L. X. Jia

Design parameters for gas-cooled electrical leads of the g-2 magnets

This report presents the design parameters for a pair of 5300 A gas-cooled electrical leads for the g-2 solenoids and a pair of 2850 A leads for the inflector magnet. The lead design parameters are derived from a scale analysis of two one-dimensional, thermo-fluid-electro-quasi-coupled, and non-linear differential equations. The analysis may apply to general gas-cooled electrical lead design. As an illustration, these design parameters are applied to multi-tube gas-cooled leads that are proposed for the g-2 solenoid magnet system. Multiple electrical current carrying tubes and multiple gas flow cooling channels will increase the lead current capacity and lead efficiency for enhanced heat transfer and low flow pressure drop.

A Design Method for Multiple Tube Gas-Cooled Electrical Leads for the g-2 Superconducting Magnets

This report presents a method for designing 5300 A gas cooled electrical leads for the g-2 solenoids and 2850 A leads for the g-2 self shielded inflector dipole magnet. Empirical design equations for annular tube gas cooled leads are presented. The leads are bundled tube leads which are cooled by helium flowing in annular cooling passages between tubes. Each tube in the bundle consists of nested circular copper tubes that can be cooled on both sides. Multiple current carrying tubes will increase the lead current capacity and cooling the tubes on both sides will increase lead efficiency for a given helium flow pressure drop. The design method presented here can applied to leads made from a variety of materials.

AC Losses in the MICE Channel Magnets -- Is This a Curse or aBlessing?

This report discusses the AC losses in the MICE channel magnets during magnet charging and discharging. This report talks about the three types of AC losses in the MICE magnets; the hysteretic AC loss in the superconductor, the coupling AC loss in the superconductor and the eddy current AC loss in the magnet mandrel and support structure. AC losses increase the heat load at 4 K. The added heat load increases the temperature of the second stage of the cooler. In addition, AC loss contributes to the temperature rise between the second stage cold head and the high field point of the magnet, which is usually close to the magnet hot spot. These are the curses of AC loss in the MICE magnet that can limit the rate at which the magnet can be charge or discharged. If one is willing to allow some of the helium that is around the magnet to boil away during a magnet charge or discharge, AC losses can become a blessing. The boil off helium from the AC losses can be used to cool the upper end of the HTS leads and the surrounding shield. The AC losses are presented for all three types of MICE magnets. The AC loss temperature drops within the coupling magnet are presented as an example of how both the curse and blessing of the AC losses can be combined.

Cryogenics for the muon g-2 superconducting magnet system

Abstract The g-2 muon storage ring magnet system consists of four large superconductingsolenoids that are up to 15.1 m in diameter[1,2]. In addition there is a 1.8 meter long actively shielded inflector dipole that is to guide the beam into the storage ring. The g-2 superconducting magnets will be cooled using forced two-phase helium in tubes that is provided from the J-T circuit of a 625 W refrigerator. The two-phase helium flows from the refrigerator J-T circuit through a heat exchanger in a storage dewar that acts as a phase separator and a buffer for helium returning from the magnets. The g-2 magnet cooling system consists of three parallel two-phase helium flow circuits that provide cooling to. the four large superconducting solenoids, the current interconnects between the solenoids with the 5300 A solenoid gas cooled electrical leads, and the inflector dipole with its 2850 A gas cooled electrical leads.

Cryogenic Design and Operation of Liquid Helium in Electron Bubble Chamber

We are developing a new cryogenic neutrino detector: electron bubble chamber, using liquid helium as the detecting medium, for the detection of low‐energy neutrinos (<1 MeV), from the Sun. The program focuses in particular on the interactions of neutrinos scattering off atomic electrons in the detecting medium of liquid helium, resulting in recoil electrons which can be measured. We designed and constructed a small test chamber with 1.5L active volume to start the detector R&D, and performed experimental proofs of the operation principle. The test chamber is a stainless steel cylinder equipped with five optical windows and ten high voltage cables. To shield the liquid helium chamber against the external heat loads, the chamber is made of double‐walled jacket cooled by a pumped helium bath and is built into a LN2/LHe cryostat, equipped with 80 K and 4 K radiation shields. A needle valve for vapor helium cooling was used to provide a 1.7∼4.5 K low temperature environments. The paper gives an introduction to...

A five-watt G-M/J-T refrigerator for LHe target at BNL

A five-watts G-M/J-T refrigerator was built and installed for the high-energy physics research at Brookhaven National Laboratory in 2001. A liquid helium target of 8.25 liters was required for an experiment in the proton beam line at the Alternating Gradient Synchrotron (AGS) of BNL. The large radiation heat load towards the target requires a five-watts refrigerator at 4.2 K to support a liquid helium flask of 0.2 meter in diameter and 0.3 meter in length which is made of Mylar film of 0.35 mm in thickness. The liquid helium flask is thermally exposed to the vacuum windows that are also made of 0.35 mm thickness Mylar film at room temperature. The refrigerator uses a two-stage Gifford-McMahon cryocooler for precooling the Joule-Thomson circuit that consists of five Linde-type heat exchangers. A mass flow rate of 0.8 {approx} 1.0 grams per second at 17.7 atm is applied to the refrigerator cold box. The two-phase helium flows between the liquid target and liquid/gas separator by means of thermosyphon. The paper presents the system design as well as the test results including the control of thermal oscillation.

Cryogenic tests of the g-2 superconducting solenoid magnet system

SC-HAG 525 LBL-37S02 CRYOGENIC TESTS OF THE g-2 SUPERCONDUCTING SOLENOID MAGNET SYSTEM L. X. Jia, J. R. Cullen Jr., A. J. Esper, R. E. Meier C. Pai, L. Snydstrup and T. Tallerico, Brookhaven National Laboratory Upton, NY 11973 M. A. Green E. O. Lawrence Berkeley National Laboratory Uni versity of California Berkeley, CA 94720 July 1995 * This work was performed at the Lawrence Berkeley Laboratory and at Brookhaven National Laboratory with the support of the Director of the Office of Energy Research, Office of High Energy and Nuclear Physics, High Energy Physics Division, United States Department of Energy under BNL contract number DE-AC02-76CHOOOI6 and LBL contract number DE-AC03-76SF00098.

Dynamic Modeling and Simulation of Liquid Helium Level in SRF Cryomodule for BEPCII

Two 500MHz superconducting RF cavities will be applied for Beijing Electron‐Positron Collider Upgrade (BEPCII), and their cooling system is being built. In addition to limiting the pressure fluctuations within ± 3mbar, the fluctuations of the liquid helium level in the cryomodules have to be kept within ±1% during the operation of SRF cavities. Due to relatively long distances between the distribution valve box and the two cavity cryostats, a time‐delay problem in the level control loop arises, which will lead to a long commissioning time in the future. Hence, a dynamic process simulation model for the level control loop is presented in this paper. The basic dynamic response characteristics of the level control and optimized PID controller parameters for one of the SRF cavity are presented.

Thermal oscillations in liquid helium targets

A liquid helium target for the high-energy physics was built and installed in the proton beam line at the Alternate Gradient Synchrotron of Brookhaven National Laboratory in 2001. The target flask has a liquid volume of 8.25 liters and is made of thin Mylar film. A G-M/J-T cryocooler of five-watts at 4.2K was used to produce liquid helium and refrigerate the target. A thermosyphon circuit for the target was connected to the J-T circuit by a liquid/gas separator. Because of the large heat load to the target and its long transfer lines, thermal oscillations were observed during the system tests. To eliminate the oscillation, a series of tests and analyses were carried out. This paper describes the phenomena and provides the understanding of the thermal oscillations in the target system.

Cryogenic control system for the g-2 muon ring

The g-2 Muon storage ring consists of three superconducting solenoids 15 meters in diameter, and a beam Inflector solenoid 1.7 meters in length. All superconducting solenoids are indirectly cooled by forced two-phase helium. Cryogenic cooling is accomplished via a J-T circuit and a LHe control dewar. The control System for this cryogenic system is built around commercially available Programmable Logic Controllers (PLC’s) and cryogenic hardware for monitoring temperature, pressure and flow control. The complexity of this system necessitated the use of a graphical user interface (GUI) which permitted operators to perform monitoring and control functions from a central control room. The graphical interface allowed for rapid operator training and, with the cooling circuit schematic shown graphically they can respond to critical situations promptly. Critical data points on the experiment are logged in the software and historical trends are provided for. Using a software based system allowed for rapid system revisions as they were required. Flow control can be performed manually by the operator or automatically by the software based on linear control algorithms. The system has been in use for two years with successful results.