P. Gros, S. Amano, D. Attié, D. Bernard, P. Bruel, D. Calvet, P. Colas, S. Daté, A. Delbart, M. Frotin, Y. Geerebaert, B. Giebels, D. Götz, S. Hashimoto, D. Horan, T. Kotaka, Marc Louzir, Y. Minamiyama, S. Miyamoto, H. Ohkuma, Patrick Poilleux, I. Semeniouk, P. Sizun, A. Takemoto, M. Yamaguchi, S. Wang
Current γ-ray telescopes suffer from a gap in sensitivity in the energy range between 100 keV and 100 MeV, and no polarisation measurement has ever been done on cosmic sources above 1 MeV. Past and present e+e- pair telescopes are limited at lower energies by the multiple scattering of electrons in passive tungsten converter plates. This results in low angular resolution, and, consequently, a drop in sensitivity to point sources below 1 GeV. The polarisation information, which is carried by the azimuthal angle of the conversion plane, is lost for the same reasons.
HARPO is an R&D program to characterise the operation of a gaseous detector (a Time Projection Chamber or TPC) as a high angular-resolution and sensitivity telescope and polarimeter for γ-rays from cosmic sources. It represents a first step towards a future space instrument in the MeV-GeV range.
We built and characterised a 30cm cubic demonstrator [SPIE 91441M], and put it in a polarised γ-ray beam at the NewSUBARU accelerator in Japan. Data were taken at photon energies from 1.74MeV to 74MeV and with different polarisation configurations.
We describe the experimental setup in beam. We then describe the software we developed to reconstruct the photon conversion events, with special focus on low energies. We also describe the thorough simulation of the detector used to compare results. Finally we will present the performance of the detector as extracted from this analysis and preliminary measurements of the polarisation asymmetry.
This beam-test qualification of a gas TPC prototype in a γ-ray beam could open the way to high-performance -ray astronomy and polarimetry in the MeV-GeV energy range in the near future.
In this paper, characterizations of a cryogenic Xe capillary jet target for a laser-produced plasma extreme ultraviolet (EUV) light source are reported. The capillary jet target is a candidate of fast-supplying targets for mitigating debris generation and target consumption in a vacuum chamber without reducing the EUV conversion efficiency. Xe capillary jets (jet velocity ~ 0.4 m/s) were generated in vacuum by using annular nozzles chilled to ~ 170 K at a Xe backing pressure of ~ 0.7 MPa. Forming mechanisms of the capillary jet targets were studied by using numerical calculations. Furthermore, laser-produced plasma EUV generation was performed by irradiating a Nd:YAG laser (1064 nm, ~ 0.5 J, 10 ns, 120 μmφ, ~ 4×1011 W/cm2) on a Xe capillary jet target (outer / inner diameter = 100 / 70 μmφ). The angular distribution of EUV generation was approximately uniform around the Xe capillary jet target, and the peak kinetic energy of the fast-ions was evaluated to be ~ 2 keV.
We intended to use deposition-free target such as cryogenic Xe target as a laser produced plasma EUV source. We reported an enhancement of conversion efficiency (CE) by double pulse irradiation and a CE dependence on wavelength of drive laser. Lithium target used with hot multi-layer mirror was proposed by Cymer, as a new deposition-free target. We made EUV source studies experimentally on cryogenic Xe target and lithium new scheme target. In this paper, we report newly made double pulse irradiation experiments on cryogenic Xe target and an enhanced EUV generation with new "forced recombination" and/or "expansion energy re-conversion" lithium target. Laser systems used in the experiments were a 320 Hz repetition rate Nd:YAG slab laser and a 10 Hz Nd:YAG rod laser with maximum pulse energy of 1J. EUV emissions were measured by a time resolved and a time integrated imaging cameras, a transmission and a grazing incidence spectrometers, fast EUV photo-diodes and a Flying Circus 3 for power monitor. Temporal resolved EUV images from Li target indicate relatively long emission time and large emission area. The size of emission area is improved and the emission intensity is enhanced by adding a wall in front of the Li target. Experimental results indicate the expected forced recombination and expansion energy re-conversion characteristics.
X-ray emissions form Xe cryogenic target, Kr cryogenic target and Xe gas target were studied and compared. A high average high peak brightness pulsed Nd:YAG laser was successfully developed as a driver for high average power laser plasmas x-ray sources. A target system that can supply cryogenic targets without interrupting the operation was also developed. Any discrete images of fast debris of several 10 micrometers or more in diameter were not observed in backlighting experiments. A new approach to extinguish the fast debris from the cryogenic target by using 'laser shower' was proposed and proved to be practical.
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