Author: Young, A.
Paper Title Page
TUPC13 System Overview and Design Considerations of the BPM System of the ESS Linac 388
  • H. Hassanzadegan, A. Jansson, R. Zeng
    ESS, Lund, Sweden
  • A.J. Johansson
    Lund University, Lund, Sweden
  • K. Strniša
    Cosylab, Ljubljana, Slovenia
  • A. Young
    SLAC, Menlo Park, California, USA
  The ESS Linac will include in total more than 140 Beam Position Monitors of different sizes and types. The BPM system needs to measure the beam position, phase and intensity in all foreseen beam modes with a pulse rate of 14 Hz, duration of 2.86 ms and amplitude ranging form 5 mA to 62.5 mA. With respect to the BPM connection to the Machine Interlock System, the total response time must be less than 10 us. The signal level variations from one BPM to another along the Linac should be as small as possible to meet the requirements on the analog gain of the front-end electronics and the dynamic range of the digitizer card input. The other requirement is that the BPM system needs to give at least a rough estimation of the beam position and phase, even if the beam is significantly debouched, ex. during the Linac tuning phase. These requirements and their impact on the design of the BPM detector, the analog front-end electronics and the selection of the digitizer card are discussed in this paper along with a general description of the BPM system.  
poster icon Poster TUPC13 [3.050 MB]  
WEPC23 Design of an Ultra-Compact Stripline BPM Receiver using MicroTCA for LCLS-II at SLAC 731
  • C. Xu, S. Babel, S. L. Hoobler, R.S. Larsen, J.J. Olsen, S.R. Smith, T. Straumann, D. Van Winkle, A. Young
    SLAC, Menlo Park, California, USA
  Funding: Work supported by U.S. Department of Energy under Contract Numbers DE-AC02-06CH11357 and DE-AC02-76SF00515
The Linac Coherent Light Source II (LCLS II) is a free electron laser (FEL) light source. LCLS II will be able to produce 0.5 to 77 Angstroms soft and hard x-rays. In order to achieve this high level of performance, the electron beam needs to be stable and accurate. The LCLS II stripline BPM system has a dynamic range of 10pC to 1nC beam charge. The system has a 3.5 micrometer resolution at 250pC beam charge in an one inch diameter stripline BPM structure. The BPM system uses the MicroTCA physics platform that consists of analog front-end (AFE) and 16-bit analog to digital convertor (ADC) module. The paper will discuss the hardware design, architecture, and performance measurements on the SLAC LINAC. The hardware architecture includes bandpass filter at 300MHz with 15 MHz band-width, and BPM calibration process without communicating with the CPU module. The system will be able to process multibunch beams with 40ns spacing.
poster icon Poster WEPC23 [1.769 MB]  
WEPC24 Performance Measurements of the New X-Band Cavity BPM Receiver 735
  • A. Young, J.E. Dusatko, S. L. Hoobler, J.J. Olsen, T. Straumann
    SLAC, Menlo Park, California, USA
  • C. Kim
    PAL, Pohang, Kyungbuk, Republic of Korea
  Funding: Work supported by U.S. Department of Energy under Contract Numbers DE-AC02-06CH11357 and DE-AC02-76SF00515
SLAC is developing a new X-band Cavity BPM receiver for use in the LCLS-II. The Linac Coherent Light Source II (LCLS-II) will be a free electron laser (FEL) at SLAC producing coherent 0.5-77 Angstroms hard and soft x-rays. To achieve this level of performance precise, stable alignment of the electron beam in the undulator is required. The LCLS-II cavity BPM system will provide single shot resolution better than 50 nm resolution at 200 pC*. The Cavity BPM heterodyne receiver is located in the tunnel close to the cavity BPM. The receiver will processes the TM010 monopole reference cavity signal and a TM110 dipole cavity signal at approximately 11 GHz using a heterodyne technique. The heterodyne receiver will be capable of detecting a multibunch beam with a 50ns fill pattern. A new LAN communication daughter board will allow the receiver to talk to an input-output-controller (IOC) over 100 meters to set gains, control the phase locked local oscillator, and monitor the status of the receiver. We will describe the design methodology including noise analysis, Intermodulation Products analysis.
* Commissioning and Performance of LCLS Cavity BPMs, Stephen Smith, et al., Proc. of PAC 2009
poster icon Poster WEPC24 [0.251 MB]  
LCLS-II Cavity BPMs Electronics  
  • A. Young
    SLAC, Menlo Park, California, USA
  Andrew presented the related read-out electronics for the new LCLS X-Band cavity BPM pickup. It turned out that the waveguide mixers in the current system suffer from a bias voltage degradation, which alters the overall gain. These components are not anymore available, and start to cause a serious issue. The new read-out system with coaxial inputs is based on the same classical heterodyne RF downconverter schema and a digitizer to convert the IF to baseband, which actually is used in most cavity BPM implementations. The 3-channel (X, Y, REF) RF section is located in the tunnel, and includes a commercial communication interface for remote operations on attenuators, etc. A 4th spare channel is also located on the PCB. The LO, based on a commercial PLL board (?), and is phase-locked to the accelerator RF system. The 14-bit digitizer from Struck rests in a μTCA crate, located outside the tunnel. The RF board is made from a multilayer PCB, made from FR4, with embedded Rogers Duroid layers for the high frequency sections. The RF front-end provides ~80dB dynamic range, plus attenuator settings, and a NF=3dB. The IF section provides 34dB gain. In the following we shortly mentioned the pros and cons of a downconverter schema versus a simple diode detector. The common opinion is that the direct diode baseband detection results in substantially higher noise floor. It also was mentioned that the limited return loss of diodes (or input filters in case of a downconverter) might cause an unwanted asymmetries between the two arms of the cavity BPM outputs. Other discussion points where on the PLL. Great care has to be taken on the loop filter design, particular in case of fractional PLLs. A high frequency for the PLL should be considered, this would result in a lower phase noise. Is phase-locking to the accelerator RF beneficial? It may result in a better resolution measurement, but the resolution stops reacting to some systematic effects, and it is beneficial to keep it sensitive to have an indicator of the system health. In addition, unlocked LO is beneficial for model-independent methods applied to waveforms as the whole phase space is covered in that case.  
slides icon Slides FRWMJ2 [0.745 MB]