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Register a new userDevelopment of a high-efficiency pulsed slow positron beam for measurements with orthopositronium in vacuum
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We have developed a high-efficiency pulsed slow positron beam for experiments with orthopositronium in vacuum. The new pulsing scheme is based on a double-gap coaxial buncher powered by an RF pulse of appropriate shape. The modulation of the positron velocity in the two gaps is used to adjust their time-of-flight to a target. This pulsing scheme allows to minimize non-linear aberrations in the bunching process and to efficiently compress positron pulses with an initial pulse duration ranging from 300 to 50 ns into bunches of 2.3 to 0.4 ns width, respectively, with a repetition period of 1 mks. The compression ratio achieved is ~100, which is a factor 5 better than has been previously obtained with slow positron beams based on a single buncher. Requirements on the degree, to which the moderated positrons should be mono-energetic and on the precision of the waveform generation are presented. Possible applications of the new pulsed positron beam for measurements of thin films are discussed.
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Beam diagnostics is important to guarantee good quality of beam in particle accelerator. Both the electron and positron run in the tunnel in some modern electron positron colliders such as Circular Electron Positron Collider (CEPC) to be built and Beijing Electron Positron Collider II (BEPC II). To measure the electron and positron beams, picking up of these two different bunches in real time is of notable concern. Because the time interval between adjacent electron and positron bunches is quite small, for example, 6 ns in CEPC, high-speed switch electronics is required. This paper presents the prototype design of a high-speed radio frequency (RF) electronics that can pick up nanosecond positron-electron beam bunches with a switching time of less than 6 ns. Fast separation of electron and positron is achieved based on RF switches and precise delay adjustment of the controlling signals (~10 ps). Initial tests have been conducted in the laboratory to evaluate the performance of electronics, the results indicate that this circuit can successfully pick up the bunch signal within a time interval of 6 ns, which makes it possible to further measure the electron and position beams simultaneously.
Advanced technical solution for the design of a low perveance electron gun with a high quality beam dedicated to high power Ka-band klystrons is presented in this paper. The proposed electron gun can be used to feed linear accelerating structures at 36 GHz with an estimated input power of 20 MW, thus achieving an effective accelerating electric field in the (100-150) MV/m range. additionally, in the framework of the Compact Light XLS project, a short Ka-band accelerating structure providing an integrated voltage of at least 15 MV, has been proposed for bunch-phase linearization. For the klystron, a very small beam dimension is needed and the presented electron gun responds to this requirement. An estimate of the rotational velocity at beam edge indicates that the diamagnetic field due to rotational currents are small compared to the longitudinal volume. A detailed analysis of how this is arrived at, by compression of the beam, rotation in the magnetic field, and analysis of the subsequently generated diamagnetic field has been discussed.
Muon beams are customarily obtained via $K/pi$ decays produced in proton interaction on target. In this paper we investigate the possibility to produce low emittance muon beams from electron-positron collisions at centre-of-mass energy just above the $mu^{+}mu^{-}$ production threshold with maximal beam energy asymmetry, corresponding to a positron beam of about 45 GeV interacting on electrons on target. We present the main features of this scheme with an outline of the possible applications.
We present results of an experiment where, using a 200 GW CO2 laser seed, a 65 MeV electron beam was decelerated down to 35 MeV in a 54 cm long strongly tapered helical magnetic undulator, extracting over 30$%$ of the initial electron beam energy to coherent radiation. These results demonstrate unparalleled electro-optical conversion efficiencies for a relativistic beam in an undulator field and represent an important step in the development of high peak and average power coherent radiation sources.
Accelerating particles to high energies in plasma wakefields is considered to be a promising technique with good energy efficiency and high gradient. While important progress has been made in plasma-based electron acceleration, positron acceleration in plasma has been scarcely studied and a fully self-consistent and optimal scenario has not yet been identified. For high energy physics applications where an electron-positron collider would be desired, the ability to accelerate positrons in plasma wakefields is however paramount. Here we show that the preservation of beam quality can be compromised in a plasma wakefield loaded with a positron beam, and a trade-off between energy efficiency and beam quality needs to be found. For electron beams driving linear plasma wakefields, we have found that despite the transversely nonlinear focusing force induced by positron beam loading, the bunch quickly evolves toward an equilibrium distribution with limited emittance growth. Particle-in-cell simulations show that for {mu}m-scale normalized emittance, the growth of uncorrelated energy spread sets an important limit. Our results demonstrate that the linear or moderately nonlinear regimes with Gaussian drivers provide a good trade-off, achieving simultaneously energy-transfer efficiencies exceeding 30% and uncorrelated energy spread below 1%, while donut-shaped drivers in the nonlinear regime are more appropriate to accelerate high-charge bunches at higher gradients, at the cost of a degraded trade-off between efficiency and beam quality.
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