M. J. Hogan

University of California, Los Angeles, Los Angeles, California, United States

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Publications (192)396.35 Total impact

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    ABSTRACT: We describe a beam profile monitor design based on Cherenkov light emitted from a charged particle beam in an air gap. The main components of the profile monitor are silicon wafers used to reflect Cherenkov light onto a camera lens system. The design allows for measuring large beam sizes, with large photon yield per beam charge and excellent signal linearity with beam charge. The profile monitor signal is independent of the particle energy for ultrarelativistic particles. Different design and parameter considerations are discussed. A Cherenkov light-based profile monitor has been installed at the FACET User Facility at SLAC. We report on the measured performance of this profile monitor.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 02/2015; 783. DOI:10.1016/j.nima.2015.02.003 · 1.32 Impact Factor
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    ABSTRACT: For the further development of plasma based accelerators, phase space matching between plasma acceleration stages and between plasma stages and traditional accelerator components becomes a very critical issue for high quality high energy acceleration and its applications in light sources and colliders. Without proper matching, catastrophic emittance growth in the presence of finite energy spread may occur when the beam propagating through different stages and components due to the drastic differences of transverse focusing strength. In this paper we propose to use longitudinally tailored plasma structures as phase space matching components to properly guide the beam through stages. Theoretical analysis and full 3-dimensional particle-in-cell simulations are utilized to show clearly how these structures may work in four different scenarios. Very good agreements between theory and simulations are obtained.
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    ABSTRACT: High-efficiency acceleration of charged particle beams at high gradients of energy gain per unit length is necessary to achieve an affordable and compact high-energy collider. The plasma wakefield accelerator is one concept being developed for this purpose. In plasma wakefield acceleration, a charge-density wake with high accelerating fields is driven by the passage of an ultra-relativistic bunch of charged particles (the drive bunch) through a plasma. If a second bunch of relativistic electrons (the trailing bunch) with sufficient charge follows in the wake of the drive bunch at an appropriate distance, it can be efficiently accelerated to high energy. Previous experiments using just a single 42-gigaelectronvolt drive bunch have accelerated electrons with a continuous energy spectrum and a maximum energy of up to 85 gigaelectronvolts from the tail of the same bunch in less than a metre of plasma. However, the total charge of these accelerated electrons was insufficient to extract a substantial amount of energy from the wake. Here we report high-efficiency acceleration of a discrete trailing bunch of electrons that contains sufficient charge to extract a substantial amount of energy from the high-gradient, nonlinear plasma wakefield accelerator. Specifically, we show the acceleration of about 74 picocoulombs of charge contained in the core of the trailing bunch in an accelerating gradient of about 4.4 gigavolts per metre. These core particles gain about 1.6 gigaelectronvolts of energy per particle, with a final energy spread as low as 0.7 per cent (2.0 per cent on average), and an energy-transfer efficiency from the wake to the bunch that can exceed 30 per cent (17.7 per cent on average). This acceleration of a distinct bunch of electrons containing a substantial charge and having a small energy spread with both a high accelerating gradient and a high energy-transfer efficiency represents a milestone in the development of plasma wakefield acceleration into a compact and affordable accelerator technology.
    Nature 11/2014; 515(7525):92-5. DOI:10.1038/nature13882 · 42.35 Impact Factor
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    ABSTRACT: The Facility for Advanced Accelerator and Experimental Tests (FACET) at SLAC installed a 10-TW Ti : sapphire laser system for pre-ionized plasma wakefield acceleration experiments. High energy (500 mJ), short (50 fs) pulses of 800 nm laser light at 1 Hz are used at the FACET experimental area to produce a plasma column. The laser pulses are stretched to 250 fs before injection into a vapor cell, where the laser is focused by an axicon lens to form a plasma column that can be sustained over the desired radius and length. A 20 GeV electron bunch interacts with this preformed plasma to generate a non-linear wakefield, thus accelerating a trailing witness bunch with gradients on the order of several GV m−1. The experimental setup and the methods for producing the pre-ionized plasma for plasma wakefield acceleration experiments performed at FACET are described.
    Plasma Physics and Controlled Fusion 07/2014; 56(8):084011. DOI:10.1088/0741-3335/56/8/084011 · 2.39 Impact Factor
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    ABSTRACT: We present here the results of measurements made showing 1 GV/m accelerating fields using a hollow dielectric-lined waveguide. The results are comprised of measurement of the energy loss of a high charge ( 3 nC) ultrashort (200 fs), ultra relativistic (20 GeV) beam and concomitant auto-correlation interferometeric techniques to obtain the frequency content of simultaneously generated coherent Cherenkov radiation (CCR). Experiments were conducted at the Facility for Advanced aCcelerator Experimental Tests (FACET) at the SLAC National Laboratory using metal-coated sub-millimeter diameter, ten-centimeter long fused silica tubes. We present simulation and theoretical results in support of the conclusions reached through experiment. These results build on previous work to provide a path towards high gradient accelerating structures for use in compact accelerator schemes, future linear colliders and free-electron lasers.
    2014 International Particle Accelerator Conference, Dresden, Germany; 06/2014
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    ABSTRACT: Synchronized, independently tunable and focused $\mu$J-class laser pulses are used to release multiple electron populations via photo-ionization inside an electron-beam driven plasma wave. By varying the laser foci in the laboratory frame and the position of the underdense photocathodes in the co-moving frame, the delays between the produced bunches and their energies are adjusted. The resulting multibunches have ultra-high quality and brightness, allowing for hitherto impossible bunch configurations such as spatially overlapping bunch populations with strictly separated energies, which opens up a new regime for light sources such as free-electron-lasers.
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    ABSTRACT: We show through experiments and supporting simulations that propagation of a highly relativistic and dense electron bunch through a plasma can lead to distributed injection of electrons, which depletes the accelerating field, i.e., beam loads the wake. The source of the injected electrons is ionization of the second electron of rubidium (Rb II) within the wake. This injection of excess charge is large enough to severely beam load the wake, and thereby reduce the transformer ratio T. The reduction of the average T with increasing beam loading is quantified for the first time by measuring the ratio of peak energy gain and loss of electrons while changing the beam emittance. Simulations show that beam loading by Rb II electrons contributes to the reduction of the peak accelerating field from its weakly loaded value of 43 GV/m to a strongly loaded value of 26 GV/m.
    Physical Review Letters 01/2014; 112(2):025001. DOI:10.1103/PhysRevLett.112.025001 · 7.73 Impact Factor
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    ABSTRACT: Strategies for mitigating ionization-induced beam head erosion in an electron-beam-driven plasma wakefield accelerator (PWFA) are explored when the plasma and the wake are both formed by the transverse electric field of the beam itself. Beam head erosion can occur in a preformed plasma because of a lack of focusing force from the wake at the rising edge (head) of the beam due to the finite inertia of the electrons. When the plasma is produced by field ionization from the space charge field of the beam, the head erosion is significantly exacerbated due to the gradual recession (in the beam frame) of the 100% ionization contour. Beam particles in front of the ionization front cannot be focused (guided) causing them to expand as in vacuum. When they expand, the location of the ionization front recedes such that even more beam particles are completely unguided. Eventually this process terminates the wake formation prematurely, i.e., well before the beam is depleted of its energy. Ionization-induced head erosion can be mitigated by controlling the beam parameters (emittance, charge, and energy) and/or the plasma conditions. In this paper we explore how the latter can be optimized so as to extend the beam propagation distance and thereby increase the energy gain. In particular we show that, by using a combination of the alkali atoms of the lowest practical ionization potential (Cs) for plasma formation and a precursor laser pulse to generate a narrow plasma filament in front of the beam, the head erosion rate can be dramatically reduced. Simulation results show that in the upcoming “two-bunch PWFA experiments” on the FACET facility at SLAC national accelerator laboratory the energy gain of the trailing beam can be up to 10 times larger for the given parameters when employing these techniques. Comparison of the effect of beam head erosion in preformed and ionization produced plasmas is also presented.
    Physical Review Special Topics - Accelerators and Beams 10/2013; 16(10). DOI:10.1103/PhysRevSTAB.16.101301 · 1.52 Impact Factor
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    ABSTRACT: Plasma wakefield acceleration (PWFA) holds much promise for advancing the energy frontier because it can potentially provide a 1000-fold or more increase in acceleration gradient with excellent power efficiency in respect with standard technologies. Most of the advances in beam-driven plasma wakefield acceleration were obtained by a UCLA/USC/SLAC collaboration working at the SLAC FFTB[ ]. These experiments have shown that plasmas can accelerate and focus both electron and positron high energy beams, and an accelerating gradient in excess of 50 GeV/m can be sustained in an 85 cm-long plasma. The FFTB experiments were essentially proof-of-principle experiments that showed the great potential of plasma accelerators. The FACET[ ] test facility at SLAC will in the period 2012-2016 further study several issues that are directly related to the applicability of PWFA to a high-energy collider, in particular two-beam acceleration where the witness beam experiences high beam loading (required for high efficiency), small energy spread and small emittance dilution (required to achieve luminosity). The PWFA-LC concept presented in this document is an attempt to find the best design that takes advantage of the PWFA, identify the critical parameters to be achieved and eventually the necessary R&D to address their feasibility. It best benefits from the extensive R&D that has been performed for conventional rf linear colliders during the last twenty years, especially ILC[ ] and CLIC[ ], with a potential for a comparably lower power consumption and cost.
  • IPAC, Shanghai; 05/2013
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    ABSTRACT: High accelerating gradients generated by a high density electron beam moving through plasma has been used to double the energy of the SLAC electron beam [1]. During that experiment, the electron current density was high enough to generate its own plasma without significant head erosion. In the newly commissioned FACET facility at SLAC, the peak current will be lower and without pre-ionization, head erosion will be a significant challenge for the planned experiments. In this work we report on our design of a meter scale plasma source for these experiments to effectively avoid the problem of head erosion. The plasma source is based on a homogeneous metal vapor gas column that is generated in a heat pipe oven [2]. A lithium oven over 30 cm long at densities over 10{sup 17} cm{sup -3} has been constructed and tested at UCLA. The plasma is then generated by coupling a 10 TW short pulse Ti:Sapphire laser into the gas column using an axicon lens setup. The Bessel profile of the axicon setup creates a region of high intensity that can stretch over the full length of the gas column with approximately constant diameter. In this region of high intensity, the alkali metal vapor is ionized through multi-photon ionization process. In this manner, a fully ionized meter scale plasma of uniform density can be formed. Methods for controlling the plasma diameter and length will also be discussed.
    04/2013; 1507(1). DOI:10.1063/1.4773774
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    ABSTRACT: The Facility for Advanced Accelerator and Experimental Tests (FACET) is a new user facility at the SLAC National Accelerator Laboratory, servicing next-generation accelerator experiments. The 1.5% RMS energy spread of the FACET beam causes large chromatic aberrations in optics. These aberrations necessitate updated quadrupole scan fits to remain accurate.
    04/2013; 1507(1). DOI:10.1063/1.4773759
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    ABSTRACT: The interaction of a beam of electrons with an excited gaseous medium is formulated and a few examples are presented. In the framework of the model, the dielectric properties of the gaseous medium are represented by a finite set of resonances corresponding to spectral lines of the gas constituents. Both stimulated emission and absorption from the various states are considered. It is assumed that the population of one of the energy states is inverted. Longitudinal and transverse dynamics are evaluated analytically and Panofsky-Wenzel theorem for such a medium is derived. Based on the numerical simulations performed, possible operation is discussed.
    04/2013; 1507(1). DOI:10.1063/1.4773775
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    ABSTRACT: SLAC has two electron accelerators, the Linac Coherent Light Source (LCLS) and the Facility for Advanced Accelerator Experimental Tests (FACET), providing high-charge, high-peak-current, femtosecond electron bunches. These characteristics are ideal for generating intense broadband terahertz (THz) pulses via coherent transition radiation. For LCLS and FACET respectively, the THz pulse duration is typically 20 and 80 fs RMS and can be tuned via the electron bunch duration; emission spectra span 3-30 THz and 0.5 THz-5 THz; and the energy in a quasi-half-cycle THz pulse is 0.2 and 0.6 mJ. The peak electric field at a THz focus has reached 4.4 GV∕m (0.44 V∕Å) at LCLS. This paper presents measurements of the terahertz pulses and preliminary observations of nonlinear materials response.
    The Review of scientific instruments 02/2013; 84(2):022701. DOI:10.1063/1.4790427 · 1.58 Impact Factor
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    ABSTRACT: We study the various physical processes and their timescales involved in the excitation of wakefields in relativistically hot plasma. This has relevance to the design of a high repetition-rate plasma wakefield collider in which the plasma has not had time to cool between bunches in addition to understanding the physics of cosmic jets in relativistically hot astrophysical plasmas. When the plasma is relativistically hot (plasma temperature near m{sub e}c{sup 2}), the thermal pressure competes with the restoring force of ion space charge and can reduce or even eliminate the accelerating field of a wake. We will investigate explicitly the case where the hot plasma is created by a preceding Wakefield drive bunch 10's of picoseconds to many nanoseconds ahead of the next drive bunch. The relativistically hot plasma is created when the excess energy (not coupled to the driven e{sup -} bunch) in the wake driven by the drive e{sup -} bunch is eventually converted into thermal energy on 10's of picosecond timescale. We will investigate the thermalization and diffusion processes of this non-equilibrium plasma on longer time scales, including the effects of ambi-polar diffusion of ions driven by hot electron expansion, possible Columbic explosion of ions producing higher ionization states and ionization of surrounding neutral atoms via collisions with hot electrons. Preliminary results of the transverse and longitudinal wakefields at different timescales of separation between a first and second bunch are presented and a possible experiment to study this topic at the FACET facility is described.
    12/2012; 1507(1). DOI:10.1063/1.4773768
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    ABSTRACT: Head erosion is one of the limiting factors in plasma wakefield acceleration (PWFA). We present a study of head erosion with emittance growth in field-ionized plasma from the PWFA experiments performed at the FACET user facility at SLAC. At FACET, a 20.3 GeV bunch with 1.8 Multiplication-Sign 10{sup 10} electrons is optimized in beam transverse size and combined with a high density lithium plasma for beam-driven plasma wakefield acceleration experiments. A target foil is inserted upstream of the plasma source to increase the bunch emittance through multiple scattering. Its effect on beamplasma interaction is observed with an energy spectrometer after a vertical bend magnet. Results from the first experiments show that increasing the emittance has suppressed vapor field-ionization and plasma wakefields excitation. Plans for the future are presented.
    12/2012; 1507(1). DOI:10.1063/1.4773762
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    ABSTRACT: We investigate transverse effects in the plasma-wakefield acceleration experiments planned and ongoing at FACET. We use PIC simulation tools, mainly QuickPIC, to simulate the interaction of the drive electron beam and the plasma. In FACET a number of beam dynamics knobs, including dispersion and bunch length knobs, can be used to vary the beam transverse characteristics in the plasma. We present simulation results and the status of the FACET experimental searches.
    12/2012; 1507(1). DOI:10.1063/1.4773755
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    ABSTRACT: For wakefield based acceleration schemes, use of an asymmetric (or linearly ramped) drive bunch current profile has been predicted to enhance the transformer ratio and generate large accelerating wakes. We discuss plans and initial results for producing such bunches using the 20 to 23 GeV electron beam at the FACET facility at SLAC National Accelerator Laboratory and sending them through plasmas and dielectric tubes to generate transformer ratios greater than 2 (the limit for symmetric bunches). The scheme proposed utilizes the final FACET chicane compressor and transverse collimation to shape the longitudinal phase space of the beam.
    12/2012; 1507(1). DOI:10.1063/1.4773757
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    ABSTRACT: The Facility for Accelerator science and Experimental Tests (FACET) at SLAC provides a high charge, high peak current, sub-picosecond bunched electron beam that is ideal for 0.1 to 2 THz radiation generation via coherent transition radiation. This paper presents preliminary characterization of the terahertz pulses generated by the FACET electron beam. The measured THz frequency content spans from 0.25 THz to 2.3 THz and peaks at around 0.5 THz. The radiation has been focused down to a 4.4 × 4.8 mm2 transverse spot with 0.69 mJ collected total energy per pulse. Fitting the energy to the spatiotemporal profile of the THz pulse yields peak e-field amplitude of 1.5 MV/cm.
    12/2012; DOI:10.1063/1.4773753
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    ABSTRACT: Recent PWFA experiments at FACET use Rb gas ionized by the beam as the plasma source. The Rb has a lower ionization threshold than the Li, which was used in earlier experiments, consequently a smaller peak current beam can still produce a field ionized plasma. But the Rb vapor is confined by Ar and as a result it is possible to ionize both the first electron of Ar (I.P. 14eV) as well as the second electron of Rb (I.P.24 eV). This secondary ionization can lead to a source of dark current in a PWFA. In this work QuickPIC simulation results are presented for studying the influence by the ``unwanted'' ionization. In the simulation, both Ar and Rb vapor profiles are initialized as measured in the laboratory. We use different beam parameters (including different focal position) in the simulation. The ion density of the gas is a useful diagnostic showing the ionization level of the neutral gas in the simulation. Other simulation results related FACET experiments are also presented.

Publication Stats

1k Citations
396.35 Total Impact Points

Institutions

  • 1993–2011
    • University of California, Los Angeles
      • • Department of Electrical Engineering
      • • Department of Physics and Astronomy
      Los Angeles, California, United States
  • 2001–2008
    • Stanford University
      • SLAC National Accelerator Laboratory
      Palo Alto, California, United States
  • 2005
    • CSU Mentor
      Long Beach, California, United States
  • 2001–2005
    • University of Southern California
      • Department of Electrical Engineering
      Los Angeles, CA, United States
  • 1999
    • Lawrence Berkeley National Laboratory
      Berkeley, California, United States