IPAC2011 - List of Authors (Masaki, M.)

Paper	Title	Page
THPC028	A Proposal of Short X-ray Pulse Generation from Compressed Bunches by mm-wave iFEL in the SPring-8 Upgrade Plan	2969
	M. Masaki, K. Fukami, C. Mitsuda, T. Watanabe JASRI/SPring-8, Hyogo-ken, Japan
	In the SPring-8 upgrade plan, short pulse options are prepared for time-resolved experiments of pico-second order with high repetition rate. The best scenario is that selected bunches have equilibrium bunch length of 1 ps or less. A mm-wave storage-ring iFEL may be one possible solution for it. If resonant wavelength of the FEL is a few millimeters, which is about ten times longer than typical short bunch length of 0.3 mm corresponding to 1 ps, almost all electrons of a bunch can be confined in one valley of ponderomotive potentials formed by the FEL mechanism. The system consists of a helical wiggler with period length of several meters and a mm-wave resonator. Numerical simulations with coherent synchrotron radiation effect at bunch charge of 479 pC show that an ultra-short injection bunch is trapped in a mm-wave “bucket” and kept shorter than 1 ps (r.m.s.) even after twice the longitudinal damping time from the injection. The ultra-short bunches need to be injected from the XFEL linac. XFEL-to-Storage Ring beam transport line is designed to suppress dispersions which cause bunch lengthening. Tracking calculations show promising results for bunch qualities at the transport line.

THPC031	Measurement of Longitudinal Dynamics of Injected Beam in a Storage Ring	2978
	T. Watanabe, T. Fujita, M. Masaki, K. Soutome, S. Takano, M. Takao, K. Tamura JASRI/SPring-8, Hyogo-ken, Japan
	Experimental observation of longitudinal dynamics of injected beam in a storage ring has been demonstrated. Since the injected beam undergoes synchrotron oscillation in a longitudinal phase space, two projected values, i.e., a bunch duration and an energy spread, oscillate at twice the synchrotron frequency. At SPring-8, the initial energy spread (~0.126%) at the injection goes up and down until it reaches the equilibrium energy spread (~0.11%). If the injection timing should not be optimized, an asymmetrically enhanced oscillation could distort the injection efficiency. The observation of such an oscillation helps make sure that no significant injection loss occurs. More importantly, the scheme is expected to enable us to observe non-linear longitudinal dynamics of ultra-short bunches injected from the XFEL linac; the bunches are in near future going to be transferred from the linac to the storage ring via 600-meter long transports, in which strong coherent synchrotron radiation and other high peak-current effects will not be ignorable. Experimental results obtained by a dual-scan streak camera and other devices as well as numerical simulations will be presented.

THPC032	Current Status of SPring-8 Upgrade Plan	2981
	T. Watanabe, T. Asaka, H. Dewa, H. Ego, T. Fujita, K. Fukami, M. Masaki, C. Mitsuda, A. Mochihashi, T. Nakamura, H. Ohkuma, Y. Okayasu, Y. Shimosaki, K. Soutome, M. Takao JASRI/SPring-8, Hyogo-ken, Japan T. Tanaka RIKEN Spring-8 Harima, Hyogo, Japan
	The SPring-8 upgrade plan has been discussed. The main goal is to replace the storage ring in the existing tunnel so that the resulting emittance will get as close to the diffraction limit in hard x-ray region as possible. For 10 keV photons, for instance, the diffraction limit corresponds to the emittance of as small as 10 pm.rad. For the challenging goal, the new ring features a multi-bend lattice with damping wigglers, which presumably enables us to reduce an emittance by two orders of magnitudes or more compared with the current double-bend lattice without damping wigglers. Up to now, a six-bend lattice has been mainly studied, which is supposed to generate a natural emittance of 60–70 pm.rad for 6 GeV. In addition, damping wigglers and coupling control should assist to reduce the emittance even more for approaching the ultimate goal. The major modification requires not only an advanced lattice design via manipulation of non-linear beam dynamics but also extensive technological developments in almost every component such as magnets, monitors, and RF systems. The overall review of the upgrade plan, including some detailed discussions on the critical issues, will be presented.

Paper

Title

Page

A Proposal of Short X-ray Pulse Generation from Compressed Bunches by mm-wave iFEL in the SPring-8 Upgrade Plan

2969

M. Masaki, K. Fukami, C. Mitsuda, T. Watanabe
JASRI/SPring-8, Hyogo-ken, Japan

In the SPring-8 upgrade plan, short pulse options are prepared for time-resolved experiments of pico-second order with high repetition rate. The best scenario is that selected bunches have equilibrium bunch length of 1 ps or less. A mm-wave storage-ring iFEL may be one possible solution for it. If resonant wavelength of the FEL is a few millimeters, which is about ten times longer than typical short bunch length of 0.3 mm corresponding to 1 ps, almost all electrons of a bunch can be confined in one valley of ponderomotive potentials formed by the FEL mechanism. The system consists of a helical wiggler with period length of several meters and a mm-wave resonator. Numerical simulations with coherent synchrotron radiation effect at bunch charge of 479 pC show that an ultra-short injection bunch is trapped in a mm-wave “bucket” and kept shorter than 1 ps (r.m.s.) even after twice the longitudinal damping time from the injection. The ultra-short bunches need to be injected from the XFEL linac. XFEL-to-Storage Ring beam transport line is designed to suppress dispersions which cause bunch lengthening. Tracking calculations show promising results for bunch qualities at the transport line.

THPC031

Measurement of Longitudinal Dynamics of Injected Beam in a Storage Ring

2978

T. Watanabe, T. Fujita, M. Masaki, K. Soutome, S. Takano, M. Takao, K. Tamura
JASRI/SPring-8, Hyogo-ken, Japan

Experimental observation of longitudinal dynamics of injected beam in a storage ring has been demonstrated. Since the injected beam undergoes synchrotron oscillation in a longitudinal phase space, two projected values, i.e., a bunch duration and an energy spread, oscillate at twice the synchrotron frequency. At SPring-8, the initial energy spread (~0.126%) at the injection goes up and down until it reaches the equilibrium energy spread (~0.11%). If the injection timing should not be optimized, an asymmetrically enhanced oscillation could distort the injection efficiency. The observation of such an oscillation helps make sure that no significant injection loss occurs. More importantly, the scheme is expected to enable us to observe non-linear longitudinal dynamics of ultra-short bunches injected from the XFEL linac; the bunches are in near future going to be transferred from the linac to the storage ring via 600-meter long transports, in which strong coherent synchrotron radiation and other high peak-current effects will not be ignorable. Experimental results obtained by a dual-scan streak camera and other devices as well as numerical simulations will be presented.

THPC032

Current Status of SPring-8 Upgrade Plan

2981

T. Watanabe, T. Asaka, H. Dewa, H. Ego, T. Fujita, K. Fukami, M. Masaki, C. Mitsuda, A. Mochihashi, T. Nakamura, H. Ohkuma, Y. Okayasu, Y. Shimosaki, K. Soutome, M. Takao
JASRI/SPring-8, Hyogo-ken, Japan
T. Tanaka
RIKEN Spring-8 Harima, Hyogo, Japan

The SPring-8 upgrade plan has been discussed. The main goal is to replace the storage ring in the existing tunnel so that the resulting emittance will get as close to the diffraction limit in hard x-ray region as possible. For 10 keV photons, for instance, the diffraction limit corresponds to the emittance of as small as 10 pm.rad. For the challenging goal, the new ring features a multi-bend lattice with damping wigglers, which presumably enables us to reduce an emittance by two orders of magnitudes or more compared with the current double-bend lattice without damping wigglers. Up to now, a six-bend lattice has been mainly studied, which is supposed to generate a natural emittance of 60–70 pm.rad for 6 GeV. In addition, damping wigglers and coupling control should assist to reduce the emittance even more for approaching the ultimate goal. The major modification requires not only an advanced lattice design via manipulation of non-linear beam dynamics but also extensive technological developments in almost every component such as magnets, monitors, and RF systems. The overall review of the upgrade plan, including some detailed discussions on the critical issues, will be presented.