Primary study of high power graphene beam window *

Beam windows are usually used to isolate vacuum or other special environments, which is a key device for highpower accelerators. Graphene has extremely high thermal conductivity, high strength and high transparency to high energy ions. It is highly suitable for beam windows if the technology is allowable. This paper will discuss the primary tests of graphene films, including vacuum performance and thermal conductivity performance, as well as the simulated performance of an assumed graphene window. INTRODUCTION Beam window is a key device for the high-power hadron beam accelerators such as neutrino factory, spallation neutron sources and accelerator-driven systems. It is used to separate different atmospheres. The commonly used materials are Aluminium alloy [1-4], Inconel alloy [5], Beryllium/ AlBeMet [6], and so on. The cooling methods can be air cooling [5], side water cooling [1], surface water cooling [2] or multi-pipe water cooling [3-4], according to the beam power. Among the ever-fabricated beam windows, the multi-pipe water cooling window made of the Aluminium alloy has the best cooling ability, which can endure about 5 MW beam power while the beam size is double Gaussian with ± 2σ·within footprint of 200 × 60 mm. Generally, the low-Z materials are preferred for the beam window, because they have low scattering effect, which may change the distribution of the beam [7]. The energy deposition generalized by the beam can lead the temperature and stress increases of the window, which are the two bottlenecks of high-power beam windows. Beryllium has good thermal and mechanical properties among the commonly used metals, but is has some usage restrictions and cannot improve the endurable beam power largely. Some graphitized polyimide film such as GPI has very high thermal conductivity up to 1750 W/mK but it is too brittle to be used (tensile strain about 3%), as well as the diamond film (thermal conductivity 900-2320 W/mK and strain 0.4%-0.6%) [8]. Graphene is a monolayer 2D carbon allotrope which has extremely high thermal conductivity up to 5300 W/mK [9], high strength up to 130 GPa intrinsic strength [10], and high transparency to high-energy ions [11]. Owing to these ideal material performance, we proposed the concept of high-power graphene beam window [12]. This paper will focus on the recent progress of our study, including the vacuum performance tests, the thermal conductivity performance and the simulated performance of an assumed window. Particularly, the monolayer or multilayer graphene by now are too thin to be used as a macroscopic material, in this paper we call them graphene. Meanwhile, there are some graphene-based macroscopic materials such as reduced graphene oxide, in this paper we call them graphene film. VACUUM PERFORMANCE TESTS An experiment facility has been built for the vacuum performance tests, which is shown in Fig. 1. After a 24 hours baking and the detection of background, the GV2 was opened and the 1 atm helium was connected. The P-t curve of the sample film was recorded, the helium leak rate can be calculated as well. The detailed principles and data processing in in Reference 13 [13]. Figure 1 : Diagram of the vacuum test facility. Figure 2 : P-t curves of the vacuum test. ___________________________________________ *Work supported by the National Natural Science Foundation of China (Project 11505159) †wanghaijing@ihep.ac.cn 9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW Publishing ISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-MOZGBE3 07 Accelerator Technology T31 Subsystems, Technology and Components, Other MOZGBE3 47 Co nt en tf ro m th is w or k m ay be us ed un de rt he te rm so ft he CC BY 3. 0 lic en ce (© 20 18 ). A ny di str ib ut io n of th is w or k m us tm ai nt ai n at tri bu tio n to th e au th or (s ), tit le of th e w or k, pu bl ish er ,a nd D O I.