Pepperpot Emittance Meter

The Pepperpot Emittance Meter is an imaging system which allows for detecting and evaluating beam parameters of particles as well as x-rays in real-time. The setup is mounted onto a single DN 160 CF flange with a linear motion vacuum feedthrough, two SHV high voltage feedthroughs, a glass viewport, and a camera holder. The main components of the diagnostics unit are the pepperpot-like pinhole mask, a micro channel plate (MCP) and phosphor screen assembly, a mirror, and a CCD camera. The camera, the Pepperpot power supplies, and, optionally, also the linear feedthrough can be remote controlled which is especially important in case operators do not have access to the measurement setup during charged particle beam operation.

For high-intensity beams or x-rays the imaging system can be modified according to the different requirements in these cases. For example, high-intensity beams do not demand signal amplification through an MCP system. Instead, high beam intensities may require the use of special Pepperpot mask materials or an additional shutter system with active cooling to reduce the power introduced to the Pepperpot by the incident beam. Customer-oriented solutions can be offered to find the optimal setup for a specific application.

Functional Principle

The functional principle of the system is based on the incident beam being separated into several beamlets by the Pepperpot mask. In case of low-intensity charged particle beams, the beamlets are converted to secondary electrons using the MCP and finally an optical image is produced by the phosphor screen. In this standard setup, the MCP-produced electrons are accelerated onto a phosphor screen producing visible light which can be monitored through the glass vacuum window. With the help of an analyzing and control software, the emittance and Twiss parameters of the beam can be calculated from the captured image.

The control software of the Pepperpot system allows to adjust the high voltage for the MCP and the phosphore screen. The voltages define the amplification factor of the system. After having adjusted the voltages, the image of the ion beamlets created by the Pepperpot can be observed in real time. With an image of the beamlets taken by the CCD camera, the emittance and Twiss parameters of the incident ion beam can be calculated using the analyzing software. The software uses the x- and y-projection of the beamlets which are fitted by multiple Gaussians for the following calculations.