实验室能实现巨磁级磁场？

诸平

Figure 1. Illustration of a microtube implosion. Due to the laser-produced hot electrons with megaelectron volt energies, cold ions in the inner wall surface implode toward the central axis. By pre-seeding uniform magnetic fields of the kilotesla order, the Lorentz force induces a Larmor gyromotion of the imploding ions and electrons. Due to the resultant collective motion of relativistic charged particles around the central axis, strong spin currents of approximately peta-ampere/cm2 are produced with a few tens of nm size, generating megatesla-order magnetic fields. Credit: Masakatsu Murakami

Figure 2. Perspective views of the normalized ion density ni/ni0 and the z-component of the magnetic field Bz, respectively, observed at t～200 fs, which is obtained by a 3D EPOCH simulation. A cubic aluminum target with a size of 14 μm × 14 μm × 14 μm is set at the center, which has a cylindrical cavity with a radius of R₀ = 5 μm and an axis overlapping the z-axis. The seed magnetic field B₀ = 6 kT parallel to the z-axis is uniformly set over the entire domain. The four faces of the target parallel to the z-axis are normally irradiated by uniform laser pulses simultaneously, which are characterized by λ_L = 0.8 μm, I_L =3×10²¹ Wcm⁻² and τ_L =50 fs. Credit: Masakatsu Murakami et al., High Power Laser Science and Engineering 

据日本大阪大学（Osaka University）2021年12月9日提供的消息，最近，大阪大学的一个研究小组通过激光与物质相互作用的三维粒子模拟，成功地证明了巨磁级磁场的产生（Toward achieving megatesla magnetic fields in the laboratory）。相关研究结果于2021年10月14日已经在《高能激光科学与工程》（High Power Laser Science and Engineering）杂志网站发表——D. Shokov, M. Murakami, J. J. Honrubia. Laser scaling for generation of megatesla magnetic fields by microtube implosions, High Power Laser Science and Engineering, 2021, Volume 9 , e56. DOI: 10.1017/hpl.2021.46. Published online by Cambridge University Press:  14 October 2021. http://dx.doi.org/10.1017/hpl.2021.46 

兆特斯拉（megatesla简称MT）磁场的强度是地磁(0.3 ~ 0.5 G)的（10-100）亿倍（1–10 billion times），只能在中子星或黑洞等天体附近观测到。这一结果将有助于在实验室中实现MT级磁场的雄心勃勃的实验，该实验目前正在进行中。

自19世纪以来，科学家们一直努力在实验室中实现最高磁场。到目前为止，在实验室中观测到的最高磁场是千特斯拉(kT)级。2020年，大阪大学的村上正松(Masakatsu Murakami)提出了一个名为微管内爆(microtube implosions简称MTI)的新方案，以产生MT级的超高磁场。用超强超短激光脉冲（ultrashort laser pulses）照射微米大小的空心圆柱体，产生速度接近光速的热电子（hot electrons）。这些热电子向中轴发射了一个圆柱形对称的内壁离子内爆。应用一个平行于中轴的kT级的预先播种磁场(pre-seeded magnetic field)，由于洛伦兹力(Lorentz force)，使离子和电子的轨迹向相反的方向弯曲。在目标轴附近，那些弯曲的离子和电子轨迹共同形成了一个强大的自旋电流，产生了MT级磁场。

在这项研究中，团队成员（team members）之一迪达尔·肖科夫(Didar Shokov)在大阪大学网络媒体中心（Osaka University's Cybermedia Center）使用超级计算机OCTOPUS广泛地进行了三维模拟。结果发现，MTI产生磁场的性能与外部参数(如激光强度、激光能量和靶尺寸)之间存在明显的比例法则（scaling law）。

村上正松说：“我们的模拟显示，超高的巨火山磁场，过去被认为是不可能在地球上实现的，但是可以使用当今的激光技术来实现。目标磁场的标度规律和详细的时间行为有望促进大阪大学激光工程研究所（Osaka University's Institute of Laser Engineering）的千万亿瓦特（Peta-watt）激光系统“LFEX”的实验室实验，该实验目前正在进行中。”

上述介绍，仅供参考。欲了解更多信息，敬请注意浏览原文或者相关报道。

Could megatesla magnetic fields be realized on Earth?

Abstract

Microtube implosions are a novel scheme to generate ultrahigh magnetic fields of the megatesla order. These implosions are driven by ultraintense and ultrashort laser pulses. Using two- and three-dimensional particle simulations where megatesla-order magnetic fields can be achieved, we demonstrate scaling and criteria in terms of laser parameters, such as laser intensity and laser energy, to facilitate practical experiments toward the realization of extreme physical conditions, which have yet to be realized in laboratories. Microtube implosions should provide a new platform for studies in fundamental and applied physics relevant to ultrahigh magnetic fields.