Frank Patrick Romero

Design and Application of a Diode-Directed Solid-State Marx Modulator

Researchers at Los Alamos National Laboratory (LANL) are developing a new solid-state high-voltage Marx modulator for the generation of pulsed power. The initial application of the LANL modulator is to provide power to a magnetron that requires a 46-kV, 160-A, 5-mus rectangular pulse. This modulator technology is also being developed for other applications, including portable millimeter wave sources, a beam energy corrector for induction accelerators, and space-based power systems. The LANL solid-state modulator has several benefits, including wave shape control, switch protection, efficiency, and compactness. The present paper describes this source technology and its design.

Performance of a Diode-Directed Solid-State Marx Modulator

The diode-directed solid-state Marx modulator is a new high-voltage modulator developed at Los Alamos National Laboratory (LANL) to drive a high-power magnetron. In its normal mode of operation the modulator produces 46-kV, 160-A, 5-mus rectangular pulses at 50 Hz. The modulator is also capable of running in burst mode and generating arbitrary waveforms at full voltage. The current paper describes modulator testing and performance results. Also shown are several of the unique features of this design, such as pulse width variability, wave shape variability, and switch protection.

29 mm Diameter Test Target Design Report

The Northstar target for Mo99 production is made up of Mo100 disks in a stack separated by coolant gaps for helium flow. A number of targets have been tested at ANL for both production of Mo99 and for thermal-hydraulic performance. These have all been with a 12 mm diameter target, even while the production goals have increased the diameter to now 29 mm. A 29 mm diameter target has been designed that is consistent with the ANL beam capabilities and the capabilities of the helium circulation system currently in use at ANL. This target is designed for 500 μA at 35 MeV electrons. While the plant design calls for 42 MeV, the chosen design point is more favorable and higher power given the limits of the ANL accelerator. The intended beam spot size is 12 mm FWHM, but the thermal analysis presented herein conservatively assumed a 10 mm FWHM beam, which results in a 44% higher beam current density at beam center.

Performance Characterization of the Production Facility Prototype Helium Flow System

The roots blower in use at ANL for in-beam experiments and also at LANL for flow tests was sized for 12 mm diameter disks and significantly less beam heating. Currently, the disks are 29 mm in diameter, with a 12 mm FWHM Gaussian beam spot at 42 MeV and 2.86 μA on each side of the target, 5.72 μA total. The target design itself is reported elsewhere. With the increased beam heating, the helium flow requirement increased so that a larger blower was need for a mass flow rate of 400 g/s at 2.76 MPa (400 psig). An Aerzen GM 12.4 blower was selected, and is currently being installed at the LANL facility for target and component flow testing. This report describes this blower/motor/pressure vessel package and the status of the facility preparations. Blower performance (mass flow rate as a function of loop pressure drop) was measured at 4 blower speeds. Results are reported below.

Production Facility Prototype Blower Installation Report

The roots blower in use at ANL for in-beam experiments and also at LANL for flow tests was sized for 12 mm diameter disks and significantly less beam heating. Currently, the disks are 29 mm in diameter, with a 12 mm FWHM Gaussian beam spot at 42 MeV and 2.86 μA on each side of the target, 5.72 μA total. The target design itself is reported elsewhere. With the increased beam heating, the helium flow requirement increased so that a larger blower was need for a mass flow rate of 400 g/s at 2.76 MPa (400 psig). An Aerzen GM 12.4 blower was selected, and is currently being installed at the LANL facility for target and component flow testing. This report describes this blower/motor/ppressure vessel package and the status of the facility preparations.

Design and experimental activities supporting commercial U.S. electron accelerator production of Mo-99

99mTc, the daughter isotope of 99Mo, is the most commonly used radioisotope for nuclear medicine in the United States. Under the direction of the National Nuclear Security Administration (NNSA), Los Alamos National Laboratory (LANL) and Argonne National Laboratory (ANL) are partnering with North Star Medical Technologies to demonstrate the viability of large-scale 99Mo production using electron accelerators. In this process, 99Mo is produced in an enriched 100Mo target through the 100Mo(γ,n)99Mo reaction. Five experiments have been performed to date at ANL to demonstrate this process. This paper reviews the current status of these activities, specifically the design and performance of the helium gas target cooling system.

LANL Activities Supporting Electron Accelerator Production of 99Mo for NorthStar Medical Radioisotopes, LLC

Summary of LANL FY12 Activities are: (1) Preparation, performance, and data analysis for the FY12 accelerator tests at ANL - (a) LANL designed and installed a closed-loop helium target cooling system at ANL for the FY12 accelerator tests, (b) Thermal test was performed on March 27, (c) 24 h production test to follow the accelerator upgrade at ANL; (2) Local target shielding design and OTR/IR recommendations - (a) Target dose rate and activation products were calculated with MCNPX, (b) {sup 206}Pb({gamma},2n){sup 204m}Pb vs {sup 204g}Pb branching ratio unpublished, will measure using the LANL microtron, (c) OTR system nearing final configuration, (d) IR prototype system demonstrated during the recent thermal test at ANL; (3) Target housing lifetime estimation - Target housing material specifications and design to be finalized following the thermal test, lifetime not believed to be an issue; and (4) Target cooling system reliability - Long duration system characterizations will begin following the thermal test.