A.I. Ogoyski

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.

Code OK3 – An upgraded version of OK2 with beam wobbling function ☆

Abstract For computer simulations on heavy ion beam (HIB) irradiation onto a target with an arbitrary shape and structure in heavy ion fusion (HIF), the code OK2 was developed and presented in Computer Physics Communications 161 (2004). Code OK3 is an upgrade of OK2 including an important capability of wobbling beam illumination. The wobbling beam introduces a unique possibility for a smooth mechanism of inertial fusion target implosion, so that sufficient fusion energy is released to construct a fusion reactor in future. New version program summary Program title: OK3 Catalogue identifier: ADST_v3_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADST_v3_0.html Program obtainable from: CPC Program Library, Queens University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 221 517 No. of bytes in distributed program, including test data, etc.: 2 471 015 Distribution format: tar.gz Programming language: C++ Computer: PC (Pentium 4, 1 GHz or more recommended) Operating system: Windows or UNIX RAM: 2048 MBytes Classification: 19.7 Catalogue identifier of previous version: ADST_v2_0 Journal reference of previous version: Comput. Phys. Comm. 161 (2004) 143 Does the new version supersede the previous version?: Yes Nature of problem: In heavy ion fusion (HIF), ion cancer therapy, material processing, etc., a precise beam energy deposition is essentially important [1]. Codes OK1 and OK2 have been developed to simulate the heavy ion beam energy deposition in three-dimensional arbitrary shaped targets [2, 3]. Wobbling beam illumination is important to smooth the beam energy deposition nonuniformity in HIF, so that a uniform target implosion is realized and a sufficient fusion output energy is released. Solution method: OK3 code works on the base of OK1 and OK2 [2, 3]. The code simulates a multi-beam illumination on a target with arbitrary shape and structure, including beam wobbling function. Reasons for new version: The code OK3 is based on OK2 [3] and uses the same algorithm with some improvements, the most important one is the beam wobbling function. Summary of revisions: 1. In the code OK3, beams are subdivided on many bunches. The displacement of each bunch center from the initial beam direction is calculated. 2. Code OK3 allows the beamlet number to vary from bunch to bunch. That reduces the calculation error especially in case of very complicated mesh structure with big internal holes. 3. The target temperature rises during the time of energy deposition. 4. Some procedures are improved to perform faster. 5. The energy conservation is checked up on each step of calculation process and corrected if necessary. New procedures included in OK3 1. Procedure BeamCenterRot( ) rotates the beam axis around the impinging direction of each beam. 2. Procedure BeamletRot( ) rotates the beamlet axes that belong to each beam. 3. Procedure Rotation( ) sets the coordinates of rotated beams and beamlets in chamber and pellet systems. 4. Procedure BeamletOut( ) calculates the lost energy of ions that have not impinged on the target. 5. Procedure TargetT( ) sets the temperature of the target layer of energy deposition during the irradiation process. 6. Procedure ECL( ) checks up the energy conservation law at each step of the energy deposition process. 7. Procedure ECLt( ) performs the final check up of the energy conservation law at the end of deposition process. Modified procedures in OK3 1. Procedure InitBeam( ): This procedure initializes the beam radius and coefficients A1, A2, A3, A4 and A5 for Gauss distributed beams [2]. It is enlarged in OK3 and can set beams with radii from 1 to 20 mm. 2. Procedure kBunch( ) is modified to allow beamlet number variation from bunch to bunch during the deposition. 3. Procedure ijkSp( ) and procedure Hole( ) are modified to perform faster. 4. Procedure Espl( ) and procedure ChechE( ) are modified to increase the calculation accuracy. 5. Procedure SD( ) calculates the total relative root-mean-square (RMS) deviation and the total relative peak-to-valley (PTV) deviation in energy deposition non-uniformity. This procedure is not included in code OK2 because of its limited applications (for spherical targets only). It is taken from code OK1 and modified to perform with code OK3. Running time: The execution time depends on the pellet mesh number and the number of beams in the simulated illumination as well as on the beam characteristics (beam radius on the pellet surface, beam subdivision, projectile particle energy and so on). In almost all of the practical running tests performed, the typical running time for one beam deposition is about 30 s on a PC with a CPU of Pentium 4, 2.4 GHz. References: [1] A.I. Ogoyski, et al., Heavy ion beam irradiation non-uniformity in inertial fusion, Phys. Lett. A 315 (2003) 372–377. [2] A.I. Ogoyski, et al., Code OK1 – Simulation of multi-beam irradiation on a spherical target in heavy ion fusion, Comput. Phys. Comm. 157 (2004) 160–172. [3] A.I. Ogoyski, et al., Code OK2 – A simulation code of ion-beam illumination on an arbitrary shape and structure target, Comput. Phys. Comm. 161 (2004) 143–150.

Beam Final Transport and Direct-Drive Pellet Implosion in Heavy-Ion Fusion

Key issues of heavy-ion beam (HIB) inertial confinement fusion (ICF) include an efficient beam transport, beam focus, uniform fuel pellet implosion, etc. The HIB final transport and a direct-drive fuel pellet implosion by computer simulations in HIB ICF are examined. To realize a fine focus on a fuel pellet, space charge neutralization of incident-focusing HIBs may be required at HIB final transport. First, an insulator annular tube guide is proposed at the final portion of the transport, through which an HIB is transported. The physical mechanism of HIB charge neutralization based on an insulator guide is as follows: The local electric field created by HIB induces local discharges, and a plasma is produced on the insulator inner surface. Then electrons are extracted from the plasma by HIB net space charge. The emitted electrons neutralize the beam space charge and move together with the HIB. After the final transport, the HIBs enter a reactor gas and illuminate a fuel pellet. Direct-drive DT pellet implosion were also simulated. The simulation results present a density valley formation by a Pb HIB deposition in a fuel pellet energy absorber layer and a radiation-smoothing effect along the density valley. The density valley provides radiation confinement, and beam nonuniformity can be smoothed along the valley.

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.

Illumination non-uniformity of spirally wobbling beam in heavy ion fusion

In inertial confinement fusion, the driver beam illumination non-uniformity leads a degradation of fusion energy output. The illumination non-uniformity allowed is less than a few percent in inertial fusion target implosion. Heavy ion beam (HIB) 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. In this paper the HIBs wobbling illumination scheme was optimized.

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.

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.

Implosion uniformity improvement of fuel target in heavy ion fusion

A dynamic mitigation mechanism for instability growth was proposed and discussed in the paper [Phys. Plasmas 19, 024503 (2012)]. In the present paper the robustness of the dynamic instability mitigation mechanism is discussed further. The results presented here show that the mechanism of the dynamic instability mitigation is rather robust against changes in the phase, the amplitude and the wavelength of the wobbling perturbation applied.

Spirally Wobbling Beam Illumination Nonuniformity in Heavy Ion Inertial Fusion

In inertial confinement fusion, the driver beam illumination nonuniformity leads to a degradation of fusion energy output. 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 nonuniformity. A fuel target alignment error may happen in a fusion reactor; the target alignment error induces heavy ion beam illumination nonuniformity on a target. Therefore, first we study the effect of driver irradiation nonuniformity induced by the target alignment error on the target implosion. Then we optimize the wobbling beam illumination; spiral wobbling heavy ion beams provide a lower illumination nonuniformity. In addition, by optimizing the beam irradiation scheme, the illumination nonuniformity is reduced further.

Rayleigh-Taylor instability growth control by an oscillating acceleration in heavy ion inertial fusion

Uniformity of heavy ion beam (HIB) illumination is one of key issues in HIB inertial confinement fusion (HIF) in order to compress a fuel sufficiently and release fusion energy effectively. In this paper a new mitigation method of the Rayleigh-Taylor (R-T) instability growth is presented to make a HIF target robust against a non-uniform implosion. In this study a new mitigation method of the R-T instability growth is proposed based on an oscillating perturbed acceleration, which can be realized by a rotation or oscillation of the HIB illumination axis onto a fuel pellet. The R-T instability analyses and fluid simulations demonstrate that the oscillating acceleration reduces the R-T instability growth significantly. In this paper a baseline steady acceleration g0 is perturbed by a perturbed oscillating acceleration ?g, which is spatially non-uniform and oscillates in time (g0 >> ?g). An example result shows an 84% reduction of the R-T instability growth. In the analytical work two stratified inviscid fluids are treated under the perturbed oscillating acceleration. The linear analysis shows that the R-T instability growth rate does not change from the standard expression of ?. However, the R-T instability growth is strongly affected and mitigated by the oscillating acceleration; The transverse velocity of w is derived at the interface of the two stratified fluids. The R-T instability is induced by ?g. The result presents that the perturbed oscillating acceleration reduces the R-T instability growth significantly depending on the magnitude of the HIB oscillation frequency.