Hansheng Peng

Fusion energy from plasma block ignition

Generation of high speed dense plasma blocks is well known from hydrodynamic theory and computations (PIC) with experimental confirmation by Badziak et al. (2005) since ps laser pulses with power above TW are available. These blocks may be used for fusion flame generation (thermonuclear propagation) in uncompressed solid state deuterium and tritium for very high gain uncomplicated operation in power stations. Hydrodynamic theory from computations from the end of 1970s to recent, genuine two fluid computations support the skin layer accelerations (SLA), by nonlinear (ponderomotive) forces as measured now in details under the uniquely selected conditions to suppress relativistic self-focusing by high contrast ratio and to keep plane geometry interaction. It is shown how the now available PW-ps laser pulses may provide the very extreme conditions for generating the fusion flames in solid state density DT.

Status of the SG-III solid state laser project

High power solid state laser technologies for application to inertial confinement fusion have been developed over the past three decades in China. The XG-1 laser facility was built in 1984 and upgraded into XG-II in 1993. The SG-1 was completed in 1985 and the upgrade into SG-II will be finished in a few months. As the next step, the SG-III laser facility has been proposed to produce 60-kJ blue light for ICF target physics experiments and is one being conceptually designed. A preliminary baseline design suggest that he SG- III be a 64-beam facility with an output beam size of 25 cm X 25cm. The main amplifier column of 4 high by 2 wide has been chosen as a module. New laser technologies, including multipass amplification, large aperture plasma electrode switches, fast growth of KDP, laser glass with fewer platinum grains, Ce-doped quartz long flash lamps, capacitors with higher energy density, Ce-doped quartz long flash lamps, capacitors with higher energy density and precision manufacturing technique of large optical components have been developed to meet the requirements of the SG-III Project. In addition, numerical simulations are being conducted to optimize the optical design of the facility. The technical integration line with a 4 X 2 segmented aperture array of the amplifiers as a prototype beamline of the SG-III has been scheduled for the next few years.

SILEX-I: 300-TW Ti:sapphire laser

Based on chirped pulse amplification technology, we have built a Ti:sapphire laser system, called SILEX-I (superintense laser for experiments on extremes), at CAEP, which consists of three stages with 5-, 30-, and 300-TW outputs, respectively. The first and the second stages work at 10 Hz, while the third works at single shot. Pulse durations of 30 fs have been obtained by installing an acousto-optic programmable dispersive filter (AOPDF) to compensate for the spectral gain narrowing in the regen. By taking a number of advanced measures for spatial beam control, such as spatial beam shaping, relay-imaged propagation, precise alignment of compressor gratings, and OAP, near-diffraction limited focal spots (FWHM) have been obtained. Focused intensities are calculated at (1–3) × 1020 W/cm2 with an f/2.2 OAP.SILEX-I has shown an excellent stability and reliability in operations for applications since its completion and will soon be able to operate at 500 TW.

High-power solid-state lasers for high-energy-density physics applications at CAEP

High-power solid-state laser programs at China Academy of Engineering Physics have made great progresses in recent years. A three-stage Ti:sapphire laser system, SILEX-I, was completed early in 2004 which could deliver 26-fs pulses at 5TW, 30TW, and 300TW to the corresponding target chambers for diverse applications. SILEX-I has been working very stably since its completion for experiments, demonstrating that it is the most powerful femtosecond Ti:sapphire laser for exploring strong-field phenomena in the world. The SG-III Nd:glass laser facility has been under conceptual design to meet the requirements from laser fusion applications. The SG-III facility is planned to have sixty-four beamlines divided into eight bundles with an output energy more than 100kJ at 0.35μm for 3- to 5-ns pulses. The eight-beamline TIL (Technical Integration Line), the prototype of the SG-III laser facility, has been installed in the new laboratory in Mianyang. The commissioning experiments have been conducted and one of the eight beams has produced 1-ns pulses of 3.0kJ and 1.2kJ at 1.053μm and 0.35μm, respectively. All the eight beamlines will be activated by the end of 2005 and completed in 2006 for operation. Meanwhile, the eight-beam SG-II laser in Shanghai Institute of Optics and Fine Mechanics has been operated for the experiments since 2001 and an additional beam, built in 2004, has been used for plasma backlighting experiments.

286-TW Ti:sapphire laser at CAEP

We have built a three-stage Ti:sapphire laser system at CAEP which could deliver 5-TW, 30-TW and 286-TW pulses to the corresponding target chambers for diverse applications with innovative high-power Ti:sapphire crystal amplifiers. Pulse durations of 30fs have been obtained by installing an acousto-optic programmable dispersive filter (AOPDF) before the stretcher to compensate for the spectral gain narrowing. By taking a number of advanced measures for spatial beam control, near-diffraction limited focal spots (FWHM) have been obtained which, to our knowledge, are the best far fields ever measured for the existing high-power Ti:sapphire laser systems without deformable mirror correction. Focused laser intensity is about 1021W/cm2 measured with an f/1.7 OAP. The laser system has the potential to operate at 500TW and even higher and laser intensities of 1022W/cm2 are expected with deformable mirror for wavefront correction and small f-number fine OAP for tighter focus added to the system in the near future.

TW-ps laser driven blocks for light ion beam fusion in solid density DT

It is being clarified why the observations of plane wave geometry interaction within the skin depth of a laser irradiated target are very unique exceptions from the broad stream of the usual experiments of laser plasma interaction. This permits a much more simplified description by plane wave interaction theory for laser pulses of about ps or shorter duration and powers above TW and simplifies computations in contrast to the usual cases with relativistic self-focusing. After establishing theoretically and experimentally the generation of highly directed plasma blocks with ion current densities above 1010 A/cm2 moving against the laser light or into the target, applications for laser fusion, and a completely new improvement of ion sources for the next generation of accelerators are discussed.

New skin depth plasma interaction by ps-TW laser pulses and consequences for fusion energy

A new type of MeV ion generation at laser-plasma interaction has been measured based on the observation [1] that ps neodymium glass laser pulses of about TW and higher power do not produce the relativistic self-focusing based very high ion energies but more than 50 times lower energies. On top the strange observation was reported [fl that the number of the emitted fast ions did not change at variation of the laser focus intensity by a factor 30. This can be explained by the effect that without an inadiating prepulse, a pui plane gcmetnc skin layer interaction mechathsm occurs [2]. Neither relativistic self-focusing is possible nor the process of thermalization of quiver energy by quantum modified collisions. Following our conclusions about the difficulties for the fast ignitor concept of laser fi.ision [3], we can explain how these mechanisms can be used for studying the self-sustained fusion combustion waves [4] as known from the spark ignition at laser fusion. We further expect an improvement of the conditions for the experiments [5]with the highest laser fusion gains ever reported where even no pre-compression of the ftision plasma was necessary.

Preliminary design of Technical Integration Line (TIL) for the SG-III laser facility

In this paper, we present the preliminary design of Technical Integration Line (TIL). TIL is a full scale 4 X 2 module of Shenguang-III (SG-III). laser facility with a two-aperture output of 3.0kJ at 3 (omega) in a temporally shaped pulse of 1.0-3.0 ns. The goal of TIl is to demonstrate the laser technology of the proposed SG-III. TIL consists of front-end, pre-amplifier stage, main amplifier stage, diagnostic target systems and control system and the average fluency is designed to operate at 5.0J/cm2 in a 1.0 ns output pulse. The optical scheme of a four-pass main amplifier and a booster amplifier have been chosen. The clear aperture of amplifier is 30 X 30cm2, and the numbers of Nd:glass disks in the two amplifiers are optimized in system design. Two spatial filters are inserted in the system to remove high spatial frequencies from the beam, and SF1 is the multi-pass spatial filter and SF2 is the transport spatial filter. In order to correct the output wavefront for static and dynamic wavefront aberrations of disk amplifiers, a deformable mirror system is used in the main amplifier stage of TIL.

Introduction of SILEX-I Femto-second Ti:sapphire laser Facility

We have built a Ti:sapphire laser system, referred to as SILEX-I, with a peak power of 286TW for a pulse duration of 30fs using chirped-pulse amplification technique. A number of spectral and spatio-temporal beam control measures have been taken and near-diffraction limited focal spots have been obtained which, to our knowledge, are the best far fields ever measured for any existing high-power Ti:sapphire laser system without deformable mirror corrections.

Focal spot measurement in ultra-intense ultra-short pulse laser facility

A peak power of 286-TW Ti:sapphire laser facility referred to as SILEX-I was successfully built at China Academy of Engineering Physics, for a pulse duration of 30 fs in a three-stage Ti:sapphire amplifier chain based on chirped-pulse amplification. The beam have a wavefront distortion of 0.63μm PV and 0.09μm RMS, and the focal spot with an f/2.2 OAP is 5.7μm, to our knowledge, this is the best far field obtained for high-power ultra-short pulse laser systems with no deformable mirror wavefront correction. The peak focused intensity of ~1021W /cm2 were expected.