Heavy Ion Beam Illumination Non-uniformity Research Articles

Uniformity improvement of fuel target implosion by phase control in heavy ion inertial fusion

A dynamic smoothing method was proposed based on a phase control to stabilize plasma instabilities and smooth plasma non-uniformities. In this paper, the dynamic smoothing method is applied to a spherical fuel target implosion in heavy ion inertial fusion (HIF). We found that the wobbling motion of each heavy ion beam (HIB) axis induces a phase-controlled HIBs energy deposition, and consequently the phase-controlled implosion acceleration is realized, so that the HIBs illumination non-uniformity is successfully smoothed. HIB accelerators provide a well-established capability to oscillate the HIBs axes with a high frequency. In inertial confinement fusion, a fuel implosion uniformity is essentially important to compress the DT fuel and release the fusion energy, and the non-uniformity of the implosion acceleration should be less than a few %. The results in this paper also demonstrate that the wobbling HIBs would provide an improvement in the fusion energy output gain.

Uniform fuel target implosion in heavy ion inertial fusion

For a steady operation of a fusion power plant the target implosion should be robust against the implosion non-uniformities. In this paper the non-uniformity mitigation mechanisms in the heavy ion beam (HIB) illumination are discussed in heavy ion inertial fusion (HIF). A density valley appears in the energy absorber, and the large-scale density valley also works as a radiation energy confinement layer, which contributes to the radiation energy smoothing for the HIB illumination non-uniformity. The large density-gradient scale, which is typically ∼500μm in HIF targets, also contributes to a reduction of the Rayleigh- Taylor instability growth rate. In HIF a wobbling HIBs illumination would also reduce the Rayleigh-Taylor instability growth and to realize a uniform implosion.

Direct-driven target implosion in heavy ion fusion

In inertial confinement fusion, the driver beam illumination non-uniformity leads a degradation of fusion energy output. A fuel target alignment error would happen in a fusion reactor; the target alignment error induces heavy ion beam illumination non-uniformity on a target. On the other hand, heavy ion beam accelerator provides a capability to oscillate a beam axis with a high frequency. The wobbling beams may provide a new method to reduce or smooth the beam illumination non-uniformity. First we study the effect of driver irradiation non-uniformity induced by the target alignment error (dz) on the target implosion. We found that dz should be less than about 130 μm for a sufficient fusion energy output. We also optimize the wobbling scheme. The spiral wobbling heavy ion beams would provide a promissing scheme to the uniform beam illumination.

Nonuniformity mitigation of beam illumination in heavy ion inertial fusion

In inertial fusion, a target DT fuel should be compressed to typically 1000 times the solid density. The target implosion nonuniformity is introduced by a driver beam’s illumination nonuniformity, for example. The target implosion should be robust against the implosion nonuniformities. In this paper, the requirement for implosion uniformity is first discussed. The implosion non-uniformity should be less than a few percent. The implosion dynamics is also briefly reviewed in heavy ion inertial fusion (HIF). Heavy ions deposit their energy inside the target energy absorber, and the energy deposition layer is rather thick, depending on the ion particle energy. Then nonuniformity mitigation mechanisms of the heavy ion beam (HIB) illumination in HIF are discussed. A density valley appears in the energy absorber, and the large-scale density valley also works as a radiation energy confinement layer, which contributes to a radiation energy smoothing. In HIF, wobbling heavy ion beam illumination was also introduced to realize a uniform implosion. The wobbling HIB axis oscillation is precisely controlled. In the wobbling HIBs’ illumination, the illumination nonuniformity oscillates in time and space on an HIF target. The oscillating-HIB energy deposition may contribute to the reduction of the HIBs’ illumination nonuniformity by its smoothing effect on the HIB illumination nonuniformity and also by a growth mitigation effect on the Rayleigh–Taylor instability.

Wobblers and Rayleigh–Taylor instability mitigation in HIF target implosion

A few percent wobbling-beam illumination nonuniformity is realized in heavy ion inertial confinement fusion (HIF) by a spiraling beam axis motion in the paper. The wobbling heavy ion beam (HIB) illumination was proposed to realize a uniform implosion in HIF. However, the initial imprint of the wobbling HIBs was a serious problem and introduces a large unacceptable energy deposition nonuniformity. In wobbling the HIBs illumination, the illumination nonuniformity oscillates in time and space. The oscillating-HIB energy deposition may contribute to the reduction of the HIBs' illumination nonuniformity and also the mitigation of the Rayleigh–Taylor instability. The wobbling HIBs can be generated in HIB accelerators and the oscillating frequency may be from several 100MHz to 1GHz. Three-dimensional HIBs illumination computations presented here show that the few percent wobbling HIBs illumination nonuniformity oscillates successfully with the same wobbling HIBs frequency.

Wobbling Heavy Ion Beam Illumination in Heavy Ion Inertial Fusion

A few % wobbling-beam illumination nonuniformity is realized in heavy ion inertial confinement fusion (HIF) by a spiraling beam axis motion. So far the wobbling heavy ion beam (HIB) illumination was proposed to realize a uniform implosion in HIF. However, the initial imprint of the wobbling HIBs introduces a large unacceptable energy deposition nonuniformity. In the wobbling HIBs illumination, the illumination nonuniformity oscillates in time and space. The oscillating-HIB energy deposition may contribute to the reduction of the HIBs’ illumination nonuniformity. The wobbling HIBs can be generated in HIB accelerators and the oscillating frequency may be several 100MHz ∼1GHz. Three-dimensional HIBs illumination computations presented here show that the few % wobbling HIBs illumination nonuniformity oscillates successfully with the same wobbling HIBs frequency.

Spiral wobbling beam illumination uniformity in HIF fuel target implosion

A few % wobbling-beam illumination nonuniformity is realized in heavy ion inertial confinement fusion (HIF) throughout the heavy ion beam (HIB) driver pulse by a newly introduced spiraling beam axis motion in the first two rotations. The wobbling HIB illumination was proposed to realize a uniform implosion in HIF. However, the initial imprint of the wobbling HIBs was a serious problem and introduces a large unacceptable energy deposition nonuniformity. In the wobbling HIBs illumination, the illumination nonuniformity oscillates in time and space. The oscillating-HIB energy deposition may produce a time-dependent implosion acceleration, which reduces the Rayleigh-Taylor (R-T) growth [Laser Part. Beams 11, 757 (1993), Nuclear Inst. Methods in Phys. Res. A 606, 152 (2009), Phys. Plasmas 19, 024503 (2012)] and the implosion nonuniformity. The wobbling HIBs can be generated in HIB accelerators and the oscillating frequency may be several 100 MHz ∼ 1 GHz [Phys. Rev. Lett. 104, 254801 (2010)]. Three-dimensional HIBs illumination computations present that the few % wobbling HIBs illumination nonuniformity oscillates with the same wobbling HIBs frequency.

Study on target structure for direct–indirect hybrid implosion mode in heavy ion inertial fusion

The key issues in heavy ion beam (HIB) inertial confinement fusion (ICF) include particle accelerator, physics of intense beam, beam final transport, target-plasma hydrodynamics, etc. In this paper, we focus on fuel implosion. In order to realize an effective implosion, beam illumination non-uniformity on a fuel target must be suppressed less than a few percent. In this study a direct–indirect hybrid implosion mode is discussed in heavy ion beam inertial confinement fusion (HIF) in order to release sufficient fusion energy in a robust manner. In the direct–indirect hybrid mode target, a low-density foam layer is inserted, and the radiation energy is confined in the foam layer. In the foam layer, the radiation transport is expected to smoothen the HIB illumination non-uniformity in the lateral direction. In this paper, we study the influences of the foam thickness and the inner radiation-shield Al density on implosion uniformity. Two-dimensional fluid simulations demonstrate that the hybrid target contributes to the HIB non-uniformity smoothing and releases a sufficient fusion energy output in HIF.

Direct-indirect hybrid mode implosion in heavy ion inertial fusion

A direct-indirect hybrid implosion mode is proposed and discussed in heavy ion beam (HIB) inertial confinement fusion (HIF) in order to release sufficient fusion energy in a robust manner. On the other hand, the HIB illumination non-uniformity depends strongly on a target displacement dz from the centre of a fusion reactor chamber. In a direct-driven implosion mode, dz of ~ 20 μm was tolerable, and in an indirect-implosion mode, dz of ~ 100 μm was allowable. In the direct-indirect mixture mode target, a low-density foam layer is inserted, and the radiation energy is confined in the foam layer. In the foam layer the radiation transport is expected to smooth the HIB illumination non-uniformity in the lateral direction. Two-dimensional implosion simulations are performed, and show that the HIB illumination non-uniformity is well smoothed in the direct-indirect hybrid-mode target. Our simulation results present that a large pellet displacement of ~ a few hundred μm is allowed in order to obtain a sufficient fusion energy output in HIF.

Direct–indirect mixed implosion mode in heavy ion inertial fusion

In order to realize an effective implosion, beam illumination non-uniformity on a fuel target must be suppressed less than a few percent. In this study, a direct–indirect mixture implosion mode is proposed and discussed in heavy ion beam (HIB) inertial confinement fusion (HIF) in order to release sufficient fusion energy in a robust manner. On the other hand, the HIB illumination non-uniformity depends strongly on a target displacement dz from the center of a fusion reactor chamber. In a direct-driven implosion mode, dz of ∼20 μm was tolerable, and in an indirect-implosion mode, dz of ∼100 μm was allowable. In the direct–indirect mixture mode target, a low-density foam layer is inserted, and the radiation energy is confined in the foam layer. In the foam layer, the radiation transport is expected to smooth the HIB illumination non-uniformity in the lateral direction. Two-dimensional implosion simulations are performed, and show that the HIB illumination non-uniformity is well smoothed in the direct–indirect mixture target. Our simulation results present that a large pellet displacement of approximately a few hundred microns is allowed in order to obtain a sufficient fusion energy output in HIF.

Robust heavy-ion-beam illumination in direct-driven heavy-ion inertial fusion

In heavy ion beam (HIB) inertial confinement fusion (HIF), implosion asymmetry should be less than a few percent in order to compress a fuel sufficiently and release fusion energy effectively. It is known that the HIB illumination nonuniformity and implosion symmetry are sensitive to a little pellet displacement from a reactor chamber center. We present a new HIB illumination scheme which is robust against the displacement of a direct-driven fuel pellet in an HIF reactor chamber. In conventional HIB illumination schemes a pellet displacement of 25–100 μm was tolerable. The new robust HIB illumination scheme is examined by three-dimensional computer simulations. In the new HIB illumination scheme the tolerable pellet displacement is about 200–300 μm.

Direct-indirect mixture implosion in heavy ion fusion

In order to realize an effective implosion, the beam illumination non-uniformity and implosion non-uniformity must be suppressed to less than a few percent. In this paper, a direct-indirect mixture implosion mode is proposed and discussed in heavy ion beam (HIB) inertial confinement fusion (HIF) in order to release sufficient fusion energy in a robust manner. On the other hand, the HIB illumination non-uniformity depends strongly on a target displacement (dz) in a reactor. In a direct-driven implosion mode dz of ∼20 μm was tolerance and in an indirect-implosion mode dz of ∼100 μm was allowable. In the direct-indirect mixture mode target, a low-density foam layer is inserted, and radiation is confined in the foam layer. In the foam layer the radiation transport is expected in the lateral direction for the HIB illumination non-uniformity smoothing. Two-dimensional implosion simulations are performed and show that the HIB illumination non-uniformity is well smoothed. The simulation results present that a large pellet displacement of ∼300 μm is tolerable in order to obtain sufficient fusion energy in HIF.

Robust heavy-ion-beam illumination against a direct-drive-pellet displacement in inertial confinement fusion

Nonuniformity of heavy-ion-beam (HIB) illumination is one of key issues in the HIB inertial confinement fusion (ICF): implosion symmetry should be less than a few percent in order to compress a fuel sufficiently and release fusion energy effectively. In this paper a new HIB illumination scheme is presented in order to realize a robust illumination scheme against a displacement of a direct-driven fuel pellet in an ICF reactor. It is known that the HIB illumination nonuniformity is sensitive to a little pellet displacement from a reactor chamber center; a pellet displacement of only 50–100μm was tolerable in the conventional HIB illumination schemes. In this paper by three-dimensional computer simulations a new robust HIB illumination scheme was found, in which a 200–300μm displacement is allowed.

Heavy-ion beam illumination on a direct-driven pellet in heavy-ion inertial fusion

Key issues in heavy-ion beam (HIB) inertial confinement fusion (ICF) include an accelerator design for an intense HIB, an efficient HIB transport, a HIB-target interaction, a reactor design, and so on. In this paper, three-dimensional computer simulations are performed for a HIB irradiation onto a direct-driven spherical fuel pellet in HIB-ICF in order to clarify dependence of multi-HIB illumination nonuniformity on parameter values of HIB illumination. For various beam parameters and reactor chamber radii we investigate the energy deposition nonuniformity using 12, 20, 32, 60, 92, and 120-beam irradiation systems. In this study, the effects of HIB temperature, HIB illumination systems, HIB emittance, and pellet temperature on the HIB illumination nonuniformity are also evaluated. In addition, the nonuniformity growth due to a little pellet displacement from a reactor chamber center is investigated. The calculation results demonstrate that we can realize a rather low nonuniform energy deposition, for example, less than 2.0 % even for a 32-beam irradiation system.

K5 Laser driven implosion of microspheres

In this review paper on heavy ion inertial fusion (HIF), the state-of-the-art scientific results are presented and discussed on the HIF physics, including physics of the heavy ion beam (HIB) transport in a fusion reactor, the HIBs-ion illumination on a direct-drive fuel target, the fuel target physics, the uniformity of the HIF target implosion, the smoothing mechanisms of the target implosion non-uniformity and the robust target implosion. The HIB has remarkable preferable features to release the fusion energy in inertial fusion: in particle accelerators HIBs are generated with a high driver efficiency of ∼30%–40%, and the HIB ions deposit their energy inside of materials. Therefore, a requirement for the fusion target energy gain is relatively low, that would be ∼50–70 to operate a HIF fusion reactor with the standard energy output of 1 GW of electricity. The HIF reactor operation frequency would be ∼10–15 Hz or so. Several-MJ HIBs illuminate a fusion fuel target, and the fuel target is imploded to about a thousand times of the solid density. Then the DT fuel is ignited and burned. The HIB ion deposition range is defined by the HIB ions stopping length, which would be ∼1 mm or so depending on the material. Therefore, a relatively large density-scale length appears in the fuel target material. One of the critical issues in inertial fusion would be a spherically uniform target compression, which would be degraded by a non-uniform implosion. The implosion non-uniformity would be introduced by the Rayleigh-Taylor (R-T) instability, and the large density-gradient-scale length helps to reduce the R-T growth rate. On the other hand, the large scale length of the HIB ions stopping range suggests that the temperature at the energy deposition layer in a HIF target does not reach a very-high temperature: normally about 300 eV or so is realized in the energy absorption region, and that a direct-drive target would be appropriate in HIF. In addition, the HIB accelerators are operated repetitively and stably. The precise control of the HIB axis manipulation is also realized in the HIF accelerator, and the HIB wobbling motion may give another tool to smooth the HIB illumination non-uniformity. The key issues in HIF physics are also discussed and presented in the paper.