This shows also that only a fraction of theenergy will be retained in any reasonably small experimental apparatus. We thus need to consider what is indeed measurable in the present experiments. Let us first assume that the entire laser pulse-energy Q entering the apparatus is used to initiate theprocess thus is not observed as thermal energy. If thegain is = 1 thus as muchenergy is produced as the incoming laser energy, the thermal energy observed will be only 0.34Q due to the loss of theTo reach a thermal energy of Q in this case means that a gain of around 3 is required. But such a result is not reliable since it may just correspond to the laser energy. To generate a thermal energy of 2Q, which cannot be mistaken for laser energy, a gain of around 6 is needed. If only 10% of the laser pulse-energy inducesa gain of around 30 is required to give 2Q. Thus, an observable heat release of 2Q by theprocess in the present experiments requires either (1) a gain of at least 6, more likely > > 10 in theprocess, or (2) aprocess with a smaller neutronicity than 0.66. Some experimental facts specific to the ultra-dense deuterium fuel made a test of the heat release in the laser-inducedprocess feasible and worth the effort. These were (1) the gain to kinetic energy of MeV particles was found to be >300 for short periods of time in the experiments,and (2) the flux offrom the process was observed to be small by several different measurement methods,thus the neutronicity appeared to be low. However,at very high energy >20 MeV would avoid detection. Thus a positive outcome of the experiments seemed likely. This analysis also shows that a heat generation of 2Q means aprocess safely above break-even for all possible neutronicities.

One hoped-for advantage of laser-inducedis that the reactor may be relatively small with little influence on the environment. In the most often considered form ofD+T, the neutronicity thus the energy fraction carried away by theis 0.80.This means that 80% of the energy released is difficult to contain and use since it leaves the reactor with theif the reactor is not large enough (several m) to retain theenergy. This means that small reactors are not possible, also from a radiation protection point of view. For this reason, aneutroniclike D +He are preferable, since only charged particles p +He are produced. The high neutronicity of D+T means that only a small fraction of the energy generated can be used for electric power generation in a smallreactor, maybe only 0.3 × 0.2 = 6%, assuming a thermal efficiency of 0.3 for converting heat to electricity which is normal for nuclear power plants. Theprocess D+D used here is better in principle, easily shown to have a neutronicity of 0.66 (values from Ref.) sinceHe is assumed not to react efficiently at the low reactorwhile T reacts on rapidly with D to form n +He. This is supported by TOF-MS laser-drivenexperiments in the same system, whereHe is observed but not T.This means that a maximum of 34% of the energy released may be retained in the apparatus in the present experiments. If alsoHe reacts with D at high enoughthe neutronicity of D+D is only 0.34, leaving 66% of the energy in charged particles.Of course, some radiation losses (for example bremsstrahlung in the reactor walls) may occur from the charged products, making it difficult to use (or even measure) all the energy in the chargedproducts.

The nuclear processes taking place in the D(0) material are probably not only ordinary D+DHowever, the typicalHe andHe particle emissions from the processes have been reportedtogether with asignal with aof 80-600 MK (7-60 keV). Thus, this point will not be discussed further here. The initiation of theprocesses in D(0) is not due to laser heating to highwhich has been shown to be inconvenient.Instead, the process is a laser-induced transfer to the spin state= 1 which has adistance of only 0.56 pm.From this distance,is spontaneous. This type of process is described more in detail in Ref.

Laser-inducedprocessesare expected to occur quite easily in ultra-dense deuterium D(0). The theoretical understanding of this material has recently been improved.Laser-inducedin D(0) using nanosecond and picosecond pulsed lasers has been reported.The reason for the quite facileprocesses is the high density of D(0), close to 10cmor 140 kg cm. This means an energy density of 10J monly from the bonding energy, and an energy density at least 10higher fromLipson et al.have reported experimental results on very high density hydrogen clusters in voids (Schottky defects) measured by SQUIDS in palladium crystals. The close relation between these hydrogen clusters and D(0) has been pointed out.Theoretical results for the laser intensity needed for break-evenand extrapolations from experimental results on D(0)indicate that approximately 1 J laser pulses are required for break-even. It was recently reportedthat break-even has been reached inin D(0) even with 0.2 J laser pulses. The proof ofin the processes published so far lies mainly in the generation of massive particles with energy >10 MeV uat the low laser intensity of <3 × 10W cm. Recently, also laser-generated penetrating particle emission has been observed by pulse height analysis.These results give definitive proof of nuclear processes. Here, the goal is extended to give proof also for heat generation around break-even, of direct interest for the application offor power generation. The results also show that laser-inducedis easier to use with other fuels than the normalice which appears to give compression instabilities even when using MJ laser pulses.Note that in the following H means all isotopes of hydrogen, with p, D and T used explicitly only when needed.

II. DESIGN Section: Choose Top of page ABSTRACT I.INTRODUCTION II.DESIGN << III.EXPERIMENTAL IV.RESULTS V.DISCUSSION VI.CONCLUSIONS REFERENCES CITING ARTICLES

chamber (with 100 mm tube diameter) and the need for gas transport in and around the laser target and the metal part, a cylindric form with 2 cm wall thickness was chosen. This thickness stops only a few percent of 1 MeV neutrons and much less of the 3 and 14 MeV neutrons generated by an ordinary D+D fusion process. It will stop deuterons, protons and alpha particles even with many MeV energy, for example protons with < 100 MeV. 21 21. NIST, Physics Laboratory, PSTAR program, http://physics.nist.gov/PhysRefData/Star/Text/PSTAR.html N (0) with energy > 10 MeV u−1 will pass through the metal container. 22 32, 537. doi:10.1017/S0263034614000494 (2014). 22. F. Olofson and L. Holmlid, Laser Part. Beams, 537. doi:10.1017/S0263034614000494 (2014). https://doi.org/10.1017/S0263034614000494 copper (Cu) was chosen as the cylinder material instead of lead which is a factor of 10 worse than copper with respect to heat conduction. The main heat accumulating device needs to be a thick metal part, to stop and retain as many particles of various types as possible. Tests with a thin metal shield were unsuccessful. Due to the relatively small size of the existing(with 100 mm tube diameter) and the need for gas transport in and around the laser target and the metal part, a cylindric form with 2 cm wall thickness was chosen. This thickness stops only a few percent of 1 MeVand much less of the 3 and 14 MeVgenerated by an ordinary D+Dprocess. It will stop deuterons, protons and alpha particles even with many MeV energy, for example protons with < 100 MeV.It will also stop electrons with energy < 10 MeV. However, it will not stop gamma rays with > 0.1 MeV energy. Also small neutral fragments of ultra-dense hydrogen H(0) with energy > 10 MeV uwill pass through the metal container.To have optimum heat conduction,was chosen as the cylinder material instead of lead which is a factor of 10 worse thanwith respect to heat conduction.

The temperature of the Cu cylinder is measured using a small NTC (negative temperature coefficient) sensor. It had been observed that the walls of the chamber also increased in temperature during the experiments, thus making the use of thermocouples with their cold junction (or at least a conductor material change) at the vacuum wall unsuitable. The NTC resistor with its 3 mm head diameter was attached in a small hole with depth of a few mm bored into the Cu cylinder, using heat-conductive silicon paste for heat transfer. This mounting hole was on the outer surface of the cylinder, turned away from the incoming laser beam and at 3/4 of the height of the cylinder. The response of the thermal measurement was very fast relative to the 8 min time for each measurement, and the slight temperature rise after the laser was turned off (due to heat from the source target) after a full 8 min run was included in the total temperature rise. To minimize the heat loss from the Cu cylinder, it was mounted on four silica glass tube legs. At the low pressure of 5 × 10−3 mbar maintained in the chamber with no gas inlet, the temperature of the cylinder decreased very slowly and a temperature higher than that of the chamber wall was observed even after 16 hours on the next day. Laser test runs with no gas admission gave fast temperature response and very small loss of thermal energy. Thus, no correction for heat loss through the gas in the chamber is used at low pressure and temperature close to the ambient. However, in most experiments a D 2 gas pressure of 0.1-1 mbar needs to be used to form D(0), giving large heat loss both to the gas which is pumped away and through the gas to other parts in the vacuum chamber. Corrections are measured during cooling in the experiments and applied to remove the influence of this cooling.

fusion process, simplifications in the previous construction 19,22 23, 1450050. DOI: 10.1142/S0218301314500505 (2014). 19. F. Olofson and L. Holmlid, Int. J. Modern Phys. E, 1450050. DOI: 10.1142/S0218301314500505 (2014). https://doi.org/10.1142/S0218301314500505 32, 537. doi:10.1017/S0263034614000494 (2014). 22. F. Olofson and L. Holmlid, Laser Part. Beams, 537. doi:10.1017/S0263034614000494 (2014). https://doi.org/10.1017/S0263034614000494 2 gas was leaked in through the tube, passing over catalyst pieces located inside the tube, and reaching the Ir metal piece which acted as a target at the laser focus in the center of the Cu cylinder. See Fig. 1 plasma formed was much smaller than in previous experiments. 7,19,22 7. F. Olofson, A. Ehn, J. Bood, and L. Holmlid, in 39th EPS Conference on Plasma Physics 2012 (EPS 2012) and the 16th International Congress on Plasma Physics, Europhysics Conference Abstracts , edited byS. Ratynskaya ( Curran Associates , 2013), Vol. 36F, pp. 472- 475 , ISBN: 9781622769810 . 23, 1450050. DOI: 10.1142/S0218301314500505 (2014). 19. F. Olofson and L. Holmlid, Int. J. Modern Phys. E, 1450050. DOI: 10.1142/S0218301314500505 (2014). https://doi.org/10.1142/S0218301314500505 32, 537. doi:10.1017/S0263034614000494 (2014). 22. F. Olofson and L. Holmlid, Laser Part. Beams, 537. doi:10.1017/S0263034614000494 (2014). https://doi.org/10.1017/S0263034614000494 plasma intensity with laser focus position on the Ir piece was relatively small, simplifying the needed temperature rise measurements lasting 8-10 minutes for each point. It is worth noting that this situation is far from the expected use for energy generation, where one-shot conditions may be assumed to be chosen. Here, the average over 4800 - 6000 laser shots during 8-10 minutes is observed, thus under very different conditions than in likely future energy producing applications. Due to the requirements of no internal heating and efficient energy collection from the laser inducedprocess, simplifications in the previous constructionwere needed. These simplifications implied degrading the performance, for the sake of correct energy measurements. The main change was the removal of the target structure, thus removing the possibility to store ultra-dense deuterium for subsequent laser probing at higher densities, as used previously. Instead, a simplified source (just a steel tube) was augmented with a small holder for a piece of Ir metal at its end. Dgas was leaked in through the tube, passing over catalyst pieces located inside the tube, and reaching the Ir metal piece which acted as a target at the laser focus in the center of thecylinder. See Fig.. This design means that the visibleformed was much smaller than in previous experiments.However, the variation inintensity with laser focus position on the Ir piece was relatively small, simplifying the neededrise measurements lasting 8-10 minutes for each point. It is worth noting that this situation is far from the expected use for energy generation, where one-shot conditions may be assumed to be chosen. Here, the average over 4800 - 6000 laser shots during 8-10 minutes is observed, thus under very different conditions than in likely future energy producing applications.