IPAC2011 - List of Authors (Zhou, D.M.)

Paper

Title

Page

Beam Tilt due to Transverse Wakefields for DAΦNE, SuperB, KEKB and SuperKEKB

601

D.M. Zhou, K. Ohmi
KEK, Ibaraki, Japan
A. Chao
SLAC, Menlo Park, California, USA

When a beam bunch traverses a transverse impedance, the bunch head generates a transverse wakefield that kicks the bunch tail, generating a betatron motion of the tail relative to the head. In a storage ring, in a steady state, this kick to the bunch tail produces a transverse closed orbit (e.g. in the y-direction) of the bunch tail relative to the bunch head, which means the beam now has a y-z tilt. Such beam tilt due to transverse wakefields may cause a loss of luminosity in storage ring colliders or loss of brightness in light sources. In this paper, we present a preliminary study of the beam tilt effect for the colliders DAΦNE, SuperB, KEKB and SuperKEKB.

MOPS007

Interference of CSR Fields in a Curved Waveguide

604

D.M. Zhou, K. Ohmi
KEK, Ibaraki, Japan

CSR fields generated by a bunched beam passing through a series of bending magnets may interfere with each other due the reflections of outer chamber wall. This kind of multi-bend interference causes sharp peaks and long-range tail in the CSR impedance and wake potentials, respectively. Using a dedicated computer code, CSRZ, we calculated the longitudinal CSR impedance in the SuperKEKB positron damping ring for purpose of demonstration. It was found that multi-bend interference may enhance the CSR fields within a distance comparable to the bunch length, which is typically in the order of several millimeters. A simple instability analysis was performed and it suggested that multi-bend interference might play a role in the single-bunch instabilities of small electron/positron rings.

MOPS058

KEKB Linac Wakefield Studies of Comparing Theoretical Calculation, Simulation and Experimental Measurement*

739

L. Zang, N. Iida, Y. Ogawa, M. Satoh, M. Yoshida, D.M. Zhou
KEK, Ibaraki, Japan

For superKEKB, in order to achieve aiming luminosity machine need to run with a nano-beam scheme so that a small beam emittance is critical important. During the beam propagation, the short-range wake field in the accelerating structure will cause the beam instability and emittance growth. In practical, injecting beam with certain offset could compensate wakfield. And beam emittance could be measured by tuning the quadruple known as quadscan method. In this paper, wakefield theoretical calculation, simulation results will be presented. And then the wakefield impact to beam emittance and wakefield compensation will be discussed. Finally, we will show the comparison of the results getting from theoretical calculation and experimental measurement.

WEPC108

CSR Impedance for an Ultrarelativistic Beam moving in a Curved Trajectory

2268

D.M. Zhou, K. Ohmi, K. Oide
KEK, Ibaraki, Japan

A dedicated computer code, CSRZ, has been developed to calculate the coherent synchrotron radiation (CSR) impedance for an ultrarelativistic beam moving in a curved trajectory. Following the pioneering work of T. Agoh and K. Yokoya*, the code solves the parabolic equation in the frequency domain in a curvilinear coordinate system. The beam is assumed to move along a vacuum chamber which has a uniform rectangular cross section but with variable bending radius. Using this code, we did investigations in calculating the longitudinal CSR impedance of a single and a series of bending magnets. The calculation results indicate that the shielding effect due to outer chamber wall can be well explained by a simple optical approximation model at high frequencies. The CSR fields reflected by the outer wall may interfere with each other in a long bending magnet and lead to sharp narrow peaks in the CSR impedance.
* T. Agoh and K. Yokoya, Phys. Rev. ST Accel. Beams, 7(5):054403 (2004).

THYA01

Beam Dynamics in Positron Injector Systems for Next Generation B Factories

2857

N. Iida, H. Ikeda, T. Kamitani, M. Kikuchi, K. Oide, D.M. Zhou
KEK, Ibaraki, Japan

SuperKEKB, the upgrade plan of KEKB, aims to boost the luminosity up to 8x10³5 /cm²/s. The beam energy of the Low Energy Ring (LER) is 4 GeV for positrons, and that of the High Energy Ring is 7 GeV for electrons. SuperKEKB is designed to produce low emittance beams. The horizontal and vertical emittances of the injection beams are 12.5 nm and 0.9 nm, respectively, which are one or two orders smaller than those of KEKB. The normal and maximum required charges are 4 nC and 8nC, respectively. The positron injector system consists of the source, capture systems, L-band and S-band linacs, collimators, an energy compression system (ECS), a 1.1-GeV damping ring, a bunch compression system (BCS), S-band and C-band linacs, another ECS and a beam transport line into the LER. For the low emittance beam with a huge amount of the positron charge like 8nC, some kinds of issues by the instabilities will be predicted due to such as Coherent Synchrotron Radiation (CSR), beam loading, beam-beam effects, and so on. This paper reports a design of the positron beam injection system for SuperKEKB. In addition, comparisons with SuperB are described.

Slides THYA01 [7.572 MB]

THPZ021

Effect of Coherent Synchrotron Radiation at the SuperKEKB Damping Ring

3732

H. Ikeda, T. Abe, M. Kikuchi, K. Oide, K. Shibata, M. Tobiyama, D.M. Zhou
KEK, Ibaraki, Japan

The longitudinal wake field dominated by the CSR is important at the SuperKEKB damping ring. The peak of the CSR wake field is 100 times higher than those of the vacuum chamber components. We calculated the CSR effect for different vacuum chamber cross-sections, and adopted one which reduced longitudinal instability.

Paper	Title	Page
MOPS006	Beam Tilt due to Transverse Wakefields for DAΦNE, SuperB, KEKB and SuperKEKB	601
	D.M. Zhou, K. Ohmi KEK, Ibaraki, Japan A. Chao SLAC, Menlo Park, California, USA
	When a beam bunch traverses a transverse impedance, the bunch head generates a transverse wakefield that kicks the bunch tail, generating a betatron motion of the tail relative to the head. In a storage ring, in a steady state, this kick to the bunch tail produces a transverse closed orbit (e.g. in the y-direction) of the bunch tail relative to the bunch head, which means the beam now has a y-z tilt. Such beam tilt due to transverse wakefields may cause a loss of luminosity in storage ring colliders or loss of brightness in light sources. In this paper, we present a preliminary study of the beam tilt effect for the colliders DAΦNE, SuperB, KEKB and SuperKEKB.

MOPS007	Interference of CSR Fields in a Curved Waveguide	604
	D.M. Zhou, K. Ohmi KEK, Ibaraki, Japan
	CSR fields generated by a bunched beam passing through a series of bending magnets may interfere with each other due the reflections of outer chamber wall. This kind of multi-bend interference causes sharp peaks and long-range tail in the CSR impedance and wake potentials, respectively. Using a dedicated computer code, CSRZ, we calculated the longitudinal CSR impedance in the SuperKEKB positron damping ring for purpose of demonstration. It was found that multi-bend interference may enhance the CSR fields within a distance comparable to the bunch length, which is typically in the order of several millimeters. A simple instability analysis was performed and it suggested that multi-bend interference might play a role in the single-bunch instabilities of small electron/positron rings.

MOPS058	KEKB Linac Wakefield Studies of Comparing Theoretical Calculation, Simulation and Experimental Measurement*	739
	L. Zang, N. Iida, Y. Ogawa, M. Satoh, M. Yoshida, D.M. Zhou KEK, Ibaraki, Japan
	For superKEKB, in order to achieve aiming luminosity machine need to run with a nano-beam scheme so that a small beam emittance is critical important. During the beam propagation, the short-range wake field in the accelerating structure will cause the beam instability and emittance growth. In practical, injecting beam with certain offset could compensate wakfield. And beam emittance could be measured by tuning the quadruple known as quadscan method. In this paper, wakefield theoretical calculation, simulation results will be presented. And then the wakefield impact to beam emittance and wakefield compensation will be discussed. Finally, we will show the comparison of the results getting from theoretical calculation and experimental measurement.

WEPC108	CSR Impedance for an Ultrarelativistic Beam moving in a Curved Trajectory	2268
	D.M. Zhou, K. Ohmi, K. Oide KEK, Ibaraki, Japan
	A dedicated computer code, CSRZ, has been developed to calculate the coherent synchrotron radiation (CSR) impedance for an ultrarelativistic beam moving in a curved trajectory. Following the pioneering work of T. Agoh and K. Yokoya, the code solves the parabolic equation in the frequency domain in a curvilinear coordinate system. The beam is assumed to move along a vacuum chamber which has a uniform rectangular cross section but with variable bending radius. Using this code, we did investigations in calculating the longitudinal CSR impedance of a single and a series of bending magnets. The calculation results indicate that the shielding effect due to outer chamber wall can be well explained by a simple optical approximation model at high frequencies. The CSR fields reflected by the outer wall may interfere with each other in a long bending magnet and lead to sharp narrow peaks in the CSR impedance. T. Agoh and K. Yokoya, Phys. Rev. ST Accel. Beams, 7(5):054403 (2004).

THYA01	Beam Dynamics in Positron Injector Systems for Next Generation B Factories	2857
	N. Iida, H. Ikeda, T. Kamitani, M. Kikuchi, K. Oide, D.M. Zhou KEK, Ibaraki, Japan
	SuperKEKB, the upgrade plan of KEKB, aims to boost the luminosity up to 8x10³5 /cm²/s. The beam energy of the Low Energy Ring (LER) is 4 GeV for positrons, and that of the High Energy Ring is 7 GeV for electrons. SuperKEKB is designed to produce low emittance beams. The horizontal and vertical emittances of the injection beams are 12.5 nm and 0.9 nm, respectively, which are one or two orders smaller than those of KEKB. The normal and maximum required charges are 4 nC and 8nC, respectively. The positron injector system consists of the source, capture systems, L-band and S-band linacs, collimators, an energy compression system (ECS), a 1.1-GeV damping ring, a bunch compression system (BCS), S-band and C-band linacs, another ECS and a beam transport line into the LER. For the low emittance beam with a huge amount of the positron charge like 8nC, some kinds of issues by the instabilities will be predicted due to such as Coherent Synchrotron Radiation (CSR), beam loading, beam-beam effects, and so on. This paper reports a design of the positron beam injection system for SuperKEKB. In addition, comparisons with SuperB are described.
	Slides THYA01 [7.572 MB]

THPZ021	Effect of Coherent Synchrotron Radiation at the SuperKEKB Damping Ring	3732
	H. Ikeda, T. Abe, M. Kikuchi, K. Oide, K. Shibata, M. Tobiyama, D.M. Zhou KEK, Ibaraki, Japan
	The longitudinal wake field dominated by the CSR is important at the SuperKEKB damping ring. The peak of the CSR wake field is 100 times higher than those of the vacuum chamber components. We calculated the CSR effect for different vacuum chamber cross-sections, and adopted one which reduced longitudinal instability.