Takahiro Kozawa

Radiation-induced reactions of chemically amplified x-ray and electron-beam resists based on deprotection of t-butoxycarbonyl groups

Radiation-induced reactions in chemically amplified resists based on deprotection of t-butoxycarbonyl groups have been investigated by both time-resolved (the pulse radiolysis methods) and steady-state optical absorption spectroscopy. Upon exposure of a partially tBOC-protected novolak by electron and synchrotron radiation beams, the yields of the intermediates contributing to the acid generation (phenoxyl radical and proton adducts of base resin) decreased with increasing the protection ratio of hydroxyl groups. Therefore, the efficiency of the acid generation is closely related with the protection ratio. The relation of the acid generation mechanism with the protection ratio was discussed.

Precise measurement of a subpicosecond electron single bunch by the femtosecond streak camera

Abstract Precise measurement of a subpicosecond electron single bunch by the femtosecond streak camera is presented. The subpicosecond electron single bunch of energy 35 MeV was generated by the achromatic magnetic pulse compressor at the S-band linear accelerator of Nuclear Engineering Research Laboratory (NERL), University of Tokyo. The electric charge per bunch and beam size are 0.5 nC and the horizontal and vertical beam sizes are 3.3 and 5.5 mm (full width at half maximum; FWHM), respectively. Pulse shape of the electron single bunch is measured via Cherenkov radiation emitted in air by the femtosecond streak camera. Optical parameters of the optical measurement system were optimized based on much experiment and numerical analysis in order to achieve a subpicosecond time resolution. By using the optimized optical measurement system, the subpicosecond pulse shape, its variation for the differents rf phases in the accelerating tube, the jitter of the total system and the correlation between measured streak images and calculated longitudinal phase space distributions were precisely evaluated. This measurement system is going to be utilized in several subpicosecond analyses for radiation physics and chemistry.

Femtosecond single-bunched linac for pulse radiolysis based on laser wakefield acceleration

A conceptual design of a linac for pulse radiolysis is presented based on laser wakefield acceleration. Pulse radiolysis spectroscopically studies the initial stage of chemical reactions induced by electron beams. Single-bunched beams with a bunch-length on the order of a femtosecond are ideal for this purpose. The present design gives pure 20 pC single-bunches with an RMS bunch length of less than 10 fs. It accelerates and compresses only the head part of a high-current beam from a photocathode. Some practical problems concerning the design are also presented.

Generation of high-current (1kA) subpicosecond electron single pulse

Abstract An achromatic pulse compressor and a grid pulser system were designed for generation of a high-current single pulse in a subpicosecond time domain and were installed to the S-band (2856 MHz) linear accelerator of the University of Tokyo. 35 MeV electron pulses with the pulse width of 10 ps have been compressed by the achromatic magnetic pulse compression system. Generation of subpicosecond single-electron pulse with the charge of 1 nC has been succeeded. The shortest and average pulse widths in FWHM are 670 and 890 fs, respectively. The length of the pulse has been measured by a femtosecond streak camera with a time resolution of 200 fs. No satellite of the main pulse could be observed.

Interaction of terawatt laser with plasma

Abstract Experimental investigations on interactions of a terawatt laser (0.5–2.5 TW) wth an underdense plasma are reported. Formation of self-channeling longer than the vacuum Rayleigh length is observed when ultrashort (100 fs in FWHM) high power (∼ 2 TW) laser pulses are focused into a gas (He, Ar, N 2 ) filled chamber. In addition to the formation of self-channeling along the laser axis, a bright radiation in the transverse direction of the channel was observed for the highly excited dense gases. This sideway radiation was observed for all three gases and especially for N 2 , sideway jet-like radiation (we call it electron sideway-jet) was monitored. The energy of the emitted electrons were estimated to be ∼ 10 keV from the range of electron trajectories in N 2 .

Acid generation process by radiation‐induced reaction in chemically amplified resist films

A new interpretation of the acid generation process in novolak resin systems is reported. To investigate the acid generation process in chemically amplified resist, a novolak resin system with an acid generator (PAG) was employed. In order to analyze the acid generation process, the visible absorption characteristics from a conventional spectrophotometer, and nanosecond and millisecond pulse radiolysis systems, were analyzed. For m‐cresol novolak with triphenylsulfonium triflate, it was hypothesized that acid would be generated during exposure; however, it is asserted that a protonated intermediate was generated during exposure and that acid was generated during exposure, and more acid was formed during PEB. The yield of the acid during PEB, rather than that of the protonated intermediate during exposure, was strongly influenced by the presence of triphenylamine. A comparison of the experimental result for m‐cresol novolak which contains PAG with that for p‐cresol novolak which also contains PAG indicates...

Bunch-Shape Monitor for a Picosecond Single-Bunch Beam of a 35 MeV Electron Linear Accelerator

A non-interactive-type bunch-shape and beam intensity monitor for a 35 MeV electron linear accelerator (linac) has been developed. The monitor consists of an electric SMA-type connector and an Al pipe of 50 mm inner diameter. Test measurements of the present monitor have been made under the conditions of the accelerated charges of lower than 27 nC/pulse and the pulse width ranging from 6 to 30 ps (Full Width at Half Maximum). The results show that the present monitor is applicable to bunch-shape measurement of the picosecond single-bunch beam. The monitor output is also found to be proportional to the beam intensity of more than 0.05 nC/pulse.

Nonlinear acceleration caused by a plasma wakefield in an underdense regime

Acceleration greater than an order of magnitude larger than that predicted by a linear theory was observed in a moderate underdense plasma wakefield when the time delay between the drive and test bunches was less than one plasma oscillation period.

Nondestructive beam position monitor using high-permeability chips

Abstract The construction and performance of a nondestructive beam position monitor using high-permeability chips (high-permeability chips: HPCs) are presented. This monitoring system consists of the HPCs, pickup coils, a monitor housing, an automatic precision XY -stage and a four-channel fast-response digitizing oscilloscope. The beam aperture of the beam position monitor has a diameter of 45 mm. The beam position was detected by a pickup coil which is wound around the HPC. Four of these sensors were positioned 90° apart in azimuth about the beam axis. The development of a nondestructive beam position monitor for experiments requiring linear accelerator operations has been long awaited. This monitoring system measures beam positions in the horizontal and vertical directions independently of each other. The magnetic field induced by an electron beam is measured by the four sensors. It is possible to measure the beam position with an accuracy of 0.5 mm for a calibration area of 30 mm × 20 mm. Agreement between results from the experiment using a linear accelerator and test bench is obtained.

Characterestics of pico-second single bunch at the S-band linear accelerator

Abstract Measurement of the bunch structure of a pico-second single bunch was performed using a femto-second streak camera at the S-band linear accelerator of the University of Tokyo. The aim of this research is to investigate the feasibility of the generation of a femto-second single bunch at the S-band linac. The details of the bunch structure and energy spectrum of an original single bunch were precisely investigated in several operation modes where the RF phases in accelerating tubes and a prebuncher were varied. The femto-second streak camera was utilized to measure the bunch structure by one shot via Cherenkov radiation emitted by the electrons in the bunch. Next, an experiment for magnetic pulse compression of the original single bunch was carried out. Pulse shapes of the compressed bunchs for different energy modulation were also obtained by measuring Cherenkov radiation by one shot using the femto-second streak camera. Prior to the experiment, numerical tracking analysis to determine operating parameters for the magnetic pulse compression was also done. Measured pulse widths were compared with calculated ones. Finally, a 2 ps (full width at half maximum; FWHM) single bunch with an electric charge of 0.3 nC could be generated by the magnetic pulse compression.