Return of Experience in the Commissioning of the New CLS LINAC Injector

Flexible materials are being used already today as base substrates for electronic assembly. A lot of mounted components, both active and passive components, could be integrated in flexible polyimide substrates. Very interesting advantages of integrating components into the flex are compactness and enhanced flexibility: not only the interconnection but also the components themselves can be mechanically flexible. Two polyimide based embedding technologies are described. First, a polyimide based 60 μm foldable chip package is presented: the ultra-thin chip package (UTCP). Chips thinned down to 20 μm are packaged in between two polyimide layers.Next, very thin, flexible RF structures are realized. Multilayers are built-up on temporary rigid carrier substrates by repetitive application of polyimide layers by a spin-on process and metal layers by sputtering. Sputtered NiCr is used as resistor material, a thin spincoated PI as capacitor dielectric. Inductors, capacitors and resistors are interconnected with microstrip transmission lines, realizing multilayer RF structures. Key words: chip package, RF structure, flexible, 3D.

LANL has developed a new vane loaded waveguide RF structure for a sheet electron beam traveling wave tube (TWT). The goal was to create a new class of wideband RF structures that allow simple mechanical fabrication and have geometry suitable for interaction with sheet electron beams. We have concentrated on structures at 94 GHz. We have achieved 6% bandwidth and believe that 10% is possible. We have performed 3D electromagnetic simulations using the codes Microwave Studio and HFSS, and fabricated several aluminium cold models of RF structures at 10GHz to confirm the design. Agreement between the 10 GHz cold test data and computer simulations was excellent. An RF structure at 94GHz was fabricated using electrical discharge machining (EDM) with a 0.004 inch wire and cold tested.

A theory and general method for calculating self-excitation thresholds for a large class of standing and traveling-wave structures used in amplifiers, klystrons, traveling-wave tubes, and other vacuum electronic devices (VED) is presented. One determines the circuit parameters of RF structures that are changed due to the presence of electron beam and analyze the stability of the obtained matrices. New determinant equations defined by such stability matrices are derived in a general form applicable to any RF structure and as an important special case for RF structures with electron beams. The theory and computational methods described here are essential for stability analysis of RF structures and VED.

RF breakdown is one of the major factors determining performance of high power rf components and rf sources. RF breakdown limits working power and produces irreversible surface damage. The breakdown limit depends on the rf circuit, structure geometry, and rf frequency. It is also a function of the input power, pulse width, and surface electric and magnetic fields. In this paper we discuss multi‐megawatt operation of X‐band rf structures at pulse width on the order of one microsecond. These structures are used in rf systems of high gradient accelerators. Recent experiments at Stanford Linear Accelerator Center (SLAC) have explored the functional dependence of breakdown limit on input power and pulse width. The experimental data covered accelerating structures and waveguides. Another breakdown limit of accelerating structures was associated with high magnetic fields found in waveguide‐to‐structure couplers. To understand and quantify these limits we simulated 3D structures with the electrodynamics code Ansoft HFSS and the Particle‐In‐Cell code MAGIC3D. Results of these simulations together with experimental data will be discussed in this paper.

The ELI-NP project is now working on the design of their conventional facility. Dr. Gheorghe Cata-Danil recently requested that I provide them with information on the location and amount of electron-beam loss in the MEGa-ray source they have proposed for ELI-NP. This memo is intended to document that information, for transmission to ELI-NP. The ELI-NP MEGa-ray source, as presently proposed, consists of two x-band accelerator sections separated by a large chicane, as show in figure 1. The basic parameters of the machine that are pertinent for specifying the radiation source terms are shown in table 1. These are the parameters of the intentionall-produced photobeam. In addition to the photobeam, the electron gun and accelerator will produce 'dark current' that originates throughout the RF structures (that is, distributed along the accelerator axis) and therefore has a distribution of energy below the energy of the photobeam. Because it is emitted from surfaces inside the RF structures, much of it is not transported through the accelerator and is lost in the accelerator RF structures. A large fraction of the total dark current is produced in the photogun and lost at the entrance of the 1st accelerator RF structure. Important sources of radiation during operation are beam alignment screens that are used for observing the image of the electron beam, during adjustment of beam steering and for general diagnostic purposes. Each screen consists of a 1 mm thick Ce:YAG plate that is moved into the path of the beam when desired. This destroys the electron beam, spraying all beam current into the structures downstream of the screen. Only one screen is inserted at a time. These screens may be located after each accelerator RF structure, and after each set of bend magnets, as shown in figure 3. The photobeam energy and currents at each location are listed in table 2; for simplicity, the dark current energy is (conseratively) assumed to be the same as the photobeam energy. In normal operation, the locations of other beam losses and the estimated current and energy of the lost beam are listed in table 3. In addition to these 'normal' beam losses, it is assumed that the beam may be accidentally mis-steered by up to 1 degree at every steering magnet, so that it hits the surrounding beam tube and other structures. This loss can be modeled as occurring at the locations listed in table 2, numbers 1-7 and 16-21. Similarly, it is assumed that any of the dipole magnets, in chicanes or at the beam dump, may fail, resulting in total beam loss straight ahead. These locations can be assumed to be the same as listed in table 2, numbers 8-10, 12-14, 22-24, 26, and 27. The data provided above are estimates of the beam loss, for the purpose of calculating radiation source terms. Dark current estimates are conservative, until we acquire actual operational data. Neither the estimated currents nor the estimated energies listed above contain any intentional margin. when they have performed similar calculations for their own purposes, they have typitally added approximately 10% to the beam energy to provide some overall margin in the analysis.

The Spallation Neutron Source (SNS) project is a collaboration among Argonne, Brookhaven, Lawrence Berkeley, Los Alamos, and Oak Ridge National Laboratories. Los Alamos is responsible for the linac that accelerates the H/sup -/ beam from 2.5 MeV to 1 GeV. For the baseline design, scheduled for completion in 2005, the linac will deliver to the accumulator ring a beam of 1.1-MW average power. In the SNS linac, a conventional 402.5-MHz drift-tube linac (DTL) accelerates the beam from 2.5 to 20 MeV, at which point 805-MHz structures take over. The 805-MHz linac consists of a coupled-cavity drift-tube linac (CCDTL), followed by a coupled-cavity linac (CCL). The DTL uses permanent magnet quadrupoles inside the drift tubes arranged in FOFODODO lattice; the focusing period is 4/spl beta//spl lambda/ long at 402.5 MHz. The CCDTL and CCL use electromagnetic quadrupole magnets external to the rf structure; the FODO lattice period is 12 ph long at 805 MHz. The cavity field profile maintains smooth longitudinal focusing strength per unit length. High cavity stored energy reduces the effect of beam chopping on the cavity fields. The bore radius is 1.25 cm in the DTL, and increases in the CCDTL and CCL in several steps consistent with adequate shunt impedance, to a final value of 2.0 cm. The rf structures are compatible with a future upgrade to a beam power of 4.4 MW.

The reciprocity principal exploited for deriving perturbation formulae which relate the local electric and magnetic fields at the position of a perturbing body inside an rf structure to the fields induced by the body in an output lead or, in case of a resonant cavity, to the change in the resonant frequency or the quality factor of the cavity. The present theory applies to any rf structure which is linear and passive; it enables us to apply perturbation techniques to a wider class of structures than hitherto considered possible. It affords us a theoretical basis for some experimental methods which have been used without duly theoretical consideration. As one such example, absorption measurements of fields in Fabry-Perot resonators are discussed. Another example is measurements of travelling waves inside electron linear accelerator structures, for which a result of analyzing some experimental data is given.

Although reciprocal frame structures have been known since ancient times, the development of digital tools has enabled the exploration of more complex forms and the improvement of the design and fabrication processes of such structures. The design process employs digital Rhinoceros and Grasshopper, along with plugins Kangaroo3D, Engon, Karamba3D, and Ladybug. The project uses a 'top-down' approach, where the basic form is first developed as a minimal surface, onto which the RF structure is mapped and placed. After setting up the RF structure, structural and solar analysis are performed. Despite the complexity of RF structures, the methodology demonstrates that they can be accessible and practical for broader application in architecture.

LANL has developed a new vane loaded waveguide RF structure for a sheet beam TWT. The goal was to create a new class of wideband RF structures that allow simple mechanical fabrication and have geometry suitable for interaction with sheet electron beams. LANL has developed an RF structure using planar geometry for simple EDM machining at 94GHz .Structure gain was demonstrated with a 2A pencil beam.

Role of recovery pass beam phase error in RF system design for same cell energy recovery FELs

The Canadian Light Source (CLS) is a third-generation synchrotron located inSaskatoon, Canada. A superconducting radio frequency (SRF) cavity contained in a 4.43 Kliquid helium I cryostat is used at the CLS to replenish energy loss in the electron beam. Adynamic simulation of this cryostat has been generated to examine pressure and levelfluctuations due to variations in heat loading or other system parameters. This simulatorhas led to some interesting observations in system behavior, which have been shown tooccur in the actual system as well. For example, mass rates of vaporization appear to dropas heat loading increases under certain conditions. Also, the relationship between pressureand SRF tuning characteristics is examined, and the abilities and limitations of thesimulator are presented.

Superconducting radiofrequency (SRF) cavities have been used for more than 50 years to increase the energy of charged particles. In Canada there are two accelerator centres which use SRF technology, i.e TRIUMF and the Canadian Light Source (CLS). The CLS was the first light source to use an SRF cavity in a storage ring from the beginning of operations in 2004. TRIUMF began developing SRF technology in 2000 which led in 2006 to the commissioning of the ISAC-II heavy ion superconducting linac for the post-acceleration of radioactive beams. More recently, the ARIEL SRF electron accelerator was installed at TRIUMF as a second driver for radioactive isotope production. In this talk, I will first give an overview of Canada’s SRF infrastructure and the underlying concepts. Then, I will briefly present how performance has globally evolved since the early days. Nowadays, state of the art niobium cavities reach fundamental limitations in terms of accelerating gradient (energy gain per unit length) and power dissipation. Increasing performance requires specialized chemical and surface treatments which must be tailored to specific cavity types and exploring materials beyond bulk niobium. I will highlight recent research highlights from TRIUMF and UVic including results from testing new surface treatments on unique multimode coaxial resonators and material science investigations using beta detected nuclear magnetic resonance (beta-NMR) and muon spin rotation and relaxation (muSR).

The NBS-LASL racetrack microtron (RTM) is a joint research project of the National Bureau of Standards and the Los Alamos Scientific Laboratory. The project goals are to determine the feasibility of, and develop the necessary technology for building high-energy, high-current, continuous-beam (cw) electron accelerators using beam recirculation and room-temperature rf accelerating structures. To achieve these goals, a demonstration accelerator will be designed, constructed, and tested. Parameters of the demonstration RTM are: injection energy - 5 MeV; energy gain per pass - 12 MeV; number of passes - 15; final beam energy - 185 MeV; maximum current 550 ?A. One 450 kW cw klystron operating at 2380 MHz will supply rf power to both the injector linac and the main accelerating section of the RTM. The disk and washer standing wave rf structure being developed at LASL will be used. SUPERFISH calculations indicate that an effective shunt impedance (ZT2) of about 100 M?/m can be obtained. Thus, rf power dissipation of 25 kW/m results in an energy gain of more than 1.5 MeV/m. Accelerators of this type should be attractive for many applications. At beam energies above about 50 MeV, an RTM should be considerably cheaper to build and operate than a conventional pulsed rf linac of the same maximum energy and time-average beam power. In addition, the RTM provides superior beam quality and a continuous beam which is essential for nuclear physics experiments requiring time-coincidence measurements between emitted particles.

To demonstrate that synchrotron radiation phase-contrast imaging (SR-PCI) can be used to visualize the intrascalar structures in implanted human cochleae and to find the optimal combination of the parameters object-to-detector distance (ODD) and beam energy (E) for visualization. Three cadaveric implanted human temporal bones underwent SR-PCI with varying combinations of parameters ODD (3, 2 and 1 m) and E (47, 60 and 72 keV). All images were then reconstructed to a three-dimensional (3D) stack of slices. The acquired 3D images were compared using contrast-to-noise ratios (CNRs) of the basilar membrane ( ) and the electrode array (CNRE ) and the standard deviation of the beam streaks ( ). Postprocessing calculations were performed using Matlab (Version 2017b, MathWorks Inc., Natick, MA, U.S.A.) with a standard significance level p < 0.05 to determine the most optimal combination of parameters. SR-PCI with computed tomography reconstruction provided good visualization of the anatomical features of the implanted cochleae, specifically the exact location of the electrode with respect to the BM. A single-factor ANOVA revealed a significant difference of variance for both CNRE and CNRBM , but failed to show significance for . A two-sample t-test failed to show any significant difference between CNRE columns of (3 m, 72 keV) and (2 m, 60 keV). The CNRBM was significantly different only at two pairs of columns, when (1 m, 72 keV) was compared against (2 m, 72 keV) and (3 m, 72 keV). The results of this study show that SR-PCI is a viable method to visualize implanted human cochleae. SR-PCI is less invasive, less labour intensive and is associated with a much lower acquisition time compared to other methods for postimplantation imaging in humans, such as histological sectioning. We found that the optimal combination of E and ODD parameters was 72 keV and 2 m, respectively. These parameters resulted in high-contrast images of the electrode as well as all internal structures of the cochleae. Cochlear implants (CI) are currently the preferred method of treatment for hearing loss. Cochlear implantation surgery involves placement of a metallic, wire-shaped electrode inside the cochlea, the main organ of the human hearing system. Knowledge of the exact location of the electrode after implantation is beneficial in improving the extent of restored hearing. Common clinical imaging modalities such as computed-tomography (CT) are not ideal for providing such information, due to lack of resolution and streaking caused by the metallic electrode. Recent studies have developed algorithms to extract the electrode location from clinical computed-tomography images and have been validated using histology or micro computed-tomography (micro-CT). Synchrotron radiation phase contrast imaging (SR-PCI) is a high-resolution imaging technique used to visualize small structures in three dimensions. Recently, SR-PCI has been shown to be an alternative to histology or micro-CT for imaging the human cochlea. However, it has not been optimized for imaging implanted human cochleae. The main objective of the present work was to find the optimal organization of imaging parameters (i.e., object-to-detector distance and beam energy) for using SR-PCI to image implanted human cochleae. Three cadaveric human cochleae were imaged using five different combinations of imaging parameters at the Canadian Light Source Inc., Saskatoon, SK, Canada. The resulting images were compared both quantitatively and qualitatively. An optimal combination of parameters was found to produce high-contrast images of the both the CI electrode and all internal structures of the cochlea with minimal streaking. SR-PCI is therefore a viable alternative to histological or micro-CT studies for post-surgical imaging of implanted human cochleae.

X-ray image formation using scattered radiation can yield a superior contrast-to-noise ratio compared to conventional transmission x-ray imaging. A barrier to practical implementation of scatter imaging systems has been slow image acquisition. We have developed a projection imaging system which uses five monoenergetic pencil beams in combination with continuous phantom motion to achieve acquisition times that are practical for medical and security applications. The system was configured at the Canadian Light Source synchrotron and consists of a primary collimator, motorized stages for phantom translation, a flat-panel x-ray detector for measuring scattered x rays, and photodiodes for simultaneously measuring transmitted x rays. Image generation requires several corrections to raw data artifacts arising from the nature of the detector, x-ray source, and acquisition procedure. We developed a novel correction for pixel location inaccuracy arising from continuous phantom motion. A five-beam system had nearly five times faster acquisition than a single-beam system. Continuous motion acquisition was approximately 30 times faster than step-and-shoot acquisition. The total acquisition time for a 9 cm × 5 cm phantom with 8425 pixels was just over 2 min. Image quality was also assessed, in part to determine its relation to acquisition speed. The width of sharp material boundaries was found to be at a minimum equal to the pencil beam width (1.75 mm) and to have an additional width equal to the product of the phantom translation speed and the acquisition time per pixel (up to 1.0 mm in our experiments). Contrast-detail performance was independent of acquisition speed, depending only on phantom entrance x-ray fluence. Pixel signal-to-noise ratio measurements indicate that detector readout noise is important for the scatter data, even for phantom air kerma as high as 30 mGy. Images could be improved with a detector having lower readout noise and higher sensitivity. Its spatial resolution could be moderate. We confirmed that for the same range of λ-1 sin(θ/2), where λ is the x-ray wavelength and θ is the scattering angle, scatter images acquired using different beam energies (33-70 keV) had nearly identical contrast.