\subsubsection*{Purpose and Requirements}

The Solenoid is the magnetic element selected for the GLueX Experiment to provide momentum analysis in the central tracking chambers. The Solenoid is a large (73 inch) warm bore super conducting (SC) device that produces a nominal maximum central field of 2.2 Tesla at 1800 Amps. The Magnet is 195 inches long and weighs  approximately 300 tons. The solenoid was originally designed as a highly reliable and thermally stable SC magnet. The typical field quality of the solenoid is consistent with GlueX requirements for momentum resolution. The Solenoid - as originally designed - had a slotted yoke and separately cooled SC coils, with the upstream end closed and the  downstream end with a full aperture opening. There were several problematic areas related to both construction and design: the specific magnetic geometry had the unfortunate side effect of creating large external magnetic fields, particularly in regions where phototubes would likely be present; many of the solenoid systems were inconsistent with JLAB operations; the Solenoid had a persistent history of internal leaks and had accumulated a substantial amount of wear and tear - as well as failed instrumentation - during its 30 year history.  Despite these problems, the robust design and the good state of preservation made selection of the Lass/MEGA solenoid a cost effective choice for Hall D, even after the necessary costs of modernization and maintenance were taken into consideration.

\subsubsection*{Status of Upgrading, Modernization and Repair.}

The Solenoid was originally designed in 1970 as the LASS spectrometer at SLAC and was subsequently used as the MEGA spectrometer at LANL. The Solenoid was mothballed in place
in 1995 and first inspected by JLAB Hall D in 2000. The first task performed after the initial evaluation of the Solenoid was to redesign the yoke magnetic geometry to match the Solenoid to the requirements of Hall D and to reduce substantially the external fields. The modifications entailed filling the yoke slots and adding steel at the end to reduce yoke saturation and the escape of internal fields, thus reducing the external fields by creating a symmetric yoke with a large upstream opening. This modification also changed the solenoid to a clear bore from end to end.  There are obvious benefits to detector access and installation, while the redesign of the yoke supports now allows the magnet installation at the beam elevation of 3.5 Meters in Hall D.

New Solenoid systems were proposed and planned that include a new DC power supply and energy dump system recently purchased from Danfysik for GlueX, a new cryogenic interface with JLAB compatible automatic valves and connections and a new control and instrumentation package. The new control package is to be based upon the current control upgrade for the HMS spectrometer for JLAB Hall C. The new cryogenic interface is based on the proven designs currently in use on seven different SC magnets at JLAB.

At the completion of the  visual inspections, the Solenoid was dismantled and shipped to IUCF where it has been undergoing some long needed maintenance and repairs.  Following a series of detailed coil tests, the first two of the four coils were dismantled, repaired and modernized. The repairs consisted of finding and repairing the numerous leaks that have plagued the solenoid for 30 years. Three of the coils had leaks in the LN2 shields while the fourth had a leak in the coil LHe vessel. The shield thermometry, which originally was based on thermalcouples, was replaced with more accurate and modern PT-102 Pt
resistance thermometers - now the industry standard.  The coil support strain gauges were all replaced, since many of the originals had failed over the years. Finally, the multi layer super insulation, which had deteriorated due to previous maintenance practices and the operation with oil diffusion pumps, was replaced. During the course of this maintenance work, corrosion was discovered in some internal plumbing and all four 18 inch coil junction bellows. These have all been replaced.

Starting in July of 2004, the two completed coils were cooled down with LN2 to perform a final leak proof test and quality check and were determined leak-free. At the completion of work at IUCF early in 2005 on coils 3 and 4, all four coils will have been repaired and modernized.

\subsubsection*{Manpower, R\&D and Production Schedules}

Current plans are to ship the solenoid to JLab's test lab beginning in Jan. 2005 and perform single coil cryogenic tests there to prove out all systems. The coils will be integrated with the new cryogenic interface, controls and DC system and be fully tested prior to installation in Hall D.
