Petawatt High Energy Laser for Heavy Ion Experiments
1. Near field with fill factor and energy density, 2. Beam quality in the far field, 3. Pulse duration and spectral width ( line width )
The Petawatt High Energy Laser for Heavy Ion experiment ( PHELIX ) is a high - and high energy - laser for basic research in the field of high energy physics at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt . The facility is intended to research fundamental processes in plasma , astro and atomic physics .
It is currently (as of 2015) Germany's largest laser system in pulse mode . Its special scientific position is characterized by the possibility of combining high-energy photons and particles, which is unique in Europe, as it is given at GSI by the already existing heavy ion particle accelerators .
history
Work on PHELIX began in 1995 with preliminary studies on nuclear fusion using the combination of lasers and heavy ions up to the project study of the laser system from 1998 and approval for construction in the same year. In cooperation with the French CEA , the first devices from the decommissioned PHEBUS laser system in France (counterpart of the American Nova laser system ) were delivered as early as 1999 and 2000. The project and construction phase of the main building and supply technology was from 1998 to 2000 (inauguration for 30 year celebration of GSI ). With the commissioning of the FS front-end system in 2001 by our own employees and physicists from General Atomics , a quick path was taken.
The construction of the main amplifier chain, the main components and the beam guidance to the first light versus particle experiment station turned out to be much more difficult. On the one hand, because the contract between the DOE of the USA and the BMBF on cooperation in the field of physics of dense plasmas was only concluded in 2002 (components at GSI 2003). Secondly, because many components had to be rebuilt or rebuilt after intensive renovation.
High demands on beam quality and stabilization challenged the feasible technological limit; This mainly concerned the flatness of the optics with a diameter of over half a meter, especially the mirrors , their coating and interferometric control. The requirements in the beam area must be better than clean room class ISO-5 (clean room class 100 according to US Federal Standard 209E) in order to avoid damage to the optics. The procurement and installation of the high-performance optics, the complete reconstruction of diagnostics and the conversion of the beam guidance between the laser building and the experiment station led to a delay in commissioning the entire system. The first experiments with partial systems of the laser took place as early as 2004.
Structure and technology
The structure was developed in close scientific and material cooperation with the French Commissariat à l'énergie atomique (CEA) and the Lawrence Livermore National Laboratory (LLNL) of the USA. Components of the Nova laser system , which were used to set up the main amplifier, the high-voltage charging system and the diagnostics, come from both research institutions .
PHELIX is a combination of lasers connected in series to generate high levels of energy and power. The main system is an Nd: glass solid-state laser pulsed by flash lamps , which is designed for a current energy of 0.5–1 kilojoules and an output of 0.5 petawatts . 5 kJ and 1 PW were planned for the final stage, but cannot currently be implemented for cost reasons.
Two front-end systems generate laser beams with a nanosecond (1–10 ns) or femtosecond (≈500 fs ) pulse duration ( ultra-short pulse laser ).
Front-end systems
Femtosecond front end (short pulse)
A commercially acquired titanium: sapphire laser oscillator from Coherent generates pulses of 76 MHz, a pulse duration of 100 fs and energies less than 5 nJ.
If the energy per unit area and pulse length is too high, technical limits (for example the laser damage threshold LDT of optical coatings) or non-linear optical effects lead to the destruction of the optical elements. The femtosecond laser pulse of the high-energy laser must therefore be spatially expanded and temporally stretched before amplification.
The beam is stretched over time using the Chirped Pulse Amplification process. The stretched pulse is then amplified in two regenerative Ti: sapphire amplifiers with a repetition rate of 10 Hz. The energy that can be achieved is around 30 mJ. By using ultra-fast Pockels cells , an intensity contrast of more than 60 dB can be achieved. A Mach-Zehnder interferometer in the beam path, developed in -house , makes it possible to generate double pulses with adjustable spacing, energy and aspect ratio.
While small optics are used (on the order of a few centimeters ) for the pulse expansion required for this, a large petawatt compressor is required for the recompression. The laser pulse is compressed again to femtoseconds via two dielectrically coated (MLD - multilayer dielectric grating ) optical reflection gratings (with grating constants of typically 1600-1800 lines per mm). The size of the chamber (2 × 6 m²) is given by the spatial expansion via telescopes to a typical beam diameter of around 250 mm.
Nanosecond front end (long pulse)
With the system modified according to the LLNL model, it is possible to generate laser pulses with pulse lengths between 700 fs and 20 ns and freely selectable pulse shapes. A commercial cw laser is amplified, an acousto-optical modulator generates pulses of around 100 ns, which allow time and intensity-modulated pulses or pulse chains to be generated via an intensity modulator and a subsequent programmable waveform generator . The whole thing takes place in a fiber system. The approximately 10 nJ pulses are amplified in a flash lamp-pumped regenerative Nd: glass ring amplifier to energies of approximately 20 mJ with a repetition rate of half a Hertz.
Preamplifier (both pulses)
The preamplifier consists of rod lasers - two flash lamp pumped Nd: glass amplifiers 19 mm and a diameter 45 mm. Short or long pulses can be coupled in and expanded step by step in Kepler telescopes in order to keep the intensity below the damage threshold of the optical components . Image errors of the laser beam are corrected or pre-corrected with the help of adaptive optics , a deformable mirror that can correct wavefront distortions with the help of a Shack-Hartmann sensor . The preamplifier system amplifies the pulses up to the Joule energy range. Spatial filters serve as a further correction element for imaging errors.
The main amplifier
The main system of the laser, the so-called DPA ( Double Pass Amplifier ) or MA ( Main Amplifier ) amplifier system , generates the high-energy laser pulse when it is passed twice (folded in itself) . The amplifiers each contain two laser glass panes, which consist of platinum-free potassium - barium - aluminum - phosphate glass with around 2 percent by weight of Nd 3+ ions and are arranged at a non-reflective Brewster angle . The population inversion in the laser glass is generated by two flash tube panels attached to the side , which are operated with a maximum of 18 kV and 3.5 kA in approx. 1 ms pulse duration. The inside is mirrored to ensure maximum coupling of the energy into the laser glass and to avoid reflection losses. A downstream Faraday - isolator is necessary to prevent possible back reflections.
The frequency doubling module
In the frequency doubling module (also known as SHG ) from PHELIX, infrared laser pulses with a duration of 10 −9 to 10 −8 seconds can be converted into green laser pulses with a wavelength of 527 nm. A type II DKDP crystal ( deuterated potassium dihydrogen phosphate ), which has a diameter of 310 mm and a thickness of 25 mm, is used as the non-linear crystal . The model calculations for the optimal conversion efficiency were carried out in close cooperation with the manufacturing companies. The hygroscopic crystal is located in a box that is temperature-stabilized to 0.5 ° C and flushed with dry nitrogen, which is installed in a mobile clean room of clean room class ISO-5 (RR 100). The new module, which is so important for the generation and heating of plasmas , was put into operation in December 2010. The maximum measured conversion efficiency is 60% ( as of March 2011 ). The module is used for the laser beam in the direction of experiment station 2 .
technology
The laser system has its own building. This is supported vibration-free by a thick concrete floor as an optical table . From there, the laser beam is either reflected directly into the Laserbay ( experiment station 1 ) or via an 80 m long beam tube system to Z6 ( experiment station 2 ) to the actual destination, the experiment . Depending on the place of experimentation, the laser beam is focused on the target with the help of a parabolic mirror or a lens and thus achieves intensities of up to 10 21 W · cm −2 in the focus (diameter here typically ≈10–30 µm) . This can be used to generate plasma states as they occur in the sun , in gas giants or in neutron stars .
Depending on the energy and output, a laser shot can be fired every 20 minutes or only every two hours. The laser must be timed in all subsystems , with the GSI accelerator UNILAC and the diagnostics of the experiments via a trigger system. It has its own control system, a framework that is object-oriented , scalable, distributed, event-driven and freely available in accordance with the GNU Public License . The programming is done with LabVIEW .
The laser belongs to the class of high-energy petawatt lasers (HEPW), of which only a dozen exist or are under construction worldwide.
Application and research
The laser started working in 2006 with the first shot. In 2007 the first stage was reached with 0.5 kJ. Since 2008, experiments have been carried out for the first time at experiment station Z6 in combination with the ion beam from the UNILAC accelerator. These experiments include a. X-ray scattering experiments , laser-induced particle acceleration , investigations into warm dense matt states of matter or energy loss experiments on ions . The experiments benefit from the unique combination of coherent photons and ions (charged particles) of high energy and intensity. The PHELIX laser can be used as a heating beam for the plasma or as a diagnostic beam ( spectroscopy ). Pure laser experiments are also possible and are already taking place ( laser-induced X-ray laser ).
With the knowledge gained from this and the further expansion of PHELIX, in addition to pure basic research , studies can also be carried out that lay the foundations for inertial fusion, especially with heavy ions, which was investigated in a study group at GSI from 1995 onwards. PHELIX is a partner of the European infrastructure project Integrated European Laser Laboratories (Laserlab Europe) and thus also connected to the large European laser projects ELI and HiPER , which focus on basic research at the highest field strengths (ELI) and energy generation via laser-induced fusion (inertial fusion through rapid ignition - Target Inertial Confinement Fusion by Fast Ignition ) (HiPER). On emerging FAIR project of GSI is an upgrade to a new high-energy Petawattlaser in preparation.
In teaching and research , the physics departments of the universities of the TU Darmstadt , the University of Frankfurt am Main , the University of Mainz and the University of Applied Sciences Münster work closely together. The University of Jena is working together primarily on the establishment of the newly founded Helmholtz Institute Jena .
The 1000th laser shot was fired at the end of October 2009. There have been 16 research campaigns since May 2008, when experiments began .
In 2013, the researchers succeeded in coupling protons generated by the PHELIX laser, which are created by laser bombardment of a target and have a pulse length of only a few nanoseconds, into a conventional acceleration structure.
Research partner
- USA : National Ignition Facility at LLNL , Omega EP of the Laboratory for Laser Energetics at the University of Rochester , Z-pinch at Sandia Lab
- United Kingdom : The Central Laser Facility of the Rutherford Appleton Laboratory , especially the Vulcan laser
- France : Laser Mégajoule (LMJ) from CEA , LULI Laboratory at Ecole Polytechnique , PETAL (PETawatt Aquitaine Laser) as successor to LIL from CEA and as "Fore-runner" for HiPER
- Germany: Helmholtz Institute Jena , POLARIS Laser at Friedrich Schiller University Jena , Max Planck Institute for Quantum Optics in Munich
- International: EU FP7 framework program (Laserlab Europe), ELI, HiPER
swell
literature
- Stefan Borneis: High-energy petawatt laser - the generation of ultra-intensive pulses . In: Photonics . tape 37 , no. 3 , June 7, 2005, pp. 76-79 ( abstract ).
- FAIR Baseline Technical Report - 5.3 WDM - Warm Dense Matter ( Memento from November 11, 2012 in the Internet Archive ) (586 pages; PDF file; 24.93 MB)
- JD Zuegel, S. Borneis, C. Barty et al. : Laser Challenges for Fast Ignition . In: Fusion Science & Technology . tape 49 , no. 3 , April 2006, p. 453–482 , doi : 10.13182 / FST06-A1161 ( abstract (article chargeable) ).
Web links / references
- Official website. gsi.de
- High-power laser at GSI went into operation. In: press release. gsi.de, May 16, 2008.
- Details on experiments with PHELIX in the GSI Scientific Reports (from 2008, in English)
- Participation in the international HiPER Laser Project ( Memento from December 5, 2010 in the Internet Archive ) (PDF file; 242 kB)
- Fast Ignition Fusion ( Memento from November 12, 2011 in the Internet Archive )
- Lena Weitz: At the limit of destruction. In: Blog. helmholtz.de, October 29, 2014 .
- Video: High-intensity laser beams to fathom our universe. Deutsche Welle, August 8, 2013(English).
- Podcast: HR Online: Radio report from September 29, 2011 : Harald Lesch explains the big world machines : The laser in Darmstadt
Individual evidence
- ↑ As of 2009 or planning 2010, values are compendium of publications from 2009, cf. and. Individual references and website
- ↑ ( Page no longer available , search in web archives: GSI Kurier # 24-2002 (not archived) )
- ↑ a b replaced by ISO 14644-1 and ISO 14644-2 Notice of Cancellation of the GSA from November 29, 2001, reproduced on the IEST website ( Memento from April 6, 2008 in the Internet Archive ), accessed on June 23, 2008
- ↑ http://www.gsi.de/informationen/kurier/archiv/2004-40/ ( Memento from February 18, 2007 in the Internet Archive )
- ↑ LDT: laser density threshold (sometimes also LIDT - laser induced density threshold - in German slightly incorrectly referred to as the destruction threshold of the optical material ) is the quotient of peak power to beam cross-section, depending on the operating mode, pulse shape and duration at which the optical material is Laser or the optics are not destroyed. See also: Explanation of damage thresholds Explanation of damage threshold measurement ( Memento of November 11, 2012 in the Internet Archive ) (PDF; 98 kB)
- ↑ This is the quotient used in laser physics between the intensity of the main pulse and the background or the intensity of possible pre- or post-pulses
- ↑ Double passage means that the beam is reflected in itself and is passed a second time through the five flash lamp-pumped Nd: glass amplifier heads. This allows better utilization of the gain .
- ↑ SHG stands for second harmonic generation ; the English term is used equally in German in the specialist literature.
- ↑ JDZügel, S. Borneis, C. Barty et al, "Laser Challenges for Fast Ignition", Fusion Science & Technology, Vol. 49, April 2006, p. 455 Tab. 1 and p. 470f
- ↑ Scientific Report: PHELIX in 2007 ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ↑ PHELIX - TUD - Particle Acceleration - in the Darmstadt Echo
- ↑ Structure and mode of operation of the x-ray laser (in English) ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ↑ A 180 eV X-ray laser pumped by PHELIX ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ↑ The HIDIF study - 1995-1998
- ↑ Inertial fusion with heavy ion beams. Concept study (PDF file, 77 kB; possibly only accessible after accepting a security certificate)
- ↑ Press release on the establishment of the Helmholtz Institute Jena ( page can no longer be accessed , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ↑ GSI-Kurier 45/2009, article: "1000th laser shot at the PHELIX - Successful experiments for over a year" ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ↑ GSI Magazin target , Issue 10 ( Memento of the original from March 28, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. November 2013, p. 10
Coordinates: 49 ° 55 ′ 53.7 " N , 8 ° 40 ′ 51.1" E