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Magnetized Cylindrial Targets for Heavy Ion Fusion

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Cylindrical targets are promising as an alternative approach to heavy ion fusion (HIF)[1], as well as for basic science-oriented experiments in the near future [2]. In my PhD thesis (available as download), I have investigated basic properties of such targets. In difference to spherical heavy ion fusion targets, the cylindrical targets can be driven directly by a single ion beam, while axial magnetic fields (for heat insulation) can be applied to the targets prior to  implosions. In cylindrical targets,  the magnetic field geometry is consistent with the target; this is the main difference to other approaches to magnetized target fusion [3].

  

Figure: Schematic view of a magnetized cylindrical target. The target consists of a metallic tube filled with fuel plasma at low density. An axial magnetic field ( indicated by B) is applied externally before the implosion. The driving ion beam then heats the outer part of of the hollow cylinder; it expands radially and drives the inner part of the tube (pusher) towards the axis, as indicated by arrows. A typical size of the targets is approximately 1-3mm in radius and 10-30mm in length.

The most prominent features of magnetized cylindrical fusion targets are:

• ignition at reduced fuel \rhor, 
• relaxed demands on the driver pulse duration and power,  
• total energies comparable to standard ICF

Targets operate in the hot-spot ignition mode: a fuel reservoir is ignited from a small spark, high gain relies on the propagation of a burn wave along the cylinder axis. Due to the absence of shock heating during implosions, one has to start from high fuel temperatures (T\simeq100 eV) brought into the target from outside; this is essentially the scheme of injected  entropy as suggested by Caruso et al. [4]Heavy ion beams planned for the near future at GSI and  ITEP may allow implosion experiments at pulse energies below 100kJ. Magnetization effects would manifest in enhanced peak fuel temperatures and corresponding DD fusion neutron yields. To prevent rapid diffusive loss of the magnetic flux, one has to fulfill certain conditions on the initial fuel temperature and the product of implosion velocity and fuel radius. Detailed results can be found in MPQ Report 261. 

References:
[1] R.Ramis, J.Honrubia and J.Meyer-ter-Vehn, Hohlraum targets for HIDIF. In  C.Labaune, W.Hogan and K.Tanaka (Eds)
Inertial Fusion Sciences and Applications, p.88, Elsevier, Paris (1988)
[2] M.M. Basko, Magnetized implosions driven by intense ion beams, Physics of Plasmas 7, 4579 (2000)
[3] Kirkpatrick et al, Magnetized Target Fusion: An Overview, Fusion Technology 27, 201 (1995)
[4] A.Caruso and C.Strangio, The injected entropy approach for the ignition and high targets by heavy ion beams or incoherent x-ray pulses, in C.Labaune, WHogan and K.Tanaka (Eds) ibid.


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