Industrial Linacs Research Articles

Design, simulation and implementation of an efficient vacuum system and gas load calculations for a 6 MeV industrial LINAC

The design of vacuum system for a 6 MeV, commercial LINAC is presented. Unlike many commercial LINACs, the LINAC being developed has demountable electron gun, RF-waveguide and X-ray target assemblies. This design scheme is more efficient and economical. The LINAC has a total internal volume of 1.9 land surface area of ~3.2 × 103cm2, and is operated at Ultra High Vacuum. An iterative Simulation-Experimental approach is adopted to freeze a viable vacuum system for the LINAC. The vacuum simulations are performed in MOLFLOW+2.7.7, and the results are benchmarked experimentally. Due to compact geometry of the LINAC, reduced pumping speeds are experienced. The system was implemented using two 550 l/s commercially available turbo molecular pumps backed by rotary pumps, consuming ~2.4 kW. Particle dynamics simulations were performed using PARMELA 3. These simulations quantified the beam loss in the LINAC and predicted the sites of beam impingement. The system was experimentally verified for establishment of base pressure, activation of dispenser cathode, electron gun conditioning and the full power operation of LINAC at repetition rate of 50–110 Hz. Through all these regimes the vacuum system performed within permissible limits. The gas loads induced in the system were also evaluated using steady state and transient analysis. The pumping speed is optimized, and it is shown that base pressure of 1 × 10−9mbarcan be achieved at reduced pumping speed of ~100 l/s at the pumping ports. This reduced pumping speed also performed well for routine LINAC operation. Therefore, using benchmarked simulated results, an optimized and commercially economical vacuum system is proposed with reduced pumping speed of ~100 l/s consuming 6 times reduced power (0.4 kW) and ~40% reduced cost.

ESTIMATION OF BBU THRESHOLD CURRENT IN AN INHOMOGENEOUS ACCELERATING SECTION

In this work we describe the procedure of estimation of regenerative beam blowup threshold current in an inhomogeneous accelerating section. The self-consistent problem of transverse motion of particles in the field of dipole mode excited by the beam is solved. The distribution of dipole field near the structure axis and the energy variation of beam particles were calculated before simulating the transverse dynamics. The threshold current for S-band industrial linac designed for radiation sterilization of medical products is estimated.

Faraday Cup for high current and duty cycle electron LINACs

The design of a Faraday Cup (FC) is presented. The FC is designed to be used at an industrial LINAC test beamline. The present study gives the comprehensive design of FC to minimize the effects of secondary electrons. It also describes the heat dissipation at collector and its cooling design. A 200 mm long FC with aperture diameter of 20 mm and back wall thickness of 30 mm with repeller ring is simulated in CST particle studio software. A repeller ring is optimized for its thickness and axial distance to minimize the escape percentage of secondary charges from FC. The change in the thickness of repeller ring, axial distance and barrier potential greatly influence the escaped percentage. The study incorporates the secondary electron source at back wall of FC with fixed emission of 1.5 × 104 particles having energy 500 eV (10% dispersion) with different angular spread i.e. 0°, 45°, 90°. The escape percentage less than 1% is observed for 7 mm repeller ring-FC distance and 3 mm thickness with barrier potential of −700 V. The optimized design of the repeller ring reduces the physical dimensions of the FC. Moreover, the study also presents the mechanical design and heat transport analysis of Faraday cup. The designed square type channels with water circulating at 20 L/min limits the temperature to 333 K at the surface of the FC. Initial experimental results for thermal design are also presented, showing that temperature rise under 6 MeV, 4 μsec pulse width and 100 Hz repetition rate; is limited to 304 K. The cooling efficiently mitigates the heat load at water flow rate of 7.5 L/min.

Influence of the Frequency Detuning to Electrodynamics Parameters of an Electron Linac

It is very important task to define the tolerances necessary for correct operation of an electron linac. The detuning of linac main parameters as frequency, RF field amplitude and phase can sufficiently influence to the beam parameters. It is highly important for linacs with high brightness beams which are necessary for light sources and colliders. It is also sufficient for industrial linacs. A linac section consists of regular and bunching parts. The influence of one cell detuning on electrodynamics parameters of the whole section was studied. Results of such simulation will discuss in this paper.

Studies on the S-band bunching system with the Hybrid Bunching-accelerating Structure

Generally, a standard bunching system is composed of a standing-wave (SW) pre-buncher (PB), a traveling-wave (TW) buncher (B) and a standard accelerating structure. In the industrial area, the bunching system is usually simplified by eliminating the PB and integrating the B and the standard accelerating structure together to form a β-varied accelerating structure. The beam capturing efficiency for this kind of simplified system is often worse than that for the standard one. The hybrid buncher (HB) has been proved to be a successful attempt to reduce the cost but preserve the beam quality as much as possible. Here we propose to exclusively simplify the standard bunching system by integrating the PB, the B and the standard accelerating structure together to form a Hybrid Bunching-accelerating Structure (HBaS). Compared to the standard bunching system, the one based on the HBaS is more compact, and the cost is lowered to the largest extent. With almost the same beam transportation efficiency (∼70%) from the electron gun to the linac exit, the peak-to-peak (p-to-p) beam energy spread and the 1σ emittance of the linac with the HBaS are ∼20% and ∼60% bigger than those of the linac based on the split PB/B/standard accelerating structure system. Nonetheless, the proposed HBaS can be widely applied in the industrial linacs to greatly increase the beam capturing efficiency without fairly increasing the construction cost.

Terahertz radiation source using a high-power industrial electron linear accelerator

High-power (∼ 100 kW) industrial electron linear accelerators (linacs) are used for irradiations, e.g., for pasteurization of food products, disinfection of medical waste, etc. We propose that high-power electron beam from such an industrial linac can first pass through an undulator to generate useful terahertz (THz) radiation, and the spent electron beam coming out of the undulator can still be used for the intended industrial applications. This will enhance the utilization of a high-power industrial linac. We have performed calculation of spontaneous emission in the undulator to show that for typical parameters, continuous terahertz radiation having power of the order of μW can be produced, which may be useful for many scientific applications such as multispectral imaging of biological samples, chemical samples etc.

Fabrication of an Ultra High Vacuum Compatible Faraday Cup for Qualification of Electron Gun for 10 kW Industrial LINAC

In this paper, we report fabrication and testing of a unique Faraday Cup designed for qualification of Electron Gun for a 10 kW industrial LINAC. This is a compact device consisting of a tapered copper cavity electrically isolated by a ceramic cylinder metalized at both ends. Kovar tubes matching with the diameter of ceramic isolator were used at both ends to facilitate high quality UHV compatible joints with copper cavity at one end and standard knife edge stainless steel flange at the other end. The Kovar tube was flared at both ends to form a collar matching with the outer diameter of the ceramic isolator. The joint between Kovar collar and ceramic isolator was done by hydrogen brazing using copper silver eutectic alloy. All the joints were tested with helium leak detector and leak rates were found to be below 1 × 10−10mbar.litre/second.

Linac with integrated power source based on radio frequency energy compression

The basic feasibility of a proposal to simplify the conventional low energy rf electron linear accelerator (linac), is considered. The design suggested foresees replacement of the traditional high power systems of external rf generator and modulator by a more passive switched energy storage system. The proposed conception of a compact linac is based on known rf energy compression techniques and an efficient self-excited oscillation in a special accelerating/oscillating linac structure. The principal relations, performance estimations, and one-dimensional time-dependent simulation results for such a linac are presented. The possibility of self-excited oscillation by an unbunched low voltage beam in a waveguide linac section is proved and investigated experimentally. The common features and differences compared with a conventional backward-wave tube are analyzed. An application of this effect is proposed for impedance and group velocity measurements in slow-wave structures. Since the rf energy commutation may be one or two orders faster than the electric high voltage energy commutation (conventional modulator), combining the structure proposed and rf energy compression system can give high levels of the average beam power (10–100 kW). The linac facility would have considerably reduced weight and sizes (more than 2.5 times) as compared to similar industrial linacs. The power supply required is in 40–120 kV range dc source, and an estimated overall wall plug efficiency is a few percent.

Energy characteristics of a short-pulse S-band industrial linac

The time-averaged and time-dependent energy spectra of an S-band, standing-wave industrial linac with direct injection are examined during steady-state and stored-energy mode operation. The effective fill-time for the structure under heavy beam-loading conditions is found to be significantly shorter than that predicted from an unloaded structure.

Possibilities of the DAW structure for application to industrial linacs

A brief description of the disk and washer (DAW) accelerating structure is presented. Based on their experience of the manufacturing of the DAW structure and the results of successful operation of the structure at the Moscow meson factory linac, the authors conclude that this accelerating structure is a very attractive candidate for production of powerful industrial linacs.

Resonance Neutron Radiography Using an Electron Linac

It has been shown that resonance neutron radiography is a technique that can provide information on the amount and distribution of individual isotopes in samples with a complex matrix. The technique is applicable for a wide range of purposes, from the examination of industrial components to the analysis of nuclear materials that are highly radioactive. Although presently instrumented in a research laboratory, the technique can be realized in a small device for field applications using a small industrial linac, as pointed out in an earlier paper of this conference by C. D. Bowman.

Linear Electron Accelerators for Medicine and Radiation Processing Developed in Beijing, Chinia

In recent years, the low energy linear electron accelerators have been developed in China. In this paper, the performance feature and the applications of an 8 MeV medical linac and a 5 MeV industrial linac are described briefly.