Simulations of slow positron production using a low energy electron accelerator

Monte Carlo simulations of slow positron production via energetic electron interaction with a solid target have been performed. The aim of the simulations was to determine the expected slow positron beam intensity from a low energy, high current electron accelerator. By simulating (a) the fast positron production from a tantalum electron-positron converter and (b) the positron depth deposition profile in a tungsten moderator, the slow positron production probability per incident electron was estimated. Normalizing the calculated result to the measured slow positron yield at the present AIST LINAC the expected slow positron yield as a function of energy was determined. For an electron beam energy of 5 MeV (10 MeV) and current 240 $\mu$A (30 $\mu$A) production of a slow positron beam of intensity 5 $\times$ 10$^{6}$ s$^{-1}$ is predicted. The simulation also calculates the average energy deposited in the converter per electron, allowing an estimate of the beam heating at a given electron energy and current. For low energy, high-current operation the maximum obtainable positron beam intensity will be limited by this beam heating.Comment: 11 pages, 15 figures, submitted to Review of Scientific Instrument

A new technique for seeding chondrocytes onto solvent-preserved human meniscus using the chemokinetic effect of recombinant human bone morphogenetic protein-2

Many investigators are currently studying the use of decellularized tissue allografts from human cadavers as scaffolds onto which patients’ cells could be seeded, or as carriers for genetically engineered cells to aid cell transplantation. However, it is difficult to seed cells onto very dense regular connective tissue which has few interstitial spaces. Here, we discuss the development of a chemotactic cell seeding technique using solvent-preserved human meniscus. A chemokinetic response to recombinant human bone morphogenetic protein-2 (rhBMP-2) was observed in a monolayer culture of primary chondrocytes derived from femoral epiphyseal cartilage of 2-day-old rats. The rhBMP-2 significantly increased their migration upto 10 ng/ml in a dose-dependent manner. When tested with solvent-preserved human meniscus as a scaffold, which has few interstitial spaces, rhBMP-2 was able to induce chondrocytes to migrate into the meniscus. After a 3-week incubation, newly-formed cartilaginous extracellular matrix was synthesized by migrated chondrocytes throughout the meniscus, down to a depth of 3 mm. These findings demonstrate that rhBMP-2 may be a natural chemokinetic factor in vivo, which induces migration of proliferative chondrocytes into the narrow interfibrous spaces. Our results suggest a potential application of rhBMP-2 for the designed distribution of chondrocytes into a scaffold to be used for tissue engineering

Development Of The Jaeri Fel Driven By A Superconducting Accelerator

INTRODUCTION As well known, a laser system consists of three major parts, i.e., a laser driver like a flash lamp, a gain medium like a glass or a crystal, and an optical resonator of paired mirrors. Since the invention of the laser in 1950's or 1960's, efficiency and average power level of the conventional lasers have been seriously limited to very low by their huge heat losses in the laser drivers and gain media, and damages in the mirrors. Because a free electron laser (FEL) has an high energy electron beam in alternating magnetic field as the gain media, we could neglect the heat losses in the FEL gain media. Unfortunately, as long as conventional normal conducting accelerators were used to produce the high energy electron beam as the FEL driver, we still have the large heat losses in the accelerator cavity wall of the FEL driver. Therefore, in order to make a highly-efficient, and high average power FEL, we resultantly have to minimize the heat losses in the driver to ver

A THERMIONIC ELECTRON GUN SYSTEM FOR THE JAERI SUPERCONDUCTING FEL

Abstract A highly stable and bright electron beam source was developed at the JAERI Free Electron Laser (FEL) facility. Though the electron beam source is a traditional thermionic electron gun, improvement of the gun greatly contributed to recent high brightness electron beam production at the JAERI FEL. The high voltage of the gun is set to 230 kV to reduce space charge effects in the low energy region. The initial pulse width from the gun is 0.81 ns at 0.51 nC/pulse. The amplitude fluctuation in peak to peak is less than 1 %. The root mean square (rms) timing jitter is 23 ps

JAERI ERL-FEL: status and future plans”, The

Abstract An energy-recovery linac (ERL) for a high-power freeelectron laser (FEL) is under development in JAERI. We completed the construction of the ERL, and demonstrated the first energy-recover operation and FEL lasing in 2002. For realizing FEL lasing in 5-10kW average power, further upgrade of the ERL is carrying on, which includes reinforcement of the injector, replacement of the RF control system and so on. Future plans for high-power FEL application and basic research towards future ERL light sources are also described