IPAC2012 - List of Authors (Billing, M.G.)

Paper

Title

Page

Using TE Wave Resonances for the Measurement of Electron Cloud Density

960

J.P. Sikora, M.G. Billing, D. L. Rubin, R.M. Schwartz
CLASSE, Ithaca, New York, USA
D. Alesini
INFN/LNF, Frascati (Roma), Italy
B.T. Carlson
CMU, Pittsburgh, Pennsylvania, USA
S. De Santis
LBNL, Berkeley, California, USA
K.C. Hammond
Harvard University, Cambridge, Massachusetts, USA

Funding: This work is supported by the US National Science Foundation PHY-0734867, PHY-1002467, and the US Department of Energy under Contracts DE-FC02-08ER41538, DE-AC02-05CH11231.
In the past few years, electron cloud density has been measured by means of its effect on TE waves propagated through the accelerator vacuum chamber. This technique has been the object of careful studies and has been used in several laboratories around the world (CERN, SLAC, FNAL, Cornell, INFN-LNF). Recent measurements at CesrTA and DAΦNE show that in a majority of practical cases, the theoretical model that relates the cloud density to the phase shift induced on a TE wave propagating in beam pipe may not be the correct one. Instead, the measurement results have to be analyzed considering the effect of the electron cloud on a standing wave excited between the input and output couplers - typically Beam Position Monitors (BPMs). This standing wave pattern is not confined to the portion of beampipe between the BPMs and must be understood in order to correctly interpret the measurement. In this paper we present evidence that the transmission function near cutoff between two BPMs is the result of coupling to standing waves trapped in the vacuum chamber. This evidence includes measurements at DAΦNE, Cesr-TA, a test waveguide, computer EM simulations, and analytical calculations.

WEYA02

Studies at CesrTA of Electron-Cloud-Induced Beam Dynamics for Future Damping Rings

2081

G. Dugan, M.G. Billing, K.R. Butler, J.A. Crittenden, M.J. Forster, D.L. Kreinick, R.E. Meller, M.A. Palmer, G. Ramirez, M.C. Rendina, N.T. Rider, K.G. Sonnad, H.A. Williams
CLASSE, Ithaca, New York, USA
R.F. Campbell, R. Holtzapple, M. Randazzo
CalPoly, San Luis Obispo, California, USA
J.Y. Chu
CMU, Pittsburgh, Pennsylvania, USA
J.W. Flanagan, K. Ohmi
KEK, Ibaraki, Japan
M.A. Furman, M. Venturini
LBNL, Berkeley, California, USA
M.T.F. Pivi
SLAC, Menlo Park, California, USA

Funding: US National Science Foundation PHY-0734867, PHY-1002467, and PHY-1068662; US Dept. of Energy DE-FC02-08ER41538; and the Japan/US Cooperation Program.
Electron clouds can adversely affect the performance of accelerators, and are of particular concern for the design of future low emittance damping rings. Studies of the impact of electron clouds on the dynamics of bunch trains in CESR have been a major focus of the CESR Test Accelerator program. In this paper, we report measurements of coherent tune shifts, emittance growth, and coherent instabilities carried out using a variety of bunch currents, train configurations, beam energies, and transverse emittances, similar to the design values for the ILC damping rings. We also compare the measurements with simulations which model the effects of electron clouds on beam dynamics, to extract simulation model parameters and to quantify the validity of the simulation codes.

Slides WEYA02 [2.033 MB]

WEPPC074

HOM Studies on the Cornell ERL Prototype Cavity in a Horizontal Test Cryomodule

2384

N.R.A. Valles, M.G. Billing, G.H. Hoffstaetter, M. Liepe, C.E. Mayes
CLASSE, Ithaca, New York, USA

The main linac 7-cell cavity for Cornell's Energy Recovery Linac was optimized to maximize threshold current through the ERL. This was achieved by designing center and end cells that reduce the strength of dipole higher-order modes. A prototype cavity was fabricated based on the optimized RF design and found to meet fundamental mode specifications in a vertical test. The higher-order-mode spectrum was measured when the cavity was installed in a horizontal test cryomodule and is compared to 2D and 3D EM simulations.

WEPPR086

Computed Wake Field Effects from Measured Surface Roughness in the Walls of the Cornell ERL

3132

M.G. Billing, G.H. Hoffstaetter, C.E. Mayes, K.W. Smolenski, H.A. Williams
CLASSE, Ithaca, New York, USA

Funding: Work supported by the NSF ERL Phase 1B Cooperative Agreement (DMR-0807731)
Wake fields arise from the discontinuities in a smooth vacuum chamber and will cause energy spread in the passing bunch. In an energy recovery linac (ERL), the spent bunches are decelerated before they are dumped to reuse the beam’s energy for the acceleration of new bunches. While the energy spread accumulated from wakes before deceleration is small compared to the beam’s energy after full acceleration, it becomes more important relatively as the beam’s energy decreases.* Thus, in an ERL wake fields can produce very significant energy spread in the beam as it is decelerated to the energy of the beam dump. We report on calculations of wake fields due to the roughness of the surface of the vacuum chamber walls as it affects the Cornell ERL design. These calculations include the effects from the measured roughness for real vacuum chamber wall surfaces.
* M. Billing, “Effect of Wake Fields in an Energy Recovery Linac”, PAC’09, Vancouver, BC, Canada, 4-8 May 2009.

WEPPR087

Dependence of Beam Instabilities Caused by Electron Clouds at CesrTA Due to Variations in Chromaticity, Bunch Current and Train Length

3135

M.G. Billing, G. Dugan, M.J. Forster, D.L. Kreinick, R.E. Meller, M.A. Palmer, G. Ramirez, M.C. Rendina, N.T. Rider, J.P. Sikora, K.G. Sonnad, H.A. Williams
CLASSE, Ithaca, New York, USA
J.Y. Chu
CMU, Pittsburgh, Pennsylvania, USA
J.W. Flanagan
KEK, Ibaraki, Japan
R. Holtzapple, M. Randazzo
CalPoly, San Luis Obispo, California, USA

Funding: Work supported by DOE Award DE-FC02-08ER41538, NSF Award PHY-0734867 and the Lepton Collider R&D Coop Agreement: NSF Award PHY-1002467.
Electron cloud-induced beam dynamics is being studied at CESRTA under various conditions. These measurements detect the the coherent self-excited spectrum for each bunch within a train and bunch-by-bunch beam size. In the position spectrum coherent betatron dipole and head-tail motion is detectable for each individual bunch within the train with a sensitivity for the motion of 1.1 (2) microns-rms in the vertical (horizontal) direction for a 1 mA bunch current. These techniques are utilized to study the electron cloud-related interactions, which cause the growth of coherent motion and beam size along the train. We report on the observations and results from studies of the instability growth vs. changes in chromaticity, the current per bunch and the length of the train.

Paper	Title	Page
MOPPR074	Using TE Wave Resonances for the Measurement of Electron Cloud Density	960
	J.P. Sikora, M.G. Billing, D. L. Rubin, R.M. Schwartz CLASSE, Ithaca, New York, USA D. Alesini INFN/LNF, Frascati (Roma), Italy B.T. Carlson CMU, Pittsburgh, Pennsylvania, USA S. De Santis LBNL, Berkeley, California, USA K.C. Hammond Harvard University, Cambridge, Massachusetts, USA
	Funding: This work is supported by the US National Science Foundation PHY-0734867, PHY-1002467, and the US Department of Energy under Contracts DE-FC02-08ER41538, DE-AC02-05CH11231. In the past few years, electron cloud density has been measured by means of its effect on TE waves propagated through the accelerator vacuum chamber. This technique has been the object of careful studies and has been used in several laboratories around the world (CERN, SLAC, FNAL, Cornell, INFN-LNF). Recent measurements at CesrTA and DAΦNE show that in a majority of practical cases, the theoretical model that relates the cloud density to the phase shift induced on a TE wave propagating in beam pipe may not be the correct one. Instead, the measurement results have to be analyzed considering the effect of the electron cloud on a standing wave excited between the input and output couplers - typically Beam Position Monitors (BPMs). This standing wave pattern is not confined to the portion of beampipe between the BPMs and must be understood in order to correctly interpret the measurement. In this paper we present evidence that the transmission function near cutoff between two BPMs is the result of coupling to standing waves trapped in the vacuum chamber. This evidence includes measurements at DAΦNE, Cesr-TA, a test waveguide, computer EM simulations, and analytical calculations.

WEYA02	Studies at CesrTA of Electron-Cloud-Induced Beam Dynamics for Future Damping Rings	2081
	G. Dugan, M.G. Billing, K.R. Butler, J.A. Crittenden, M.J. Forster, D.L. Kreinick, R.E. Meller, M.A. Palmer, G. Ramirez, M.C. Rendina, N.T. Rider, K.G. Sonnad, H.A. Williams CLASSE, Ithaca, New York, USA R.F. Campbell, R. Holtzapple, M. Randazzo CalPoly, San Luis Obispo, California, USA J.Y. Chu CMU, Pittsburgh, Pennsylvania, USA J.W. Flanagan, K. Ohmi KEK, Ibaraki, Japan M.A. Furman, M. Venturini LBNL, Berkeley, California, USA M.T.F. Pivi SLAC, Menlo Park, California, USA
	Funding: US National Science Foundation PHY-0734867, PHY-1002467, and PHY-1068662; US Dept. of Energy DE-FC02-08ER41538; and the Japan/US Cooperation Program. Electron clouds can adversely affect the performance of accelerators, and are of particular concern for the design of future low emittance damping rings. Studies of the impact of electron clouds on the dynamics of bunch trains in CESR have been a major focus of the CESR Test Accelerator program. In this paper, we report measurements of coherent tune shifts, emittance growth, and coherent instabilities carried out using a variety of bunch currents, train configurations, beam energies, and transverse emittances, similar to the design values for the ILC damping rings. We also compare the measurements with simulations which model the effects of electron clouds on beam dynamics, to extract simulation model parameters and to quantify the validity of the simulation codes.
	Slides WEYA02 [2.033 MB]

WEPPC074	HOM Studies on the Cornell ERL Prototype Cavity in a Horizontal Test Cryomodule	2384
	N.R.A. Valles, M.G. Billing, G.H. Hoffstaetter, M. Liepe, C.E. Mayes CLASSE, Ithaca, New York, USA
	The main linac 7-cell cavity for Cornell's Energy Recovery Linac was optimized to maximize threshold current through the ERL. This was achieved by designing center and end cells that reduce the strength of dipole higher-order modes. A prototype cavity was fabricated based on the optimized RF design and found to meet fundamental mode specifications in a vertical test. The higher-order-mode spectrum was measured when the cavity was installed in a horizontal test cryomodule and is compared to 2D and 3D EM simulations.

WEPPR086	Computed Wake Field Effects from Measured Surface Roughness in the Walls of the Cornell ERL	3132
	M.G. Billing, G.H. Hoffstaetter, C.E. Mayes, K.W. Smolenski, H.A. Williams CLASSE, Ithaca, New York, USA
	Funding: Work supported by the NSF ERL Phase 1B Cooperative Agreement (DMR-0807731) Wake fields arise from the discontinuities in a smooth vacuum chamber and will cause energy spread in the passing bunch. In an energy recovery linac (ERL), the spent bunches are decelerated before they are dumped to reuse the beam’s energy for the acceleration of new bunches. While the energy spread accumulated from wakes before deceleration is small compared to the beam’s energy after full acceleration, it becomes more important relatively as the beam’s energy decreases.* Thus, in an ERL wake fields can produce very significant energy spread in the beam as it is decelerated to the energy of the beam dump. We report on calculations of wake fields due to the roughness of the surface of the vacuum chamber walls as it affects the Cornell ERL design. These calculations include the effects from the measured roughness for real vacuum chamber wall surfaces. * M. Billing, “Effect of Wake Fields in an Energy Recovery Linac”, PAC’09, Vancouver, BC, Canada, 4-8 May 2009.

WEPPR087	Dependence of Beam Instabilities Caused by Electron Clouds at CesrTA Due to Variations in Chromaticity, Bunch Current and Train Length	3135
	M.G. Billing, G. Dugan, M.J. Forster, D.L. Kreinick, R.E. Meller, M.A. Palmer, G. Ramirez, M.C. Rendina, N.T. Rider, J.P. Sikora, K.G. Sonnad, H.A. Williams CLASSE, Ithaca, New York, USA J.Y. Chu CMU, Pittsburgh, Pennsylvania, USA J.W. Flanagan KEK, Ibaraki, Japan R. Holtzapple, M. Randazzo CalPoly, San Luis Obispo, California, USA
	Funding: Work supported by DOE Award DE-FC02-08ER41538, NSF Award PHY-0734867 and the Lepton Collider R&D Coop Agreement: NSF Award PHY-1002467. Electron cloud-induced beam dynamics is being studied at CESRTA under various conditions. These measurements detect the the coherent self-excited spectrum for each bunch within a train and bunch-by-bunch beam size. In the position spectrum coherent betatron dipole and head-tail motion is detectable for each individual bunch within the train with a sensitivity for the motion of 1.1 (2) microns-rms in the vertical (horizontal) direction for a 1 mA bunch current. These techniques are utilized to study the electron cloud-related interactions, which cause the growth of coherent motion and beam size along the train. We report on the observations and results from studies of the instability growth vs. changes in chromaticity, the current per bunch and the length of the train.