No abstract available

[en] A high-gradient, meter scale Plasma Wakefield Accelerator (PWFA) module operating in the nonlinear, electron blow-out regime is demonstrated experimentally. The beam and plasma parameters are chosen such that the matched beam channels through the plasma over more than twelve beta functions without spreading or oscillating over a range of densities for observing both deceleration and acceleration. The wakefield decelerates the bulk of the initially 28.5 GeV beam by up to 155 MeV, however particles in the back of the same beam are accelerated by up to 280 MeV at a density of 1.9 x 10¹⁴ cm^-3 as the wakefield changes sign

[en] A method to accurately measure the density of Rb vapor is described. We plan on using this method for the Advanced Wakefield (AWAKE) (Assmann et al., 2014 [1]) project at CERN , which will be the world's first proton driven plasma wakefield experiment. The method is similar to the hook (Marlow, 1967 [2]) method and has been described in great detail in the work by Hill et al. (1986) [3]. In this method a cosine fit is applied to the interferogram to obtain a relative accuracy on the order of 1% for the vapor density–length product. A single-mode, fiber-based, Mach–Zenhder interferometer will be built and used near the ends of the 10 meter-long AWAKE plasma source to be able to make accurate relative density measurement between these two locations. This can then be used to infer the vapor density gradient along the AWAKE plasma source and also change it to the value desired for the plasma wakefield experiment. Here we describe the plan in detail and show preliminary results obtained using a prototype 8 cm long novel Rb vapor cell.

[en] We describe a novel plasma source developed at the Max Planck Institute for Physics that will be used for a proton driven plasma wakefield accelerator experiment at CERN. Rubidium vapor is confined in a 10 meter -long, 4 cm diameter, oil-heated stainless steel pipe. A laser pulse tunnel ionizes the vapor forming a 10-meter long, ∼1mm radius plasma with a range of densities around ∼10¹⁵cm⁻³. Access to the source is provided using custom manufactured fast valves. The source is designed to produce a plasma with a density uniformity of at least ∼0.2% during the beam–plasma interaction

[en] The working group has identified the parameters of an afterburner based on the design of a future linear collider. The new design brings the center of mass energy of the collider from 1 to 2 TeV. The afterburner is located in the final focus section of the collider, operates at a gradient of ∼4 GeV/m, and is only about 125 m long. Very important issues remain to be addressed, and include the physics and design of the positron side of the afterburner, as well as of the final focus system. Present plasma wakefield accelerator experiments have reached a level of maturity and of relevance to the afterburner, that make it timely to involve the high energy physics and accelerator community in the afterburner design process. The main result of this working group is the first integration of the designs of a future linear collider and an afterburner

[en] A new approach for positron acceleration in non-linear plasma wakefields driven by electron beams is presented. Positrons can be produced by colliding an electron beam with a thin foil target embedded in the plasma. Integration of positron production and acceleration in one stage is realized by a single relativistic, intense electron beam. Simulations with the parameters of the proposed SABER facility [1] at SLAC suggest that this concept could be tested there

No abstract available

[en] Recently a proton-bunch-driven plasma wakefield acceleration experiment using the CERN-SPS beam was proposed. Different types of plasma cells are under study, especially laser ionization, plasma discharge, and helicon sources. One of the key parameters is the spatial uniformity of the plasma density profile along the cell that has to be within < 1% of the nominal density (6 × 10¹⁴ cm⁻³). Here a setup based on a photomixing concept is proposed to measure the plasma cut-off frequency and determine the plasma density.

[en] Recently new schemes have been proposed for plasma based microwave sources that could lead to output power increases by orders of magnitude, as well as offer new possibilities such as broad band tuning and frequency chirping, ultra-short pulse generation, pulse design, etc. In the first scheme, the static field of an alternatively biased capacitor is directly converted into short pulses of turnable electromagnetic (em) radiation upon transmission through a relativistic; under dense ionization front. The structure presently under investigation consists of pin pairs (capacitors) inserted into an X-band waveguide through its narrow sidewall and separated by 1.134 cm. The generated frequency is in the X-band frequency range (8.4--12.4 GHz) when operated with plasma densities between 10¹¹ and 10¹² cm^-3. The output power is in the 100 W range with an applied voltage of 6 kV and is limited by high voltage (HV) breakdown inside the structure. Much higher output power levels are expected with the new, shorter pulse, HV pulser, since the output power is proportional to the square of the applied voltage. At larger plasma densities, generation of a higher order mode traveling in the backward direction is also observed. In the second scheme, a fraction of the large amplitude electrostatic (es) wave generated in a plasma beat wave acceleration (PBWA) experiment (up to 3 GeV/m) is converted into em radiation by applying a static magnetic field perpendicularly to the driving laser beam. The two-frequency CO₂ laser beam resonantly drives the es wave, and couples to the L branch of the XO mode of the magnetized plasma through Cherenkov radiation. The radiation is emitted predominantly in the forward direction (direction of the laser beam), and is at the plasma frequency (n_c ∼10¹⁶ cm^-3, f∼1 THz). With an applied magnetic field of 6 kG the output power is calculated to be in the megawatt range (for a sharp plasma/vacuum boundary). The parameters of the emitted radiation will also be used as a diagnostic for the plasma wave of a PBWA experiment, measuring its amplitude, phase, lifetime, etc. Design and experimental results are presented

[en] 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