Diamond Dielectrics for Advanced Wakefield Accelerators
- PDF / 8,207,189 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 10 Downloads / 178 Views
Diamond Dielectrics for Advanced Wakefield Accelerators Stanley S. Zuo1, James E. Butler1, Bradford B. Pate2, Sergey P. Antipov1, Alexei Kanareykin1, Chunguang Jing1 1 Euclid TechLabs, 5900 Harper Rd, #102, Solon, OH 44139, U.S.A 2 Naval Research Laboratory, 4555 Overlook Ave. SW, Washington, DC 20375, U.S.A ABSTRACT Diamond was investigated as one of the superior dielectric materials for advanced wakefield accelerators. Both planar and cylindrical wakefield accelerating structures were constructed. An AsTex microwave plasma-enhanced CVD system was modified for synthesis of cylindrical polycrystalline diamond tubes. Cylindrical diamond tubes were successfully synthesized from hydrogen and methane and are characterized with micro Raman, photoluminescence spectroscopy and optical tests. In addition, planar wakefield structures were constructed from commercially available diamond. Wakefield tests on a rectangular diamond structure confirm that diamond can sustain microwave electric field strengths of 0.3 GV/m at its surface without material breakdown. INTRODUCTION Dielectric loaded accelerating (DLA) structures excited by high current electron beams or an external high frequency, high power, RF source have been under extensive study for many years [1,2,3,4]. In recent years, electromagnetic wakefields produced by high energy electrons transiting through dielectric loaded waveguides have pushed electric fields to GV/m levels in the microwave and mm-wave frequency range [3,4,5,6,7]. Dielectric materials such as metal oxide ceramics and fused silica are encountering their physical limits. Diamond is an attractive material for dielectric loaded accelerating structures [5,8,9,10] due to its low microwave loss tangent at Ka-W frequency bands, excellent thermal conductivity, and high RF breakdown field [2,5]. The basic RF structure is very simple - a cylindrical, dielectric loaded waveguide with an axial vacuum channel is inserted into a conductive sleeve (Figures 1,2). A high charge, (10 – 100 nC), short, (1 – 4 mm) electron drive beam generates TM01 mode electromagnetic Cherenkov radiation (wakefields) while propagating down the vacuum channel. Following at a delay adjusted to catch the accelerating phase of the wakefield is a trailing electron (witness) bunch. The witness beam is accelerated to high energy by the wakefield produced by the drive beam.
Figure 1. Cross-sectional view of a rectangular (or cylindrical if a and b are radii) dielectric-loaded waveguide.
Figure 2. Design of cylindrical and rectangular diamond DLA structures and their correlated waveguides.
The principal goal of this investigation is to develop a diamond-based DLA to allow a sustained accelerating gradient larger than 600 MV/m, far in excess of the limits experimentally observed for conventional metallic accelerating structures. The key element to achieve this is to obtain diamond material with low impurity content and uniform quality over the finished geometry that can sustain such high fields. The use of microwave plasma-enhanced CVD (MPCVD)
Data Loading...
