Sayed Rokni

E-157: A 1.4-m-long plasma wake field acceleration experiment using a 30 GeV electron beam from the Stanford Linear Accelerator Center Linac

In the E-157 experiment now being conducted at the Stanford Linear Accelerator Center, a 30 GeV electron beam of 2×1010 electrons in a 0.65-mm-long bunch is propagated through a 1.4-m-long lithium plasma of density up to 2×1014 e−/cm3. The initial beam density is greater than the plasma density, and the head of the bunch expels the plasma electrons leaving behind a uniform ion channel with transverse focusing fields of up to several thousand tesla per meter. The initial transverse beam size with σ=50–100 μm is larger than the matched size of 5 μm resulting in up to three beam envelope oscillations within the plasma. Time integrated optical transition radiation is used to study the transverse beam profile immediately before and after the plasma and to characterize the transverse beam dynamics as a function of plasma density. The head of the bunch deposits energy into plasma wakes, resulting in longitudinal accelerating fields which are witnessed by the tail of the same bunch. A time-resolved Cherenkov imag...

Neutron Energy and Time-of-flight Spectra Behind the Lateral Shield of a High Energy Electron Accelerator Beam Dump,Part I: Measurements

Neutron energy and time-of-flight spectra were measured behind the lateral shield of the electron beam dump at the Final Focus Test Beam (FFTB) facility at the Stanford Linear Accelerator Center. The neutrons were produced by a 28.7 GeV electron beam hitting the aluminum beam dump of the FFTB which is housed inside a thick steel and concrete shield. The measurements were performed using a NE213 organic liquid scintillator behind different thicknesses of the concrete shield of 274 cm, 335 cm, and 396 cm, respectively. The neutron energy spectra between 6 and 800 MeV were obtained by unfolding the measured pulse height spectrum with the detector response function. The attenuation length of neutrons in concrete was then derived. The spectra of neutron time-of-flight between beam on dump and neutron detection by NE213 were also measured. The corresponding experimental results were simulated with the FLUKA Monte Carlo code. The experimental results show good agreement with the simulated results.

Neutron energy and time-of-flight spectra behind the lateral shield of a high energy electron accelerator beam dump. Part II: Monte Carlo simulations

Energy spectra of high-energy neutrons and neutron time-of-flight spectra were calculated for the setup of experiment T-454 performed with a NE213 liquid scintillator at the Final Focus Test Beam (FFTB) facility at the Stanford Linear Accelerator Center. The neutrons were created by the interaction a 28.7 GeV electron beam in the aluminum beam dump of the FFTB which is housed inside a thick steel and concrete shielding. In order to determine the attenuation length of high-energy neutrons additional concrete shielding of various thicknesses was placed outside the existing shielding. The calculations were performed using the FLUKA interaction and transport code. The energy and time-of-flight were recorded for the location of the detector allowing a detailed comparison with the experimental data. A generally good description of the data is achieved adding confidence to the use of FLUKA for the design of shielding for high-energy electron accelerators.

The Next Linear Collider damping ring complex

We report progress on the design of the Next Linear Collider (NLC) damping rings complex (DRC). The purpose of the DRC is to provide 120 Hz, low emittance electron and positron bunch trains to the NLC linacs. It consists of two 1.98 GeV main damping rings, one positron pre-damping ring, two pairs of bunch length and energy compressor systems and interconnecting transport lines. The 2 main damping rings store up to 0.8 amp in 3 trains of 95 bunches each and have normalized extracted beam emittances /spl gamma//spl isin//sub x/=3 /spl mu/m-rad and /spl gamma//spl isin//sub y/=0.03 /spl mu/m-rad. The preliminary optical design, performance specifications and tolerances are given. Key subsystems include: 1) the 714 MHz RF system, 2) the 60 ns risetime injection/extraction pulsed kicker magnets, 3) the 44 m wiggler magnet system, 4) the arc and wiggler vacuum system, 5) the radiation management system, 6) the beam diagnostic instrumentation, 7) special systems used for downstream machine protection and 8) feedback-based stabilization systems.

90° Bremsstrahlung Source Term Produced in Thick Targets by 50 MeV to 10 GeV Electrons

The 90° bremsstrahlung source terms produced in thick targets were studied using the EGS4 and FLUKA Monte Carlo codes. Calculations were performed for cylindrical targets of aluminum, iron, copper and lead. In the calculations, the electron beam energies varied from 50 MeV to 10 GeV, and the target radii varied from 0.5 to 3 Moliere units. The results were compared with the SLAC SHIELD 11 code.

Radiation Shielding at High-Energy Electron and Proton Accelerators

The goal of accelerator shielding design is to protect the workers, general public, and the environment against unnecessary prompt radiation from accelerator operations. Additionally, shielding at accelerators may also be used to reduce the unwanted background in experimental detectors, to protect equipment against radiation damage, and to protect workers from potential exposure to the induced radioactivity in the machine components. The shielding design for prompt radiation hazards is the main subject of this chapter.

Radiological Protection Studies For NGLS XTOD

R ADIOLOGICAL P ROTECTION S TUDIES FOR NGLS XTOD S HANJIE X IAO , M ARIO S ANTANA -L EITNER AND S AYED R OKNI SLAC N ATIONAL A CCELERATOR L ABORATORY R ICK D ONAHUE , P AUL E MMA , J AMES F LOYD AND T ONY W ARWICK L AWRENCE B ERKELEY N ATIONAL L ABORATORY SLAC-TN-13-003 LBNL-DOC-### December, 2013 P REPARED FOR THE D EPARTMENT OF E NERGY U NDER C ONTRACT N UMBER DE-AC02-76SF00515 & DE-AC02-05CH11231

Radiation Protection Aspects in the Design of the Linac Coherent Light Source II

*Since 2009, the Linac Coherent Light Source at the SLAC National Accelerator Laboratory produces ultra-fast, ultra-bright X-ray pulses with which atoms and molecules can be visualized as they move, hence revealing the mechanics of chemistry and revolutionizing the research in fields ranging from biology to energy sciences. LCLS-II is a sister vicinal facility with new features that will be soon constructed to address the surging demand of FEL beams. In this paper we summarize the radiation protection scheme for LCLS-II and we describe diverse challenges and the adopted solutions. In particular we present the access modes of LCLS-II that allow simultaneous operation with LCLS. Monte Carlo simulations have been used to design beam components like stoppers and to define the thickness of walls. Also, by carefully analyzing the contributors to the residual dose, the shielding of the main dumps has been optimized to meet engineering constraints while allowing access after short cool down.

Monte Carlo Studies for the Radiation Shielding Design of LCLS-II

Intensive Monte Carlo simulations performed with state-of-the-art computation codes are applied to the radiation shielding design of LCLS-II, which will be the extension of Linac Coherent Light Source (LCLS) at SLAC and will use the middle one-third of SLAC two-mile Linac. This paper describes the Monte Carlo studies of the first and last system where electron beams are involved, namely the LCLS-II Injector and the X-ray Transport and Diagnostics System (XTOD).

TOP-OFF INJECTION AND HIGHER CURRENTS AT THE STANFORD SYNCHROTRON RADIATION LIGHTSOURCE

Abstract The Stanford Synchrotron Radiation Lightsource (SSRL) at the SLAC National Accelerator Laboratory (SLAC) is currently working on increasing its stored current from originally 100 to 500 mA. SSRL worked with the SLAC Radiation Protection Department on mitigating the possible radiological hazards from these upgrades. This paper describes the related analyses, new safety systems, and beam tests. The top-off injection mode (injection with beamline stoppers open) is essential for operation at high currents. The radiological consequences of various situations were analyzed, a new Beam Containment System (BCS) was implemented, and radiation surveys were performed during tests. Since March 2010, all beamlines have been operating in top-off mode. Operation with higher beam currents was also analyzed for radiological hazards, and a new Beamline BCS was installed. The storage ring is now operating with 200 mA during user runs, and tests are ongoing with higher beam currents. Soon the power of the injection current will also be raised from 1.5 W at present to 5 W maximal.