Operational experience and consolidations for the current lead control valves of the large hadron collider

Abstract

The Large Hadron Collider superconducting magnets are powered by more than 1400 gas cooled current leads ranging from 120 A to 13000 A. The gas flow required by the leads is controlled by solenoid proportional valves with dimensions from DN 1.8 mm to DN 10 mm. During the first months of operation, signs of premature wear were found in the active parts of the valves. This created major problems for the functioning of the current leads threatening the availability of the LHC. Following the detection of the problems, a series of measures were implemented to keep the LHC running, to launch a development program to solve the premature wear problem and to prepare for a global consolidation of the gas flow control system. This article describes first the difficulties encountered and the measures taken to ensure a continuous operation of the LHC during the first year of operation. The development of new friction free valves is then presented along with the consolidation program and the test equipment developed to validate the upgraded valves prior to their installation into the LHC.

Upgrade of the gas flow control system of the resistive current leads of the LHC inner triplet magnets: Simulation and experimental validation

“…Figure 6 shows that the model accurately reproduces the dynamic behaviour of the system. The small discrepancies on the absolute values of the flows are due to the fact that the valve is simulated by a linear function while in reality the valve characteristic is not perfectly linear at the maximum opening range [3]. …”

“…The typical reaction time needed to control the current leads is about 10 s. The goal of this study was to determine, both theoretically and experimentally, the effect of the buffer volume and of the measuring system on the control dynamics. A numerical model was developed and tests were performed on a test bench that was previously used for the calibration of the control valves [3]. Based on the measured characteristics, a PID control loop was optimized on the simulated model and was then applied to the test bench for comparison with the requirements for regulation of the current leads.…”

“…All measurements were performed at a helium temperature in the range of 293 K -295 K. The typical mass flows required by the current leads are 0.02 g/s for the 120 A current leads and 0.06 g/s for the 600 A current leads, so a maximum mass flow of 0.08 g/s was used for the measurements. The valve CV2 is a DN1.8 proportional valve with a Kv of 0.087 m 3 /s, its characteristics is approximately linear op to an opening of approximately 70% [3], for the purpose of this study it is simulated with a linear characteristic. As the pressure across the valve CV2 varies only by about 10% over the investigated flow range, the flow through the valve (and through the current lead) is essentially proportional to the valve position.…”