JLab, Newport News, Virginia, USA
Jefferson Lab (JLab) is in collaboration with Fermi Na-tional Accelerator Laboratory (Fermilab) to build 18 cryomodules to install at the SLAC National Accelerator Laboratory's tunnel as part of the Linac Coherent Light Source upgrade project (LCLS-II). Each LCLS-II cry-omodule hosts 8 superconducting niobium cavities that adopt the nitrogen doping technique, which aims to en-hance the cavity quality factor Qo to reduce the consumption of liquid helium used to cool down the cavities. It is known that the Qo of niobium cavities is affected by cavity surface magnetic field. Traditionally, magnetic shields made of high magnetic permeability mu-metals are employed as a passive shielding of the ambient magnetic fluxes. During the LCLS-II cryomodule development, magnetic hygiene control that includes magnetic shielding and demagnetization of parts and the whole-machine is implemented. JLab and Fermilab worked closely on developing magnetic hygiene control procedures, identifying relevant tools, investigating causes of magnetization, magnetic field monitoring, etc. This paper focuses on JLab's experiences with LCLS-II cryomodule magnetic hygiene control during its fabrication.
Authored by Jefferson Science Associates, LLC. The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for Government purposes.
JLab, Newport News, Virginia, USA
The LCLS-II cryomodule construction program leverages the mature XFEL cryomodule design to produce technologically sophisticated cryomodules with a minimum of R&D according to an accelerated manufacturing schedule. Jlab, as one of the partner labs, is producing 18 cryomodules for LCLS-II. To meet the quality and schedule demands of LCLS-II, many upgrades to the JLAB cryomodule assembly infrastructure and techniques have been made. JLab has installed a new cleanroom for string assembly and instituted new protocols to minimize particulate transfer into the cavities during the cryomodule construction process. JLab has also instituted a set of magnetic hygiene protocols to be used during the assembly process to minimize magnetic field impingement on the finished cavity structure. The goal has been to have gradients, both maximum and field emission onset, that do not degrade between the cavity vertical test and final cryomodule qualification, while maximizing the Q0 of each finished cavity. Results from the prototype cryomodule assembly are presented.
JLab, Newport News, Virginia, USA
The CEBAF cryomodule rework program has been a successful tool to recover and maintain the energy reach of the original baseline 6 GeV accelerator. The weakest original modules with eight five-cell cavities assembled in four 'pairs', with a specification when new of 20 MV per cryomodule (5 MV/m), are disassembled, re-cleaned with modern techniques and re-qualified to at least 50 MV (12.5 MV/m), (leading to the acronym 'C50'). The cost per recovered MV is much less than building new modules. However over time the stock of weak modules is being used up and the voltage gain per rework cycle is diminishing. In an attempt to increase the gain per cycle it is proposed to rework the cavities by replacing the original accelerating cells with new ones of an improved shape and better material. The original CEBAF HOM and FPC end groups are retained. The goal is to achieve up to 75 MV (18.75 MV/m) for the reworked module ('C75'). We report on the fabrication experience and test results of the first trial pair, containing two such reworked cavities.
JLab, Newport News, Virginia, USA
Cryomodule production for LCLS-II is well underway at Jefferson Lab. This paper explains the process flow for production cavities, from being received at the Test Lab to being assembled onto cavity strings. Taking our facility and infrastructure into consideration, process optimization and process control are implemented to ensure high quality products.