Laser-plasma accelerators of only a centimetre’s length have produced nearly monoenergetic electron bunches with energy as high as 1 GeV. Scaling these compact accelerators to multi-gigaelectronvolt energy would open the prospect of building X-ray free-electron lasers and linear colliders hundreds of times smaller than conventional facilities, but the 1 GeV barrier has so far proven insurmountable. Here, by applying new petawatt laser technology, we produce electron bunches with a spectrum prominently peaked at 2 GeV with only a few per cent energy spread and unprecedented sub-milliradian divergence. Petawatt pulses inject ambient plasma electrons into the laser-driven accelerator at much lower density than was previously possible, thereby overcoming the principal physical barriers to multi-gigaelectronvolt acceleration: dephasing between laser-driven wake and accelerating electrons and laser pulse erosion. Simulations indicate that with improvements in the laser-pulse focus quality, acceleration to nearly 10 GeV should be possible with the available pulse energy.

The kinetic energy of hot (multi-keV) ions from the laser-driven Coulomb explosion of deuterium clusters and the resulting fusion yield in plasmas formed from these exploding clusters has been investigated under a variety of conditions using the Texas Petawatt laser. An optimum laser intensity was found for producing neutrons in these cluster fusion plasmas with corresponding average ion energies of 14 keV. The substantial volume (1-10 mm 3 ) of the laser-cluster interaction produced by the petawatt peak power laser pulse led to a fusion yield of 1.6 ×10 7 neutrons in a single shot with a 120 J, 170 fs laser pulse. Nuclear fusion from laser-heated deuterium clusters has been studied since 1999 [1]. Deuterium clusters are nanometerscale assemblies of atoms bound at liquid density by van der Waals forces, which can be produced by forcing cold deuterium gas under high pressure through a supersonic nozzle into vacuum. In these experiments, the deuterium clusters are irradiated by an intense ultrashort laser pulse. The clusters absorb the pulse energy very efficiently [2] and the process by which the ions attain their high kinetic energies has been well explained by the Coulomb explosion model [3,4]. In this model, the electrons in the atomic cluster first absorb the laser pulse energy as the atoms are ionized. The electrons further gain energy through other absorption mechanisms such as above-threshold ionization [5], inverse bremsstrahlung heating [6], resonant heating [6][7][8], and escape from the space-charge forces of the cluster, on the time scale of tens of fs. At high enough laser intensity, almost all of the electrons are removed from the cluster on a time scale short relative to the ion motion. What remains is a highly charged cluster of ions at liquid density, which promptly explodes by Coulomb repulsion.In experiments with peak laser intensities of 10 16 -10 18 W/cm 2 , deuterium ions with average kinetic energies up to about 10 keV have been observed, which were energetic enough to drive DD fusion events in a plasma with an average ion density near 10 19 cm −3 [9][10][11][12]. DD fusion can also occur when energetic ions collide with cold atoms in the background gas jet [13]. As a result of both of these fusion reactions, quasimonoenergetic 2.45 MeV neutrons are produced from the localized fusion plasma in a subnanosecond burst until the plasma disassembles in about 100 ps.Neutron yields greater than 10 8 n/shot would yield neutron fluences near the cluster jet greater than 10 10 n/cm 2 enabling subnanosecond time-resolved pump-probe experiments of neutron damage studies [14]. The petawatt lasers currently operating and being built with pulse durations below 200 fs have the potential to drive such sources. Therefore, the laser-cluster-generated fusion plasma is attractive as a bright, * Author to whom correspondence should be addressed: dws223@physics.utexas.edu short, and localized neutron source that is potentially useful for material damage studies.In this paper, we describe the scaling of cluster pl...

Two different methods have been employed to determine the plasma temperature in a laser-cluster fusion experiment on the Texas Petawatt laser. In the first, the temperature was derived from time-of-flight data of deuterium ions ejected from exploding D(2) or CD(4) clusters. In the second, the temperature was measured from the ratio of the rates of two different nuclear fusion reactions occurring in the plasma at the same time: D(d,(3)He)n and (3)He(d,p)(4)He. The temperatures determined by these two methods agree well, which indicates that (i) the ion energy distribution is not significantly distorted when ions travel in the disassembling plasma; (ii) the kinetic energy of deuterium ions, especially the "hottest part" responsible for nuclear fusion, is well described by a near-Maxwellian distribution.

The plasma astrophysical S factor for the 3He(d,p)4He fusion reaction was measured for the first time at temperatures of few keV, using the interaction of intense ultrafast laser pulses with molecular deuterium clusters mixed with 3He atoms. Different proportions of D2 and 3He or CD4 and 3He were mixed in the gas target in order to allow the measurement of the cross section for the 3He(d,p)4He reaction. The yield of 14.7 MeV protons from the 3He(d,p)4He reaction was measured in order to extract the astrophysical S factor at low energies. Our result is in agreement with other S factor parametrizations found in the literature.

In the last decade, the availability in high-intensity laser beams capable of producing plasmas with ion energies large enough to induce nuclear reactions has opened new research paths in nuclear physics. We studied the reactions 3He(d, p)4He and d(d,n)3He at temperatures of few keV in a plasma, generated by the interaction of intense ultrafast laser pulses with molecular deuterium or deuterated-methane clusters mixed with 3He atoms. The yield of 14.7 MeV protons from the 3He(d, p)4He reaction was used to extract the astrophysical S factor. Results of the experiment performed at the Center for High Energy Density Science at The University of Texas at Austin will be presented