A new experiment on plasma wake-field acceleration has been designed at the Budker Institute of Nuclear Physics in Novosibirsk. An intense modulated driving beam from the electron–positron booster (BEP), a storage ring, will be used to excite a nonlinear plasma wave in a dense plasma (n=1015 cm−3). Important advantages of this beam are its very low emittance (10−8 cm⋅rad in the vertical direction), high energy (850 MeV), and high intensity (1012 particles). A new technique for modulating this beam at a submillimeter wavelength is proposed. A simple numerical code has been developed to simulate the plasma wave excitation with plasma nonlinearity and with three-dimensional effects taken into account. The code allows the calculation of the radial structure of the nonlinear wake field including the focusing force which was mostly neglected in previous studies but which is especially important for experiment. The present numerical simulations show that, in the proposed experiment, a 1 GeV/m accelerating gradient over a macroscopic distance is attainable.
A device developed at the Budker Institute of Nuclear Physics (BINP) to measure with a high precision the direction of the magnetic field lines in the vicinity of the solenoid axis is described. The transverse field components are automatically measured by a small (<15 cm 3 in volume) compass-based sensor during its motion along the axis. The sensor's absolute sensitivity is ~0.1-0.9 mG and is limited only by external vibration noise. The upper bound of this range (~1 G) is governed by the current in the circuits producing the fields that compensate for the local misalignments of the field lines. The capabilities of the device are illustrated by the results from adjusting the solenoid fields in electron coolers recently built by the BINP. The procedures used to do this are described. The feasibility of obtaining the highest-quality field is shown. For one plant with a field intensity of ~1 kG, the rms deviation of the field lines from the axis is <10 -5 rad within a length of 3 m.
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