Quench Circuit Research Articles

Design and Test of Quench Protection for Superconducting Generator Field Coils

The quench protection for an LTS superconducting field winding within a 15+ MW direct-drive superconducting wind generator is presented. The quench protection circuit comprises multiple superconducting field coils, one quench protection switch (QPS), a set of trigger heaters thermally attached to the QPS, and a set of quench protection heaters in thermal contact with each field coil. Trigger heaters are electrically connected across each field coil. All quench protection heaters are electrically connected across the QPS. The quench of any field coil will power at least one trigger heater and heat the QPS to quench. Consequently, the QPS voltage will power all the quench protection heaters and trigger all field coils to quench nearly simultaneously. This QPS-based quench protection circuit has been successfully validated by experiments. Alternatively, one of the field coils, designated as trigger-coil, can also function as the QPS. Simulation results of the two quench circuits are compared.

Mutual Induction Caused by IVCC Currents on Quench Detection Circuits of the KSTAR TF Coils

The Quench Detection System (QDS) for the Toroidal Field (TF) coils and the Poloidal Field (PF) coils made of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn or NbTi cable-in-conduit conductors is using Wheatstone bridges to compensate induced voltages, which are generated by electrical currents of the superconducting coils and a plasma, on the quench detection circuits of the Korea Superconducting Tokamak Advanced Research (KSTAR) device. On the other hand, the KSTAR device is equipped with In-Vessel Control Coils (IVCCs), which consist of 16 segmented windings made of normal conductors, for fast plasma position control, field error correction, and resistive wall mode stabilization. Electrical currents of the middle Field Error correction Coil (FEC) in a part of the IVCCs have strong mutual induction on the quench detection circuits of the TF coils due to the paths of the FEC's conductors, and the middle FEC currents, which had unusually long and very steep ramps, raised an emergency protection sequence of the TF coils in a KSTAR plasma experiment. Quench detection circuits only using traditional Wheatstone bridges are insufficient to cancel out such a mutual induction; whereas, the mutual induction can be numerically compensated in a theoretically straightforward calculation.

High-Speed Active Quench and Reset Circuit for SPAD in a Standard 65 nm CMOS Technology

A compact high-speed active quench and reset (AQR) circuit integrated with a p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> /n-well single-photon avalanche diode (SPAD) is designed and fabricated in a standard 65 nm CMOS technology. The post-layout simulations showed that the quenching time for this AQR circuit is only 0.1 ns, and the smallest dead time is 3.35 ns which corresponds a maximum count rate of ~300 Mcps. The measurements showed that the SPAD pixel achieved a dark count rate of 21 kHz, a peak photon detection probability of 23.8% at a 420 nm wavelength and a timing jitter of 139 ps (using a 405 nm pulsed laser) when the excess voltage was 0.5 V. Also, due to the short quenching time, negligible afterpulsing was observed during the measurements.

Differential Quench and Reset Circuit for Single-Photon Avalanche Diodes

A differential quench and reset (QR) configuration for single-photon avalanche diodes (SPADs) is proposed and investigated in this work. Compared to the traditional single QR configuration in which only one QR circuit is connected to either the cathode or anode of the SPAD, the differential QR configuration consists of two QR circuits to quench and reset through both the cathode and anode terminals. Using a SPAD fabricated in a 65 nm CMOS process, the measurement results of the traditional single passive quench and reset (SPQR) circuit and the proposed differential passive quench and reset (DPQR) circuit shows that the SPAD with the DPQR circuit presented a reduced reset time, an improved timing performance, an increased count rate and a decreased afterpulsing. In addition, the differential output pair from the DPQR circuit has the potential to increase the signal-to-noise ratio of the detection system due to its ability to reject common-mode noise and interference.

Quench Protection System of a Whole-Body Non-impregnated 1.5 T Superconducting MRI Magnet

A quench protection system for an actively-shielded whole-body 1.5 T MRI magnet made with wire-in-channel NbTi conductor is presented with two types of coil sub-divisions. The MRI magnet must operate for many years in the hospital, and thereby, it must be completely self-protecting by means of self-activating quench propagation heaters to spread the normal zone in a larger volume of the magnet during a quench i.e. the passive protection system. The total stored energy of the magnet is about 3.7 MJ. The voltage and the temperature of the coils have been simulated with two types of passive quench protection systems using OPERA-Quench program. The maximum inter-layer quench voltage generated in the asymmetric sub-division is 70 V/layer with a peak voltage of 2.6 kV and a hot spot temperature of 248 K. The maximum inter-layer quench voltage generated in the symmetric sub-division is 45 V/layer with a peak voltage of 1.7 kV and a hot spot temperature of 185 K. During a quench, an average driving voltage of 1.3 kV and the associated current of 1.75 A is generated in both quench propagation circuits of the magnet with the symmetric sub-division. The 5 G safety line explodes beyond the permissible limits during a quench of the magnet with the asymmetric sub-division, whereas the 5 G safety region is retained within the permissible limit in case of quench of the magnet with symmetric sub-division.

Design and Implementation of a Compact Single-Photon Counting Module

A compact single-photon counting module that can accurately control the bias voltage and hold-off time is developed in this work. The module is a microcontroller-based system which mainly consists of a microcontroller, a programmable negative voltage generator, a silicon-based single-photon avalanche diode, and an integrated active quench and reset circuit. The module is 3.8 cm × 3.6 cm × 2 cm in size and can communicate with the end user and be powered through a USB cable (5 V). In this module, the bias voltage of the single-photon avalanche diode (SPAD) is precisely controllable from −14 V ~ −38 V and the hold-off time (consequently the dead time) of the SPAD can be adjusted from a few nanoseconds to around 1.6 μs with a setting resolution of ∼6.5 ns. Experimental results show that the module achieves a minimum dead time of around 28.5 ns, giving a saturation counting rate of around 35 Mcounts/s. Results also show that at a controlled reverse bias voltage of 26.8 V, the dark count rate measured is about 300 counts/s and the timing jitter measured is about 158 ps. Photodetection probability measurements show that the module is suited for detection of visible light from 450 nm to 800 nm with a 40% peak photon detection efficiency achieved at around 600 nm.

Fast-Gated 16 × 1 SPAD Array for Non-Line-of-Sight Imaging Applications

In this paper we present a novel single-photon detector specifically designed for Non-Line-Of-Sight (NLOS) imaging applications within the framework of the DARPA REVEAL program. The instrument is based on a linear 16 × 1 Complementary Metal-Oxide-Semiconductor (CMOS) Single-Photon Avalanche Diode (SPAD) array operated in fast-gated mode by a novel fast-gating Active Quenching Circuit (AQC) array, which enables the detectors with sub-ns transitions thanks to a SPAD-dummy approach. The detector exhibits a timing resolution better than 50 ps (Full Width at Half Maximum - FWHM) at a measurement repetition rate up to 40 MHz, and provides 16 independent outputs compatible with commercial Time-Correlated Single-Photon Counting (TCSPC) instrumentation. The instrument has been experimentally characterized and operated in preliminary NLOS imaging acquisitions where a 40 × 60 cm hidden object is successfully reconstructed by scanning over a grid of 150 × 150 positions.

Thermohydraulic analysis of Tore Supra/WEST TF coil quench: Associated smooth quench occurrence in tokamak

The Toroidal Field (TF) system of the Tore Supra/WEST tokamak comprises 18 NbTi superconducting coils, cooled by a static superfluid helium bath at 1.8 K and carrying a nominal current of 1255 A. The 19th December 2017, at the end of plasma run #52205, a quench of TFC-09 was detected first on a secondary thermohydraulical signal (helium liquid level) and triggered the current Fast Safety Discharge (FSD). A numerical model of this quench has been developed with SuperMagnet (CryoSoft). The whole TFC-09 circular coil is modelled by THEA as a single large Cable-In-Conduit Conductor (CICC) with 2028 large rectangular strands (monolithic conductors of length equal to coil average perimeter). The external quench helium relief circuit (cold and warm safety valves, rupture disk and magnetic valve with corresponding pressure set) is modelled by FLOWER.The helium pressure in the coil, upstream of the cold safety valve (maximum value of 9 bar), and the expulsed helium temperature have been used as comparison between measurements and calculations which depend on the Minimum Quench Energy (MQE) used in THEA with small initial heat deposition length (few tens of centimeters) at low field region (external leg). This energy, in the order of few kJ, is compared to the real shape and energy of neutron and gamma flux caused by highly energetic runaway electrons colliding the outboard plasma facing components and which induced the quench. The expulsed helium mass flow rate of nearly 6 kg/s during 5 s has also been calculated. This event confirms on one hand the criticality and the possible occurrence of a so called “smooth quench” caused by small initial heat deposition length and at low field region and on the other hand the important interest of secondary quench detection which can be useful for other tokamak magnets safe operation and protection.

A 256 Pixelated SPAD readout ASIC with in-Pixel TDC and embedded digital signal processing for uniformity and skew correction

Abstract Coincidence timing resolution (CTR) of 10 ps FWHM would drastically increase the contrast of images in pre-clinical and clinical positron emission tomography (PET) due to the capability to localize the annihilation site along the line of response with unprecedented accuracy. Currently, the scintillators and the photodetectors with their electronic readout are the two limiting factors to reach such a timing resolution. On the photodetector side, the single photon timing resolution (SPTR) must be improved below 4 ps RMS to reach a CTR of 10 ps FWHM. To this end, we propose to use a 3D digital silicon photomultiplier (3DdSiPM) where each single photon avalanche diode (SPAD) has its own quenching circuit (QC) and time-to-digital converter (TDC). To reach an SPTR of 4 ps RMS in an array of SPAD requires to correct each readout pixel individually to minimize the impact of TDC least significant bit (LSB) non-uniformities and SPAD-to-SPAD skew. For this purpose, we developed an array of 256 pixels of SPAD readout circuits optimized for high timing precision with embedded digital signal processing. The latter is a code-to-time conversion where each pixel is individually corrected for TDC LSB variation and skew. Measurement results on single pixels (QC and TDC) show timing jitter down to 8 ps RMS. The uncorrected array timing jitter is about 87 ps RMS and is reduced to 18 ps RMS after skew correction and TDC LSB correction.

Quenching Circuit and SPAD Integrated in CMOS 65 nm with 7.8 ps FWHM Single Photon Timing Resolution

This paper presents a new quenching circuit (QC) and single photon avalanche diode (SPAD) implemented in TSMC CMOS 65 nm technology. The QC was optimized for single photon timing resolution (SPTR) with a view to an implementation in a 3D digital SiPM. The presented QC has a timing jitter of 4 ps full width at half maximum (FWHM) and the SPAD and QC has a 7.8 ps FWHM SPTR. The QC adjustable threshold allows timing resolution optimization as well as SPAD excess voltage and rise time characterization. The adjustable threshold, hold-off and recharge are essential to optimize the performances of each SPAD. This paper also provides a better understanding of the different contributions to the SPTR. A study of the contribution of the SPAD excess voltage variation combined to the QC time propagation delay variation is presented. The proposed SPAD and QC eliminates the SPAD excess voltage contribution to the SPTR for excess voltage higher than 1 V due to its fixed time propagation delay.

Fast fully-integrated front-end circuit to overcome pile-up limits in time-correlated single photon counting with single photon avalanche diodes.

Time-Correlated Single Photon Counting (TCSPC) is an essential tool in many scientific applications, where the recording of optical pulses with picosecond precision is required. Unfortunately, a key issue has to be faced: distortion phenomena can affect TCSPC experiments at high count rates. In order to avoid this problem, TCSPC experiments have been commonly carried out by limiting the maximum operating frequency of a measurement channel below 5% of the excitation frequency, leading to a long acquisition time. Recently, it has been demonstrated that matching the detector dead time to the excitation period allows to keep distortion around zero regardless of the rate of impinging photons. This solution paves the way to unprecedented measurement speed in TCSPC experiments. In this scenario, the front-end circuits that drive the detector play a crucial role in determining the performance of the system, both in terms of measurement speed and timing performance. Here we present two fully integrated front-end circuits for Single Photon Avalanche Diodes (SPADs): a fast Active Quenching Circuit (AQC) and a fully-differential current pick-up circuit. The AQC can apply very fast voltage variations, as short as 1.6ns, to reset external custom-technology SPAD detectors. A fast reset, indeed, is a key parameter to maximize the measurement speed. The current pick-up circuit is based on a fully differential structure which allows unprecedented rejection of disturbances that typically affect SPAD-based systems at the end of the dead time. The circuit permits to sense the current edge resulting from a photon detection with picosecond accuracy and precision even a few picoseconds after the end of the dead time imposed by the AQC. This is a crucial requirement when the system is operated at high rates. Both circuits have been deeply characterized, especially in terms of achievable measurement speed and timing performance.

Fast Cascoded Quenching Circuit for Decreasing Afterpulsing Effects in 0.35-&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\mu$ &lt;/tex-math&gt; &lt;/inline-formula&gt;m CMOS

In this letter, we present a fully integrated single-photon avalanche diode (SPAD) using a fast cascoded quenching circuit (QC) fabricated in a 0.35- ${\mu }\text{m}$ CMOS process. The QC features a fast active quenching time of only 0.48 ns and an adjustable total dead time (9.5–17 ns) to further reduce afterpulsing effects. To prove the quenching performance, the circuit was integrated together with a large-area SPAD having an active diameter of 80 ${\mu }\text{m}$ . Experimental verification of reduction of afterpulsing with early quenching is shown. Thus, a minimal afterpulsing probability of 0.9% was measured at 6.6 V excess bias and a photon detection probability of 22% at a wavelength of 850 nm was achieved.

Digital SiPM channel integrated in CMOS 65 nm with 17.5 ps FWHM single photon timing resolution

Single photon avalanche diodes (SPAD) are detectors used for applications requiring high timing resolution and single photon sensitivity. Medical imaging modalities such as positron emission tomography benefit from higher timing resolution enabling time-of-flight (ToF) measurements. One of the current challenge in the development of SiPM detectors is combining both high photodetection efficiency (PDE) and high single photon timing resolution (SPTR). Although SiPM have a high fill factor, they are limited for sub-10 ps FWHM SPTR for two reasons: the high output capacitance directly affects the rise time and a timing skew is associated with the SPAD position in the array. The proposed solution to obtain ToF capabilities with both high SPTR and PDE is to make a 3D digital SiPM where every SPAD is individually connected to a quenching circuit (QC) and a time-to-digital converter (TDC). While the 3D integration process is underway, we designed and tested a 2D version of a single channel of the detector composed of a SPAD, a QC and a TDC in TSMC CMOS 65 nm. This paper presents a SPAD and QC with 9 ps FWHM SPTR and a chain composed of a SPAD, a QC and a TDC with 17.5 ps FWHM SPTR.

Simulation optimization on quench analysis of wide aperture superconducting quadrupole magnet

Wide aperture superconducting magnets are used in different accelerator laboratories as spectrometer magnets. These magnets are used in the accelerator facilities like ANURIB project, Kolkata, newly constructed BIGRips facility in Japan and FAIR project in GSI, Germany. Quench simulation is an important part of the design of superconducting magnet. The present simulation has been carried out using QUENCH code and QUENCH-ELECTRA coupled code of Vector Fields software for wide aperture superconducting quadrupole magnet. Since the quench calculation is highly nonlinear in nature, Computation time is generally high. As increased computation time increases cost of design, choosing proper mesh size and time stepping tolerances play an important role during quench calculation. This paper will discuss about convergence of hot spot temperature and maximum voltage on mesh size, tolerance criteria. Computation time for each case, effect of delay in actuation of quench circuit will also be discussed.

Development of radiation tolerant components for the Quench Protection System at CERN

This paper describes the results of irradiation campaigns with the high resolution Analog to Digital Converter (ADC) ADS1281. This ADC will be used as part of a revised quench detection circuit for the 600 A corrector magnets at the CERN Large Hadron Collider (LHC) . To verify the radiation tolerance of the ADC an irradiation campaign using a proton beam, applying doses up to 3,4 kGy was conducted. The resulting data and an analysis of the found failure modes is discussed in this paper. Several mitigation measures are described that allow to reduce the error rate to levels acceptable for operation as part of the LHC QPS.

A novel approach to quench detection for high temperature superconducting coils

A novel approach to quench detection for high temperature superconducting (HTS) coils is proposed, which is mainly based on phase angle between voltage and current of two coils to detect the quench resistance voltage. The approach is analyzed theoretically, verified experimentally and analytically by MATLAB Simulink and LabVIEW. An analog quench circuit is built on Simulink and a quench alarm system program is written in LabVIEW. Experiment of quench detection is further conducted. The sinusoidal AC currents ranging from 19.9A to 96A are transported to the HTS coils, whose critical current is 90A at 77K. The results of analog simulation and experiment are analyzed and they show good consistency. It is shown that with the increase of current, the phase undergoes apparent growth, and it is up to 60° and 15° when the current reaches critical value experimentally and analytically, respectively. It is concluded that the approach proposed in this paper can meet the need of precision and quench resistance voltage can be detected in time.

Upgrade of the Protection System for the Superconducting Elements of the LHC During LS1

During the first long shutdown (LS1) of the Large Hadron Collider (LHC), the protection system for the superconducting elements of the LHC will substantially be upgraded with the principal objectives to extend its diagnostic capabilities and to enhance the system immunity to ionizing radiation. All proposed measures will improve the overall system dependability as well. The supervision of the quench heater circuits of the LHC main dipoles will be enhanced by adding additional measurement channels for the discharge current and increasing the sampling frequency and resolution of the related data acquisition systems. By these measures it will be possible to identify potential fault states of the quench heater circuits, which may affect the integrity of the concerned magnets. At this occasion all main dipole protection systems will be submitted to general overhaul after four years of successful operation. Within the radiation to electronics project, the upgrade of the protection systems will be concluded by installing the latest versions of radiation tolerant quench detection electronics. In addition some equipment will be relocated to shielded areas.

Experimental Evaluation of the Influence of External Current on the KSTAR TF Quench Detection System

The quench detection system (QDS) for 16 toroidal field (TF) coils of the Korea Superconducting Tokamak Advanced Research (KSTAR) is using Wheatstone bridges to naturally reduce induced voltage in the quench detection circuits. The TF coils have to be quickly discharged to save the superconductors from thermal runaway if quench occurs; on the other hand, the fast discharge brings about many side effects. Thus, malfunction of the TF QDS should be avoided. According to the results of the TF QDS operation in KSTAR campaigns, the single Wheatstone bridges can sufficiently reduce self-induced voltage even though the induced voltage may remain due to unbalancing the bridges by ferromagnetism of the cable-in-conduit conductor (CICC) jackets at small TF coil current. In contrast, mutually induced voltage by central solenoid (CS) and poloidal field (PF) coils may not be sufficiently reduced by using a single Wheatstone bridge comparing voltages across a number of TF coils due to larger electric circuits in the cryostat. On the other hand, a single Wheatstone bridge comparing single TF coil voltages could not effectively reduce the sharp impulse voltage caused by locally induced current on the vacuum vessel at the end of plasma current with vertical displacement event (VDE).

Experimental Evaluation of a Mutually Induced Voltage Correction Method to Improve the KSTAR Quench Detection System

The superconducting state of the coils and bus lines of the Korea Superconducting Tokamak Advanced Research is monitored by a quench detection system. The system utilizes co-wound conductive strips and Wheatstone bridges, and in addition compares two quench detection signals for upper and lower coils to reduce induced voltage. The co-wound conductive strips and Wheatstone bridges, however, are very sensitive to mutual induction by neighboring coil currents, and on the other hand the comparison of the quench detection signals is not assured in a vertically asymmetric magnetic field. Thus, a numerical correction method of the inductances and induced voltages on quench detection circuits for the CS and PF coils was evaluated using actual measurements. The inductance on each quench detection circuit had a peculiar profile probably caused by magnetism of the conductors. The amplitudes of the induced voltages certainly reflected the magnitudes of the inductances; however, the correction of the quench detection signals was difficult because the inductances available for the correction were obtained by alternately applying each coil current.

High-Speed, Single-Photon Avalanche-Photodiode Imager for Biomedical Applications

The design of a low-light level pixel in CMOS technology for biomedical applications is described. This pixel is also suitable for very high-speed applications, such as fluorescence lifetime imaging (FLIM) used for drug discovery and/or minimally-invasive optical biopsy. In order to achieve high-speed imaging using single-photon detection, a detector with a very low dead-time is needed. The single-photon avalanche-photodiode (SPAD) discussed in this work uses a mainstream deep-submicron CMOS technology in order to achieve ultrahigh-speed operation and high pixel fill-factor, with in-pixel active quench and reset circuits. The paper also presents an innovative approach for reducing the deadtime of the detector and an attractive technique for simultaneous high-speed image acquisition by all the pixels of an array in parallel.