DIAMOND AMPLIFIER DESIGN AND PRELIMINARY TEST RESULTS T. Xin #, 1, 2 , S. Belomestnykh 1, 2 , I. Ben-Zvi 1, 2 , M. Gaowei 1, 2 , E. Muller 1, 2 , T. Rao 1 , J. Skaritka 1 J. Smedley 1 , E. Wang 1 , Q. Wu 1 , 1 Brookhaven National Laboratory, Upton NY 11973 2 Stony Brook University, Stony Brook NY 11794 Abstract Diamond as a large band gap material can be easily made to have negative electron affinity (NEA) surface. Using a few keV primary electrons as input and a few kV bias, the NEA diamond will emit cold electrons into vacuum with a large gain. We had tested and reported the performance of the diamond amplifier in our DC system. The best amplification achieved so far was above 170. Next step of the experiment is to test the diamond amplifier in a 112 MHz superconducting RF electron gun. In this report we describe the design of the amplifier containing a DC primary gun and light optics, to be tested in our SRF gun and relevant simulations. We also provide preliminary test results of the laser and electron beam transport. INTRODUCTION In previous papers, works on hydrogenation of CVD diamond and on measurements of secondary electron gain in a DC system at Brookhaven National Lab were reported [1-3]. The next step will be testing the diamond amplifier in a Superconducting RF (SRF) gun. For this purpose a specially designed cathode stalk is needed to work as a transporter/holder of a diamond in the gun. Besides that, we also designed a subsystem, which will be inserted into the cathode stalk and act as the DC stage of the amplifier. DIAMOND AMPLIFIER A basic diagram of a diamond amplifier is shown in Figure 1. A primary beam, with a few keV energy, hits the Pt coated back of the diamond and generates a cloud of electron/hole pairs inside the diamond. This entrance surface of the diamond is negatively biased hence the electrons separate from the cloud and drift across the bulk of diamond to the opposite, hydrogenated NEA emission surface. An anode is placed 200 m away from the emission surface so that the electric field will extract the secondary electrons from the NEA surface of diamond into vacuum. Figure 1: DC test of Diamond Amplifier (conceptual diagram) [1]. Design of Amplifier for SRF n Test For the test of the Diamond Amplifier in an SRF gun, we need a special stalk to position the diamond in right location in the cavity and hold it there. The detailed description of the stalk can be found in previous papers [4, 5]. As for the source of primary electrons, we decided to use a newly designed DC assembly with a UV driven copper cathode. A CAD model and a photo of this system, which will hereby be called Amplifier, is shown in Figure 2. Figure 2: Section view of the Amplifier: red lines show the path of UV light. Smal insert is a photo of the first prototype Amplifier with a penny on the side as size reference. This is the first prototype amplifier we made for SRF test. There are four major pieces. A gold plated copper top plate is used to hold the diamond and ground it to the cavity. A ceramic spacer serves as an insulator between the grounded top plate and biased molybdenum base. It also acts as a holder for the cathode and mirror and defines the crucial distance between the cathode and diamond. The third part is the cathode/mirror pair that will provide electron beam and guide the laser beam out of the cavity. The fourth part is the molybdenum base that works as the connection between the Amplifier and the transport arm. Laser will come in through a hole in the top plate and illuminate the cathode. There is an aluminium electrode surrounding the cathode optimized for beam focusing. After the laser bounces off the mirror-finished cathode, it will hit a metal-coated mirror on the other side, which will redirect the laser out of the amplifier through an exit hole in the top plate. Figure 3 shows how the amplifier will be positioned in the stalk and cavity as well as depicts the paths of laser and electron beams. The angles of the cathode and mirror are chosen to meet two conditions. The first one allows the laser beam to escape the cavity with no obstacles. And the second condition is that the electron beam must hit the center of the diamond so that we do not * This work was carried out at Brookhaven Science Associates, LLC under Contracts No. DE-AC02-98CH10886 and at Stony Brook University under grant DE-SC0005713 with the U.S. DOE. #txin@bnl.gov Gu Proceedings of PAC2013, Pasadena, CA USA THPAC34 07 Accelerator Technology T02 - Electron Sources and Injectors ISBN 978-3-95450-138-0 1211 Copyright c  2013 CC-BY-3.0 and by the respective authors