PAC2013 - List of Authors (Adli, E.)

Paper

Title

Page

The CLIC Project - Status and Prospects

6

E. Adli
University of Oslo, Oslo, Norway
E. Adli
CERN, Geneva, Switzerland
E. Adli
SLAC, Menlo Park, California, USA

Funding: The Research Council of Norway.
Following the feasibility demonstration of the novel CLIC technology and the publication in 2012 of a CLIC Conceptual Design Report for a Multi-TeV Linear Collider to be built in stages, a new phase towards a technical design is being launched by a global collaboration of volunteer institutes. This paper reviews the status and plans of the CLIC study outlining the developments planned for the next project phase.

Slides MOYBA1 [16.090 MB]

MOPAC02

Electron and Positron Bunch Self-modulation Experiments at SLAC-FACET

84

P. Muggli
MPI, Muenchen, Germany
E. Adli, S.J. Gessner, M.J. Hogan, S.Z. Li, M.D. Litos
SLAC, Menlo Park, California, USA
Y. Fang
USC, Los Angeles, California, USA
C. Joshi, K.A. Marsh, W.B. Mori, N. Vafaei-Najafabadi
UCLA, Los Angeles, California, USA
N.C. Lopes, L.O. Silva, J. Vieira
Instituto Superior Tecnico, Lisbon, Portugal
O. Reimann
MPI-P, München, Germany

A self-modulated proton-driven plasma wakefield acceleration experiment is being designed at CERN and will occur within 3-5 years. Uncompressed 20GeV lepton bunches currently available at SLAC-FACET could be used to test key physics of the CERN experiment (e.g. self-modulation instability (SMI), SMI seeding, ion motion, hosing, differences between electrons (e-) and positrons (e+), etc)*. The E-209 collaboration was formed to carry SMI experiments at SLAC-FACET. Here we show through full-scale Osiris simulations that electron self-modulation grows and saturates in less than 10cm. Wakefield excitation in the blowout regime leads to acceleration gradients in excess of 20GeV/m. The self-modulated e^- bunch then sustains stable wakefields over meter-long plasmas. As a result, 7(12)GeV e^- energy gain(loss) could be observed. In the blowout regime, most of the wakefield phase defocuses e+. Thus, uncompressed e⁺ bunches drive lower acceleration gradients, but still in excess of 10GeV/m, over 1m of plasma. We will discuss the experimental setup, diagnostics to measure SMI (e.g. CTR, energy spectrometer, OTR, etc) and expected results. First experimental results may also be available.
*J. Vieira et al., Phys. Plasmas 19, 063105 (2012).

MOPAC30

Multibunch Beam Physics at FACET

132

S.J. Gessner, E. Adli, K.L.F. Bane, F.-J. Decker, Z.D. Farkas, R.K. Jobe, M.D. Litos, M.C. Ross
SLAC, Menlo Park, California, USA
T.C. Katsouleas, A. A. Sahai
Duke ECE, Durham, North Carolina, USA

Funding: Work supported [optional: in part] by the U.S. Department of Energy under contract number DE AC0276SF00515.
Plasma wakefield studies are normally conducted as single-shot experiments. Here, single-shot means that the plasma returns to its original state before the next bunch passes through the plasma. The time scale for the plasma to return to equilibrium is 10-100 ns, which is comparable to the bunch separation in proposed linear colliders. The SLAC linac typically delivers beam at a rate of 10 Hz to FACET but can be operated in a manner that delivers two electron bunches per RF pulse. We explore operation modes with beam separations as small 5.6 ns so that high repetition rate plasma wakefield acceleration can be studied at FACET.

MOPAC38

A Betatron-Analysis Technique for Identifying Narrowband Trapped Charge within a Broadband Energy Tail in PWFA Experiments at FACET

147

C.E. Clayton, W. An, C. Joshi, K.A. Marsh, W.B. Mori, N. Vafaei-Najafabadi
UCLA, Los Angeles, California, USA
E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, M.D. Litos, D.R. Walz, Z. Wu
SLAC, Menlo Park, California, USA
W. Lu
TUB, Beijing, People's Republic of China
P. Muggli
MPI, Muenchen, Germany

Funding: The work at UCLA was supported by DOE grant DE-FG02-92-ER40727 and NSF grant PHY-0936266. Work at SLAC was supported in part by Department of Energy contract DE-AC02-7600515.
Plasma accelerators driven by ultra-relativistic electron beams have demonstrated greater than 50 GeV/m acceleration gradients over a distance of a meter though the accelerated particles typically have had a 100% energy spread when a single drive bunch was used. However, it is known that by locally producing electrons via ionization within the beam-driven plasma wake, they can become trapped and accelerated so that high-energy, mono-energetic electron bunches can be produced. We propose a technique to help identify these bunches of electrons at the 10’s of pC level arising from the ionization injection of Ar electrons that may otherwise be lost or overlooked as part of the discrete betatron-focusing maxima or the maxima inherent the chromaticity of the imaging electron spectrometer.

MOPAC46

Suppression of the Transformer Ratio Due to Distributed Injection of Electrons in a Plasma Wakefield Accelerator

165

N. Vafaei-Najafabadi, W. An, C.E. Clayton, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori
UCLA, Los Angeles, California, USA
E. Adli
University of Oslo, Oslo, Norway
E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, M.D. Litos, D.R. Walz, Z. Wu
SLAC, Menlo Park, California, USA
W. Lu
TUB, Beijing, People's Republic of China
P. Muggli
MPI, Muenchen, Germany

Funding: The work at UCLA was supported by DOE grant DE-FG02-92-ER40727 and NSF grant PHY-0936266. Simulations used the UCLA Hoff man cluster. Work at SLAC was supported by DOE contract DE-AC02-7600515.
Evidence of beam loading due to distributed injection in Plasma Wakefield Accelerator experiments carried out at the FACET facility at SLAC during the year 2012 is presented. The source of the injected charge is tunnel ionization of Rb⁺ inside the wake, which occurs along the length of the interaction at each minima of envelope betatron oscillation. Rb was used specifically to mitigate the problem of head erosion, which limited the energy gain in earlier experiments using Li that were carried out at FFTB in SLAC. In the present experiment however, electrons produced via secondary ionization of Rb were injected in the wake and led to a severe depletion of the accelerating wake, i.e. beam loading, which is observed as a reduction of mean, i.e. measured, transformer ratio. This ‘‘dark current" limitation on the maximum achievable accelerating gradient is also pertinent to other heavier ions that are potential candidates for high-gradient PWFA.

THYAA2

Latest Plasma Wakefield Acceleration Results from the FACET Project

1101

M.D. Litos, E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, D.R. Walz, G.R. White, Z. Wu, V. Yakimenko
SLAC, Menlo Park, California, USA
E. Adli
University of Oslo, Oslo, Norway
W. An, C.E. Clayton, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori, N. Vafaei-Najafabadi
UCLA, Los Angeles, California, USA
P. Muggli
MPI, Muenchen, Germany

SLAC’s new FACET facility had its second user run in April–June, 2013. Several new milestones were reached during this run, including the achievement of beam driven plasma wakefield acceleration of a discrete witness bunch for the first time, and energy doubling in a noble gas plasma source. The FACET beam is a 20 GeV electron bunch with a charge of 3.2 nC that can be compressed and focused to a size of 20 μm × 20 μm × 20 μm rms. To create the two-bunch, drive/witness beam structure, a chirped and over-compressed beam was dispersed horizontally in a chicane and a bite was taken from its middle with a tantalum finger collimator, corresponding to a longitudinal notching of the beam due to the head-tail energy correlation. A new 10 terawatt Ti:Sapphire laser was commissioned and used during this run to pre-ionize the plasma source in order to increase the efficiency of energy transfer from the beam to the wake. Ultimately, a witness beam of hundreds of pC in charge was accelerated by a drive beam of similar charge in a pre-formed lithium plasma with a density of 5×10¹⁶ cm^−3, experiencing gradients reaching several GeV/m in magnitude.

Slides THYAA2 [22.217 MB]

THOCA1

X-ray Radiation and Electron Injection from Beam Envelope Oscillations in Plasma Wakefield Accelerator Experiments at FACET

1105

K.A. Marsh, W. An, C.E. Clayton, C. Joshi, W. Lu, W.B. Mori, N. Vafaei-Najafabadi
UCLA, Los Angeles, California, USA
E. Adli
University of Oslo, Oslo, Norway
E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, M.D. Litos, D.R. Walz, Z. Wu
SLAC, Menlo Park, California, USA
W. Lu
TUB, Beijing, People's Republic of China
P. Muggli
MPI, Muenchen, Germany

Funding: The work at UCLA was supported by DOE grant DE-FG02-92-ER40727 and NSF grant PHY-0936266. The work at SLAC was supported by Department of Energy Contract DE-AC02-76SF00515.
Plasma wakefield accelerator experiments at FACET at the SLAC National Accelerator Laboratory have shown a correlation between ionization-injected electrons and the betatron x-ray yield. Emittance spoiling foils were inserted into the beam and the x-ray yield, excess charge, and beam energy loss was measured. The excess charge and x-ray yield are attributed to the beam envelope oscillations where at the minima, the field of the beam is strong enough to create secondary ionization, and at the electron oscillation maxima, the beam electrons spontaneously radiate x-rays. Large amplitude beam oscillations are expected to yield more x-rays and create more excess charge, but the results show beam head erosion strongly limits the wakefield excitation.

Slides THOCA1 [3.281 MB]

MOPAC46

Suppression of the Transformer Ratio Due to Distributed Injection of Electrons in a Plasma Wakefield Accelerator

165

N. Vafaei-Najafabadi, W. An, C.E. Clayton, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori
UCLA, Los Angeles, California, USA
E. Adli
University of Oslo, Oslo, Norway
E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, M.D. Litos, D.R. Walz, Z. Wu
SLAC, Menlo Park, California, USA
W. Lu
TUB, Beijing, People's Republic of China
P. Muggli
MPI, Muenchen, Germany

Funding: The work at UCLA was supported by DOE grant DE-FG02-92-ER40727 and NSF grant PHY-0936266. Simulations used the UCLA Hoff man cluster. Work at SLAC was supported by DOE contract DE-AC02-7600515.
Evidence of beam loading due to distributed injection in Plasma Wakefield Accelerator experiments carried out at the FACET facility at SLAC during the year 2012 is presented. The source of the injected charge is tunnel ionization of Rb⁺ inside the wake, which occurs along the length of the interaction at each minima of envelope betatron oscillation. Rb was used specifically to mitigate the problem of head erosion, which limited the energy gain in earlier experiments using Li that were carried out at FFTB in SLAC. In the present experiment however, electrons produced via secondary ionization of Rb were injected in the wake and led to a severe depletion of the accelerating wake, i.e. beam loading, which is observed as a reduction of mean, i.e. measured, transformer ratio. This ‘‘dark current" limitation on the maximum achievable accelerating gradient is also pertinent to other heavier ions that are potential candidates for high-gradient PWFA.

THYAA2

Latest Plasma Wakefield Acceleration Results from the FACET Project

1101

M.D. Litos, E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, D.R. Walz, G.R. White, Z. Wu, V. Yakimenko
SLAC, Menlo Park, California, USA
E. Adli
University of Oslo, Oslo, Norway
W. An, C.E. Clayton, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori, N. Vafaei-Najafabadi
UCLA, Los Angeles, California, USA
P. Muggli
MPI, Muenchen, Germany

SLAC’s new FACET facility had its second user run in April–June, 2013. Several new milestones were reached during this run, including the achievement of beam driven plasma wakefield acceleration of a discrete witness bunch for the first time, and energy doubling in a noble gas plasma source. The FACET beam is a 20 GeV electron bunch with a charge of 3.2 nC that can be compressed and focused to a size of 20 μm × 20 μm × 20 μm rms. To create the two-bunch, drive/witness beam structure, a chirped and over-compressed beam was dispersed horizontally in a chicane and a bite was taken from its middle with a tantalum finger collimator, corresponding to a longitudinal notching of the beam due to the head-tail energy correlation. A new 10 terawatt Ti:Sapphire laser was commissioned and used during this run to pre-ionize the plasma source in order to increase the efficiency of energy transfer from the beam to the wake. Ultimately, a witness beam of hundreds of pC in charge was accelerated by a drive beam of similar charge in a pre-formed lithium plasma with a density of 5×10¹⁶ cm^−3, experiencing gradients reaching several GeV/m in magnitude.

Slides THYAA2 [22.217 MB]

THOCA1

X-ray Radiation and Electron Injection from Beam Envelope Oscillations in Plasma Wakefield Accelerator Experiments at FACET

1105

K.A. Marsh, W. An, C.E. Clayton, C. Joshi, W. Lu, W.B. Mori, N. Vafaei-Najafabadi
UCLA, Los Angeles, California, USA
E. Adli
University of Oslo, Oslo, Norway
E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, M.D. Litos, D.R. Walz, Z. Wu
SLAC, Menlo Park, California, USA
W. Lu
TUB, Beijing, People's Republic of China
P. Muggli
MPI, Muenchen, Germany

Funding: The work at UCLA was supported by DOE grant DE-FG02-92-ER40727 and NSF grant PHY-0936266. The work at SLAC was supported by Department of Energy Contract DE-AC02-76SF00515.
Plasma wakefield accelerator experiments at FACET at the SLAC National Accelerator Laboratory have shown a correlation between ionization-injected electrons and the betatron x-ray yield. Emittance spoiling foils were inserted into the beam and the x-ray yield, excess charge, and beam energy loss was measured. The excess charge and x-ray yield are attributed to the beam envelope oscillations where at the minima, the field of the beam is strong enough to create secondary ionization, and at the electron oscillation maxima, the beam electrons spontaneously radiate x-rays. Large amplitude beam oscillations are expected to yield more x-rays and create more excess charge, but the results show beam head erosion strongly limits the wakefield excitation.

Slides THOCA1 [3.281 MB]

Paper	Title	Page
MOYBA1	The CLIC Project - Status and Prospects	6
	E. Adli University of Oslo, Oslo, Norway E. Adli CERN, Geneva, Switzerland E. Adli SLAC, Menlo Park, California, USA
	Funding: The Research Council of Norway. Following the feasibility demonstration of the novel CLIC technology and the publication in 2012 of a CLIC Conceptual Design Report for a Multi-TeV Linear Collider to be built in stages, a new phase towards a technical design is being launched by a global collaboration of volunteer institutes. This paper reviews the status and plans of the CLIC study outlining the developments planned for the next project phase.
	Slides MOYBA1 [16.090 MB]

MOPAC02	Electron and Positron Bunch Self-modulation Experiments at SLAC-FACET	84
	P. Muggli MPI, Muenchen, Germany E. Adli, S.J. Gessner, M.J. Hogan, S.Z. Li, M.D. Litos SLAC, Menlo Park, California, USA Y. Fang USC, Los Angeles, California, USA C. Joshi, K.A. Marsh, W.B. Mori, N. Vafaei-Najafabadi UCLA, Los Angeles, California, USA N.C. Lopes, L.O. Silva, J. Vieira Instituto Superior Tecnico, Lisbon, Portugal O. Reimann MPI-P, München, Germany
	A self-modulated proton-driven plasma wakefield acceleration experiment is being designed at CERN and will occur within 3-5 years. Uncompressed 20GeV lepton bunches currently available at SLAC-FACET could be used to test key physics of the CERN experiment (e.g. self-modulation instability (SMI), SMI seeding, ion motion, hosing, differences between electrons (e-) and positrons (e+), etc). The E-209 collaboration was formed to carry SMI experiments at SLAC-FACET. Here we show through full-scale Osiris simulations that electron self-modulation grows and saturates in less than 10cm. Wakefield excitation in the blowout regime leads to acceleration gradients in excess of 20GeV/m. The self-modulated e^- bunch then sustains stable wakefields over meter-long plasmas. As a result, 7(12)GeV e^- energy gain(loss) could be observed. In the blowout regime, most of the wakefield phase defocuses e+. Thus, uncompressed e⁺ bunches drive lower acceleration gradients, but still in excess of 10GeV/m, over 1m of plasma. We will discuss the experimental setup, diagnostics to measure SMI (e.g. CTR, energy spectrometer, OTR, etc) and expected results. First experimental results may also be available. J. Vieira et al., Phys. Plasmas 19, 063105 (2012).

MOPAC30	Multibunch Beam Physics at FACET	132
	S.J. Gessner, E. Adli, K.L.F. Bane, F.-J. Decker, Z.D. Farkas, R.K. Jobe, M.D. Litos, M.C. Ross SLAC, Menlo Park, California, USA T.C. Katsouleas, A. A. Sahai Duke ECE, Durham, North Carolina, USA
	Funding: Work supported [optional: in part] by the U.S. Department of Energy under contract number DE AC0276SF00515. Plasma wakefield studies are normally conducted as single-shot experiments. Here, single-shot means that the plasma returns to its original state before the next bunch passes through the plasma. The time scale for the plasma to return to equilibrium is 10-100 ns, which is comparable to the bunch separation in proposed linear colliders. The SLAC linac typically delivers beam at a rate of 10 Hz to FACET but can be operated in a manner that delivers two electron bunches per RF pulse. We explore operation modes with beam separations as small 5.6 ns so that high repetition rate plasma wakefield acceleration can be studied at FACET.

MOPAC38	A Betatron-Analysis Technique for Identifying Narrowband Trapped Charge within a Broadband Energy Tail in PWFA Experiments at FACET	147
	C.E. Clayton, W. An, C. Joshi, K.A. Marsh, W.B. Mori, N. Vafaei-Najafabadi UCLA, Los Angeles, California, USA E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, M.D. Litos, D.R. Walz, Z. Wu SLAC, Menlo Park, California, USA W. Lu TUB, Beijing, People's Republic of China P. Muggli MPI, Muenchen, Germany
	Funding: The work at UCLA was supported by DOE grant DE-FG02-92-ER40727 and NSF grant PHY-0936266. Work at SLAC was supported in part by Department of Energy contract DE-AC02-7600515. Plasma accelerators driven by ultra-relativistic electron beams have demonstrated greater than 50 GeV/m acceleration gradients over a distance of a meter though the accelerated particles typically have had a 100% energy spread when a single drive bunch was used. However, it is known that by locally producing electrons via ionization within the beam-driven plasma wake, they can become trapped and accelerated so that high-energy, mono-energetic electron bunches can be produced. We propose a technique to help identify these bunches of electrons at the 10’s of pC level arising from the ionization injection of Ar electrons that may otherwise be lost or overlooked as part of the discrete betatron-focusing maxima or the maxima inherent the chromaticity of the imaging electron spectrometer.

MOPAC46	Suppression of the Transformer Ratio Due to Distributed Injection of Electrons in a Plasma Wakefield Accelerator	165
	N. Vafaei-Najafabadi, W. An, C.E. Clayton, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori UCLA, Los Angeles, California, USA E. Adli University of Oslo, Oslo, Norway E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, M.D. Litos, D.R. Walz, Z. Wu SLAC, Menlo Park, California, USA W. Lu TUB, Beijing, People's Republic of China P. Muggli MPI, Muenchen, Germany
	Funding: The work at UCLA was supported by DOE grant DE-FG02-92-ER40727 and NSF grant PHY-0936266. Simulations used the UCLA Hoff man cluster. Work at SLAC was supported by DOE contract DE-AC02-7600515. Evidence of beam loading due to distributed injection in Plasma Wakefield Accelerator experiments carried out at the FACET facility at SLAC during the year 2012 is presented. The source of the injected charge is tunnel ionization of Rb⁺ inside the wake, which occurs along the length of the interaction at each minima of envelope betatron oscillation. Rb was used specifically to mitigate the problem of head erosion, which limited the energy gain in earlier experiments using Li that were carried out at FFTB in SLAC. In the present experiment however, electrons produced via secondary ionization of Rb were injected in the wake and led to a severe depletion of the accelerating wake, i.e. beam loading, which is observed as a reduction of mean, i.e. measured, transformer ratio. This ‘‘dark current" limitation on the maximum achievable accelerating gradient is also pertinent to other heavier ions that are potential candidates for high-gradient PWFA.

THYAA2	Latest Plasma Wakefield Acceleration Results from the FACET Project	1101
	M.D. Litos, E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, D.R. Walz, G.R. White, Z. Wu, V. Yakimenko SLAC, Menlo Park, California, USA E. Adli University of Oslo, Oslo, Norway W. An, C.E. Clayton, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori, N. Vafaei-Najafabadi UCLA, Los Angeles, California, USA P. Muggli MPI, Muenchen, Germany
	SLAC’s new FACET facility had its second user run in April–June, 2013. Several new milestones were reached during this run, including the achievement of beam driven plasma wakefield acceleration of a discrete witness bunch for the first time, and energy doubling in a noble gas plasma source. The FACET beam is a 20 GeV electron bunch with a charge of 3.2 nC that can be compressed and focused to a size of 20 μm × 20 μm × 20 μm rms. To create the two-bunch, drive/witness beam structure, a chirped and over-compressed beam was dispersed horizontally in a chicane and a bite was taken from its middle with a tantalum finger collimator, corresponding to a longitudinal notching of the beam due to the head-tail energy correlation. A new 10 terawatt Ti:Sapphire laser was commissioned and used during this run to pre-ionize the plasma source in order to increase the efficiency of energy transfer from the beam to the wake. Ultimately, a witness beam of hundreds of pC in charge was accelerated by a drive beam of similar charge in a pre-formed lithium plasma with a density of 5×10¹⁶ cm^−3, experiencing gradients reaching several GeV/m in magnitude.
	Slides THYAA2 [22.217 MB]

THOCA1	X-ray Radiation and Electron Injection from Beam Envelope Oscillations in Plasma Wakefield Accelerator Experiments at FACET	1105
	K.A. Marsh, W. An, C.E. Clayton, C. Joshi, W. Lu, W.B. Mori, N. Vafaei-Najafabadi UCLA, Los Angeles, California, USA E. Adli University of Oslo, Oslo, Norway E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, M.D. Litos, D.R. Walz, Z. Wu SLAC, Menlo Park, California, USA W. Lu TUB, Beijing, People's Republic of China P. Muggli MPI, Muenchen, Germany
	Funding: The work at UCLA was supported by DOE grant DE-FG02-92-ER40727 and NSF grant PHY-0936266. The work at SLAC was supported by Department of Energy Contract DE-AC02-76SF00515. Plasma wakefield accelerator experiments at FACET at the SLAC National Accelerator Laboratory have shown a correlation between ionization-injected electrons and the betatron x-ray yield. Emittance spoiling foils were inserted into the beam and the x-ray yield, excess charge, and beam energy loss was measured. The excess charge and x-ray yield are attributed to the beam envelope oscillations where at the minima, the field of the beam is strong enough to create secondary ionization, and at the electron oscillation maxima, the beam electrons spontaneously radiate x-rays. Large amplitude beam oscillations are expected to yield more x-rays and create more excess charge, but the results show beam head erosion strongly limits the wakefield excitation.
	Slides THOCA1 [3.281 MB]

MOPAC46	Suppression of the Transformer Ratio Due to Distributed Injection of Electrons in a Plasma Wakefield Accelerator	165
	N. Vafaei-Najafabadi, W. An, C.E. Clayton, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori UCLA, Los Angeles, California, USA E. Adli University of Oslo, Oslo, Norway E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, M.D. Litos, D.R. Walz, Z. Wu SLAC, Menlo Park, California, USA W. Lu TUB, Beijing, People's Republic of China P. Muggli MPI, Muenchen, Germany
	Funding: The work at UCLA was supported by DOE grant DE-FG02-92-ER40727 and NSF grant PHY-0936266. Simulations used the UCLA Hoff man cluster. Work at SLAC was supported by DOE contract DE-AC02-7600515. Evidence of beam loading due to distributed injection in Plasma Wakefield Accelerator experiments carried out at the FACET facility at SLAC during the year 2012 is presented. The source of the injected charge is tunnel ionization of Rb⁺ inside the wake, which occurs along the length of the interaction at each minima of envelope betatron oscillation. Rb was used specifically to mitigate the problem of head erosion, which limited the energy gain in earlier experiments using Li that were carried out at FFTB in SLAC. In the present experiment however, electrons produced via secondary ionization of Rb were injected in the wake and led to a severe depletion of the accelerating wake, i.e. beam loading, which is observed as a reduction of mean, i.e. measured, transformer ratio. This ‘‘dark current" limitation on the maximum achievable accelerating gradient is also pertinent to other heavier ions that are potential candidates for high-gradient PWFA.

THYAA2	Latest Plasma Wakefield Acceleration Results from the FACET Project	1101
	M.D. Litos, E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, D.R. Walz, G.R. White, Z. Wu, V. Yakimenko SLAC, Menlo Park, California, USA E. Adli University of Oslo, Oslo, Norway W. An, C.E. Clayton, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori, N. Vafaei-Najafabadi UCLA, Los Angeles, California, USA P. Muggli MPI, Muenchen, Germany
	SLAC’s new FACET facility had its second user run in April–June, 2013. Several new milestones were reached during this run, including the achievement of beam driven plasma wakefield acceleration of a discrete witness bunch for the first time, and energy doubling in a noble gas plasma source. The FACET beam is a 20 GeV electron bunch with a charge of 3.2 nC that can be compressed and focused to a size of 20 μm × 20 μm × 20 μm rms. To create the two-bunch, drive/witness beam structure, a chirped and over-compressed beam was dispersed horizontally in a chicane and a bite was taken from its middle with a tantalum finger collimator, corresponding to a longitudinal notching of the beam due to the head-tail energy correlation. A new 10 terawatt Ti:Sapphire laser was commissioned and used during this run to pre-ionize the plasma source in order to increase the efficiency of energy transfer from the beam to the wake. Ultimately, a witness beam of hundreds of pC in charge was accelerated by a drive beam of similar charge in a pre-formed lithium plasma with a density of 5×10¹⁶ cm^−3, experiencing gradients reaching several GeV/m in magnitude.
	Slides THYAA2 [22.217 MB]

THOCA1	X-ray Radiation and Electron Injection from Beam Envelope Oscillations in Plasma Wakefield Accelerator Experiments at FACET	1105
	K.A. Marsh, W. An, C.E. Clayton, C. Joshi, W. Lu, W.B. Mori, N. Vafaei-Najafabadi UCLA, Los Angeles, California, USA E. Adli University of Oslo, Oslo, Norway E. Adli, C.I. Clarke, S. Corde, J.-P. Delahaye, R.J. England, A.S. Fisher, J.T. Frederico, S.J. Gessner, M.J. Hogan, S.Z. Li, M.D. Litos, D.R. Walz, Z. Wu SLAC, Menlo Park, California, USA W. Lu TUB, Beijing, People's Republic of China P. Muggli MPI, Muenchen, Germany
	Funding: The work at UCLA was supported by DOE grant DE-FG02-92-ER40727 and NSF grant PHY-0936266. The work at SLAC was supported by Department of Energy Contract DE-AC02-76SF00515. Plasma wakefield accelerator experiments at FACET at the SLAC National Accelerator Laboratory have shown a correlation between ionization-injected electrons and the betatron x-ray yield. Emittance spoiling foils were inserted into the beam and the x-ray yield, excess charge, and beam energy loss was measured. The excess charge and x-ray yield are attributed to the beam envelope oscillations where at the minima, the field of the beam is strong enough to create secondary ionization, and at the electron oscillation maxima, the beam electrons spontaneously radiate x-rays. Large amplitude beam oscillations are expected to yield more x-rays and create more excess charge, but the results show beam head erosion strongly limits the wakefield excitation.
	Slides THOCA1 [3.281 MB]