-
I Blumenfeld,
C E Clayton,
F J Decker,
M J Hogan,
C Huang,
R Ischebeck,
R H Iverson,
C Joshi,
T Katsouleas,
N Kirby,
W Lu,
K A Marsh,
W B Mori,
P Muggli,
E Oz, R H Siemann,
D R Walz,
M Zhou
[show abstract]
[hide abstract]
ABSTRACT: The scaling of the two important figures of merit, the transformer ratio T and the longitudinal electric field Ez, with the peak drive-bunch current Ip, in a nonlinear plasma wakefield accelerator is presented for the first time. The longitudinal field scales as Ip^0.623, in good agreement with nonlinear wakefield theory (~ Ip^0.5), while the unloaded transformer ratio is shown to be greater than unity and scales weakly with the bunch current. The effect of bunch head erosion on both parameters is also discussed.
Physical Review Special Topics - Accelerators and Beams 11/2010; 13(11):111301. · 1.52 Impact Factor
-
P Muggli,
I Blumenfeld,
C E Clayton,
F J Decker,
M J Hogan,
C Huang,
R Ischebeck,
R H Iverson,
C Joshi,
T Katsouleas,
N Kirby,
W Lu,
K A Marsh,
W B Mori,
E Oz, R H Siemann,
D R Walz,
M Zhou
[show abstract]
[hide abstract]
ABSTRACT: We present plasma wakefield acceleration experimental results showing that the energy gain by 28.5 GeV electrons scales with plasma length and reaches 14 GeV over a plasma with a density of 2.6×1017 cm−3 and a length of 31 cm. At this plasma density the average accelerating gradient is 36 GeV m−1. These results are in good agreement with the numbers obtained from particle in cell simulations describing the experiment. The linear scaling is also observed both at lower and higher plasma densities, at which smaller energy gains and accelerating gradients are measured. The systematic measurements of energy gain show the reproducibility and control of the acceleration process.
New Journal of Physics 04/2010; 12(4):045022. · 4.18 Impact Factor
-
N Kirby,
I Blumenfeld,
C E Clayton,
F J Decker,
M J Hogan,
C Huang,
R Ischebeck,
R H Iverson,
C Joshi,
T Katsouleas,
W Lu,
K A Marsh,
S F Martins,
W B Mori,
P Muggli,
E Oz, R H Siemann,
D R Walz,
M Zhou
[show abstract]
[hide abstract]
ABSTRACT: Multi-GeV trapped electron bunches in a plasma wakefield accelerator (PWFA) are observed with normalized transverse emittance divided by peak current, $\epsilon_{N,x}/I_t$, below the level of 0.2 $\mu$m/kA. A theoretical model of the trapped electron emittance, developed here, indicates that emittance scales inversely with the square root of the plasma density in the nonlinear ``bubble'' regime of the PWFA. This model and simulations indicate that the observed values of $\epsilon_{N,x}/I_t$ result from multi-GeV trapped electron bunches with emittances of a few $\mu$m and multi-kA peak currents.
Physical Review Special Topics - Accelerators and Beams 05/2009; 12(5):051302. · 1.52 Impact Factor
-
C E Clayton,
S F Martins,
J L Martins,
D K Johnson,
S Wang,
K A Marsh,
P Muggli,
M J Hogan,
D Walz,
R A Fonseca, [......],
R Ischebeck,
C Huang,
M Zhou,
W Lu,
S Deng,
T Katsouleas,
W B Mori, R H Siemann,
L O Silva,
C Joshi
[show abstract]
[hide abstract]
ABSTRACT: When a highly relativistic electron is injected off-axis into an ion channel, the restoring force of the radial field of the ions will cause the electron to accelerate towards the axis, overshoot, and begin to undergo oscillations about the ion-column axis at a characteristic frequency; the betatron frequency. This so-called betatron motion will cause the electron to radiate hard x-rays in the forward direction. In two recent experiments at the Stanford Linear Accelerator Center (SLAC), betatron x-rays in the 1-20kV range and in the 1-50MV range were produced with an electron beam with an energy of 28.5 GeV for ion densities of about 1 x 10(14) cm(-3) and 1 x 10(17)cm(-3), respectively. To make such an x-ray source more compact, the 3km long SLAC linac would be replaced by a source of electrons from a Laser Wakefield accelerator (LWFA). To increase the efficiency of converting laser into photons at high photon energies, we propose adding a second stage where the LWFA electrons radiate via a second ion channel, independent of the accelerating process. This two stage concept allows one to control the critical frequency of the emitted radiation as well as the efficiency of the process.
01/2009;
-
P Muggli,
B E Blue,
C E Clayton,
F J Decker,
M J Hogan,
C Huang,
C Joshi,
T C Katsouleas,
W Lu,
W B Mori,
C L O'Connell, R H Siemann,
D Walz,
M Zhou
[show abstract]
[hide abstract]
ABSTRACT: An ultrarelativistic 28.5 GeV, 700-microm-long positron bunch is focused near the entrance of a 1.4-m-long plasma with a density n(e) between approximately equal to 10(13) and approximately equal to 5 x 10(14) cm(-3). Partial neutralization of the bunch space charge by the mobile plasma electrons results in a reduction in transverse size by a factor of approximately equal to 3 in the high emittance plane of the beam approximately equal to 1 m downstream from the plasma exit. As n(e) increases, the formation of a beam halo containing approximately 40% of the total charge is observed, indicating that the plasma focusing force is nonlinear. Numerical simulations confirm these observations. The bunch with an incoming transverse size ratio of approximately 3 and emittance ratio of approximately 5 suffers emittance growth and exits the plasma with approximately equal sizes and emittances.
Physical Review Letters 09/2008; 101(5):055001. · 7.37 Impact Factor
-
R. Ischebeck,
M. Berry,
I. Blumenfeld,
F.-J. Decker,
M.J. Hogan,
R.H. Iverson,
N. Kirby, R.H. Siemann,
D. Walz,
C.E. Clayton,
Chengkun Huang,
C. Joshi,
Wei Lu,
K.A. Marsh,
T. Katsouleas,
P. Muggli,
E. Oz
[show abstract]
[hide abstract]
ABSTRACT: In the E-167 plasma wakefield acceleration experiment, electrons with an initial energy of 42 GeV are accelerated in a meter-scale lithium plasma. Particles are leaving plasma with a large energy spread. To determine the spectrum of the accelerated particles, a two-plane spectrometer has been set up.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
-
[show abstract]
[hide abstract]
ABSTRACT: The laser acceleration experiments conducted for the El63 project at the NLC Test Accelerator facility at SLAC have stringent requirements on the temporal properties of the electron and laser beams. A system has been implemented to measure the relative phase stability between the RF sent to the gun, the RF sent to the accelerator, and the laser used to generate the electrons. This system shows rms timing stability better than 1 psec. Temporal synchronicity between the 0.5 psec electron bunch, and the 0.5 psec laser pulse is also of great importance. Cherenkov radiation is used to measure the arrival time of the electron bunch with respect to the laser pulse, and the path length of the laser transport is adjusted to optimize temporal overlap. A linear stage mounted onto a voice coil is used to make shot- by-shot fine timing adjustments to the laser path. The final verification of the desired time stability and control is demonstrated by observing the peak of the laser-electron interaction signal over the course of several minutes.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
-
[show abstract]
[hide abstract]
ABSTRACT: Photonic bandgap (PBG) fibers with hollow core defects have been suggested for use as laser driven accelerator structures. The modes of a photonic crystal fiber lie in a set of allowed bands. A fiber with a central vacuum defect can support so-called defect modes with frequencies in the bandgap and electromagnetic fields confined spatially near the defect. A defect mode suitable for relativistic particle acceleration must have a longitudinal electric field in the central defect and a phase velocity at the speed of light (SOL). We explore the design of the defect geometry to support well confined accelerating modes in such PBG fibers. The dispersion diagram of an accelerating mode must cross the SOL line, and such modes form a special class of defect modes known as surface modes, which are lattice modes of the original PBG crystal that have been perturbed into the bandgap. The details of the surface boundary separating the defect from the surrounding PBG matrix are found to be the critical ingredients for optimizing the accelerator mode properties.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
-
C.M.S. Sears,
E.R. Colby,
B. Cowan,
R. Ischebeck,
C.M. McGuinness,
R. Noble, R.H. Siemann,
J.E. Spencer,
D. Walz,
R.L. Byer,
T. Plettner
[show abstract]
[hide abstract]
ABSTRACT: Photonic Bandgap (PBG) structures have recently been proposed as optical accelerators for their high coupling impedance and high damage threshold. As a first step in preparing a PBG accelerator, we propose to observe the optical wakefield induced by an electron beam traversing the structure in the absence of a coupled laser pulse. The electrons are focused into the fiber via a permanent magnet quadrupole triplet. The electrons excite fiber modes with speed-of-light (SOL) phase velocities. By observing the wakefield using a spectrometer, the SOL mode frequencies are determined.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents the initial results in laser electron acceleration from the newly commissioned E163 program at SLAC and an outline of the initial wave of experiments. These results include an inverse free electron laser (IFEL) interaction with 800 nm light from a Ti: sapphire laser which will be used along with a chicane to produce optically spaced electron microbunches. The microbunching is independently diagnosed via coherent optical transition radiation (COTR) at the second harmonic (400 nm) in order to avoid large background at the fundamental due to the laser. We will also discuss experiments that take the microbunch train formed by the IFEL/chicane and perform net acceleration using a second stage: an inverse transition radiation accelerator (ITR). This discussion includes the experiment layout and hardware as well as simulation of expected results.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
-
E Oz,
S Deng,
T Katsouleas,
P Muggli,
C D Barnes,
I Blumenfeld,
F J Decker,
P Emma,
M J Hogan,
R Ischebeck, [......],
D Walz,
D Auerbach,
C E Clayton,
C Huang,
D K Johnson,
C Joshi,
W Lu,
K A Marsh,
W B Mori,
M Zhou
[show abstract]
[hide abstract]
ABSTRACT: The onset of trapping of electrons born inside a highly relativistic, 3D beam-driven plasma wake is investigated. Trapping occurs in the transition regions of a Li plasma confined by He gas. Li plasma electrons support the wake, and higher ionization potential He atoms are ionized as the beam is focused by Li ions and can be trapped. As the wake amplitude is increased, the onset of trapping is observed. Some electrons gain up to 7.6 GeV in a 30.5 cm plasma. The experimentally inferred trapping threshold is at a wake amplitude of 36 GV/m, in good agreement with an analytical model and PIC simulations.
Physical Review Letters 03/2007; 98(8):084801. · 7.37 Impact Factor
-
D K Johnson,
D Auerbach,
I Blumenfeld,
C D Barnes,
C E Clayton,
F J Decker,
S Deng,
P Emma,
M J Hogan,
C Huang, [......],
P Krejcik,
W Lu,
K A Marsh,
W B Mori,
P Muggli,
C L O'Connell,
E Oz, R H Siemann,
D Walz,
M Zhou
[show abstract]
[hide abstract]
ABSTRACT: Positrons in the energy range of 3-30 MeV, produced by x rays emitted by betatron motion in a plasma wiggler of 28.5 GeV electrons from the SLAC accelerator, have been measured. The extremely high-strength plasma wiggler is an ion column induced by the electron beam as it propagates through and ionizes dense lithium vapor. X rays in the range of 1-50 MeV in a forward cone angle of 0.1 mrad collide with a 1.7 mm thick tungsten target to produce electron-positron pairs. The positron spectra are found to be strongly influenced by the plasma density and length as well as the electron bunch length. By characterizing the beam propagation in the ion column these influences are quantified and result in excellent agreement between the measured and calculated positron spectra.
Physical Review Letters 11/2006; 97(17):175003. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate a new particle acceleration mechanism using 800 nm laser radiation to accelerate relativistic electrons in a semi-infinite vacuum. The experimental demonstration is the first of its kind and is a proof of principle for the concept of laser-driven particle acceleration in a structure loaded vacuum. We observed up to 30 keV energy modulation over a distance of 1000 lambda, corresponding to a 40 MeV/m peak gradient. The energy modulation was observed to scale linearly with the laser electric field and showed the expected laser-polarization dependence. Furthermore, as expected, laser acceleration occurred only in the presence of a boundary that limited the laser-electron interaction to a finite distance.
Physical Review Letters 10/2005; 95(13):134801. · 7.37 Impact Factor
-
M J Hogan,
C D Barnes,
C E Clayton,
F J Decker,
S Deng,
P Emma,
C Huang,
R H Iverson,
D K Johnson,
C Joshi,
T Katsouleas,
P Krejcik,
W Lu,
K A Marsh,
W B Mori,
P Muggli,
C L O'Connell,
E Oz, R H Siemann,
D Walz
[show abstract]
[hide abstract]
ABSTRACT: A plasma-wakefield accelerator has accelerated particles by over 2.7 GeV in a 10 cm long plasma module. A 28.5 GeV electron beam with 1.8 x 10(10) electrons is compressed to 20 microm longitudinally and focused to a transverse spot size of 10 microm at the entrance of a 10 cm long column of lithium vapor with density 2.8 x 10(17) atoms/cm3. The electron bunch fully ionizes the lithium vapor to create a plasma and then expels the plasma electrons. These electrons return one-half plasma period later driving a large amplitude plasma wake that in turn accelerates particles in the back of the bunch by more than 2.7 GeV.
Physical Review Letters 08/2005; 95(5):054802. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We calculate the optimum energy efficiency of a laser-driven linear accelerator by adopting a simple linear model. In the case of single bunch operation, the energy efficiency can be enhanced by incorporating the accelerator into a cavity that is pumped by an external laser. In the case of multiple bunch operation, the intracavity configuration is less advantageous because the strong wakefield generated by the electron beam is also recycled. Finally, the calculation indicates that the luminosity of a linear collider based on such a structure is comparably small if high efficiency is desired.
Phys.Rev.ST Accel.Beams 8:031301,2005. 06/2005;
-
[show abstract]
[hide abstract]
ABSTRACT: We have observed acceleration of relativistic electrons in vacuum driven by a linearly polarized visible laser beam incident on a thin gold-coated reflective boundary. The observed energy modulation effect follows all the characteristics expected for linear acceleration caused by a longitudinal electric field. As predicted by the Lawson-Woodward theorem the laser driven modulation only appears in the presence of the boundary. It shows a linear dependence with the strength of the electric field of the laser beam and also it is critically dependent on the laser polarization. Finally, it appears to follow the expected angular dependence of the inverse transition radiation process.
Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
-
E. Oz,
S. Deng,
T. Katsouleas,
P. Muggli,
C.D. Barnes,
F.J. Decker,
M.J. Hogan,
R. Iverson,
D.K. Johnson,
P. Krejcik,
C. O'Connell, R.H. Siemann,
D. Walz,
C.E. Clayton,
C. Huang,
C. Joshi,
W. Lu,
K.A. Marsh,
W.B. Mori,
M. Zhou
[show abstract]
[hide abstract]
ABSTRACT: Evidence of particle trapping has been observed in a beam driven Plasma Wake Field Accelerator (PWFA) experiment, E164X, conducted at the Stanford Linear Accelerator Center by a collaboration which includes USC, UCLA and SLAC. Such trapping produces plasma dark current when the wakefield amplitude is above a threshold value and may place a limit on the maximum acceleration gradient in a PWFA. Trapping and dark current are enhanced when in an ionizing plasma, that is self-ionized by the beam. Here we present experimental results.
Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
-
R. Ischebeck,
C. Barnes,
I. Blumenfeld,
F. Decker,
M. Hogan,
R.H. Iverson,
P. Krejcik, R.H. Siemann,
D. Walz,
N. Kirby,
C. Clayton,
Chengkun Huang,
D.K. Johnson,
Wei Lu,
K. Marsh,
Suzhi Deng,
E. Oz
[show abstract]
[hide abstract]
ABSTRACT: The accelerating field that can be obtained in a beam-driven plasma wakefield accelerator depends on the current of the electron beam that excites the wake. In the E-167 experiment, a peak current above 10 kA will be delivered at a particle energy of 28 GeV. The bunch has a length of a few ten micrometers and several methods are used to measure its longitudinal profile. Among these, autocorrelation of coherent transition radiation (CTR) is employed. The beam passes a thin metallic foil, where it emits transition radiation. For wavelengths greater than the bunch length, this transition radiation is emitted coherently. This amplifies the long-wavelength part of the spectrum. A scanning Michelson interferometer is used to autocorrelate the CTR. However, this method requires the contribution of many bunches to build an autocorrelation trace. The measurement is influenced by the transmission characteristics of the vacuum window and beam splitter. We present here an analysis of materials, as well as possible layouts for a single shot CTR autocorrelator.
Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
-
R. Ischebeck,
F. Decker,
M. Hogan,
R.H. Iverson,
P. Krejcik, R.H. Siemann,
D. Walz,
M. Lincoln,
C.E. Clayton,
Chengkun Huang,
Wei Lu,
Suzhi Deng,
E. Oz
[show abstract]
[hide abstract]
ABSTRACT: In the plasma wakefield acceleration experiment E-167, optical transition radiation is used to measure the transverse profile of the electron bunches before and after the plasma acceleration. The distribution of the electric field from a single electron does not give a point-like distribution on the detector, but has a certain extension. Additionally, the resolution of the imaging system is affected by aberrations. The transverse profile of the bunch is thus convolved with a point spread function (PSF). Algorithms that deconvolve the image can help to improve the resolution. Imaged test patterns are used to determine the modulation transfer function of the lens. From this, the PSF can be reconstructed. The Lucy-Richardson algorithm is used to deconvolute this PSF from test images.
Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
-
[show abstract]
[hide abstract]
ABSTRACT: Coherent transition radiation is used to measure the length of the ultra-short electron bunches available at the Stanford Linear Accelerator Center. The results and the limitations of the method are described.
Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
