1 cm |
|
Min spot size (µm) |
26 µm (V) x 106 µm (H) |
25 µm x 300 µm (CCU, 1:1 focusing, 1% BW) |
|
Emittance (pm) |
3113 |
32 |
30000 |
Single-bunch brightness |
2.6e18 |
3.21e20 |
|
Pinhole flux (ph/s/0.1%BW) at 30 m, 20 keV |
2e14 (0.5 mm pinhole) |
1.9e15 (0.5 mm pinhole) |
5e13 (1 mm pinhole) |
Sources: DCS Web page; APS Upgrade Project Final Design Report (May 2019); Shanks, “CHESS-U Ring Storage Capabilities”; CHESS-U Science Case: New Science Made Possible by CHESS-U
Workshop Schedule (All Times EDT)
Wednesday, June 10
Time |
Session |
Presenter |
---|---|---|
9:00 - 9:15 | Introduction | Todd Hufnagel, JHU |
9:15 - 9:45 | An overview of the development of dynamic experiment capabilities at a synchrotron source | Brian Jensen, LANL |
9:45 - 10:15 | CESR as a Source for Timing Experiments | Jim Shanks, CHESS |
10:15 - 10:45 | Detecting photons - What modern detectors can and can’t do | Julian Becker, CHESS/DESY |
10:45 - 11:00 | Break | |
11:00 - 11:30 | Imaging: Incipient Fracture of Ceramics Under Impact | Brian Schuster, ARL |
11:30 - 12:00 | Time-resolved x-ray diffraction for exploring strength, phase transitions, and plasticity | Joel Bernier, LLNL |
12:00 - 12:30 | Ultra-fast EXAFS spectroscopy under laser-driven dynamic compression | Federica Coppari, LLNL |
12:30 - 1:00 | Lunch break | |
1:00 - 1:30 | Probing Dynamic Shock Behavior in Advanced Materials using In-Situ Phase Contrast Imaging | Brittany Branch, Sandia |
1:30 - 2:00 | Micro-scale ballistic experiments for materials characterization at high strain rates | Debjoy Mallick, ARL |
2:00 - 2:30 | Timing and Triggering Needs for the Measurement of Energy Release Rate of High Explosives | Laura Smilowitz, LANL |
2:30 - 2:45 | Break | |
2:45 - 3:15 | Diagnostic targets for understanding the fragmentation and combustion of reactive materials | Joe Hooper, NPS |
3:15 - 3:45 | The Role of Defects on Performance | Ellen Cerreta, LANL |
3:45 - 4:15 | Dynamic compression response of heterogeneous materials | Mukul Kumar, LLNL |
4:15 - 4:30 | Wrap-up/Path forward | Todd Hufnagel, JHU Brian Schuster, ARL |