External influences such as temperature variations and electromagnetic interference (EMI) also affect the measurements.The digitizer has very low temperature-dependent drift on the order of tens of ppb (parts per billion) per degree Celsius, achieved by active temperature stabilization of the sub-module that contains all precision circuits. Ultimately, the performance on longer timescales is limited by the voltage reference, which is the best one presently available on the market. To minimize low-frequency electronic noise, the voltage scaling circuits employ bulk metal foil resistors and auto-zero operational amplifiers. Electronic components exhibit various kinds of noise, including the omnipresent 1/f or “flicker” type with spectral density rising at low frequencies. Digital logic functionality is implemented in a field-programmable gate array (FPGA), which takes care of the ADC chip initialization and readout, the communication and synchronization protocol, as well as the built-in calibration and self-test features of the system.ĭifferent aspects of the HPM7177 design address the challenges generated by the need for stable measurements on the timescale of a typical LHC cycle. The digitizer employs precision circuits for the scaling of the analog signals. Its core element is a commercial high-resolution ADC integrated circuit, selected after an extensive market survey and test campaign. The HPM7177 digitizer, an entire stand-alone measurement system, was developed to answer these constraints. HL-LHC requirements are indicated by double arrows (power converter) and dashed lines (ADC). The main plot shows a 12-hour record, while the inset is a zoom-in to a 20-minute section of it. ![]() Typical measurements at the nominal digitizer full scale of 10 V using a portable voltage standard. Short-term stability (1mHz < f < 100mHz) of 0.05ppm (parts per million) rms, 12h stability of 0.2ppm p-p (in isothermal conditions) and linearity of 1ppm, are just a few of the challenging requirements imposed on the ADCs. Since power converter performance depends greatly on the quality of the measurement used for the feedback, the DCCT and the ADC are crucial for delivering the required precision. The requirements for the power converters are unprecedented in terms of current stability, noise, and repeatability. A high-precision ADC is used for that purpose. However, the current in the magnets is sensed in analog by means of a Direct-Current Current Transformer (DCCT) and therefore needs to be converted into a digital code. The reference current is sent digitally by the control room. As a consequence, both the reference current and the measured current need to be provided in the digital domain. At CERN, power converters use high-precision current feedback loops, implemented digitally, to deliver the current to the magnets. They are commonly employed as controlled current sources. To power magnets in particle accelerators, electrical power converters are used. This improvement requires a fine tuning of the beam parameters, which translates into unprecedented performance requirements for the magnetic field stability and accuracy and, consequently, for the electric current that generates it. The IT quads contribute to increasing luminosity by reducing the beam size at the interaction point. Among the most important are the Inner Triplet (IT) quadrupoles on each side of the interaction points of the ATLAS and CMS experiments. For that purpose, the project foresees the replacement of several magnets in the LHC. The main goal of the High-Luminosity LHC (HL–LHC) project is to increase the luminosity of the LHC beam, both instantaneous and integrated. This Analog-to-Digital Converter (ADC), named HPM7177, was designed at the High-Precision Measurements section and first tested in 2019. ![]() The new digitizer will be employed in the power converters of the Inner Triplet quadrupoles and separation/recombination dipole magnets of the HL-LHC. The CERN Electrical Power Converters Group developed a new metrology-grade digitizer, part of that high-precision measurement system. The new higher field magnets also call for higher precision powering, which is strongly dependent on the performance of the electric current measurement chain. One of the key elements of the LHC high-luminosity upgrade project is the replacement of the magnets that focus the beams near the interaction points of ATLAS and CMS, where particle collision occurs.
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