J. Creel

Status of the Cryogenic System Commissioning at SNS

The Spallation Neutron Source (SNS) is under construction at Oak Ridge National Laboratory. The cold section of the Linac consists of 81 superconducting radio frequency cavities cooled to 2.1K by a 2400 Watt cryogenic refrigeration system. The major cryogenic system components include warm helium compressors with associated oil removal and gas management, 4.5K cold box, 7000L liquid helium dewar, 2.1K cold box (consisting of 4 stages of cold compressors), gaseous helium storage, helium purification and gas impurity monitoring system, liquid nitrogen storage and the cryogenic distribution transfer line system. The overall system commissioning strategy and status will be presented.

SCREW COMPRESSOR CHARACTERISTICS FOR HELIUM REFRIGERATION SYSTEMS

The oil injected screw compressors have practically replaced all other types of compressors in modern helium refrigeration systems due to their large displacement capacity, minimal vibration, reliability and capability of handling heliums high heat of compression.At the present state of compressor system designs for helium systems, typically two-thirds of the lost input power is due to the compression system. Therefore it is important to understand the isothermal and volumetric efficiencies of these machines to help properly design these compression systems to match the refrigeration process. This presentation summarizes separate tests that have been conducted on Sullair compressors at the Superconducting Super-Collider Laboratory (SSCL) in 1993, Howden compressors at Jefferson Lab (JLab) in 2006 and Howden compressors at the Spallation Neutron Source (SNS) in 2006. This work is part of an ongoing study at JLab to understand the theoretical basis for these efficiencies and their loss mechanisms, as well ...

SNS Cryogenic Systems Commissioning

The Spallation Neutron Source (SNS) is under construction at Oak Ridge National Laboratory. The cold section of the Linac consists of 81 superconducting radio frequency cavities cooled to 2.1K by a 2400 watt cryogenic refrigeration system. The major cryogenic system components include warm helium compressors with associated oil removal and gas management, 4.5K cold box, 7000L liquid helium dewar, 2.1K cold box (consisting of 4 stages of cold compressors), gaseous helium storage, helium purification and gas impurity monitoring system, liquid nitrogen storage and the cryogenic distribution transfer line system. The overall system commissioning and future plans will be presented.

Cryogenic System for the Spallation Neutron Source

The Spallation Neutron Source (SNS) is a neutron‐scattering facility being built at Oak Ridge, TN for the US Department of Energy. The SNS accelerator linac consists of superconducting radio‐frequency (SRF) cavities in cryostats (cryomodules). The linac cryomodules are cooled to 2.1 K by a 2300 watt cryogenic refrigeration system. As an SNS partner laboratory, Jefferson Lab is responsible for the installed integrated cryogenic system design for the SNS linac accelerator consisting of major subsystem equipment engineered and procured from industry. Jefferson Lab’s work included developing the major vendor subsystem equipment procurement specifications, equipment procurement, and the integrated system engineering support of the field installation and commissioning. The major cryogenic system components include liquid nitrogen storage, gaseous helium storage, cryogen distribution transfer line system, 2.1‐K cold box consisting of four stages of cold compressors, 4.5‐K cold box, warm helium compressors with i...

Commissioning of helium compression system for the 12 GeV refrigerator

The compressor system used for the Jefferson Lab (JLab) 12 GeV upgrade, also known as the CHL-2 compressor system, incorporates many design changes to the typical compressor skid design to improve the efficiency, reliability and maintainability from previous systems. These include a considerably smaller bulk oil separator design that does not use coalescing elements/media, automated control of cooling oil injection based on the helium discharge temperature, a helium after-cooler design that is designed for and promotes coalescing of residual oil and a variable speed bearing oil pump to reduce oil bypass. The CHL-2 helium compression system has five compressors configured with four pressure levels that supports the three pressure levels in the cold box. This paper will briefly review several of these improvements and discuss some of the recent commissioning results.

LARGE SCALE REFRIGERATION PLANT FOR GROUND TESTING THE JAMES WEBB TELESCOPE AT NASA JOHNSON SPACE CENTER

The James Webb Telescope is the successor to the Hubble Telescope and will be placed in an orbit of 1.5 million km from earth. Before launch in 2014, the telescope will be tested in NASA Johnson Space Center’s (JSC) space simulation chamber, Chamber A. The tests will be conducted at deep space conditions. Chamber A’s helium cryo‐panels are currently cooled down to 20 K by two Linde 3.5 kW helium refrigerators. The new 12.5 kW, 20‐K helium coldbox described in this paper is part of the upgrade to the chamber systems for this large test program. The Linde coldbox will provide refrigeration in several operating modes where the temperature of the chamber is being controlled with a high accuracy due to the demanding NASA test requirements. The implementation of two parallel expansion turbine strings and the Ganni cycle—Floating Pressure process results in a highly efficient and flexible process that minimizes the electrical input power. This paper will describe the collaboration and execution of the coldbox pr...

The Liquid Nitrogen System for Chamber A: A Change from Original Forced Flow Design to a Natural Flow (Thermo Siphon) System

NASA at the Johnson Space Center (JSC) in Houston is presently working toward modifying the original forced flow liquid nitrogen cooling system for the thermal shield in the space simulation chamber‐A in Building 32 to work as a natural flow (thermo siphon) system. Chamber A is 19.8 m (65 ft) in diameter and 35.66 m (117 ft) high. The LN2 shroud environment within the chamber is approximately 17.4 m (57 ft) in diameter and 28 m (92 ft) high. The new thermo siphon system will improve the reliability, stability of the system. Also it will reduce the operating temperature and the liquid nitrogen use to operate the system. This paper will present the requirements for the various operating modes. System level thermodynamic comparisons of the existing system to the various options studied and the final option selected will be outlined. A thermal and hydraulic analysis to validate the selected option for the conversion of the current forced flow to natural flow design will be discussed. The proposed modification...

Overview and Status of the 12 GeV Cryogenic System Upgrade At Jlab

As part of the planned Jefferson Laboratory’s electron accelerator (CEBAF) power upgrade, ten additional superconducting RF cryomodules will be added to its accelerator linacs. Although physically the same size as each of the original 40 linac cryomodules, each new cryomodule will have approximately 4 times the acceleration power. To support the additional cryomodule heat loads generated, the existing 2 K, 4600 W Central Helium Liquefier (CHL) plant capacity will be doubled to a total of 9200 W at 2 K plus 24,000 W at 35 K for shield loads. The specified base line process cycle has been modeled after the laboratory’s “Ganni Helium Cycle” process technology. In addition, a fourth physics experimental “Hall D” will be constructed which will have an additional stand alone 200 W at 4 K helium cryogenic plant. In October of 2008, Jefferson Laboratory (JLab) received approval for project “Critical Decision 3” construction phase status from the US Department of Energy. An overview of the planned cryogenic system...

AN OVERVIEW OF THE PLANNED JEFFERSON LAB 12GeV HELIUM REFRIGERATOR UPGRADE

In February 2006, Jefferson Laboratory in Newport News, VA, received “Critical Decision 1” (CD-1) approval to proceed with the engineering and design of the long anticipated upgrade to increase the beam energy of CEBAF, the Continuous Electron Beam Accelerator Facility, from 6 GeV to 12 GeV. This will require the installation of 10 new cryomodules, and additional 2.1-K refrigeration beyond the available 4600 W to handle the increased heat loads. Additionally, a new experimental hall, Hall D, is planned that will require the installation of a small, available refrigerator. This paper will present an overview of the integration of the new proposed refrigeration system into CEBAF, the installation of the available refrigerator for Hall D, and includes planned work scope, current schedule plans and project status.

Design, fabrication, commissioning, and testing of a 250 g/s, 2-K helium cold compressor system

In June 1999 the Thomas Jefferson National Accelerator Facility (TJNAF) Cryogenic Systems Group had completed the design, fabrication, and commissioning of a cold compressor system capable of pumping 250 g/s of 2-K helium vapor to a pressure above 1 bar. The 2-K cold box consists of five stages of centrifugal variable speed compressors with LN 2 cooled drive motors and magnetic bearings, a plate fin heat exchanger, and an LN 2 shield system. The new 2-K cold box (referred to as the SCN) was built as a redundant system to an existing four stage cold compressor SCM cold box that was commissioned in May 1994. The SCN has been in continuous service supporting the facility experiments since commissioning. This system has achieved a significant improvement in the total 2-K refrigeration system capacity and stability and has substantially increased the operating envelope both in cold compressor flow and operating pressure range. This paper describes the cold box configuration and the experiences in the design, fabrication, commissioning and performance evaluation. The capacity of the system for various operating pressures (0.040 to 0.025 bar at the load corresponding to a total compressor pressure ratio of 28 to 54) is presented. An effort is made to characterize the components and their operating data over the tested range. This includes the return side pressure drop in the distribution system, the heat exchanger, and the cold compressor characteristics. The system design parameters and their effects on performance are outlined.