Self-pinched beam transport experiments Relevant to Heavy Ion Driven inertial fusion energy

An attractive feature of the inertial fusion energy (IFE) approach to commercial energy production is that the fusion driver is well separated from the fusion confinement chamber. This ''standoff'' feature means the driver is largely isolated from fusion reaction products. Further, inertial confinement fusion (ICF) target ignition (with modest gain) is now scheduled to be demonstrated at the National Ignition Facility (NIF) using a laser driver system. The NIF program will, to a considerable extent, validate indirectly-driven heavy-ion fusion (HIF) target designs for IFE. However, it remains that HIF standoff between the final focus system and the fusion target needs to be seriously addressed. In fact, there now exists a timely opportunity for the Office of Fusion Energy Science (OFES) to experimentally explore the feasibility of one of the attractive final transport options in the fusion chamber: the self-pinched transport mode. Presently, there are several mainline approaches for HIF beam transport and neutralization in the fusion chamber. These range from the (conservative) vacuum ballistic focus, for which there is much experience from high energy research accelerators, to highly neutralized ballistic focus, which matches well to lower voltage acceleration with resulting lower driver costs. Alternatively, Z-discharge channel transport and self-pinched transport in gas-filled chambers may relax requirements on beam quality and final focusing systems, leading to even lower driver cost. In any case, these alternative methods of transport, especially self-pinched transport, are unusually attractive from the standpoint of chamber design and neutronics. There is no requirement for low chamber pressure. Moreover, only a minuscule fraction of the fusion neutrons can escape from the chamber. Therefore, it is relatively easy to shield sensitive components, e-g., superconducting magnets from any significant neutron flux. Indeed, self-pinched transport and liquid wall protection endow DT fusion with many of the advantages of aneutronic fusion. The question is: will self-pinched transport work? Early theoretical studies indicated that self-pinched transport was not an option because net currents established in gas during beam injection were too small to cause beam pinching. However, recent numerical simulations using the 3D hybrid code IPROP3, including the effects of non-local ionization, indicate that self-pinched transport may be possible. The capability to test the concept exists today in scaled experiments using a high-current focused proton beam produced by the Gamble II pulsed-power accelerator at the Naval Research Laboratory. This White Paper describes the implications of the self-pinched transport approach to HIF power plant design and the relevance of proton experiments designed to test the concept. Near-term experiments and analysis are also suggested