The intense scientific and technological collaboration between a group of scientists and engineers coming from ELI Beamlines (IoP-ASCR, Prague) and Service des Basses Températures (INAC-CEA, Grenoble) has led to the first worldwide experimental test of a cryogenic targetry delivering system made of a very thin solid hydrogen ribbon as a source of fast protons produced by high-power lasers.
The kilojoule PALS laser facility in Prague, a joint laboratory of the Institute of Plasma Physics and the Institute of Physics of the Academy of Sciences of the Czech Republic and also part of the Laserlab Europe consortium, was chosen as test facility for this first experiment. The technologies available at PALS, together with the know-how of its highly specialized technical staff, who strongly contributed in the preparation of the experimental setup, led to the success of this preliminary campaign and further laser beam time is planned in November.
This and further planned experimental tests of this innovative cryogenic device named ELISE will be crucial to assess advantages and disadvantages of its future implementation at ELI Beamlines in the ELIMAIA beamline which will provide proton/ion beams to users coming from different multidisciplinary fields, with a special emphasis on medical applications and in particular on innovative approaches to cancer therapy. Thus, these results are expected to contribute to the world leading capabilities of the ELI Beamlines facility.
The original idea was to produce a syringe with a virtual piston and with a nozzle aperture suitable for the given H ribbon thickness. “The virtual piston is obtained by heating at -233 °C the top of the syringe, which makes the pressure rise in the syringe, whilst maintaining the extrusion nozzle, at the bottom of the syringe, at -261 °C (2 °C below the hydrogen triple point),” explains Dr Jean-Paul Perin from SBT. “Understanding the specific behavior of the flow of solid hydrogen required numerous experiments and numerical modeling,” adds Dr Denis Chatain also from SBT. A cryostat was constructed for this purpose. The functional tests conducted at SBT (CEA) have been achieved with three nozzles (100, 62 and 32 micrometer thick) and the size of the syringe used allowed extrusion of a hydrogen ribbon for several hours.
Three years on from the first conceptual design ELISE has been successfully tested. Dr Daniele Margarone from ELI Beamlines explains: “This is the result of a complex development which required the use of sophisticated cryogenic techniques in harsh laser-plasma environment. There is still a way to go; however the possibility to produce a continuous flow of “pure” solid hydrogen clearly paves the way towards the use of laser driven protons for applications in hadrontherapy.”
“This is the first time ELISE has been tested with a high power laser and several technical challenges were uncovered during the experiment at PALS,” says Dr Andriy Velyhan from ELI Beamlines. We have produced an extremely high temperature gradient through the generation of a very hot (hundreds millions degrees) plasma and a hydrogen ice ribbon (-233 °C). Beside the potential for proton acceleration and future applications in hadrontherapy, this result is also very interesting to the field of laser plasma physics and will certainly enable the scientific community to investigate new phenomena.
