LINAC2014 - Table of Session: MOPOL (Poster Oral Presentations)

Paper

Title

Page

MOPOL01

High Energy Electron Radiography Experiment Research Based on Picosecond Pulse-width Bunch

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Q.T. Zhao, S. Cao, R. Cheng, X.K. Shen, Z.M. Zhang, Y.T. Zhao
IMP, Lanzhou, People's Republic of China
Y.-C. Du
TUB, Beijing, People's Republic of China
W. Gai
ANL, Argonne, Illinois, USA

A new scheme is proposed that high energy electron beam as a probe is used for time resolved imaging measurement of high energy density materials, especially for high energy density matter and inertial confinement fusion. The first picosecond pulse-width electron radiography experiment was achieved by Institute of Modern Physics, Chinese Academy of Sciences and Tinghua University (THU), based on THU Linear electron accelerator (LINAC). It is used for principle test and certifying that this kind of LINAC with ultra-short pulse electron bunch can be used for electron radiography. The experiment results, such as magnifying factor and the imaging distortion, are consistent with the beam optical theory well. The 2.5 um RMS spatial resolution has been gotten with magnifying factor 46, with no optimization the imaging lens section. It is found that in the certain range of magnifying factor, the RMS spatial resolution will get better with bigger magnifying factor. The details of experiment set up, results, analysis and discussions are presented here.

MOPOL02

X-band Technology for FEL Sources

MOPP023

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G. D'Auria, S. Di Mitri, C. Serpico
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
E. Adli
University of Oslo, Oslo, Norway
A.A. Aksoy, Ö. Yavaş
Ankara University, Accelerator Technologies Institute, Golbasi / Ankara, Turkey
D. Angal-Kalinin, J.A. Clarke
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
C.J. Bocchetta, A.I. Wawrzyniak
Solaris, Kraków, Poland
M.J. Boland, T.K. Charles, R.T. Dowd, G. LeBlanc, Y.E. Tan, K.P. Wootton, D. Zhu
SLSA, Clayton, Australia
G. Burt
Lancaster University, Lancaster, United Kingdom
N. Catalán Lasheras, A. Grudiev, A. Latina, D. Schulte, S. Stapnes, I. Syratchev, W. Wuensch
CERN, Geneva, Switzerland
W. Fang, Q. Gu
SINAP, Shanghai, People's Republic of China
E.N. Gazis
National Technical University of Athens, Athens, Greece
M. Jacewicz, R.J.M.Y. Ruber, V.G. Ziemann
Uppsala University, Uppsala, Sweden
X.J.A. Janssen
VDL ETG, Eindhoven, The Netherlands

As is widely recognized, fourth generation Light Sources are based on FELs driven by Linacs. Soft and hard X-ray FEL facilities are presently operational at several laboratories, SLAC (LCLS), Spring-8 (SACLA), Elettra-Sincrotrone Trieste (FERMI), DESY (FLASH), or are in the construction phase, PSI (SwissFEL), PAL (PAL-XFEL), DESY (European X-FEL), SLAC (LCLS II), or are newly proposed in many laboratories. Most of the above mentioned facilities use NC S-band (3 GHz) or C-band (6 GHz) linacs for generating a multi-GeV low emittance beam. The use of the C-band increases the linac operating gradients, with an overall reduction of the machine length and cost. These advantages, however, can be further enhanced by using X-band (12 GHz) linacs that operate with gradients twice that given by C-band technology. With the low bunch charge option, currently considered for future X-ray FELs, X-band technology offers a low cost and compact solution for generating multi-GeV, low emittance bunches. The paper reports the ongoing activities in the framework of a collaboration among several laboratories for the development and validation of X-band technology for FEL based photon sources.

MOPOL03

Experimental Verification Towards Feed-Forward Ground Motion Mitigation at ATF2

MOPP032

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J. Pfingstner, K. Artoos, C. Charrondière, S.M. Janssens, M. Patecki, Y. Renier, D. Schulte, R. Tomás
CERN, Geneva, Switzerland
A. Jeremie
IN2P3-LAPP, Annecy-le-Vieux, France
K. Kubo, S. Kuroda, T. Naito, T. Okugi, T. Tauchi, N. Terunuma
KEK, Ibaraki, Japan

Without counter measures, ground motion effects would deteriorate the performance of future linear colliders to an unacceptable level. An envisioned new ground motion mitigation method (based on feed-forward control) has the potential to improve the performance and to reduce the system cost compared to other proposed methods. For the experimental verification of this feed-forward scheme, a dedicated measurement setup has been installed at ATF2 at KEK. In this paper, the progress on this experimental verification is described. An important part of the feed-forward scheme could be already demonstrated, namely the prediction of the orbit jitter due to ground motion measurements.

MOPOL04

Bridging the Gap Between Conventional RF Acceleration and Laser Driven Acceleration

MOPP128

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M.V. Fazio, V.A. Dolgashev, S.G. Tantawi
SLAC, Menlo Park, California, USA

For decades conventional RF accelerators have been built and operated with ever increasing capability through a few tens of gigahertz in frequency. More recent research takes advantage of the continuing development of high peak power short pulse lasers to drive accelerator structures at optical frequencies. This jump from RF to optical frequencies skips four orders of magnitude in wavelength. With recent experiments that demonstrate high gradients in metallic structures at millimeter wavelengths one is compelled to consider the viability of new approaches for acceleration in the millimeter-wave to terahertz regime. This paper will explore some of these possibilities.

MOPOL05

Operation of the LINAC and the LINAC RF System for the Ion-Beam Therapy Center Heidelberg

MOPP067

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E. Feldmeier, R. Cee, Th. Haberer
HIT, Heidelberg, Germany

The Heidelberg Ion Therapy Center HIT is in clinical operation since 2009. It is the first dedicated european particle accelerator for medical treatment. Its central location on the campus of the Heidelberg University Hospital fits perfectly in the clinical everyday life. The accelerator complex consists of a linear accelerator and a synchrotron and is designed for protons and carbon ions, but can also provide helium and oxygen ions. The LINAC, build in 2006, operates since 5 years in a 24/7 schema which leads to 60000 operating hours up to now. The performance with an availibility of better than 99% is much higher than expected and is caused by a solid design and a well planned and foresighted maintenance. Unavoidable failures during operation can be solved very fast with the on site experts for each section. The combination of personnel spare parts and permanent ongoing developments is very successful. An upgrade program for parts of the linac and also for the RF system is in planning to keep the uptime high and to improve the performance for further needs.

MOPOL06

SNS Linac Upgrade Plans for the Second Target Station

MOPP114

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J. Galambos, D.E. Anderson, M.P. Howell, S.-H. Kim, M.A. Plum, A.P. Shishlo
ORNL, Oak Ridge, Tennessee, USA
M.E. Middendorf
ORNL RAD, Oak Ridge, Tennessee, USA

Funding: ORNL is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.
The Second Target Station (STS) upgrade for the Spallation Neutron Source (SNS) proposes the addition of a short pulse, long wavelength neutron scattering station. In order to provide world-class intensity at the additional station, the SNS linac beam power capability is doubled, to 2.8 MW. This will be accommodated by a 30% increase in the beam energy to 1.3 GeV and a 50% increase in beam current. The beam energy increase will be provided by the addition of 7 additional cyro-modules and supporting RF equipment in space provided during the original SNS construction. The beam current increase will be provided by improved ion source and a reduced chopping fraction, and will require increases in the RF and high voltage modulator systems to accommodate the additional beam loading. Initial plans will be presented. The proposed linac upgrade path will be described.

MOPOL07

Cool Down and Flux Trapping Studies on SRF Cavities

MOPP017

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D. Gonnella, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Recent results from Cornell and FNAL have shown that cool down rate can have a strong impact on the residual resistance of a superconducting RF cavity during operation. We have studied the effect of cool down rate, gradient, and external magnetic field during cool down on the residual resistance of an EP, EP+120C baked, and nitrogen-doped cavities. For each cavity, faster cool down and large gradient resulted in lower residual resistance in vertical test. The nitrogen-doped cavities showed the largest improvement with fast cool down, while the EP+120C cavity showed the smallest. The cavities were also placed in a uniform external magnetic field and residual resistance was measured as a function of applied field and cool down rate. We show that the nitrogen-doped cavity was the most susceptible to losses from trapped flux and the EP+120C cavity was least susceptible. These measurements provide new insights into understanding the physics behind the observed impact of cool down rates and gradients on the performance of cavities with differing preparations.

MOPOL08

Nondestructive Diagnostics of Proton Beam Halo and Transverse Bunch Position by Cerenkov Slow Wave Structures

MOPP084

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S.V. Kuzikov, M.B. Goykhman, A.V. Gromov, A.V. Palitsin, Yu.V. Rodin, A.A. Vikharev
IAP/RAS, Nizhny Novgorod, Russia

An appearance of the halo around bunch of particles is very undesirable destructive phenomenon in high-intensity proton accelerators. We suggest using built-in short BWO section in form of the corrugated metallic waveguide, in order to control particle distribution in real time. In BWO low velocity proton bunch has synchronism with slow spatial harmonic of TM01 wave. Fields of slow harmonic sharply grow in direction from axis to walls and rf power, generated by flying bunch of the given charge, critically depends on transverse bunch size. Results of the simulation, carried out for 20 pC proton bunch of 10 ps duration, show that in 5 GHz BWO of 30 cm length the output rf pulse of several nanosecond duration is varied from mW- level (for 1 mm transverse bunch size) to several tens of mW (for bunch of 20 mm radius). This power level is high enough to control halo appearance in each single proton bunch. The producible rf power in a BWO is also dependent on bunch deflection from axis. This effect we plan to use, in order to provide transverse bunch position monitoring by means of two additional rectangular slow wave section which have corrugations on mutually perpendicular walls.

MOPOL09

Emittance Measurement for SPring-8 Linac Using Four Six-Electrode BPMs

MOPP095

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K. Yanagida, H. Hanaki, S. Suzuki
JASRI/SPring-8, Hyogo-ken, Japan

In the SPring-8 linear accelerator (linac) six-electrode beam position monitors (BPMs) have been installed to measure second-order moments. At the end of the linac where the electron beam energy is 1 GeV four quadrupole magnets are utilized for twiss parameter matching toward the following beam transport line. Last year four six-electrode BPMs were installed at the locations of these four quadrupole magnets for an emittance measurement. The relative second-order moments were obtained changing the magnetic field strength of the quadrupole magnets, then beam sizes, emittances and twiss parameters were deduced or calculated. At this time we applied one pair of beam sizes measured by the screen monitor for a precise determination of emittances but we try to implement non-destructive measurement with no screen monitor. Before the emittance measurement a calibration with fifth-order moment correction was carried out changing beam positions at the BPM locations using upstream steering magnets (the entire calibration).

Slides MOPOL09 [0.984 MB]

MOPOL10

Plasma Processing of Nb Surfaces for SRF Cavities

MOPP115

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P.V. Tyagi, M. Doleans, S.-H. Kim
ORNL, Oak Ridge, Tennessee, USA
R. Afanador, C.J. McMahan
ORNL RAD, Oak Ridge, Tennessee, USA

Funding: This work is supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE.
Field emission is one of the most critical issues to achieve high performances of niobium (Nb) superconducting radio frequency (SRF) cavities. Field emission is mainly related to contaminants present at top surface of SRF cavities that act as electron emitters at high gradient operation and limit the cavity accelerating gradient. An R&D program at the Spallation Neutron Source (SNS) is in place* aiming to develop an in-situ plasma processing technique to remove some of the residual contaminants from inner surfaces of Nb cavities and improve their performance. The plasma processing R&D has first concentrated on removing hydrocarbon contamination from top surface of SRF cavities. Results from the surface studies on plasma processed Nb samples will be presented in this article and showed the removal of hydrocarbons from Nb surfaces as well as improvement of the surface workfuntion (WF).
*M. Doleans et al. “Plasma processing R&D for the SNS superconducting linac RF cavities” Proceedings of 2013 SRF workshop, Paris, France

Slides MOPOL10 [1.405 MB]

MOPOL12

Studies of Coherent Synchrotron Radiation in the Jefferson Lab FEL Driver with Implications for Bunch Compression

MOPP139

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C. Tennant, D. Douglas, R. Li
JLab, Newport News, Virginia, USA
C.-Y. Tsai
Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA

Funding: Work supported by the Office of Naval Research and the High Energy Laser Joint Technology. Jefferson Laboratory work is supported under U.S. DOE Contract No. DE-AC05-06OR23177.
The Jefferson Laboratory IR FEL Driver provides an ideal test bed for studying a variety of beam dynamical effects. Recent studies focused on characterizing the impact of coherent synchrotron radiation (CSR) with the goal of benchmarking measurements with simulation. Following measurements to characterize the beam, we quantitatively characterized energy extraction via CSR by measuring beam position at a dispersed location as a function of bunch compression. In addition to operating with the beam on the rising part of the linac RF waveform, measurements were also made while accelerating on the falling part. For each, the full compression point was moved along the backleg of the machine and the response of the beam (distribution, extracted energy) measured. Initial results of start-to-end simulations using a 1D CSR algorithm show remarkably good agreement with measurements. A subsequent experiment established lasing with the beam accelerated on the falling side of the RF waveform in conjunction with positive momentum compaction (R56) to compress the bunch. The success of this experiment motivated the design of a modified CEBAF-style arc with control of CSR and microbunching effects.

Paper	Title	Page
MOPOL01	High Energy Electron Radiography Experiment Research Based on Picosecond Pulse-width Bunch
MOPP015	use link to access more material from this paper's primary paper code
	Q.T. Zhao, S. Cao, R. Cheng, X.K. Shen, Z.M. Zhang, Y.T. Zhao IMP, Lanzhou, People's Republic of China Y.-C. Du TUB, Beijing, People's Republic of China W. Gai ANL, Argonne, Illinois, USA
	A new scheme is proposed that high energy electron beam as a probe is used for time resolved imaging measurement of high energy density materials, especially for high energy density matter and inertial confinement fusion. The first picosecond pulse-width electron radiography experiment was achieved by Institute of Modern Physics, Chinese Academy of Sciences and Tinghua University (THU), based on THU Linear electron accelerator (LINAC). It is used for principle test and certifying that this kind of LINAC with ultra-short pulse electron bunch can be used for electron radiography. The experiment results, such as magnifying factor and the imaging distortion, are consistent with the beam optical theory well. The 2.5 um RMS spatial resolution has been gotten with magnifying factor 46, with no optimization the imaging lens section. It is found that in the certain range of magnifying factor, the RMS spatial resolution will get better with bigger magnifying factor. The details of experiment set up, results, analysis and discussions are presented here.

MOPOL02	X-band Technology for FEL Sources
MOPP023	use link to access more material from this paper's primary paper code
	G. D'Auria, S. Di Mitri, C. Serpico Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy E. Adli University of Oslo, Oslo, Norway A.A. Aksoy, Ö. Yavaş Ankara University, Accelerator Technologies Institute, Golbasi / Ankara, Turkey D. Angal-Kalinin, J.A. Clarke STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom C.J. Bocchetta, A.I. Wawrzyniak Solaris, Kraków, Poland M.J. Boland, T.K. Charles, R.T. Dowd, G. LeBlanc, Y.E. Tan, K.P. Wootton, D. Zhu SLSA, Clayton, Australia G. Burt Lancaster University, Lancaster, United Kingdom N. Catalán Lasheras, A. Grudiev, A. Latina, D. Schulte, S. Stapnes, I. Syratchev, W. Wuensch CERN, Geneva, Switzerland W. Fang, Q. Gu SINAP, Shanghai, People's Republic of China E.N. Gazis National Technical University of Athens, Athens, Greece M. Jacewicz, R.J.M.Y. Ruber, V.G. Ziemann Uppsala University, Uppsala, Sweden X.J.A. Janssen VDL ETG, Eindhoven, The Netherlands
	As is widely recognized, fourth generation Light Sources are based on FELs driven by Linacs. Soft and hard X-ray FEL facilities are presently operational at several laboratories, SLAC (LCLS), Spring-8 (SACLA), Elettra-Sincrotrone Trieste (FERMI), DESY (FLASH), or are in the construction phase, PSI (SwissFEL), PAL (PAL-XFEL), DESY (European X-FEL), SLAC (LCLS II), or are newly proposed in many laboratories. Most of the above mentioned facilities use NC S-band (3 GHz) or C-band (6 GHz) linacs for generating a multi-GeV low emittance beam. The use of the C-band increases the linac operating gradients, with an overall reduction of the machine length and cost. These advantages, however, can be further enhanced by using X-band (12 GHz) linacs that operate with gradients twice that given by C-band technology. With the low bunch charge option, currently considered for future X-ray FELs, X-band technology offers a low cost and compact solution for generating multi-GeV, low emittance bunches. The paper reports the ongoing activities in the framework of a collaboration among several laboratories for the development and validation of X-band technology for FEL based photon sources.

MOPOL03	Experimental Verification Towards Feed-Forward Ground Motion Mitigation at ATF2
MOPP032	use link to access more material from this paper's primary paper code
	J. Pfingstner, K. Artoos, C. Charrondière, S.M. Janssens, M. Patecki, Y. Renier, D. Schulte, R. Tomás CERN, Geneva, Switzerland A. Jeremie IN2P3-LAPP, Annecy-le-Vieux, France K. Kubo, S. Kuroda, T. Naito, T. Okugi, T. Tauchi, N. Terunuma KEK, Ibaraki, Japan
	Without counter measures, ground motion effects would deteriorate the performance of future linear colliders to an unacceptable level. An envisioned new ground motion mitigation method (based on feed-forward control) has the potential to improve the performance and to reduce the system cost compared to other proposed methods. For the experimental verification of this feed-forward scheme, a dedicated measurement setup has been installed at ATF2 at KEK. In this paper, the progress on this experimental verification is described. An important part of the feed-forward scheme could be already demonstrated, namely the prediction of the orbit jitter due to ground motion measurements.

MOPOL04	Bridging the Gap Between Conventional RF Acceleration and Laser Driven Acceleration
MOPP128	use link to access more material from this paper's primary paper code
	M.V. Fazio, V.A. Dolgashev, S.G. Tantawi SLAC, Menlo Park, California, USA
	For decades conventional RF accelerators have been built and operated with ever increasing capability through a few tens of gigahertz in frequency. More recent research takes advantage of the continuing development of high peak power short pulse lasers to drive accelerator structures at optical frequencies. This jump from RF to optical frequencies skips four orders of magnitude in wavelength. With recent experiments that demonstrate high gradients in metallic structures at millimeter wavelengths one is compelled to consider the viability of new approaches for acceleration in the millimeter-wave to terahertz regime. This paper will explore some of these possibilities.

MOPOL05	Operation of the LINAC and the LINAC RF System for the Ion-Beam Therapy Center Heidelberg
MOPP067	use link to access more material from this paper's primary paper code
	E. Feldmeier, R. Cee, Th. Haberer HIT, Heidelberg, Germany
	The Heidelberg Ion Therapy Center HIT is in clinical operation since 2009. It is the first dedicated european particle accelerator for medical treatment. Its central location on the campus of the Heidelberg University Hospital fits perfectly in the clinical everyday life. The accelerator complex consists of a linear accelerator and a synchrotron and is designed for protons and carbon ions, but can also provide helium and oxygen ions. The LINAC, build in 2006, operates since 5 years in a 24/7 schema which leads to 60000 operating hours up to now. The performance with an availibility of better than 99% is much higher than expected and is caused by a solid design and a well planned and foresighted maintenance. Unavoidable failures during operation can be solved very fast with the on site experts for each section. The combination of personnel spare parts and permanent ongoing developments is very successful. An upgrade program for parts of the linac and also for the RF system is in planning to keep the uptime high and to improve the performance for further needs.

MOPOL06	SNS Linac Upgrade Plans for the Second Target Station
MOPP114	use link to access more material from this paper's primary paper code
	J. Galambos, D.E. Anderson, M.P. Howell, S.-H. Kim, M.A. Plum, A.P. Shishlo ORNL, Oak Ridge, Tennessee, USA M.E. Middendorf ORNL RAD, Oak Ridge, Tennessee, USA
	Funding: ORNL is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. The Second Target Station (STS) upgrade for the Spallation Neutron Source (SNS) proposes the addition of a short pulse, long wavelength neutron scattering station. In order to provide world-class intensity at the additional station, the SNS linac beam power capability is doubled, to 2.8 MW. This will be accommodated by a 30% increase in the beam energy to 1.3 GeV and a 50% increase in beam current. The beam energy increase will be provided by the addition of 7 additional cyro-modules and supporting RF equipment in space provided during the original SNS construction. The beam current increase will be provided by improved ion source and a reduced chopping fraction, and will require increases in the RF and high voltage modulator systems to accommodate the additional beam loading. Initial plans will be presented. The proposed linac upgrade path will be described.

MOPOL07	Cool Down and Flux Trapping Studies on SRF Cavities
MOPP017	use link to access more material from this paper's primary paper code
	D. Gonnella, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Recent results from Cornell and FNAL have shown that cool down rate can have a strong impact on the residual resistance of a superconducting RF cavity during operation. We have studied the effect of cool down rate, gradient, and external magnetic field during cool down on the residual resistance of an EP, EP+120C baked, and nitrogen-doped cavities. For each cavity, faster cool down and large gradient resulted in lower residual resistance in vertical test. The nitrogen-doped cavities showed the largest improvement with fast cool down, while the EP+120C cavity showed the smallest. The cavities were also placed in a uniform external magnetic field and residual resistance was measured as a function of applied field and cool down rate. We show that the nitrogen-doped cavity was the most susceptible to losses from trapped flux and the EP+120C cavity was least susceptible. These measurements provide new insights into understanding the physics behind the observed impact of cool down rates and gradients on the performance of cavities with differing preparations.

MOPOL08	Nondestructive Diagnostics of Proton Beam Halo and Transverse Bunch Position by Cerenkov Slow Wave Structures
MOPP084	use link to access more material from this paper's primary paper code
	S.V. Kuzikov, M.B. Goykhman, A.V. Gromov, A.V. Palitsin, Yu.V. Rodin, A.A. Vikharev IAP/RAS, Nizhny Novgorod, Russia
	An appearance of the halo around bunch of particles is very undesirable destructive phenomenon in high-intensity proton accelerators. We suggest using built-in short BWO section in form of the corrugated metallic waveguide, in order to control particle distribution in real time. In BWO low velocity proton bunch has synchronism with slow spatial harmonic of TM01 wave. Fields of slow harmonic sharply grow in direction from axis to walls and rf power, generated by flying bunch of the given charge, critically depends on transverse bunch size. Results of the simulation, carried out for 20 pC proton bunch of 10 ps duration, show that in 5 GHz BWO of 30 cm length the output rf pulse of several nanosecond duration is varied from mW- level (for 1 mm transverse bunch size) to several tens of mW (for bunch of 20 mm radius). This power level is high enough to control halo appearance in each single proton bunch. The producible rf power in a BWO is also dependent on bunch deflection from axis. This effect we plan to use, in order to provide transverse bunch position monitoring by means of two additional rectangular slow wave section which have corrugations on mutually perpendicular walls.

MOPOL09	Emittance Measurement for SPring-8 Linac Using Four Six-Electrode BPMs
MOPP095	use link to access more material from this paper's primary paper code
	K. Yanagida, H. Hanaki, S. Suzuki JASRI/SPring-8, Hyogo-ken, Japan
	In the SPring-8 linear accelerator (linac) six-electrode beam position monitors (BPMs) have been installed to measure second-order moments. At the end of the linac where the electron beam energy is 1 GeV four quadrupole magnets are utilized for twiss parameter matching toward the following beam transport line. Last year four six-electrode BPMs were installed at the locations of these four quadrupole magnets for an emittance measurement. The relative second-order moments were obtained changing the magnetic field strength of the quadrupole magnets, then beam sizes, emittances and twiss parameters were deduced or calculated. At this time we applied one pair of beam sizes measured by the screen monitor for a precise determination of emittances but we try to implement non-destructive measurement with no screen monitor. Before the emittance measurement a calibration with fifth-order moment correction was carried out changing beam positions at the BPM locations using upstream steering magnets (the entire calibration).
	Slides MOPOL09 [0.984 MB]

MOPOL10	Plasma Processing of Nb Surfaces for SRF Cavities
MOPP115	use link to access more material from this paper's primary paper code
	P.V. Tyagi, M. Doleans, S.-H. Kim ORNL, Oak Ridge, Tennessee, USA R. Afanador, C.J. McMahan ORNL RAD, Oak Ridge, Tennessee, USA
	Funding: This work is supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE. Field emission is one of the most critical issues to achieve high performances of niobium (Nb) superconducting radio frequency (SRF) cavities. Field emission is mainly related to contaminants present at top surface of SRF cavities that act as electron emitters at high gradient operation and limit the cavity accelerating gradient. An R&D program at the Spallation Neutron Source (SNS) is in place* aiming to develop an in-situ plasma processing technique to remove some of the residual contaminants from inner surfaces of Nb cavities and improve their performance. The plasma processing R&D has first concentrated on removing hydrocarbon contamination from top surface of SRF cavities. Results from the surface studies on plasma processed Nb samples will be presented in this article and showed the removal of hydrocarbons from Nb surfaces as well as improvement of the surface workfuntion (WF). *M. Doleans et al. “Plasma processing R&D for the SNS superconducting linac RF cavities” Proceedings of 2013 SRF workshop, Paris, France
	Slides MOPOL10 [1.405 MB]

MOPOL12	Studies of Coherent Synchrotron Radiation in the Jefferson Lab FEL Driver with Implications for Bunch Compression
MOPP139	use link to access more material from this paper's primary paper code
	C. Tennant, D. Douglas, R. Li JLab, Newport News, Virginia, USA C.-Y. Tsai Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
	Funding: Work supported by the Office of Naval Research and the High Energy Laser Joint Technology. Jefferson Laboratory work is supported under U.S. DOE Contract No. DE-AC05-06OR23177. The Jefferson Laboratory IR FEL Driver provides an ideal test bed for studying a variety of beam dynamical effects. Recent studies focused on characterizing the impact of coherent synchrotron radiation (CSR) with the goal of benchmarking measurements with simulation. Following measurements to characterize the beam, we quantitatively characterized energy extraction via CSR by measuring beam position at a dispersed location as a function of bunch compression. In addition to operating with the beam on the rising part of the linac RF waveform, measurements were also made while accelerating on the falling part. For each, the full compression point was moved along the backleg of the machine and the response of the beam (distribution, extracted energy) measured. Initial results of start-to-end simulations using a 1D CSR algorithm show remarkably good agreement with measurements. A subsequent experiment established lasing with the beam accelerated on the falling side of the RF waveform in conjunction with positive momentum compaction (R56) to compress the bunch. The success of this experiment motivated the design of a modified CEBAF-style arc with control of CSR and microbunching effects.