Y. Farah

RHIC 25 kW Refrigerator and Distribution System, Construction, Testing, and Initial Operating Experience

The installation and testing of most of the Relativistic Heavy Ion Collider (RHIC) cryogenic system is complete. The RHIC cryogenic system consisting of the modified ISABELLE refrigerator, and other new cryogenic components, has been completed from the 25 kW refrigerator through one sixth of the 3.8 km circumference RHIC accelerator up to the 4:00 valve box. This paper covers the progress to date with respect to construction and installation of the helium distribution system, including the vacuum jacketed piping and valve boxes, recoolers, and controls. In addition, the 25 kW refrigerator has been operated on three seChapaute occasions over the past two years. These first experiences with the operation of the refrigerator and warm compressor system, along with some test results will be discussed here.

A Precision Cryogenic Temperature Data Acouisition System

A multiplexed temperature data acquisition system with an overall precision of ±25 PPM has been designed using state-of-the-art electronics to accurately read temperature between 2.4 K and 600 K from pre-calibrated transducers such as germanium, silicon diode, thermistor or platinum temperature sensors.

Performance of the RHIC Cryogenic Control System During the First Sextant Test

The present RHIC cryogenic process control system is a hybrid of centralized and distributed processing. The setup marries together a centralized sub-system that was designed, installed, and in operation since 1984 with six identical distributed sub-systems, whose installation began in 1996 and will be completed in 1998. For the RHIC First Sextant Test, which took place from January 21, 1997 to March 5, 1997, it was necessary to have two new distributed cryogenic control sub-systems installed and tested.

Operational Tests of the BNL 24.8 kW, 3.8 K Helium Refrigerator

The BNL 24.8 kW refrigeration system is completely installed and major portions of the acceptance tests have been completed. So far, the equipment tested has performed at or above design levels. The room temperature helium compressor station has been completely tested and accepted. The two-stage oil injected screw compressor system exhibited an isothermal efficiency of 57% while delivering a helium flow in excess of 4400 g/s. Data on the performance of the make-up gas cryogenic purifier is also given.

Design of the LHC US ATLAS Barrel Cryostat

One of the experiments of CERN’s Large Hadron Collider (LHC) is the ATLAS Liquid Argon detector. The Liquid Argon Barrel Cryostat is part of the United States contribution to the LHC project and its design is presented here. The device is made up of four concentric cylinders: the smallest and largest of which form a vacuum vessel enclosing a cold vessel cryostat filled with liquid argon. The Cryostat serves as the housing for an electromagnetic barrel calorimeter, supports and provides space in vacuum for a solenoid magnet while the toroidal opening furnishes room for a tracker detector. Design requirements are determined by its use in a collider experiment: the construction has to be compact, the material between the interaction region and the calorimeter has to be minimal and made of aluminum to reduce the amount of absorbing material. The design complies with code regulations while being optimized for its use in a physics environment.

Status, Operation and Performance of the RHIC Helium Refrigerator

The Relativistic Heavy Ion Collider RHIC helium refrigerator was modified from the refrigerator originally constructed fifteen years ago for the ISABELLE accelerator. The modifications include a new cold vacuum compressor and relocating the cold circulating compressor to the cryogenic distribution valve boxes, which are located near the cryogenic feed to the collider rings. Prior to start up, an extensive effort was spent on improving conditions of the compressor system, turbine skids, valves, instrumentation and control apChapautus. In February, 1996, the RHIC refrigerator was successfully cooled to liquid helium temperature with 10 kW of heat input at 4.5 K, 53 kW at 60 K and 44 g/s of liquefaction, using approximately two-thirds of the installed compressor capacity. In July, 1996, the refrigerator was used to cool a 350 meter vacuum jacketed transfer line and two cryogenic distribution valve boxes. In February, 1997, the refrigerator was used to cool the first RHIC sextant for over one month of operation. At the end of the first sextant test, an electric heat input of 25 kW at approximately 5.5 K was introduced to simulate a full refrigeration capacity mode. The capacity and reliability of the refrigerator have been demonstrated. The performance of the refrigerator including turbines, heat exchangers, cold vacuum compressor and circulating compressor is given.

Forced Convection Cooled Thermistors Used as Magnet Lead Flow Sensors

Brookhaven National Laboratory (BNL) has developed a simple, inexpensive method for monitoring the flow, which cools the 12×50 Amp corrector power leads for the Relativistic Heavy Ion Collider (RHIC). Since there are more than 500 leads of this type distributed around the 3.8 km circumference accelerator, each requiring flow control and monitoring, the use of conventional mass flow meters is not economically feasible. The device consists of a negative temperature coefficient thermistor mounted inside a tube, through which helium gas flows from the power lead. The helium gas cools the sensor through convection causing a temperature change and therefore a resistance change in the sensor. The electrical circuit reacts by adjusting the current supplied to the sensor to maintain the resistance at a constant value. The change in current is used to calculate the helium mass flow rate. The flow meter monitors flow in the range of .03 to .05 g/s with an accuracy of plus or minus 10%. Presented here are the design calculations as well as the flow meter performance.

RHIC Accelerator Commissioning, Cryogenic Tests and Initial Operating Experience of the 25 kW Refrigerator and Distribution System

The installation, initial cooldown, and cryogenic testing of the RHIC accelerator magnets and cryogenic system are complete. This paper covers the final phase of cryogenic equipment installation, performance of the system during the first accelerator cooldown, and difficulties encountered with cooling and commissioning. The 25 kW refrigerator, although operated for limited time periods in the past, has been running continuously for months. Operational experiences of the refrigerator and warm compressor systems will be discussed.

Performance and Operating Experience of the RHIC First Sextant Test

Installation and testing of the first sextant of RHIC magnets has been completed. The tests consisted of temperature cycling, quenching magnets, and measuring important engineering parameters of a string of magnets totaling a length of over 500 meters. This represents one sixth of the 3.8 kilometer circumference of the RHIC machine and serves as a basis for extrapolation of parameters for full machine operation. This paper gives an overview of the entire system, a detailed discussion of startup problems, operations and cryogenic system reliability over the period of the test and details of some of the important cryogenic operating parameters.

Helium Refrigeration System for BNL Colliding Beam Accelerator

A Helium Refrigeration System which will supply the cooling required for the Colliding Beam Accelerator at Brookhaven National Laboratory is under construction. Testing of the compressor system is scheduled for late 1983 and will be followed by refrigerator acceptance tests in 1984. The refrigerator has a design capacity of 24.8 kW at a temperature level near 4K while simultaneously producing 55 kW for heat shield loads at 55K. When completed, the helium refrigerator will be the worlds largest. Twenty-five oil-injected screw compressors with an installed total of 23,250 horsepower will supply the gas required. One of the unique features of the cycle is the application of three centrifugal compressors used at liquid helium temperature to produce the low temperatures (2.5K) and high flow rates (4154 g/s) required for this service.