An Update of Cryogenic Systems Operating Procedures. ERROL YUKSEK (Old Dominion University Norfolk, VA 23529) DANA ARENIUS (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)

The Cryogenic Systems Group at Thomas Jefferson National Accelerator Facility (JLab) has seen many changes to the equipment, systems, and operating procedures since their initial commissioning phases of the early 1990s. JLab's cryogenic systems include the Central Helium Liquefier (CHL), the End Station Refrigerator (ESR), the Cryogenic Test Facility (CTF), and the associated Cryogenic Distribution Systems in the Linear Accelerators (LINACS), the Experimental Halls, and the Test Lab. Because of the changes made to these systems, an update of the cryogenic operating procedures was required in order to maintain correct execution of the various transient and steady state operations. It is of great importance for large and complex operating systems, such as JLab's cryogenic systems, to maintain current operating procedures for safe, efficient, and continuous operation. Based upon a review of flow schematics, mechanical drawings, engineers' notes, inspection of systems, and observation of maintenance operations, an understanding of these systems' fundamental principles has provided enough insight and information to support revisions to the operating procedures. Once an understanding of the relevant issues had been attained, procedures which needed immediate attention and revision were identified and revised. In addition, new operating procedures were created as needed. The revised operating procedures will be available on the Cryogenic Systems Group's network drive to anyone that needs to learn how to operate the cryogenic systems.

Fabrication of a GC Power Supply for the Thomas Jefferson National Accelerator Facility (JLab) Free Electron Laser (FEL) Electronics Systems. NATHAN BELCHER (The College of William and Mary Williamsburg, VA 23186) KEVIN JORDAN (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)

The magnets designated as GC corrector dipoles provide fine vertical steering correction at two positions in each of the 180-degree bends of Jefferson Lab's FEL electron beam line. Because of the tight quarters in the beam line, a Panofsky Quadrupole was combined with a dipole to create the GC magnet. The innovation of the design comes from using the existing coils that generate quadrupole field to also generate dipole field. But, the circuitry must be designed in such a way that the dipole magnets are biased independent of the voltage across the quadrupole coils. Because of the necessity for independent biasing, the circuit was designed as a push-pull bridge circuit with a floating ground side and a real ground side. Beginning with two circuit boards that contained excessive oscillations from an incorrect offset in the push-pull circuit, tests were run to analyze the extent of the oscillations. From these tests, various resistors and capacitors were added to filter the oscillations. The gains of several parts of the boards were changed to enhance stability, and outside shunts were added to dissipate heat from the main circuitry. After this stabilization, the boards were measured against the actual input voltage to analyze the offset voltage. This offset voltage was trimmed by the potentiometers on the boards to create boards that would produce the correct output current with respect to the input voltage. These working boards will be installed in the chassis and integrated into the electronics system. In the future, another chassis will be fabricated and integrated into the electronics system.

Testing and Development of Cryogenic Radiation Detector for Superconducting Radiofrequency Cavity Field Emission Mapping. PHILLIP ZELLNER (Virginia Polytechnic Institute and State University Blacksburg, VA 24061) DAN DOTSON (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)

During operation and testing, Jefferson Lab's Superconducting Radiofrequency (SRF) cavities give off radiation known as field emissions. Field emissions greatly limit the efficiency and maximum output of SRF cavities. For optimum performance, sources of field emissions must be located and removed. Currently, field emission measurements are made outside the stainless steel cryogenic dewar, making them rough estimates. For effective field emission mapping, a radiation detector must be placed inside the helium dewar and be exposed to the 2 K liquid helium. As a result of much research and experimentation, a cesium iodide (CsI) detector has been selected to perform the task. The detector was calibrated and then mounted on a cryogenic test stand, pointing directly down the axis of an SRF cavity pair during routine testing. Data was then gathered from the detector and compared with the power levels and rough field emission data. While there was a correlation, more testing is needed to develop a stronger correlation for greater precision. Once this detector has been fully tested, a precise rotating apparatus must then be developed to carry an array of these detectors into the helium dewar. Data gathered from such a device could then produce a 3-D model of an SRF cavity's field emissions, making defect detection easy.

Web-Based Data Acquisitions Systems Utilizing the Rabbit Microprocessor. BRENDAN MATHEWS (West Virginia University Morgantown, WV 26505) JOHN MUSSON (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)

In 2004, Jefferson Lab began what is known as the trim card project to update the cards controlling the current flow to the trim magnets within the accelerator. Also a card was created a card to perform general housekeeping on the system such as take care of gain selection, and multiplex various inputs. It was decided that these cards could also be used to measure a variety of analog signals from various test equipment. However, in order to use them efficiently for data acquisitions systems, another smarter board would be required to drive the devices. The goal of this project was to find a board that would allow these cards to create a generic, web-based, and user-friendly dada acquisitions system. The card chosen to drive these boards was the Rabbit Core Microprocessor 2200 (RCM2200) because it was able to utilize Ethernet, RS232, and Serial peripheral interface (SPI) connections, which allowed for a wide variety of communication options. The Rabbit's hundreds of factory-defined functions, allow the users or programmers modify the programs interface creating a very generic system whose design could be left entirely to the system's users. Overall, the field tests have shown that the Rabbit performs very well efficiently controlling the digital meters and allowing users complete control of the system from a simple web interface.