B. L. Militsyn

Experimental plasma wake‐field acceleration project*

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.

The polarized electron source at NIKHEF

An overview of the polarized electron source used at the NIKHEF accelerator facility is given. Since its first operation in September 1996 we have obtained currents in the source larger than 150 mA, and polarization degrees up to 88%. Approximately 350 hours have been dedicated to physics with a polarized 3He internal target. Using one InGaAsP photocathode, 2 μs long pulses were produced with a current of 2 mA in the local linac, with a polarization degree of 82.5%, at a repetition rate of 1 Hz. Source operations had to be interrupted about every eleventh day for approximately an hour for photocathode reactivation. A photocathode lifetime (1/e) of 180 hours has been achieved.

Electron scattering at NIKHEF with polarized beam and targets

We present the Internal Target Facility of the NIKHEF 900 MeV polarized electron storage ring. We give some results which illustrate the presently unique opportunity offered by this facility to study the spin structure of the nucleon, 2-body and 3-body system by the measurement of spin-dependent electron scattering observables.

Longitudinally polarized electrons in a storage ring below 1 GeV

We report on the results of studies of the longitudinal electron polarization in the AmPS storage ring at NIKHEF. The ring was operated using a partial Siberian snake at the first magic energy, and a full Siberian snake between 440 MeV and 720 MeV. We have investigated the effect of high beam currents in the ring, and found that some of the electron polarization is lost if the beam current becomes larger than ≈120 mA.

The photocathode gun of the Polarized Electron Source at NIKHEF

A description is given of the 100 kV photocathode gun of the 400 kV Polarized Electron Source (PES) used for internal target physics on polarized light nuclei at the Amsterdam Pulse Stretcher (AmPS) storage ring. The gun provides 2 μs long pulses of polarized electrons with a current up to 50 mA, at a repetition rate of 1 Hz, and a polarization degree up to 85%. Using the pulsed power supply, no deterioration of the vacuum during gun operation has been observed. An operational lifetime (1/e), using an InGaAsP photocathode, of 180 hours has been measured. The injection efficiency of the polarized beam from PES into the linear Medium Energy Accelerator is measured to be ≈30%.

Experimental study of collective effects in BEP storage ring with high stored current

The results of extensive investigation of beam dynamics with high current in BEP booster are presented. Strong bunch lengthening due to the potential well distortion by the inductive impedance was observed on the background of the multiple intrabeam scattering and of the ion accumulation (in the e/sup -/ beam). The octupole and sextupole corrections enabled control of collective damping of the head-tail modes. Fast damping is also observed at zero chromaticity, this is attributed to the injection kickers acting as transmission lines. The proper tuning of the nonlinearity corrections cures the transverse instabilities and enables capability to store up to 0.8A current in a single bunch.<<ETX>>