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    • br New design of an HIF injector Since the

    2022-05-16


    New design of an HIF injector Since the invention of RFQ, RFQ-based 1 GW HIF plans have been proposed in Japan, Europe and the Soviet Union, such as HIBALL, HIDIF and HIBLIC. In these plans, driver linacs were numerous, huge and complicated. Considering the space-charge-effect of the intense heavy ions (400 mA Pb+ or Bi+ ions) in low energy regions, 16 RFQs were used to accelerate heavy ions in the HIBLIC design, however, each RFQ was over 500 m in length [6]. We are trying to design a new HIF driver using the DPIS technology and multi-beam acceleration. A simple layout of HIF driver system is shown in Fig. 4. In this system, a powerful laser will split into four and produce four high intensity Pb+ ion beams (115 mA/channel), which will be directly injected into a four-beam type IH-RFQ, where the four 125 mA beams will be accelerated to 300 keV/u from 3 keV/u. Two beam funnelling systems will be adopted to funnel the accelerated ion beams from the RFQ. The beam intensity will be enhanced to 220 mA/channel before injecting into an IH DB-DTL system. The IH DB-DTLs will accelerate the 220 mA/channel ions up to 1.2 MeV/u with an operation frequency of 81.25 MHz. When the beams came out from the DB-DTLs, another beam funnelling system will work. The driver system could also offer one-beam type DTLs, which will accelerate 410 mA/channel ions up to 4.7 MeV/u with an operation frequency of 162.5 MHz. Finally, SC linacs (HWRs and spokes [19], [20]) will offer high accelerating fields to accelerate 400 mA ions up to 50 MeV/u with operation frequencies of 162.5 MHz and 325 MHz. Compared with the initially proposed HIF driver, the total length of the renewed HIF injector is only about 2.5 km, which is buildable. The parameters of the renewed HIF driver are listed in Table 1.
    Demo facility for future plan The breakthroughs mentioned above make it highly possible to construct HIF facilities. We redesigned and upgraded our designs of a HIF driver system. Adopting many multi-beam linac-based cavities, as shown in Fig. 4 and Table 1, we have reduced the total length of the redesigned driver linac to about 2.5 km. However, beam bunching, final focusing and target heating have not been studied or tested. Thus, as shown in Fig. 17, we propose a demo facility for these researches [6]. In the demo facility, a 240 mA heavy-ion beam will be accelerated up to 10 MeV/u and 50 MeV/u by a 600-m-long linac driver and a heavy-ion synchrotron system. There is a four-time storage ring where RF storage, AZD 6244 cooling and stochastic cooling technologies can be developed. After bunch compressors, the bunched heavy-ions will be injected into four induction bunches for recompressing and strengthening. Finally, the recompressed beams will be delivered to the experimental fusion facilities. The width of the final bunch is 10–20 ns, which requires superconducting focusing technology for target heating. The design of 4-beam type IH-RFQ was done in 2014 and the structure was proposed at the 20th International Symposium on Heavy Ion Inertial Fusion (HIF2014). The thermal analysis and deformation research of the 4-beam type IH-RFQ are not finished yet, and the electromagnetic structure will be optimized based on the thermal analyses. Fortunately, the DB-DTL is being funded by National Natural Science Foundation of China with contract No. 11535016. In the future, a PoP DB-DTL will be fabricated and operate with high power proton acceleration, as mentioned in Fig. 15. An LIS was also developed [26]. With this LIS, the 4-beam injection for a 4-beam RFQ can be studied.
    Summary As an alternative energy source, the HIF facilities are much safer than Tokomak facilities. Moreover, the energy gain of HIF facilities is three times that of Tokamak facilities. Therefore, HIF facilities, especially the PoP HIF facility, are critical. However, the previously proposed HIF drivers are un-realistic for their large scale. Based on existing technologies, we proposed a multi-beam linac-based 1 GW HIF driver which could cut down the cost and has a total length of about 2.5 km. Additionally, we proposed and calculated a 4-beam type IH-RFQ and a DB-DTL. The PoP 4-beam IH-RFQ was designed for Pb12+ or Au12+ ion acceleration. The high-power proton acceleration of the DB-DTL will operate in the next few years. For future study, we propose a demo facility where multi-beam linacs are adopted as drivers. The final beam bunching and target heating can be studied by using this demo facility. And the operating system will be further developed in this demo facility for beam matching and emittance control of the high intensity heavy-ion. The biggest problem of the HIF beam matching is the magnetic field strength because of the big pipe size of the matching section. Fortunately, HIF drivers will operate at a pulse mode, thus, the beam matching and beam control are challenging. Especially, the technologies of superconducting magnet are developed at Michigan State University and Institute of Modern Physics for FRIB and HIAF projects [27], [28], which will help the beam matching and emittance control.