Final Focus Test Beam Research Articles

Performance of the beam position monitor system of the final focus test beam

The Beam Position Monitor (BPM) system for the Final Focus Test Beam (FFTB) at SLAC is designed to meet challenging specifications in the areas of single-pulse resolution, ab initio installation accuracy, and time-stability of BPM electrical centroids. We review the tolerances on these quantities and the technical choices made to achieve same, and detail the results of several studies of the actual performance of the system. These results are then related to the BPM system requirements for a future high-energy e{sup +}e{sup {minus}} linear collider.

Results of a gas-ionization beam size monitor at the final focus test beam

A new type of gas-ionization monitor, built at Orsay, has been used to optimize and measure the transverse beam dimensions of the Final Focus Test Beam at SLAC. This monitor detects the ions created by the beam to probe its space charge field and to derive both transverse dimensions. The ultimate values measured with the monitor are 1.5 μ m × 60 nm. Moreover, the high sensitivity of the monitor has been used to detect and cancel out detrimental “banana” shapes of the beam.

Plasma lens experiment at the final focus test beam

The proposed plasma lens experiment at the Final focus Test Beam (FFTB) facility of the Stanford Linear Accelerator Center (Chen et al. SLAC, 1997) [1]has been approved by the adminstration. The experiment would allow the examination of plasma focusing devices for particle beams in the parameter regime of interest to future high-energy colliders. It is expected to lead to compact plasma lens designs capable of focusing the beam to unprecedented small spot sizes.

Positron Production in Multiphoton Light-by-Light Scattering

A signal of 106 {+-} 14 positrons above background has been observed in collisions of a low-emittance 46.6-GeV electron beam with terawatt pulses from a Nd:glass laser at 527 nm wavelength in an experiment at the Final Focus Test Beam at SLAC. Peak laser intensities of {approximately} 1.3 {times} 10{sup 18} W/cm{sup 2} have been achieved corresponding to a value of 0.3 for the parameter {Upsilon} = {var_epsilon}*/{var_epsilon}{sub crit} where {var_epsilon}* = 2{gamma}{var_epsilon}{sub lab} is the electric field strength of the laser transformed to the rest frame of the electron beam and {var_epsilon}{sub crit} = m{sup 2}c{sup 3}/e{bar h} = 1.3 {times} 10{sup 16} V/cm is the QED critical field strength. The positrons are interpreted as arising from a two-step process in which laser photons are backscattered to GeV energies by the electron beam followed by a collision between the high-energy photon and several laser photons to produce an electron-positron pair. These results are the first laboratory evidence for a light-by-light scattering process involving only real photons.

Magnetic switching in ultrashort field pulses (abstract)

The Ginzburg–Landau–Lifshitz (GLL) equation, which describes the time dependence of spin precesssion in an external magnetic field1 relates the minimal field required to reverse the magnetization at fixed pulse length to the anisotropy field of the sample.23 We have systematically varied this parameter between 1.3 and about 5.0 T in a series of perpendicularly magnetized Co/Pt multilayer films and studied the magnetization reversal in picosecond in plane field pulses. Such pulses of several Tesla field strength and ultrashort duration were obtained in the final focus test beam section of the Stanford Linear Accelerator Center. The resulting magnetization pattern, which is reminiscent of the field during exposure, is subsequently analyzed with Kerr microscopy2 (see Fig. 1). As a prominent feature, we observe a beam field related switching radius from up to down magnetization which we compare to the theoretically expected field within the GLL formalism.

Radiation protection systems for the final focus test beam at SLAC.

The Final Focus Test Beam (FFTB) is a new beam line at the Stanford Linear Accelerator Center designed to test new beam optics concepts, hardware, and techniques necessary to achieve and measure the small spot sizes required for future generations of high-energy e+e- linear colliders. The FFTB takes a 47 GeVc-1, 1 kW electron beam at the end of the Stanford Linear Accelerator Center linear accelerator and transports it to the FFTB beam dump. A radiation protection system was designed and installed for the FFTB with the primary goal that the integrated dose equivalent outside the shielding resulting from beam loss would not exceed 10 mSv y-1. This system is comprised of shielding, a beam containment system and a personnel protection system. This paper presents various aspects of radiation safety at Stanford Linear Accelerator Center that were considered in the design of the FFTB radiation protection system. Beam tests were conducted in which the performance of various beam containment devices and the shielding effectiveness were evaluated. Preliminary results from these tests are presented.

Observation of nonlinear effects in Compton scattering.

Nonlinear Compton scattering has been observed in the collision of a low-emittance 46.6-GeV electron beam with terawatt pulses from a Nd:glass laser at 1054 and 527 nm wavelengths in an experiment at the Final Focus Test Beam at SLAC. Peak laser intensities of ${10}^{18}\phantom{\rule{0ex}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$ have been achieved, corresponding to a value of 0.6 for the parameter $\ensuremath{\eta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}e{E}_{\mathrm{rms}}/m{\ensuremath{\omega}}_{0}c$. Results are presented for multiphoton Compton scattering in which up to four laser photons interact with an electron, in agreement with theoretical calculations.

Precision magnet movers for the Final Focus Test Beam

Fully automated movers capable of positioning beamline magnets weighing more than 100 kg to a few microns over several millimeters have been designed and built for the Final Focus Test Beam at SLAC. These movers also provide incremental motion as small as a few tenths of a micron. We review the basic design considerations, the hardware realization of the movers, and the extensive tests conducted on these electromechanical stages. Suggestions for the improvement and augmentation of such movers are also given.

The wire scanner system of the final focus test beam at SLAC

The system of wire scanners in use at the FFTB at SLAC is described. In addition to the scanners themselves, there is a discussion of detectors for the scattering from the wires, and of the procedure for handling beam spots of large aspect ratio.

Focusing of submicron beams for TeV-scale e+e- linear colliders.

First experimental results from the final focus test beam (FFTB) are reported. The vertical dimension of a 47-GeV electron beam from the SLAC linac has been reduced at the focal point of the FFTB by a demagnification of 320 to a beam height of approximately 70 nm.

New Stanford Facility Squeezes High‐Energy Electron Beams

Accelerator physicists at the Final Focus Test Beam, a new facility at the Stanford Linear Accelerator Center, have managed to squeeze the vertical width of a high‐energy electron beam down to 75 nanometers. That's an order of magnitude smaller than the focal spots of the 50‐GeV electron and positron beams of the five‐year‐old Stanford Linear Collider. And it's almost small enough for the TeV beams envisioned for the next generation of electron‐positron colliders. (See the article by Jonathan Wurtele on page 33.) Linear colliders, in which collisions must all happen in a single pass, require much tighter focal spots than do storage rings, where the beams pass through each other again and again. But for beam energies above about 100 GeV, circulating charged particles as light as electrons radiate away so much energy that storage rings would be prohibitively expensive. A TeV electron‐positron collider will, perforce, be a pair of face‐to‐face linacs.

High resolution BPM for FFTB

The beam position monitor (BPM) for the final focus test beam (FFTB) is newly designed to have 1 μm precision and repeatability within 500 μm from center. The system design and the performance test of the prototype electronics are described.

A beam size monitor for the Final Focus Test Beam

Abstract The beam size monitor, proposed here to be installed at the focus of the FFTB, will be made of a pulsed gas target and an ion detector. The gas is ionized by the beam and the ions are kicked by its space charge field. The time of flight of Ar + ions up to the detector and the angular distribution of He + ions will allow one to obtain the two beam transverse dimensions in the range of the FFTB design.

A beam profile monitor for small electron beams

Measurement of beam properties at the foci of high energy linacs is difficult due to the small size of the waists in proposed and existing accelerators (1 nm −2 μm). This article considers the use of bremsstrahlung radiation from thin foils to measure the size and phase space density these beams using nonimaging optics. The components of the system are described, and the ultimate resolution, evaluated theoretically for the case of the Final Focus Test Beam (FFTB) at Stanford Linear Accelerator Center, is a few nm.