J. van der Laan

Measurement of the proton's electric to magnetic form factor ratio from H→1(e→,e′p)

We report the first precision measurement of the proton electric to magnetic form factor ratio from spin-dependent elastic scattering of longitudinally polarized electrons from a polarized hydrogen internal gas target. The measurement was performed at the MIT-Bates South Hall Ring over a range of four-momentum transfer squared Q2 from 0.15 to 0.65 (GeV/c)(2). Significantly improved results on the proton electric and magnetic form factors are obtained in combination with existing cross-section data on elastic electron-proton scattering in the same Q2 region.

Excitation of hexadecapole transitions in 196Pt via electron scattering and their interpretation in the interacting boson approximation

Form factors of transitions to three Iπ = 4+ states in 196Pt, obtained from electron scattering, are analyzed in the framework of the interacting boson approximation. Structure functions differ strongly from liquid drop model predictions and provide an indication for the need of including the g-boson in IBA.

Electron scattering off 110Pd, a test of the interacting boson approximation☆

Abstract An electron-scattering experiment on 110 Pd has been performed. Results have been compared with predictions of the interacting boson model. Quadrupole boson structure functions have been extracted from form-factor data of the first two 2 + transitions. From these a satisfactory prediction for a third 2 + excitation could be obtained.

IBA g-boson properties in 110Cd and Pd isotopes studied with electron scattering

Abstract Inelastic electron scattering off 110Cd and 104,106,108,110Pd was studied in an effective momentum transfer range 0.3–2.55 fm−1. The form-factor data were analyzed in a model-independent Fourier-Bessel expansion. Excitation energy spectra and transition strengths have been calculated in the framework of the interacting boson approximation, in a model space extended with one g-boson. The behaviour of the experimental transition charge densities extracted for hexadecapole excitations was used to study in detail effects of the addition of one hexadecapole g-boson on the dynamic properties of low-lying collective excitations in this mass region.

The eRHIC Ring-Ring Collider Design

The eRHIC ring-ring collider is the main design option for the future lepton-ion collider at Brookhaven National Laboratory. The baseline design is presented in the eRHIC Zeroth-Order Design Report (ZDR) [1]. We report on progress made during the past year including possible interaction region design changes, upgrade efforts on RHIC (the ion ring), and results of a new design study on the e-ring. The interaction region revision is based on a new scheme for the main detector design. RHIC upgrades are being pursued to ensure luminosity and ion polarization goals of the ring-ring option in the baseline design will be met. Higher current operation of the lepton storage ring is under serious consideration as a result of better understanding of beam-beam interaction effects.

X-ray laser seeding for short pulses and narrow bandwidth

The performance of an X-ray free electron laser can be substantially enhanced if a coherent seed source is used to provide sufficient initial power that it dominates the spontaneous emission in the early part of the undulator. The FEL output then becomes an amplified reproduction of the input seed having, under certain conditions, the same pulse length and bandwidth. For studies of molecular and atomic time dynamics the pulse length may be very short, reaching below 1 fs with a transform limited bandwidth of a few tenths of a percent. For spectroscopy and diffraction experiments the beam may alternatively be made monochromatic at the level of one part in 10/sup 5/ or better, with a pulse length of tens of femtoseconds. Simulation studies of seeded FEL performance at 0.3 nm using the code GINGER are presented.

The MIT Bates X-ray laser project

MIT and the Bates Linear Accelerator Center are exploring the construction of an X-ray free electron laser user facility. It will be based on a superconducting linac of 4-8 GeV energy, and produce XUV light in the 0.3-100 nm range at kilohertz repetition rates. The facility will be a full user facility incorporating up to 30 beamlines. Conventional lasers that produce the electron beam, seed the FEL and execute pump-probe experiments are carefully integrated. The current design of the facility is discussed.

Quadrupole boson structure form factors for proton scattering from the IBA model and electron scattering

Inelastic proton scattering from 110Pd has been measured at Ep = 30.7 MeV. Angular distributions for three low-lying 2+ states are satisfactorily reproduced by employing reduced matrix elements from the IBA model and form factors evaluated from two quadrupole transition charge densities (determined from electron scattering) folded with a nucleon—nucleon interaction. The relative phase between these two transition charge densities could be determined because of coupled channel effects in inelastic proton scattering. This leads to boson structure form factors for proton scattering resembling a Woods-Saxon first derivative for the d-boson non-conserving part and a Woods-Saxon second derivative with a reduced radius for the d-boson conserving part.

Terahertz Coherent Synchrotron Radiation in the MIT-Bates South Hall Ring

We investigate the terahertz coherent synchrotron radiation (CSR) potential of the South Hall Ring (SHR) at MIT-Bates Linear Accelerator Center. The SHR is equipped with a unique single cavity, 2.856 GHz RF system. The high RF frequency is advantageous for producing short bunch length and for having higher bunch current threshold to generate stable CSR. Combining with other techniques such as external pulse stacking cavity, femtosecond laser slicing, the potential for generating ultra-stable, high power, broadband terahertz CSR is very attractive. Beam dynamics issues related to short bunch length operation, such as multi-bunch instability (perhaps associated with the high frequency RF system), are considered. The SHR is ideal for experimental exploration of such issues, which could affect bunch length, bunch intensity and beam stability. Results of initial tests of low momentum compaction lattices and bunch length measurements are presented and compared to expectations.

Design study for the RF photoinjector for the MIT-Bates X-ray laser

A multiple cell 1.3 GHz room-temperature photoinjector is under design for the MIT Bates X-ray laser project. The design features include tunable intercavity phase shifts allowing separate phasing of the cells for velocity bunching of the beam in the following drift, and optimization of cell shape for high shunt impedance and low wall power density. Beam dynamics are studied for charges ranging from 0.1 to 1 nC using a model, non-ideal laser profile shape. It is shown that collective effects at the high end of the range cause loss of beam brightness.