Hyojin Choi

2D WPS System for Measuring the Location Changes in Real Time of PAL-XFEL Devices

Several parts that comprise the large scientific equipment should be installed and operated at precise three-dimensional location coordinates X, Y, and Z through survey and alignment to ensure their optimal performance. As time goes by, however, the ground uplifts and subsides, which changes the coordinates of the installed components and leads to alignment errors ΔX, ΔY, and ΔZ. As a result, the system parameters change, and the performance of the large scientific equipment deteriorates accordingly. Measuring the change in the locations of the systems comprising the large scientific equipment in real time would make it possible to predict alignment errors, locate any region with greater changes, realign components in the fast changing region and shorten the time of survey and alignment. For this purpose, a hydrostatic leveling sensor (HLS) with 0.2 μm resolution was installed and is operated in the PAL-XFEL building. In addition, a 2D wire position sensor (WPS) with a 0.1 μm resolution was installed and is operated in the undulator sections where measurements of the two-dimensional changes of the systems (vertical & horizontal) are necessary. This paper is designed to introduce the operating principle of the 2D WPS, the installation and operation of the WPS system, and the way in which the WPS system is utilized in order to ensure beam stability.

Results Produced after Measuring PAL-ITF Beam Diagnostic Instruments

Pohang Accelerator Laboratory (PAL) built a PAL-ITF at the end of 2012 to successfully complete PAL-XFEL in 2015. The PAL-ITF is equipped with various kinds of diagnostic equipment to produce high-quality electron bunches. An ICT and a Turbo-ICT were installed in the PAL-ITF. A Faraday Cup (FC) is installed at the end of the linear accelerator. These days, the quantity of electric charge occasionally is measured using a BPM Sum value. This paper focuses on the processes and results of electric charge quantity measurements using ICT, TurboICT, FC and BPM. The PAL-ITF is equipped with Stripline-BPM. It is important to find a way to minimize measurement errors that can appear in the process of installing or measuring the BPM. For this, PAL-ITF separately measured the BPM electrode sensitivity and minimized BPM measurement errors through generally calibrating BPM devices by applying Lambertsons Method. A plan was made to minimize BPM measurement errors through applying the BPM electrical calibration method for BPM devices to be used by the PAL-XFEL. This paper examines the processes for checking the performance of the S-BPM installed in the PAL-ITF and the results of its measurements. INTRODUCTION The three main parameters that an injection testing facility should measure are charge, energy and emittance. Although ICT and FC were installed to measure charge, the noise generated in a klystron modulator not only interrupted accurate measurement but prevented low bunch charges under tens of pC from being measured. Due to the changes in the overall voltage level of PALITF, integration of ICT measured value failed to maintain perfect accuracy in terms of methodology (measured value continuously changed by +/5pC). Accordingly, to solve the noise problems and accurately measure the quantity of electric charge, Turbo-ICT was installed. Accurate measurement of beam positions requires not only BPM pickup characteristics but comprehensive methods of checking the BPM system, which can include all factors with potential BPM offset such as alignment in the process of installing cables, electronics and BPM equipment. To check sensitivity and offset of BPM, Lambertsons method was applied. The factors that should be calibrated to improve accuracy and precision are provided in Fig.1 [1][2]. See Fig.2 for types and locations of diagnostic units installed in PAL-ITF [3]. Figure 1: Factors crucial to improving the performance of diagnostic units. Figure 2: Types and locations of diagnostic units installed in PAL-ITF. BEAM CHARGE MONITOR (BCM) In PAL-ITF, instead of installing BCM-IHR-E electronics recommended by Bergoz Instrumentation, ICT output was going to be directly connected to an oscilloscope to measure quantity of electric beam charge, but noise prevented an accurate measurement. As shown in Fig.3, use of 50 ohm impedance matching and low-pass filter resulted in some improvement, but the klystron modulator led to constant slopping of ground-level voltage and measurement failed in low beam charge due to weak ICT output current. Figure 3: Improvement of ICT measurement methods. _____________________ * Work supported by the Ministry of Science, ICT and Future Planning (MSIP) in Korea. † choihyo@postech.ac.kr 5th International Particle Accelerator Conference IPAC2014, Dresden, Germany JACoW Publishing ISBN: 978-3-95450-132-8 doi:10.18429/JACoW-IPAC2014-THPRO021 06 Instrumentation, Controls, Feedback & Operational Aspects T03 Beam Diagnostics and Instrumentation THPRO021 2903 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 14 ). 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.