Over recent decades there were three breakthroughs of high

Over recent decades, there were three breakthroughs of high intensity heavy-ion acceleration [6]. The first is the invention of radio frequency quadrupole (RFQ) type accelerator, which could accelerate more than dozens of milli-ampere ion beams and is a good solution to space-charge-effect of heavy-ion acceleration at low labetalol hydrochloride [7][8]. The second is the direct plasma injection scheme (DPIS), which provides a way to produce a very high intensity heavy-ion beam [9], [10], [11], and the third is multi-beam Interdigital H-mode (IH) RFQ type accelerating structure, which successfully accelerated 108 mA carbon ions in 2010 by using DPIS [12]. Shown in Fig. 1, the IH structure is a power-efficiency structure than Alvalez structure in the low and medium energy region because of its high shunt-impedance [13], [14], [15]. These breakthroughs, especially, the invention of multi-beam RFQ which is suitable for accelerating heavy-ions in the very low energy region, make the production and acceleration of very high intensity heavy-ion beam possible. We proposed a 4-beam type IH-RFQ in the HIF2014 conference held in Lanzhou. The goal of the Proof of Principle (PoP) multi-beam IH-RFQ is to design an IH-RFQ which can accelerate four 125 mA Pb12+ or Au12+ beams up to 100 keV/u from 3 keV/u in 3 m with over 97.6% transmission. A conceptual multi-beam type drift tube linac (DTL) was proposed in LINAC2016 conference at MSU in 2016 [16]. In this paper, a layout of a renewed HIF driver and a multi-beam linac-based demo HIF facility will be reported, including the designs of a PoP 4-beam RFQ and the designs of a PoP dual beam type DTL (DB-DTL).
Breakthroughs in high intensity heavy-ion acceleration For 1 GW HIF plant, the driver linacs must accelerate 400 mA heavy-ion (such as Pb+ ions or Bi+ ions) beams up to 50 MeV/u [4][6]. However, it is very difficult to produce and accelerate 400 mA Pb+ ions because of the limitations of existing ion sources, strong space-charge-effect and acceleration technologies. The DPIS was invented by Prof. Hattori and Dr. Okamura in the Tokyo Institute of Technology in 2001. The DPIS can produce high intensity heavy ions and inject them to the RFQ by using a laser ion source (LIS). Using multi-beam type RFQ, the driver linacs can simultaneously accelerate multiple beams in a single cavity. The schematic of the DPIS is shown in Fig. 2. The mechanism of DPIS is irradiating a high purity solid target by a pulsed laser to produce plasma, which can be efficiently injected to RFQ with the thermal expansion velocity of the plasma suppressing Coulomb repulsion [17], [18]. Compared to the traditional gas-ionized ion source, DPIS can produce high-intensity highly-charged ions from the high purity solid target. Due to directly injecting the ion plasma to the RFQ without low energy transport line, the RFQ can accelerate very high intensity ion beams. The principle test of the DPIS successfully accelerated 9.22 mA C4+ carbon ions up to 214 keV/u by using an old 4-vane type RFQ at Tokyo Institute of Technology in 2001 [9]. Moreover, using a new RFQ, the same team measured 60 mA C4+ ions and 18 mA C6+ ions accelerated to 100 keV/u from 20 keV/u at RIKEN in 2004 [10], [11]. The multi-beam accelerating structure was also developed by the Hattori Laboratory in 2005. The invention of multi-beam RFQ, which is suitable for accelerating heavy ions in the very low energy region with a weak space-charge-effect, makes HIF possible. In the prototype of multi-beam cavity, two sets of four RFQ-rods were assembled into a power-efficient IH cavity, and successfully accelerated 54 mA/beam-channel ions up to 60 keV/u from 5 keV/u with DPIS in 2010 [12]. The total accelerated C2+ beam reached 108 mA. The structure of two-beam IH-RFQ is shown in Fig. 3. These developments prove that multiple beams can be accelerated in a single cavity and it is possible to accelerate 400 mA beams using four sets of four RFQ-rods.