2011 Particle Accelerator Conference - List of Authors (Palmer, M.A.)

Paper	Title	Page
MOP214	Methods for Quantitative Interpretation of Retarding Field Analyzer Data	501
	J.R. Calvey, J.A. Crittenden, G. Dugan, M.A. Palmer CLASSE, Ithaca, New York, USA M.A. Furman LBNL, Berkeley, California, USA K.C. Harkay ANL, Argonne, USA
	Funding: US Department of Energy grant DE-FC02-08ER41538 US National Science Foundation grant PHY-0734867 Over the course of the CesrTA program at Cornell, over 30 Retarding Field Analyzers (RFAs) have been installed in the CESR storage ring, and a great deal of data has been taken with them. These devices measure the local electron cloud density and energy distribution, and can be used to evaluate the efficacy of different cloud mitigation techniques. Obtaining a quantitative understanding of RFA data requires use of cloud simulation programs, as well as a detailed model of the detector itself. In a drift region, the RFA can be modeled by postprocessing the output of a simulation code, and one can obtain best fit values for important simulation parameters with a chi-square minimization method.

MOP215	Digital Tune Tracker for CESR	504
	R.E. Meller, M.A. Palmer CLASSE, Ithaca, New York, USA
	Funding: Work supported by the DOE through DE-FC02-08ER41538 and the NSF through PHY-0734867. Numerous storage ring diagnostic operations require synchronous excitation of beam motion. An example is the lattice phase measurement, which involves synchronous detection of the driven betatron motion. In the CESR storage ring, the transverse tunes continuously vary by several times their natural width. Hence, synchronous beam excitation is impossible without active feedback control. The digital tune tracker consists of a direct digital frequency synthesizer which drives the beam through a transverse kicker, and is phase locked to the detected betatron signal from a quad button position detector. This ensures synchronous excitation, and by setting the correct locking phase, the excitation can be tuned to peak resonance. The fully digital signal detection allows a single bunch amid a long train to be synchronously driven, which allows lattice diagnostics to be performed which include collective effects. The collective effects potentially of interest in CESR include wakefield couplings within the train, and plasma effects such as ion trapping and electron cloud trapping.

MOP304	Development of an X-Ray Beam Size Monitor with Single Pass Measurement Capability for CesrTA	687
	N.T. Rider, J.P. Alexander, M.G. Billing, J. Dobbins, R.E. Meller, M.A. Palmer, D.P. Peterson, C.R. Strohman CLASSE, Ithaca, New York, USA J.W. Flanagan KEK, Ibaraki, Japan
	The CESR Test Accelerator (CesrTA) program targets the study of beam physics issues relevant to linear collider damping rings. This endeavor requires new instrumentation to study the beam dynamics along trains of ultra low emittance bunches. A key element of the program has been the development of an x-ray beam size monitor capable of collecting single pass measurements of individual bunches in a train over thousands of turns. This instrument utilizes custom, high bandwidth amplifiers and digitization hardware to collect signals from a linear InGaAs diode array. The digitizer is synchronized with the CESR timing system and is capable of recording beam size measurements for bunches spaced by as little as 4ns. The x-ray source is a bending magnet with E_c=0.6 keV during 2 GeV CesrTA operations. For these conditions the amplifier dynamic range was optimized to allow measurements with 3x10⁹ to 10¹¹ particles per bunch. Initial testing is complete. Data analysis and examples of key measurements which illustrate the instrument's performance are presented. This device offers unique measurement capabilities applicable to future high energy physics accelerators and light sources.

TUP229	Implementation and Operation of Electron Cloud Diagnostics for CesrTA	1250
	Y. Li, J.V. Conway, X. Liu, V. Medjidzade, M.A. Palmer CLASSE, Ithaca, New York, USA
	Funding: Work Supported by NSF Grant #PHY-0734867 & DOE Grant #DE-FC02-08ER41538 The vacuum system of Cornell Electron Storage Ring (CESR) was successfully reconfigured to support CesrTA physics programs, including electron cloud (EC) build-up and suppression studies. One of key features of the reconfigured CESR vacuum system is the flexibility for exchange of various vacuum chambers with minimized impact to the accelerator operations. This is achieved by creation of three short gate-valve isolated vacuum sections. Over the last three years, many vacuum chambers with various EC diagnostics (such as RFAs, shielded pickups, etc) were rotated through these short experimental sections. With these instrumented test chambers, EC build-up was studied in many magnetic field types, including dipoles, quadrupoles, wigglers and field-free drifts. EC suppression techniques by coating (TiN, NEG and amorphous-C), surface textures (grooves) and clearing electrode are incorporated in these test chambers to evaluate their vacuum performance and EC suppression effectiveness. We present the implementation and operations of EC diagnostics.

TUP230	In-situ Secondary Electron Yield Measurement System at CesrTA	1253
	Y. Li, J.V. Conway, S. Greenwald, J.-S. Kim, V. Medjidzade, T.P. Moore, M.A. Palmer, C.R. Strohman CLASSE, Ithaca, New York, USA D. Asner Carleton University, College of Natural Sciences, Ottawa, Ontario, Canada
	Funding: Work Supported by NSF Grant #PHY-0734867 & DOE Grant #DE-FC02-08ER41538 Measuring the secondary electron yield (SEY) on technical surfaces in accelerator vacuum systems provides essential information for the study of electron cloud growth and suppression, with application to many accelerator R&D projects. As a part of the CesrTA research program, we developed and deployed an in-situ SEY measurement system. A two-sample SEY system was installed in the CesrTA vacuum system with one sample exposed to direct synchrotron radiation (SR) and the other sample exposed to scattered SR. The SEYs of both samples were measured as a function of the SR dosages. In this paper, we describe the in-situ SEY measurement systems and the initial results on bare aluminum (6061-T6), TiN-coated aluminum, amorphous carbon-coated aluminum, and amorphous carbon-coated copper samples.

WEP022	Status of Low Emittance Tuning at CesrTA	1540
	J.P. Shanks, M.G. Billing, R.E. Meller, M.A. Palmer, M.C. Rendina, N.T. Rider, D. L. Rubin, D. Sagan, C.R. Strohman, Y. Yanay CLASSE, Ithaca, New York, USA
	Funding: Work supported by the National Science Foundation and by the US Department of Energy under contract numbers PHY-0734867 and DE-FC02-08ER41538. We report on the status of emittance tuning techniques at the CESR Test Accelerator CesrTA. The CesrTA experimental program requires the capability to operate in a variety of machine lattices with the smallest possible emittance. We have attempted to minimize the turn-around time of our low emittance tuning procedure. We utilize high bandwidth BPM electronics for fast, precision measurements of orbit, betatron phase, transverse coupling, and dispersion. Turn by turn data is used to measure BPM button electrode gains to a under a percent. Gain-corrected coupling data is utilized to determine BPM tilts to 10mrad, allowing for measurement of vertical dispersion at the level of 10mm. Measurement and analysis of the data for characterizing BPM response takes 5 minutes. Beam based measurement of machine functions, data analysis, and implementing corrections in the machine takes another 5 minutes. An x-ray beam size monitor provides a real time check on the effectiveness of the procedure. A typical correction results in an emittance less than 20pm at 2.1GeV in 1-2 iterations. Sub 15pm has been achieved with adjustment of closed coupling/vertical dispersion bumps and betatron tunes.

WEP108	Application of Coherent Tune Shift Measurements to the Characterization of Electron Cloud Growth	1680
	D.L. Kreinick, J.A. Crittenden, G. Dugan, M.A. Palmer, G. Ramirez CLASSE, Ithaca, New York, USA M.A. Furman, M. Venturini LBNL, Berkeley, California, USA R. Holtzapple, M. Randazzo CalPoly, San Luis Obispo, California, USA
	Funding: DOE = DE-FC02-08ER41538 NSF = PHY-0734867 Measurements of coherent tune shifts at the Cornell Electron Storage Ring Test Accelerator (CesrTA) have been made for electron and positron beams under a wide variety of beam energies, bunch charge, and bunch train configurations. Comparing the observed tunes with the predictions of several electron cloud simulation programs allows the evaluation of important parameters in these models. These simulations will be used to predict the behavior of the electron cloud in damping rings for future linear colliders. We outline recent improvements to the analysis techniques that should improve the fidelity of the modeling.

WEP109	Simulations of Electron Cloud Induced Instabilities and Emittance Growth for CesrTA	1683
	K.G. Sonnad, K.R. Butler Cornell University, Ithaca, New York, USA G. Dugan, M.A. Palmer CLASSE, Ithaca, New York, USA M.T.F. Pivi SLAC, Menlo Park, California, USA
	Funding: US Department of Energy DE-FC02-08ER41538, National Science Foundation PHY-0734867 We present results of a series of studies obtained using the simulation code CMAD to study how electron clouds affect the dynamics of positron beams in CesrTA. The study complements ongoing experiments dedicated for studying the same phenomena. The simulation involves tracking positrons through the CesrTA lattice and simultaneously computing the force exerted due to space charge of the electrons on each of the tracked positrons. The electrons themselves are allowed to evolve under the influence of the positrons. Several results bear a close resemblance to what has been observed experimentally.

WEP142	Electron Cloud Modeling Results for Time-resolved Shielded Pickup Measurements at CesrTA	1752
	J.A. Crittenden, Y. Li, X. Liu, M.A. Palmer, J.P. Sikora CLASSE, Ithaca, New York, USA S. Calatroni, G. Rumolo CERN, Geneva, Switzerland
	Funding: Support by DOE contract DE-FC02-08ER41538 and NSF contract PHY-0734867 The Cornell Electron Storage Ring Test Accelerator (CesrTA) program includes investigations into electron cloud buildup, applying various mitigation techniques in custom vacuum chambers. Among these are two 1.1 meter long sections located symmetrically in the east and west arc regions. These chambers are equipped with pickup detectors shielded against the direct beam-induced signal. Here we report on results from the ECLOUD modeling code which highlight the sensitivity of these measurements to model parameters such as the photoelectron energy distributions, and the secondary elastic yield value.

WEP194	Measurement Techniques to Characterize Instabilities Caused by Electron Clouds	1852
	M.G. Billing, G. Dugan, M.J. Forster, R.E. Meller, M.A. Palmer, G. Ramirez, J.P. Sikora, H.A. Williams CLASSE, Ithaca, New York, USA R. Holtzapple CalPoly, San Luis Obispo, California, USA K.G. Sonnad Cornell University, Ithaca, New York, USA
	Funding: Work is supported by NSF (PHY-0734867) and DOE (DE-FC02-08ER41538) grants. The study of electron cloud-related instabilities for the CESR-TA project has required the development of new measurement techniques. The dynamics of the interaction of electron clouds with trains of bunches has been undertaken employing three basic observations. Measurements of tune shifts of bunches along a train has been used extensively with the most recent observations permitting the excitation of single bunches within the train to avoid collective train motion from driving the ensemble of bunches. Another technique has been developed to detect the coherent self-excited spectrum for each of the bunches within a train. This method is particularly useful when beam conditions are near the onset of an instability. The third method was designed to study bunches within the train in conditions below the onset of unstable motion. This is accomplished by separately driving each bunch within the train for several hundred turns and then observing the damping of its coherent motion. These last two techniques have been applied to study both transverse dipole (centroid) and head-tail motion. We will report on the observation methods and give examples of typical results.

WEP195	Time Resolved Measurement of Electron Clouds at CesrTA using Shielded Pickups	1855
	J.P. Sikora, M.G. Billing, J.A. Crittenden, Y. Li, M.A. Palmer CLASSE, Ithaca, New York, USA S. De Santis LBNL, Berkeley, California, USA
	Funding: This work is supported by the US National Science Foundation PHY-0734867, and the US Department of Energy DE-FC02-08ER41538. The Cornell Electron Storage Ring has been reconfigured as a Test Accelerator (CesrTA). Shielded pickups have been installed at three locations in CesrTA for the purpose of studying time resolved electron cloud build-up and decay. The pickup design provides electromagnetic shielding from the beam wakefield while allowing cloud electrons in the vacuum space to enter the detector. This paper describes the hardware configuration and capabilities of these detectors at CesrTA, presents examples of measurements, and outlines the interpretation of detector signals with regard to electron clouds. Useful features include time-of-flight measurement of cloud electrons and the use of a solenoidal field for energy measurement of photoelectrons. Measurement techniques include the use of two bunches spaced in multiples of 4ns, where the second bunch samples the decay of the cloud produced by the first bunch.

Paper

Title

Page

Methods for Quantitative Interpretation of Retarding Field Analyzer Data

501

J.R. Calvey, J.A. Crittenden, G. Dugan, M.A. Palmer
CLASSE, Ithaca, New York, USA
M.A. Furman
LBNL, Berkeley, California, USA
K.C. Harkay
ANL, Argonne, USA

Funding: US Department of Energy grant DE-FC02-08ER41538 US National Science Foundation grant PHY-0734867
Over the course of the CesrTA program at Cornell, over 30 Retarding Field Analyzers (RFAs) have been installed in the CESR storage ring, and a great deal of data has been taken with them. These devices measure the local electron cloud density and energy distribution, and can be used to evaluate the efficacy of different cloud mitigation techniques. Obtaining a quantitative understanding of RFA data requires use of cloud simulation programs, as well as a detailed model of the detector itself. In a drift region, the RFA can be modeled by postprocessing the output of a simulation code, and one can obtain best fit values for important simulation parameters with a chi-square minimization method.

MOP215

Digital Tune Tracker for CESR

504

R.E. Meller, M.A. Palmer
CLASSE, Ithaca, New York, USA

Funding: Work supported by the DOE through DE-FC02-08ER41538 and the NSF through PHY-0734867.
Numerous storage ring diagnostic operations require synchronous excitation of beam motion. An example is the lattice phase measurement, which involves synchronous detection of the driven betatron motion. In the CESR storage ring, the transverse tunes continuously vary by several times their natural width. Hence, synchronous beam excitation is impossible without active feedback control. The digital tune tracker consists of a direct digital frequency synthesizer which drives the beam through a transverse kicker, and is phase locked to the detected betatron signal from a quad button position detector. This ensures synchronous excitation, and by setting the correct locking phase, the excitation can be tuned to peak resonance. The fully digital signal detection allows a single bunch amid a long train to be synchronously driven, which allows lattice diagnostics to be performed which include collective effects. The collective effects potentially of interest in CESR include wakefield couplings within the train, and plasma effects such as ion trapping and electron cloud trapping.

MOP304

Development of an X-Ray Beam Size Monitor with Single Pass Measurement Capability for CesrTA

687

N.T. Rider, J.P. Alexander, M.G. Billing, J. Dobbins, R.E. Meller, M.A. Palmer, D.P. Peterson, C.R. Strohman
CLASSE, Ithaca, New York, USA
J.W. Flanagan
KEK, Ibaraki, Japan

The CESR Test Accelerator (CesrTA) program targets the study of beam physics issues relevant to linear collider damping rings. This endeavor requires new instrumentation to study the beam dynamics along trains of ultra low emittance bunches. A key element of the program has been the development of an x-ray beam size monitor capable of collecting single pass measurements of individual bunches in a train over thousands of turns. This instrument utilizes custom, high bandwidth amplifiers and digitization hardware to collect signals from a linear InGaAs diode array. The digitizer is synchronized with the CESR timing system and is capable of recording beam size measurements for bunches spaced by as little as 4ns. The x-ray source is a bending magnet with E_c=0.6 keV during 2 GeV CesrTA operations. For these conditions the amplifier dynamic range was optimized to allow measurements with 3x10⁹ to 10¹¹ particles per bunch. Initial testing is complete. Data analysis and examples of key measurements which illustrate the instrument's performance are presented. This device offers unique measurement capabilities applicable to future high energy physics accelerators and light sources.

TUP229

Implementation and Operation of Electron Cloud Diagnostics for CesrTA

1250

Y. Li, J.V. Conway, X. Liu, V. Medjidzade, M.A. Palmer
CLASSE, Ithaca, New York, USA

Funding: Work Supported by NSF Grant #PHY-0734867 & DOE Grant #DE-FC02-08ER41538
The vacuum system of Cornell Electron Storage Ring (CESR) was successfully reconfigured to support CesrTA physics programs, including electron cloud (EC) build-up and suppression studies. One of key features of the reconfigured CESR vacuum system is the flexibility for exchange of various vacuum chambers with minimized impact to the accelerator operations. This is achieved by creation of three short gate-valve isolated vacuum sections. Over the last three years, many vacuum chambers with various EC diagnostics (such as RFAs, shielded pickups, etc) were rotated through these short experimental sections. With these instrumented test chambers, EC build-up was studied in many magnetic field types, including dipoles, quadrupoles, wigglers and field-free drifts. EC suppression techniques by coating (TiN, NEG and amorphous-C), surface textures (grooves) and clearing electrode are incorporated in these test chambers to evaluate their vacuum performance and EC suppression effectiveness. We present the implementation and operations of EC diagnostics.

TUP230

In-situ Secondary Electron Yield Measurement System at CesrTA

1253

Y. Li, J.V. Conway, S. Greenwald, J.-S. Kim, V. Medjidzade, T.P. Moore, M.A. Palmer, C.R. Strohman
CLASSE, Ithaca, New York, USA
D. Asner
Carleton University, College of Natural Sciences, Ottawa, Ontario, Canada

Funding: Work Supported by NSF Grant #PHY-0734867 & DOE Grant #DE-FC02-08ER41538
Measuring the secondary electron yield (SEY) on technical surfaces in accelerator vacuum systems provides essential information for the study of electron cloud growth and suppression, with application to many accelerator R&D projects. As a part of the CesrTA research program, we developed and deployed an in-situ SEY measurement system. A two-sample SEY system was installed in the CesrTA vacuum system with one sample exposed to direct synchrotron radiation (SR) and the other sample exposed to scattered SR. The SEYs of both samples were measured as a function of the SR dosages. In this paper, we describe the in-situ SEY measurement systems and the initial results on bare aluminum (6061-T6), TiN-coated aluminum, amorphous carbon-coated aluminum, and amorphous carbon-coated copper samples.

WEP022

Status of Low Emittance Tuning at CesrTA

1540

J.P. Shanks, M.G. Billing, R.E. Meller, M.A. Palmer, M.C. Rendina, N.T. Rider, D. L. Rubin, D. Sagan, C.R. Strohman, Y. Yanay
CLASSE, Ithaca, New York, USA

Funding: Work supported by the National Science Foundation and by the US Department of Energy under contract numbers PHY-0734867 and DE-FC02-08ER41538.
We report on the status of emittance tuning techniques at the CESR Test Accelerator CesrTA. The CesrTA experimental program requires the capability to operate in a variety of machine lattices with the smallest possible emittance. We have attempted to minimize the turn-around time of our low emittance tuning procedure. We utilize high bandwidth BPM electronics for fast, precision measurements of orbit, betatron phase, transverse coupling, and dispersion. Turn by turn data is used to measure BPM button electrode gains to a under a percent. Gain-corrected coupling data is utilized to determine BPM tilts to 10mrad, allowing for measurement of vertical dispersion at the level of 10mm. Measurement and analysis of the data for characterizing BPM response takes 5 minutes. Beam based measurement of machine functions, data analysis, and implementing corrections in the machine takes another 5 minutes. An x-ray beam size monitor provides a real time check on the effectiveness of the procedure. A typical correction results in an emittance less than 20pm at 2.1GeV in 1-2 iterations. Sub 15pm has been achieved with adjustment of closed coupling/vertical dispersion bumps and betatron tunes.

WEP108

Application of Coherent Tune Shift Measurements to the Characterization of Electron Cloud Growth

1680

D.L. Kreinick, J.A. Crittenden, G. Dugan, M.A. Palmer, G. Ramirez
CLASSE, Ithaca, New York, USA
M.A. Furman, M. Venturini
LBNL, Berkeley, California, USA
R. Holtzapple, M. Randazzo
CalPoly, San Luis Obispo, California, USA

Funding: DOE = DE-FC02-08ER41538 NSF = PHY-0734867
Measurements of coherent tune shifts at the Cornell Electron Storage Ring Test Accelerator (CesrTA) have been made for electron and positron beams under a wide variety of beam energies, bunch charge, and bunch train configurations. Comparing the observed tunes with the predictions of several electron cloud simulation programs allows the evaluation of important parameters in these models. These simulations will be used to predict the behavior of the electron cloud in damping rings for future linear colliders. We outline recent improvements to the analysis techniques that should improve the fidelity of the modeling.

WEP109

Simulations of Electron Cloud Induced Instabilities and Emittance Growth for CesrTA

1683

K.G. Sonnad, K.R. Butler
Cornell University, Ithaca, New York, USA
G. Dugan, M.A. Palmer
CLASSE, Ithaca, New York, USA
M.T.F. Pivi
SLAC, Menlo Park, California, USA

Funding: US Department of Energy DE-FC02-08ER41538, National Science Foundation PHY-0734867
We present results of a series of studies obtained using the simulation code CMAD to study how electron clouds affect the dynamics of positron beams in CesrTA. The study complements ongoing experiments dedicated for studying the same phenomena. The simulation involves tracking positrons through the CesrTA lattice and simultaneously computing the force exerted due to space charge of the electrons on each of the tracked positrons. The electrons themselves are allowed to evolve under the influence of the positrons. Several results bear a close resemblance to what has been observed experimentally.

WEP142

Electron Cloud Modeling Results for Time-resolved Shielded Pickup Measurements at CesrTA

1752

J.A. Crittenden, Y. Li, X. Liu, M.A. Palmer, J.P. Sikora
CLASSE, Ithaca, New York, USA
S. Calatroni, G. Rumolo
CERN, Geneva, Switzerland

Funding: Support by DOE contract DE-FC02-08ER41538 and NSF contract PHY-0734867
The Cornell Electron Storage Ring Test Accelerator (CesrTA) program includes investigations into electron cloud buildup, applying various mitigation techniques in custom vacuum chambers. Among these are two 1.1 meter long sections located symmetrically in the east and west arc regions. These chambers are equipped with pickup detectors shielded against the direct beam-induced signal. Here we report on results from the ECLOUD modeling code which highlight the sensitivity of these measurements to model parameters such as the photoelectron energy distributions, and the secondary elastic yield value.

WEP194

Measurement Techniques to Characterize Instabilities Caused by Electron Clouds

1852

M.G. Billing, G. Dugan, M.J. Forster, R.E. Meller, M.A. Palmer, G. Ramirez, J.P. Sikora, H.A. Williams
CLASSE, Ithaca, New York, USA
R. Holtzapple
CalPoly, San Luis Obispo, California, USA
K.G. Sonnad
Cornell University, Ithaca, New York, USA

Funding: Work is supported by NSF (PHY-0734867) and DOE (DE-FC02-08ER41538) grants.
The study of electron cloud-related instabilities for the CESR-TA project has required the development of new measurement techniques. The dynamics of the interaction of electron clouds with trains of bunches has been undertaken employing three basic observations. Measurements of tune shifts of bunches along a train has been used extensively with the most recent observations permitting the excitation of single bunches within the train to avoid collective train motion from driving the ensemble of bunches. Another technique has been developed to detect the coherent self-excited spectrum for each of the bunches within a train. This method is particularly useful when beam conditions are near the onset of an instability. The third method was designed to study bunches within the train in conditions below the onset of unstable motion. This is accomplished by separately driving each bunch within the train for several hundred turns and then observing the damping of its coherent motion. These last two techniques have been applied to study both transverse dipole (centroid) and head-tail motion. We will report on the observation methods and give examples of typical results.

WEP195

Time Resolved Measurement of Electron Clouds at CesrTA using Shielded Pickups

1855

J.P. Sikora, M.G. Billing, J.A. Crittenden, Y. Li, M.A. Palmer
CLASSE, Ithaca, New York, USA
S. De Santis
LBNL, Berkeley, California, USA

Funding: This work is supported by the US National Science Foundation PHY-0734867, and the US Department of Energy DE-FC02-08ER41538.
The Cornell Electron Storage Ring has been reconfigured as a Test Accelerator (CesrTA). Shielded pickups have been installed at three locations in CesrTA for the purpose of studying time resolved electron cloud build-up and decay. The pickup design provides electromagnetic shielding from the beam wakefield while allowing cloud electrons in the vacuum space to enter the detector. This paper describes the hardware configuration and capabilities of these detectors at CesrTA, presents examples of measurements, and outlines the interpretation of detector signals with regard to electron clouds. Useful features include time-of-flight measurement of cloud electrons and the use of a solenoidal field for energy measurement of photoelectrons. Measurement techniques include the use of two bunches spaced in multiples of 4ns, where the second bunch samples the decay of the cloud produced by the first bunch.