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shielding

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TUPB08 Measurement of Vertical Emittance with a system of Six -In-Air-X-Ray- Projection Monitors at the ESRF emittance, electron, photon, controls 72
 
  • K. B. Scheidt
    ESRF, Grenoble
  The ESRF Storage Ring is now equiped with a system of 5 independent imaging monitors that measure the vertical emittance of the electron beam in the middle of the bending magnet through the very hard X-rays that fully traverse the 40mm thick Copper dipole absorbers and enter the free air space behind it. The tiny power that leaks through the absorber, and carried by X-rays of ~160KeV of very narrow vertical divergence, is simply projected onto a scintillator screen at ~1.8m from the source-point and imaged by optics & camera. These inexpensive and compact detectors are fully operated in free air and can be easily installed and maintained without any vacuum intervention. They now work reliably in routine fashion and have demonstrated their high precision and resolution of the ESRF’s vertical emittance. These results will be presented in this paper together with the underlying principles of the projection detector, aswell as the practical design solutions applied to obtain the high spatial resolution, to make the system resistant to the hostile radiation environment behind the absorber, and to reduce its sensitivity to stray signals generated at this point.  
 
WEPB09 Mechanical Design of the Intensity Measurement Devices for the LHC vacuum, impedance, alignment, resonance 253
 
  • D. B. Belohrad, S. Longo, OP. Odier, S. Thoulet
    CERN, Geneva
  The intensity measurement for the LHC ring is provided by eight current transformers: 2 DC current transformers (DCCTs) and 2 fast transformers (FBCTs) per vacuum chamber. The measurement precision of 1uArms at averaging over 1s time interval for the DCCTs and ±109 charges in 25ns bunch measurements for the FBCTs is required. Such constraints call for low noise electronics and a compact magnetically shielded mechanical design. Due to ultra high vacuum requirements in the LHC the vacuum chambers are equipped with the non-evaporable getter (NEG) film. The NEG is activated by heating the vacuum chamber to 200°C and more. Such temperatures affect the structure of the magnetic materials, which form the base part of the intensity measurement devices, and degrade their performance. A cooling circuit is needed. Due to the mechanical constraints, the cooling circuit, as well as heating element must form an integral part of the design. The paper presents the solution of these problems and discusses the mechanical construction of the DCCTs and FBCTs currently being installed in the LHC.  
 
WEPB30 Current Status of the SQUID Based Cryogenic Current Comparator for Absolute Measurements of the Dark Current of Superconducting RF Accelerator Cavities pick-up, cryogenics, electron, controls 301
 
  • K. Knaack, K. Wittenburg
    DESY, Hamburg
  • R. Neubert, S. Nietzsche, F. Schiller, W. Vodel
    FSU Jena, Jena
  • A. Peters
    HIT, Heidelberg
  This contribution gives an overview on the current status of a LTS-SQUID based Cryogenic Current Comparator (CCC) for detecting dark currents, generated for example by superconducting cavities for the upcoming X-FEL project. To achieve the maximum possible energy the gradients of the superconducting RF accelerator cavities should be pushed close to the physical limit of 50 MV/m. The so-called dark current of the superconducting RF cavities at strong electric fields may limit the maximum gradient. The absolute measurement of the dark current in correlation with the gradient will give a proper value classify the cavities. The main component of the CCC is a LTS-DC SQUID system which allows us to measure extremely low magnetic fields, caused by extracted dark currents of RF cavities under test. For this reason the SQUID input coil is connected across a toroidal superconducting pick-up coil (inner diameter: about 100 mm) for the passing electron beam. A noise limited current resolution of 40 pA/sqrt(Hz) with a measurement bandwidth of up to 70 kHz was achieved. Design issues and the application for the CHECHIA cavity test stand at DESY as well as experimental results will be discussed.