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X-ray beamlines

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Two X-ray beam lines are developed in the frame of the COLA project:

- Broadband X-ray source. A broadband multi-keV X-ray source is in operation with a 1 kHz repetition rate. Derived from the “Aurore” laser sytem of CELIA (1 kHz, 10 mJ, 30 fs, 800 nm), it delivers extremely brief X-ray bursts, from a few ps down to a few hundreds of fs only. This line is dedicated to time-resolved X-ray absorption spectroscopy.
- Hard X-ray source. Another X-ray source is being developed from the “Eclipse” laser sytem of CELIA (10 Hz, 200 mJ, 35 fs, 800 nm). The objective is to achieve the hard X-ray range (10 – 100 keV) for possible applications to the medical and industrial radiography.

Each of these devices include a synchronized optical laser beam in order to perform “pump – probe” experiments. The “pump” optical pulse initiates ultra-fast phenomena, while the other laser beam is converted in an ultra-fast X-ray pulse to “probe” the phenomena dynamics with extreme time-resolution.

These X-ray beam lines are proposed to external users from the Région Aquitaine, France or European community. A first collaboration has already started with the LNE team (Laser Nuclear Excitation) of CENBG laboratory.

Application to nuclear physics:

Enhancement of activation and decay rates of nuclear levels through laser heating of plasma

It has recently been shown (A. V. Andreev et al. JETP 91, 1163 (2000)) that the activation and decay of the 6.238 keV nuclear level of 181Ta can be enhanced in femtosecond laser heated Ta plasmas. This enhancement is due to the high density surrounding plasma and high ionization states of Ta ions. A detailed knowledge of the plasma conditions is required to understand further the enhancement mechanisms. A Ta target was thus heated in CELIA using 45 fs Ti :sapphire laser pulses with intensities ranging from 1 to 6.1016 W/cm2. Langmuir probes have been used to characterize the ion emission and we employed both CCD and NaI(Tl) pulse height detection systems to measure the X-ray emission. The deposition and implantation of the escaping Ta ions and atoms were also characterized by means of Rutherford Backscattering Spectrometry. These experiments have shed light on the plasma conditions and have allowed to carry out analytical models and hydrodynamical calculations to elicit the mechanisms responsible for the enhancement of the nuclear rates.

tête ligne X (cliché CELIA)

Detail of the ultra-short broadband X-ray beam line. Two synchronized laser beams are independently compressed and their delay is tuned with a delay line. One is the optical “pump” beam. The other is used to generate the X-ray “probe” beam.

Ligne X sur Equinoxe (cliché CELIA)

Hard X-ray beam line with laser compression chamber, laser spatial shaping chamber and X-ray generation chamber. The synchronized laser beam is compressed and its delay is tuned on the optic table with black protection.