Diamond Beam Halo Monitor

The investigation of beam halo transverse distribution is of great importance for beam loss and background control in high current accelerators. Halo monitoring is also very important at modern x-ray light sources in particular the ones with in-vacuum undulators to protect permanent magnets from radiation damage caused by the beam halo. Traditional wire scanner measurement utilizing carbon or tungsten wires is limited by the damage threshold of these materials. These devices have to be routinely serviced due to beam-induced damage of the wires. Euclid Techlabs LLC proposes an electrodeless method to measure halo with a diamond scraper. This measurement utilizes a microwave resonator placed around the beamline element which is sensitive to charged particle-induced conductivity. Microwave resonator detuning measurement, having an incredible dynamic range of six orders of magnitude is expected to be very sensitive. Diamond is chosen as a radiation hard material with excellent thermal properties. The absence of electrodes makes the device robust under the beam. In Phase I, we produced a prototype resonator with a diamond sensor element that was characterized on the bench. Two version of the resonator were built. It was discovered that motorization of the scanning measurement is complicated engineering-wise due to non-existent commercially ultra-high vacuum RF cables which are flexible. A simplified resonator was used similarly to a Faraday cup in our 10 keV electron gun testing beamline. The microwave detuning measurement proved to be a lot more sensitive than a standard Faraday cup. We also simulated halo scanning process and developed a halo map retrieval procedure based on the scan results. In Phase II, we will perform a high-power test of the microwave detuning device built in phase I which will visualize electron beam via fluorescence and at the same time provide a measurement of the beam intensity. We will design and fabricate a similar device with the scanning capability. This design will be based either on custom bellows frame or will utilize an in-vacuum flexible RF cable which we are looking to develop. There is a strong interest in accelerator and plasma community to have a high quality, flexible, UHV- compatible cable. In the end of Phase II work, the halo scanner will be tested at the AWA facility of Argonne National Lab. The proposed approach is robust, plug and play and can be employed in a large number of accelerator facilities all over the world. This no-electrical-contact diamond-based halo measurement can potentially replace wire scanners which require routine maintenance.