IPAC2018 - List of Authors (Mehrling, T.J.)

Paper	Title	Page
TUPML040	Status of the Transverse Diagnostics at FLASHForward	1630
	P. Niknejadi, R.T.P. D'Arcy, A. Knetsch, V. Libov, A. Martinez de la Ossa, J. Osterhoff, K. Poder, L. Schaper DESY, Hamburg, Germany M. Kaluza, M.B. Schwab, A. Sävert, C. Wirth IOQ, Jena, Germany M. Kaluza HIJ, Jena, Germany T.J. Mehrling LBNL, Berkeley, USA C.A.J. Palmer Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
	Funding: Helmholtz Institute, Bundesministerium für Bildung und Forschung, and European Union‘s Horizon 2020 research and innovation program. Density modulations in plasma caused by a high-intensity laser or a high charge density electron pulse can generate extreme acceleration fields. Acceleration of electrons in such fields may produce ultra-relativistic, quasi-monoenergetic, ultra-short electron bunches over distances orders of magnitudes shorter than in state-of-the-art radio-frequency accelerators. FLASHForward is such a beam-driven plasma wakefield accelerator (PWFA) project at DESY with the goal of producing, characterizing, and utilizing such beams. Temporal characterization of the acceleration process is of crucial importance for improving the stability and control in PWFA beams. While measurement of the transient field of the femtosecond bunch in a single shot is challenging, in recent years novel techniques with great promise have been developed . This work discusses the plans and status of the transverse diagnostics at FLASHForward. A. Aschikhin et. al., NIMA , Volume 806 (11 January 2016) pp. 175-183. A. Buck et al., Nature Physics 7, (2011) 543. *C. J. Zhang et al., Phys. Rev. Lett. 119 (2017) 064801.
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TUPML042	Accurate Modeling of the Hose Instability in Plasma Based Accelerators	1638
	T.J. Mehrling, C. Benedetti, E. Esarey, W. Leemans, C.B. Schroeder LBNL, Berkeley, California, USA
	Funding: US Department of Energy Contract No. DE-AC02-05CH11231 The hose instability is a long standing challenge for plasma-based accelerators. It is seeded by initial transverse asymmetries of the beam or plasma phase space distributions. The beam centroid displacement is thereby amplified during the propagation in the plasma, which can lead to an unstable acceleration process. A witness beam can itself cause hosing and/or may be affected by the hosing of the drive beam. The accurate study of hosing including a witness beam is of utmost importance to facilitate stable plasma-based accelerators. In this contribution, we discuss novel methods for the mitigation of hosing and present a new model for the evolution of the plasma centroid, which enables the accurate investigation of the hose instability of drive and witness beam pair in the nonlinear blowout regime. This work enables more precise and comprehensive studies of hosing and hence, for the potential stabilization of future compact plasma-based accelerators.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML042
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TUPML046	Characterization of Self-Modulated Electron Bunches in an Argon Plasma	1645
	M. Groß, P. Boonpornprasert, Y. Chen, J. Engel, J.D. Good, H. Huck, I.I. Isaev, M. Krasilnikov, X. Li, O. Lishilin, G. Loisch, R. Niemczyk, A. Oppelt, H.J. Qian, Y. Renier, F. Stephan, Q.T. Zhao DESY Zeuthen, Zeuthen, Germany R. Brinkmann, A. Martinez de la Ossa, J. Osterhoff DESY, Hamburg, Germany F.J. Grüner CFEL, Hamburg, Germany F.J. Grüner, A. Martinez de la Ossa University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany T.J. Mehrling, C.B. Schroeder LBNL, Berkeley, California, USA I. Will MBI, Berlin, Germany
	The self-modulation instability is fundamental for the plasma wakefield acceleration experiment of the AWAKE (Advanced Wakefield Experiment) collaboration at CERN where this effect is used to generate proton bunches for the resonant excitation of high acceleration fields. Utilizing the availability of flexible electron beam shaping together with excellent diagnostics including an RF deflector, a supporting experiment was set up at the electron accelerator PITZ (Photo Injector Test facility at DESY, Zeuthen site), given that the underlying physics is the same. After demonstrating the effect* the next goal is to investigate in detail the self-modulation of long (with respect to the plasma wavelength) electron beams. In this contribution we describe parameter studies on self-modulation of a long electron bunch in an argon plasma. The plasma was generated with a discharge cell with densities in the 10¹³ cm^-3 to 1015 cm^-3 range. The plasma density was deduced from the plasma wavelength as indicated by the self-modulation period. Parameter scans were conducted with variable plasma density and electron bunch focusing. * M. Gross et al., "Observation of the self-modulation instabil-ity via time-resolved measurements", accepted for publication at Phys. Rev. Lett.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML046
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THPML002	Emittance Preservation in Plasma-Based Accelerators with Ion Motion	4654
	C. Benedetti, E. Esarey, W. Leemans, T.J. Mehrling, C.B. Schroeder LBNL, Berkeley, California, USA
	Funding: This work was supported by the Director, Office of Science, Office of High Energy Physics, of the U.S. DOE under Contract No. DE-AC02-05CH11231. In a plasma-accelerator-based linear collider, the density of matched, low-emittance, high-energy particle bunches required for collider applications can be orders of magnitude above the background ion density, leading to ion motion, perturbation of the focusing fields, and, hence, to beam emittance growth. By analyzing the response of the background ions to an ultrahigh density beam, analytical expressions, valid for non-relativistic ion motion, are obtained for the perturbed focusing wakefield. Initial beam distributions are derived that are equilibrium solutions, which require head-to-tail bunch shaping, enabling emittance preservation with ion motion.
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Paper

Title

Page

Status of the Transverse Diagnostics at FLASHForward

1630

P. Niknejadi, R.T.P. D'Arcy, A. Knetsch, V. Libov, A. Martinez de la Ossa, J. Osterhoff, K. Poder, L. Schaper
DESY, Hamburg, Germany
M. Kaluza, M.B. Schwab, A. Sävert, C. Wirth
IOQ, Jena, Germany
M. Kaluza
HIJ, Jena, Germany
T.J. Mehrling
LBNL, Berkeley, USA
C.A.J. Palmer
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom

Funding: Helmholtz Institute, Bundesministerium für Bildung und Forschung, and European Union‘s Horizon 2020 research and innovation program.
Density modulations in plasma caused by a high-intensity laser or a high charge density electron pulse can generate extreme acceleration fields. Acceleration of electrons in such fields may produce ultra-relativistic, quasi-monoenergetic, ultra-short electron bunches over distances orders of magnitudes shorter than in state-of-the-art radio-frequency accelerators. FLASHForward is such a beam-driven plasma wakefield accelerator (PWFA) project at DESY with the goal of producing, characterizing, and utilizing such beams. Temporal characterization of the acceleration process is of crucial importance for improving the stability and control in PWFA beams. While measurement of the transient field of the femtosecond bunch in a single shot is challenging, in recent years novel techniques with great promise have been developed** ***. This work discusses the plans and status of the transverse diagnostics at FLASHForward.
*A. Aschikhin et. al., NIMA , Volume 806 (11 January 2016) pp. 175-183.
**A. Buck et al., Nature Physics 7, (2011) 543.
***C. J. Zhang et al., Phys. Rev. Lett. 119 (2017) 064801.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML040

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TUPML042

Accurate Modeling of the Hose Instability in Plasma Based Accelerators

1638

T.J. Mehrling, C. Benedetti, E. Esarey, W. Leemans, C.B. Schroeder
LBNL, Berkeley, California, USA

Funding: US Department of Energy Contract No. DE-AC02-05CH11231
The hose instability is a long standing challenge for plasma-based accelerators. It is seeded by initial transverse asymmetries of the beam or plasma phase space distributions. The beam centroid displacement is thereby amplified during the propagation in the plasma, which can lead to an unstable acceleration process. A witness beam can itself cause hosing and/or may be affected by the hosing of the drive beam. The accurate study of hosing including a witness beam is of utmost importance to facilitate stable plasma-based accelerators. In this contribution, we discuss novel methods for the mitigation of hosing and present a new model for the evolution of the plasma centroid, which enables the accurate investigation of the hose instability of drive and witness beam pair in the nonlinear blowout regime. This work enables more precise and comprehensive studies of hosing and hence, for the potential stabilization of future compact plasma-based accelerators.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML042

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TUPML046

Characterization of Self-Modulated Electron Bunches in an Argon Plasma

1645

M. Groß, P. Boonpornprasert, Y. Chen, J. Engel, J.D. Good, H. Huck, I.I. Isaev, M. Krasilnikov, X. Li, O. Lishilin, G. Loisch, R. Niemczyk, A. Oppelt, H.J. Qian, Y. Renier, F. Stephan, Q.T. Zhao
DESY Zeuthen, Zeuthen, Germany
R. Brinkmann, A. Martinez de la Ossa, J. Osterhoff
DESY, Hamburg, Germany
F.J. Grüner
CFEL, Hamburg, Germany
F.J. Grüner, A. Martinez de la Ossa
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
T.J. Mehrling, C.B. Schroeder
LBNL, Berkeley, California, USA
I. Will
MBI, Berlin, Germany

The self-modulation instability is fundamental for the plasma wakefield acceleration experiment of the AWAKE (Advanced Wakefield Experiment) collaboration at CERN where this effect is used to generate proton bunches for the resonant excitation of high acceleration fields. Utilizing the availability of flexible electron beam shaping together with excellent diagnostics including an RF deflector, a supporting experiment was set up at the electron accelerator PITZ (Photo Injector Test facility at DESY, Zeuthen site), given that the underlying physics is the same. After demonstrating the effect* the next goal is to investigate in detail the self-modulation of long (with respect to the plasma wavelength) electron beams. In this contribution we describe parameter studies on self-modulation of a long electron bunch in an argon plasma. The plasma was generated with a discharge cell with densities in the 10¹³ cm^-3 to 1015 cm^-3 range. The plasma density was deduced from the plasma wavelength as indicated by the self-modulation period. Parameter scans were conducted with variable plasma density and electron bunch focusing.
* M. Gross et al., "Observation of the self-modulation instabil-ity via time-resolved measurements", accepted for publication at Phys. Rev. Lett.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML046

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THPML002

Emittance Preservation in Plasma-Based Accelerators with Ion Motion

4654

C. Benedetti, E. Esarey, W. Leemans, T.J. Mehrling, C.B. Schroeder
LBNL, Berkeley, California, USA

Funding: This work was supported by the Director, Office of Science, Office of High Energy Physics, of the U.S. DOE under Contract No. DE-AC02-05CH11231.
In a plasma-accelerator-based linear collider, the density of matched, low-emittance, high-energy particle bunches required for collider applications can be orders of magnitude above the background ion density, leading to ion motion, perturbation of the focusing fields, and, hence, to beam emittance growth. By analyzing the response of the background ions to an ultrahigh density beam, analytical expressions, valid for non-relativistic ion motion, are obtained for the perturbed focusing wakefield. Initial beam distributions are derived that are equilibrium solutions, which require head-to-tail bunch shaping, enabling emittance preservation with ion motion.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML002

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