We have developed temperature-pulse microscopy in which the temperature of a microscopic sample is raised reversibly in a square-wave fashion with rise and fall times of several ms, and locally in a region of approximately 10 m in diameter with a temperature gradient up to 2°C͞m. Temperature distribution was imaged pixel by pixel by image processing of the f luorescence intensity of rhodamine phalloidin attached to (single) actin filaments. With short pulses, actomyosin motors could be activated above physiological temperatures (higher than 60°C at the peak) before thermally induced protein damage began to occur. When a sliding actin filament was heated to 40-45°C, the sliding velocity reached 30 m͞s at 25 mM KCl and 50 m͞s at 50 mM KCl, the highest velocities reported for skeletal myosin in usual in vitro assay systems. Both the sliding velocity and force increased by an order of magnitude when heated from 18°C to 40-45°C. Temperature-pulse microscopy is expected to be useful for studies of biomolecules and cells requiring temporal and͞or spatial thermal modulation.Recent advances in optical microscopic techniques have made it possible to image single protein molecules in solution (1, 2) and investigate the dynamic nature of molecular motors (3-8).To introduce an additional dimension to this technology, we have developed temperature-pulse microscopy (TPM), in which a microscopic sample(s) in aqueous solution is heated reversibly.There have been several reports on the effects of temperature jumps under an optical microscope: for example, on physiological functions of muscle fibers (9-12) and on phase transition phenomena in membranes of phospholipid vesicles and cells (13). To prevent thermal deterioration of biological samples, and to confirm the absence of the deterioration, it is highly desirable to restore the starting temperature as soon as the measurement is finished. In our TPM, temperature is elevated spatially and temporally by illuminating a lump of metal particles by IR laser; a concentric temperature gradient is created around the lump of metal particles. When the laser beam is shut off, the heat is rapidly dissipated into the surrounding medium. Thus, a square-wave temperature pulse with rise and fall times of less than 10 ms is generated. Exposure to high temperature is minimized, and repetitive thermal cycling is easily programmed. The local heating also permits simultaneous observation of the sample behaviors at various temperatures.In the microscopic temperature-imaging techniques reported so far, the temperature was estimated either from the thermal quenching of fluorescence (14-16) or from the thermal shift of the fluorescence spectrum (13). Here, we applied the former technique. In our TPM, a concentric temperature gradient is formed around the metal aggregate, as assessed from thermal quenching of a fluorescent dye bound to actin filaments with a slope of 1-2°C͞m and extension out to 10-20 m. The temperature distribution on single actin filaments also could be imaged.We have applied ...

Operation of accelerator at low pressure is an essential requirement to reduce stripping loss of the negative ions, which in turn results in high efficiency of the NB systems. For this purpose, a vacuum insulated beam source (VIBS) has been developed at JAERI, which reduces the gas pressure in the accelerator by enhanced gas conductance through the accelerator. The VIBS achieves the high voltage insulation of 1 MV by immersing the whole structure of accelerator in vacuum with long (~ 1.8 m) insulation distance. Results of the voltage holding test using a long vacuum gap of 1.8 m indicate that a transition from vacuum discharge to gas discharge occurs at around 0.2 Pa m in the long vacuum gap. So far, the VIBS succeeded in acceleration of 20 mA (H-) beam up to 970 keV for 1 s. The high voltage holding capability of the VIBS was drastically improved by installing a new large stress ring, which reduces electric field concentration at the triple junction of the accelerator column. At present the VIBS sustains 1 MV stably for more than 1200 s. Acceleration of ampere class Hbeams at high current density is to be started soon to demonstrate ITER relevant beam optics. Operation of negative ion source at low pressure is also essential to reduce the stripping loss. However, it was not so easy to attain high current density Hions at low pressure, since destruction cross section of the negative ions becomes large if the electron temperature is > 1 eV, in low pressure discharge. Using strong magnetic filter to lower the electron temperature, and putting higher arc discharge power to compensate reduction of plasma density through the filter, an Hion beam of 310 A/m 2 was extracted at very low pressure of 0.1Pa. This satisfies the ITER requirement of current density at 1/3 of the ITER design pressure (0.3 Pa).

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