Accelerator Tunnel Research Articles

Status of Angular Distribution Measurements of Photo-Neutron Yields from Cu, Sn, and Pb Targets Irradiated by 2 GeV Electrons

The study of differential photo-neutron yields by the irradiation of 2 GeV electrons has been carried out. In this extended study of previous measurements, which were done at the angle of 90° relative to incident electrons, the differential photo-neutron yield was obtained at two other angles of 48° and 140° to study its angular characteristics. The experimental setup was improved to reduce huge photon backgrounds in a linear accelerator tunnel. Photo-neutron spectra were measured using a pulsed beam time-of-flight method. The neutron energy range of reliably measuring was from 8 MeV to 250 MeV. The status of this measurement study and differential photo-neutron yields produced from thick Cu, Sn, and Pb targets were presented. These results show the angular characteristics obviously.

KEKB accelerator control system

The KEKB accelerator control system including a control computer system, a timing distribution system, and a safety control system are described. KEKB accelerators were installed in the same tunnel where the TRISTAN accelerator was. There were some constraints due to the reused equipment. The control system is based on Experimental Physics and Industrial Control System (EPICS). In order to reduce the cost and labor for constructing the KEKB control system, as many CAMAC modules as possible are used again. The guiding principles of the KEKB control computer system are as follows: use EPICS as the controls environment, provide a two-language system for developing application programs, use VMEbus as frontend computers as a consequence of EPICS, use standard buses, such as CAMAC, GPIB, VXIbus, ARCNET, RS-232 as field buses and use ergonomic equipment for operators and scientists. On the software side, interpretive Python and SAD languages are used for coding application programs. The purpose of the radiation safety system is to protect personnel from radiation hazards. It consists of an access control system and a beam interlock system. The access control system protects people from strong radiation inside the accelerator tunnel due to an intense beam, by controlling access to the beamline area. On the other hand, the beam interlock system prevents people from radiation exposure by interlocking the beam operation. For the convenience of accelerator operation and access control, the region covered by the safety system is divided into three major access control areas: the KEKB area, the PF-AR area, and the beam-transport (BT) area. The KEKB control system required a new timing system to match a low longitudinal acceptance due to a low-alpha machine. This timing system is based on a frequency divider/multiply technique and a digital delay technique. The RF frequency of the KEKB rings and that of the injector Linac are locked with a common divisor frequency. The common divisor frequency determines the injection timing. The RF bucket selection system is also described. r 2002 Elsevier Science B.V. All rights reserved.

Evaluation of Radioactivity at Accelerator Tunnels for High-Intensity Proton Accelerator Facility

Activation evaluation is one of the most crucial issues for a shielding design of a high-intensity proton accelerator facility. Radioactivity production in air and cooling water in the accelerator tunnels of a 600-MeV linear accelerator, 3-GeV and 50-GeV proton synchrotrons and their beam transport lines was evaluated by multiplying the spectra of protons and neutrons in the tunnels with activation cross section data. The data were evaluated by calculation using the INC/GEM and the LAHET codes, supported by some experimental data.

Evaluation of internal and external doses from 11C produced in the air in high energy proton accelerator tunnels.

Air has been irradiated with high energy protons at the 12 GeV proton synchrotron to obtain the following parameters essential for the internal dose evaluation from airborne 11C produced through nuclear spallation reactions: the abundance of gaseous and particulate 11C, chemical forms, and particle size distribution. It was found that more than 98% of 11C is present as gas and the rest is aerosol. The gaseous components were only 11CO and 11CO2, and their proportions were approximately 80% and 20%, respectively. The particulate 11C was found to be sulphate and/or nitrate aerosols having a log-normal size distribution; the measurement using a diffusion battery showed a geometric mean radius of 0.035 micron and a geometric standard deviation of 1.8 at a beam intensity of 6.8 x 10(11) proton.pulse-1 and an irradiation time of 9.6 min. By taking the chemical composition and particle size into account, effective doses both from internal and from external exposures per unit concentration of 11C were calculated for various room sizes. The values can be used to evaluate the effective dose from the airborne 11C produced in the accelerator tunnels.

Benchmark Experiment for Radiation Shielding around the Beam Dump of the SPring-8 Injector

Leakage neutron spectra outside the shield wall and dose distributions within the accelerator tunnel were measured by using multi moderated 3He high sensitivity neutron counters, TLD dose meters and CR-39 detectors using 250 MeV and 961 MeV electrons of the SPring-8 injector. The measurements were compared with Jenkins’ formula with source reduction factors for the bulk shielding and the dose distributions within the tunnel. Three different types of doses (dose equivalent, effective dose equivalent and effective dose) were also compared. 206Bi production distribution due to (γ,3n) and (n,4n) nuclear reaction around the beam dump of 250 MeV was measured and compared with EGS4 simulation.

Aerosol-size distribution of radon daughter218Po in the accelerator tunnel air

Aerosol-size distributions of218Po were determined for the accelerator tunnel air sampled during machine operation and for the basement air of a concrete building, where the number and the size distribution of non-radioactive aerosols are greatly different from each other. The218Po distributions depended very much on the size distributions of ambient non-radioactive aerosols, and could be well explained by an attachment model of218Po to ambient non-radioactive aerosols.

Comparison of backgrounds in detectors for LHC, NLC and μ+μ− colliders

Background levels in detectors at future high-luminosity colliders of three different types — pp , e + e − and μ + μ − — are analyzed. Two sources — debris from the collision points and those from an accelerator tunnel — are studied. It is shown that hadron, electron and muon colliders are similar and very different at the same time with respect to background origin, integrated radiation levels and instantaneous rates of particles in the detectors.

Controlling a large physics experiment; A communication issue

In the past a physics experiment could be set up in a small laboratory by a single genius. These days, physics experiments involve international collaborations of hundreds of scientists, and the laboratory of the “crazy scientist” has been replaced by kilometers of accelerator tunnels, enormous underground caverns, tons of detector apparatus, hundreds of kilometers of cables, thousands of electronic boards and dozens of computers. The control of such an experiment is a complex system involving constraints of reliability, efficiency, reconfigurability and maintainability. This paper shows that an efficient communication system is an important issue when building such a control system.

Comparison of high-dose dosimetry systems for radiation damage studies in collider detectors and accelerators

Measurements of absorbed dose in accelerator tunnels around primary beam areas are carried out on a routine basis at CERN. Dosimetric surveillance of high-energy particle accelerators has a great importance for the assessment of the radiation induced damage to materials and components used in high-level radiation areas. Standard dosimeters used at CERN for this purpose are polymer-alanine dosimeters (PAD) and radiophotoluminescent glass dosimeters (RPL). Ethanol-chlorobenzene dosimeters (ECB) for high-dose dosimetry, developed at the Ruder Boskovic Institute (RBI), have several interesting properties making their use in future multi-TeV colliders and detectors promising. These and RPL dosimeters were compared using the CERN alanine dosimetry as the reference system and 60Co gamma rays as the reference radiation. A very good agreement between the ECB and PAD was obtained for 60Co gamma irradiation whereas RPL overestimated the dose by about 15%. In mixed accelerator radiation fields the combination of the three dosimeters opens the possibility to estimate the total dose and the quality of the principal radiations contributing to the total radiation field.

Relative abundance of HT and HTO in the accelerator tunnel air and atmospheric air

The relative abundance of tritiated-airborne species was studied for the air of the beam-line tunnel at high-energy accelerators as well as atmospheric air. The tritium produced via nuclear spallation reactions in the accelerator-tunnel air exists in the chemical forms of HTO and HT. The HT-to-HTO ratio was about 2 × 10 −2 on the average, being appreciably smaller than that in atmospheric air. The reaction mechanisms of accelerator-produced tritiums were discussed on the basis of the similarity to the reactions by cosmic-generated tritium. HT is likely to be formed directly through the reaction of a recoiling tritium with H 2O. On the other hand, the HT-to-HTO ratio for the present atmospheric air indicates that tritium distributions have been largely modified by the release of man-made tritium into the air.

The continuous electron beam accelerator facility: Project status and physics outlook

Nuclear physics research program planning, accelerator tunnel construction, and accelerator component development, assembly, and testing are under way at the Continuous Electron Beam Accelerator Facility, Newport News, Virginia. CEBAF's 4-GeV, 200-μA superconducting recirculating accelerator will provide cw beam to simultaneous experiments in three end stations for studies of the nuclear many-body system, its quark substructure, and the strong and electroweak interactions governing this form of matter. An experimental program is being defined in collaboration with the user community. The experimental halls have been designed, and preliminary experimental equipment conceptual designs have been prepared. Planned for Hall A are two 4-GeV/ c high-resolution ( δp p ≤ 10 −4 ) spectrometers (HRS) with moderate acceptance (∼ 8 msr) for a program of completely exclusive experiments in which the nuclear final state has to be fully specified. A CEBAF large acceptance spectrometer (CLAS) is planned for the program of Hall B, which will include bias-free investigation of hadronic final states in inelastic electron scattering and detection of multiple-particle final states. The CLAS will be a multi-gap device based on a toroidal magnet with six superconducting coils arranged around the beamline to produce an essentially circular magnetic field. Hall C is envisioned as serving a diversity of interests, including form factor measurements, parity violation investigations, form factors of nucleon resonances, and a high- Q 2 baryon resonance program. A moderate-resolution, high-momentum, 6-GeV/ c spectrometer (HMS) together with several specialized second arms—in particular, a symmetric toroidal array spectrometer—are being planned to carry out Hall C experimentation.

Radioactive airborne species formed in the tunnels of a high energy accelerator facility

By using a simple air filter technique, the fractions of aerosol and gaseous components were measured for individual nuclides formed in the air of a high energy accelerator tunnel. The size distributions for 7Be, 24Na and 38S aerosols were also measured by using a diffusion battery and found to be log-normal with a geometric mean radius of about 28 nm; the radioactive aerosol formation was adequately explained by simple attachment reactions.

Absorbed doses due to synchrotron radiation in the tunnel of the storage ring petra

Absorbed doses due to synchrotron radiation were measured in the accelerator tunnel of the high-energy electron-positron storage ring PETRA, at beam energies between 17 and 22.8 GeV. For energies between 17 and 30 GeV calculations were performed using the Monte Carlo code EGS. An agreement with the measured values was obtained within a factor of 2. In addition, the absorbed doses in a straight part of the accelerator tunnel were studied.

Particle size distribution of 7Be-aerosols formed in high energy accelerator tunnels

The 7Be, produced by nuclear spallation reactions in the air of high energy accelerator tunnels, is present in the form of an aerosol. The size distribution of the 7Be-aerosols was measured with a parallel plate diffusion battery and was found to be a log-normal distribution with a geometric mean radii of 27 nm and a logarithmic standard deviation of 0.36. The formation of the 7Be-aerosol is adequately explained by the attachment of 7Be to non-radioactive aerosols containing sulfates, which are produced by radiation induced oxidation reactions of SO 2 present in the air.

Induced radioactivities in concrete constituents irradiated by high-energy particles.

The powdered concrete constituents of magnetite ore, pyrites ore, marble, gravel and Portland cement were prepared and irradiated by 12- GeV protons and secondary particles at the slow extracted beam line of the National Laboratory for High Energy Physics ( KEK ) 12- GeV proton synchrotron. The saturated activities for individual nuclides produced were calculated, and the time variation of photon exposure rate due to the residual activities was also evaluated for each sample. The exposure rates ranked in the following order: magnetite ore greater than pyrites ore greater than gravel greater than or equal to cement greater than marble. The levels of photon exposure rates from heavy, ordinary and marble concretes were also estimated on the basis of the results obtained for each constituent. It is suggested that the use of marble concrete in the inside wall of accelerator tunnels can reduce considerably the exposure to the accelerator maintenance workers, compared with heavy and ordinary concretes commonly used.

Oxygen Deficiency Hazard Induced by Helium Release in Accelerator Tunnel

Tests to investigate oxygen deficiency levels due to release of helium into the CBA tunnel are described. Results of the tests indicate that the helium stratifies and spreads quickly in the horizontal plane. This demonstrates that adequate warning of possible asphyxiation hazards can be achieved. When oxygen deficiency monitors are located at ceiling level they may be spaced at intervals of 60 m. or more and still achieve acceptable results.

Measurements of radionuclides induced in the accelerator structure of the KEK-PS.

Radionuclides induced in accelerator structures were measured during each long shut-down by using a pure Ge detector and a portable multichannel pulse height analyzer. Variation in the nuclide composition for various points in the accelerator tunnel was investigated. The decay of the exposure rate was calculated using the measured nuclide composition. Radionuclide measurements of the vacuum chamber removed from the accelerator were also performed. The relation between the variation of the residual exposure rate and that of the nuclide composition was examined and it was found that the proportion of 48V, 54Mn and 56Co corresponds to variation in the beam loss pattern.

Beam Position Measurement System at the Argonne Rapid Cycling Synchrotron

The position measurement system for the Rapid-Cycling Synchrotron (RCS) was originally designed with a four-plate, combined function, capacitive pickup pi electrode situated in each of the six short straight sections. During subsequent operation, it was discovered that these electrodes were limiting the aperture and, therefore, were being activated by the circulating proton beam. In addition, the activation made it difficult to maintain the active electronic components in the RCS tunnel. The new position measurement system has been designed to eliminate these problems. The electrode's horizontal and vertical dimensions have been increased and the plates reorientated for simpler, separate function signal processing. A passive impedance matching network has replaced the active cathode follower, eliminating maintenance requirements in the accelerator tunnel. The Radio Frequency (RF) beam signals are transmitted directly to the Main Control Room (MCR) for processing.

Photon dose rate in the vicinity of a high-energy proton beam scraper

Calculated results are presented of the photon dose rate from the induced activity in the vicinity of a beam scraper for a 400 GeV proton accelerator. Proton energies of 30 and 400 GeV are considered since 30 GeV protons will be used for beam alignment studies. Results are give at various positions with respect to the scraper and as a function of time after the beam is turned off. In the case of the 30 GeV protons both borated and non-borated concrete have been considered as the material of the accelerator tunnel and the beam scraper shield. In the geometry considered here, the presence of the boron in the concrete has only a small effect on the dose rates.