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| MO3002 | Overview of TEM-Class Superconducting Cavities for Proton and Ion Acceleration | linac, proton, ion, cryogenics | 23 | ||
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Superconducting (SC) TEM-class cavities have been developed at laboratories and institututions worldwide for cw and pulsed proton and ion linac applications. New geometries spanning nearly the full velocity range from 0.1 < v/c < 0.8 include co-axial quarter- and half-wave and single- and multi-spoke cavities. Optimized designs have large beam acceptance, high shunt impedance and good microphonics properties. Rapidly evolving and improving clean surface processing techniques have been applied to TEM cavities where achieved surface fields and rf losses are comparable to the best results presently achieved in elliptical cavity designs. Recent results for a three-spoke cavity following hydrogen degassing after fabrication show very low rf losses even at high accelerating fields and now open the possibility for substantially reduced effective cryogenic load in 2 Kelvin, rather than the historically-used 4 Kelvin, operation. At present performance levels, SC TEM-class cavities constitute the technology of choice for most ion linac applications requiring cavities up to or beyond 60 percent of the speed-of-light.
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| MOP010 | Massively Parallel Wake Field Computations in Long Accelerator Structures | simulation, shielding, diagnostics, electron | 52 | ||
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The X-FEL project and the ILC require a high quality beam with ultra short bunches. The knowledge of the short-range wakefields in the TESLA cavities and the collimators is needed to predict the beam quality in terms of the single bunch energy spread and emittance. Especially for the high energy collimators these calculations are limited by numerical dispersion. Earlier we presented wake field calculations for short bunches in long structures for rotationally symmetric components with the code ECHO. Now we present first results from our new wake field code in fully 3D. To calculate the effect of the longitudinal and transverse wakefields we have used the time domain numerical approach. For sufficient resolution of the geometric boundaries and the short bunches (down to the nm-range), huge computational resources are needed. Thus in 3D massive parallelisation of the code is necessary. In addition we used the technique of a moving grid, which gives access also to very long structures, i.e. a complete module of eight TESLA cells or a high energy collimator.
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| MOP021 | Recent Operation of the ORELA Electron LINAC at ORNL for Neutron Cross-Section Research | gun, electron, klystron, target | 79 | ||
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The ORNL electron LINAC, ORELA, began operation in 1969 and has been instrumental in providing improved neutron cross section data for many isotopes over the 0.002-60 MeV energy range. The ORELA utilizes a 4-30 ns <1000 Hz pulsed gridded electron gun, a 4 section RF Linac, and a water-cooled and moderated tantalum target to generate short neutron pulses. The short pulse lengths and long flight path provide high neutron energy resolution. Beam energy can range up to 180 MeV and a neutron production rate of up to 1014 n/sec can be generated with 50 kW of beam power. Recent operation is a 8 ns, 525 Hz pulse and a target power of 5-10 kW. RF power for the accelerator sections are provided by four 24 MW 1300 MHz klystrons. Recent activities have included improvements to the accelerator vacuum, klystrons, interlocks and other upgrades. The current ORELA program is focused on cross-section measurements for the Nuclear Criticality Safety Program and for nuclear astrophysics. Detection and data analysis capabilities have been developed for making highly accurate measurements of neutron capture, neutron total, (n,alpha), and (n,fission) cross sections simultaneously on different beam lines.
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| MOP035 | Operational Aspects of High-Power Energy-Recovery Linacs | wiggler, linac, quadrupole, lattice | 115 | ||
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We have been operating a high power energy recovery linac (ERL) at Jefferson Lab for several years. In the process we have learned quite a bit about both technical and physics limitations in high power ERLs. Several groups are now considering new ERLs that greatly increase either the energy, the current or both. We will present some of our findings on what to consider when designing, building, and operating a high power ERL. These include space charge effects, halo, magnetic field quality, RF stability, short bunch formation, coherent synchrotron radiation and it effect on the beam, beam breakup instabilities, higher order mode production, and diagnostic requirements.
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| MOP037 | Applications of Time-of-Flight Measurements at FLASH | electron, linac, laser, undulator | 121 | ||
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As a prototype of the XFEL, VUV-FEL has been build and commissioned at DESY by an international collaboration. It is a linear electron accelerator with an undulator arrangement to produce laser pulses by the 'Self-Amplified Spontaneous Emission' (SASE) process. To generate the laser pulses, electron bunches are compressed in longitudinal direction to reach the necessary peak current of about 2.5 kA. To control the compression process a number of 'Phase Monitors' are installed at the accelerator. They measure the time of the bunch passages. Differences of the bunch passage times at different linac locations yield the 'Time-Of-Flight' (TOF) between these locations. The system is installed with regard to the planned installation of a further RF module operating at the third harmonic RF frequency. This 'third harmonic cavity' is required to optimize the longitudinal bunch charge distribution. Its effect is examined by the TOF measurements. The paper presents the Phase Monitor system to measure the TOF at VUV-FEL. The principle is shown, the determination of 'on-crest'-phases is demonstrated and first measurements of the momentum compaction coefficients, R56 and T566, are discussed.
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| MOP047 | An RFQ-Decelerator for HITRAP | rfq, emittance, ion, linac | 151 | ||
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The HITRAP linac at GSI will decelerate ions from 5 MeV/u to 6 keV/u for experiments with the large GSI Penning trap. The ions are decelerated at first in the existing experimental storage ring (ESR) down to an energy of 5 MeV/u and will be injected into a new Decelerator-Linac consisting of a IH-structure, which decelerates down to 500keV/u, and a 4-Rod RFQ , decelerating to 5 keV/u. The properties of the RFQ decelerator and the status of the project will be discussed.
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| MOP053 | Construction of a High-Current RFQ for ADS Study | rfq, dipole, quadrupole, coupling | 165 | ||
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A high current RFQ accelerator has been constructed in China for the basic study of Accelerator Driven Subcritical System. The ADS project is supported by a national program and aimed at the development of clean nuclear energy to meet of the rapid growth of the nuclear power plants in China. The 3.5MeV RFQ accelerator has been fabricated and installed. Field tuning and high power conditioning indicate a good agreement with our design. The beam commissioning with an ECR ion source is under development. This paper will present the recent progress in the construction and commissioning of the RFQ accelerator.
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| TU3002 | Industrial Aspects of Linac Components | linac, gun, radio-frequency, electron | 237 | ||
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The industrial aspects of producing linac components from the particle sources, the accelerator structures, the magnet systems and RF systems will be discussed. The various aspects of working with national labs and universities will be covered. Such issues as to what type of Contract Form should be used; Organizational Conflict of Interest and Intellectual Property will be covered as well as how best to work with the labs and universities on SBIRs, CRADAs and Work for Others contract. Specific examples will be addressed including the unique issues for the ILC.
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| TUP010 | The Beam Halo Monitor of SARAF | proton, target, background, scattering | 265 | ||
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A main requirement for the SARAF accelerator is ‘hands-on’ maintenance, which implies a maximum beam loss of 1 nA per meter. In Phase I of SARAF (4-5 MeV ions at full current), we need to map the beam halo (BH) down to below 1 nA in order to predict, using beam dynamics calculations, the beam loss in the full accelerator. Mapping the halo of a 4 MeV, 2 mA ion beam down to below 1 nA is unprecedented, so we developed a BH monitor, which incorporates a direct charge measurement and several nuclear techniques, including Rutherford scattering 197Au(p,p)197Au, 7Li(p,n)7Be leading to both neutrons and the radio-isotope 7Be (measured offline post irradiation) and 19F(p,alpha)16O leading to high energy gamma rays. The current is derived using published cross sections. In this paper, we present the SARAF Phase I BH monitor and describe the various measurement techniques. In addition, results of feasibility studies at the Pelletron accelerator of the Weizmann Institute are given. The results of the various current measurement techniques are consistent with the standard Pelletron Faraday Cup to better than 20%. This is sufficient for mapping the SARAF beam halo to the desired accuracy.
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| TUP011 | Upgrade of Beam Diagnostics in LEBT and MEBT of J-PARC LINAC | monitoring, linac, diagnostics, rfq | 268 | ||
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After tests in Tsukuba-site, Front end part (from an ion source upto the first drift tube linac) of J-PARC LINAC was transported to Tokai-site. From the coming December, testing with H- beam is planned. After the tests in Tsukuba, a few beam current monitors are added in the low and the medium energy transport line, and those monitors are used for the machine- and the person-protection system. In this paper, design and roles of each monitor are described.
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| TUP025 | Optimization of Surface Treatment of High-Gradient Single-Cell Superconducting Cavities at KEK | superconductivity, pick-up, cryogenics, electron | 299 | ||
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We have continued the study of a series of single cell superconducting cavities at KEK. These tests are aimed at establishing a prescription for a surface treatment that would reliably allow cavities to reach gradients in excess of 45 MV/m in vertical tests. The cavity profiles were all of the KEK Low Loss design, and were fabricated from deep drawn Niobium half shells using electron beam welding. The cavity initial surface preparation followed an established KEK procedure of centrifugal barrel polishing, high temperature annealing, light chemical polishing, electropolishing. and final a high pressure water rinse. Early results from this series test demonstrated that reaching gradients as high as 50 MV/m is feasible. However, the initial yield was of order 50%. In this paper we will discuss our studies of further improvement of the surface treatment aimed at increasing the yield.
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| TUP026 | Status of the XFEL Testcavity Program | electron, gun, superconducting-RF, superconductivity | 302 | ||
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In preparation of the European XFEL-project a testcavity program of about 25 1.3GHz niobium single-cell cavities was launched at DESY beginning of 2005 in parallel to the accelerator nine-cell structure activities. After successful start-up of the DESY in-house fabrication main topics of the program are the optimisation of cavity electron beam welding preparation, the performance of large grain niobium and the qualification of further niobium vendors for cavity production. So far reproducibly all cavities (TESLA cell shape) exceed gradients of 30 MV/m at high Q-values. An electropolished mono-cell fabricated of large grain material reached 41 MV/m at Qo = 1.4·1010. The present status and results of the program are presented.
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| TUP029 | Performance and Early Operating Experience with the ISAC-II Cryogenic System | linac, cryogenics, ion, controls | 306 | ||
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A 500 W class refrigerator has been installed and commissioned at TRIUMF to cool the new 20MV superconducting linac. The refrigerator liquifies helium into a common supply dewar. The dewar feeds a common cold manifold and the five cryomodules are fed via parallel cold distribution circuits. The system operates at 4.5K. Measurements have been done to estimate the static loads of the cryomodules and the distribution system and to characterize plant performance. The paper will include a system description, performance results and early operating experience.
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| TUP033 | Performances of High-Purity Niobium Cavities with Different Grain Sizes | pick-up, superconductivity, linear-collider, collider | 318 | ||
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Grain boundaries have for some time been suspected of influencing the performance of rf cavities made from high purity niobium by limiting the temperature dependent BCS surface resistance to a residual resistance because of impurity segregation and by causing field limitations due to flux penetration. We have carried out a comparative study of the rf behavior of 2.2 GHz TM010 cavities of identical shape, fabricated from single crystal niobium, niobium of grain sizes of the order of several cm2 and standard poly-crystalline material. This contribution reports about the results of the measurements of the temperature dependence of the surface resistance Rs(T) and the Q0 vs Eacc behavior at 2 K. From the analysis of the Rs(T) data at low rf fields material parameters such as gap value, mean free path and residual resistance could be extracted. The dependence of the Q-value on rf field was analyzed with respect to the medium field Q-slope, “Q-drop” at high fields and the “quench” fields. The best performance resulted in a breakdown field of ~ 165 mT, corresponding to an accelerating gradient of Eacc ~ 45 MV/m.
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| TUP034 | Development of a Superconducting RF Module for Acceleration of Protons and Deuterons at Very Low Energy | proton, alignment, linac, acceleration | 321 | ||
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A prototype superconducting accelerating module housing six 176 MHz half wave resonators and three superconducting solenoids is currently under production at Accel as part of a 40 MeV linear accelerator at the Soreq NRC. The module will accelerate protons and deuterons from energy of 1.5 MeV/u up to 6.5 MeV. The design is based on a peak electric field gradient of 25 MV/m and maximum 10 W of power dissipation in the helium bath by each cavity. Main design considerations of the cavities, solenoids, tuners and couplers as well as for the module especially in view of assembly and alignment will be presented. First cold cavity test results obtained in Accel’s new cold RF test facility will be presented. Prototypes of the tuner, helium vessel, solenoids and the couplers are under construction and partly under test.
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| TUP035 | Investigation of Hot Spots as a Function of Material Removal in a Large-grain Niobium Cavity | electron, pick-up | 324 | ||
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The performance of a single-cell cavity made of RRR > 200 large-grain niobium has been investigated as a function of material removal by buffered chemical polishing (BCP). Temperature maps of the cavity surface at 1.7 and 2 K were taken for each step of chemical etching and revealed several “hot-spots”, which contribute to the degradation of the cavity quality factor as a function of the radio-frequency (RF) surface field. It was found that number of “hot-spots” decreased for larger material removal. Interestingly, the losses of the “hot-spots” at different locations evolved differently for successive material removal. The cavity achieved peak surface magnetic fields of about of 130 mT and was limited mostly by thermal quench. By measuring the temperature dependence of the surface resistance at low field between 4.2 K and 1.7 K, the variation of material parameters such as the ratio between the energy gap and the critical temperature, the residual resistance and the mean free path as a function of material removal could also be investigated. This contribution shows the results of the RF tests along with the temperature maps and the analysis of the losses caused by the “hot-spots”.
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| TUP040 | Progress on a Cryogenically Cooled RF Gun Polarized Electron Source | gun, cathode, electron, ion | 339 | ||
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RF guns have proven useful in multiple accelerator applications. An RF gun capable of producing polarized electrons is an attractive electron source for the ILC or an electron-ion collider. Producing such a gun has proven elusive. The NEA GaAs photocathode needed for polarized electron production is damaged by the vacuum environment in an RF gun. Electron and ion backbombardment can also damage the cathode. These problems must be mitigated before producing an RF gun polarized electron source. In this paper we report continuing efforts to improve the vacuum environment in a normal conducting RF gun by cooling it with liquid Nitrogen after a high temperature vacuum bakeout. We also report on a design of a cathode preparation chamber to produce bulk GaAs photocathodes for testing in such a gun. Future directions are also discussed.
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| TUP049 | Metal-Based Photocathodes For High-Brightness RF Photoinjectors | laser, cathode, gun, target | 358 | ||
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Advanced high brightness RF gun injectors require photocathodes with fast response, high quantum efficiency and good surface uniformity. Metal films deposited by various techniques on the gun back wall could satisfy these requirements. Two new deposition techniques have been recently proposed, i.e. pulsed laser ablation and vacuum arc. Several samples of various materials have been deposited by the two techniques: The emission performance and morphological changes induced on the cathode surface by laser beam are compared and discussed.
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| TUP057 | A Compact, Normal-conducting, Polarized Electron, L-band PWT Photoinjector for the ILC | emittance, electron, cathode, gun | 376 | ||
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The International Linear Collider (ILC) needs a polarized electron beam with a low transverse emittance. High spin-polarization (>85%) is attainable with a GaAs photocathode illuminated by a circularly polarized laser. Low emittance is achievable with an rf photoinjector. DULY Research has been developing an rf photoinjector called the Plane Wave Transformer (PWT) which may be suitable as a polarized electron source for the ILC. A 1+2(1/2) cell, L-band PWT photoinjector with a coaxial rf coupler is proposed for testing the survivability of GaAs cathode. It is planned to produce a high-aspect-ratio beam using a round-to-flat-beam transformation. In addition to its large vacuum conductance, the modified PWT has a perforated stainless steel sieve as a cavity wall, making it easy to pump the structure to better than 10-11 Torr at the photocathode. An L-band PWT gun can achieve a low emittance (0.45 mm-mrad for a 0.8nC round beam) with a low operating peak field (<25MV/m). A low peak field is beneficial for the survivability of the GaAs photocathode because electron backstreaming is greatly mitigated.
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| TUP058 | The RF Design of a HOM Polarized RF Gun for the ILC | gun, cathode, emittance, electron | 379 | ||
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The ILC requires a polarized electron beam. While a highly polarized beam can be produced by a GaAs-type cathode in a DC gun of the type currently in use at SLAC, JLAB and elsewhere, the ILC injector system can be simplified and made more efficient if a GaAs-type cathode can be combined with a low emittance RF gun. Since this type of cathode is known to be extremely sensitive to contamination including back bombardment by ions, any successful polarized RF gun must have a significantly improved operating vacuum compared to existing RF guns. We present a new RF design for an L-Band NC RF gun for the ILC polarized electron source. This design incorporates a higher order mode (HOM) structure, whose chief virtue in this application is an improved conductance for vacuum pumping on the cathode. Both 2-D and 3-D models have been used to optimize the RF parameters with two principal goals: first to minimize the required RF power; second to reduce the peak surface field relative to the field at the cathode in order to suppress field emitted electron bombardment. The beam properties have been simulated initially using PARMELA. Vacuum and cooling considerations for this design are discussed.
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| TUP061 | The HERA RF-Driven Multicusp H- Ion Source | plasma, electron, coupling, SNS | 388 | ||
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The HERA RF-Volume Source is the only source that delivered routinely a H- current of 40 mA without Cs. This current has been improved to 60 mA. For HERA a pulse length of less than 200 μsec is necessary. It was possible to demonstrate a pulse length of 3 msec with the HERA source at DESY in a cooperation with SNS, FNAL and CERN. RF H- sources are now in permanent use for accelerators like HERA or SNS. The reliability of these sources becomes very important. Special techniques for a reliable external RF coupling to the plasma, ignition, filter field, collar transition for extraction and electron dumping have been developed at DESY. The physics of the extraction plasma region was the subject of very detailed investigations with special sets of collars, cones and Langmuir probes.
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| TUP069 | Design of 132MeV DTL for CSNS | SNS, focusing, simulation, linac | 412 | ||
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A description is given to the drift-tube-linac (DTL) of the Beijing Spallation Neutron Source (BSNS). The DTL accelerate a 3MeV, 30mA H- beam from the RFQ to the LRBT. Tank body and drift tube configuration design using the SUPERFISH code has enabled efficient optimization of the effective shunt impedance and avoided high surface field. Accelerating cells design and particle tracking were made by using PARMILA code. Special emphasis is given to the transverse focusing system design, which was compared with two usual schemes, constant phase focusing and equipartitioning focusing. Details of beam dynamics analysis will be presented in this paper.
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| TUP083 | Development of High-Power RF Vector Modulator Employing TEM Ferrite Phase Shifters | controls, SNS, impedance, linac | 451 | ||
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Construction and installation of cavity RF power distribution system in a high power superconducting RF accelerator can have cost savings if a fan-out configuration that feeds many cavities with a single high power klystron is realized. The configuration however requires independent control of RF amplitudes and phases to the cavities to perform properly. A prototype high power RF vector modulator for the control is built and tested. The vector modulator employs a quadrature hybrid and two fast ferrite phase shifters in square coaxial TEM transmission lines. The square coaxial format can provide the power handling capability and thermal stability. RF properties of the design and result of high power system testing of the design are presented.
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| WE2001 | Neutralized Drift Compression Experiments (NDCX) | plasma, ion, simulation, acceleration | 492 | ||
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Intense ion beams offer an attractive approach to heating dense matter uniformly to extreme conditions, because their energy deposition is nearly classical and volumetric. Simultaneous transverse and longitudinal beam compression, in a neutralizing plasma medium, along with rapid beam acceleration, are being studied as a means of generating such beams, which will be used for warm dense matter (WDM), high energy density physics (HEDP), and fusion studies. Recently completed experiments on radial and longitudinal compression demonstrated significant enhancements in beam intensity. In parallel with beam compression studies, a new accelerator concept, the Pulse Line Ion Accelerator (PLIA), potentially offers cost-effective high-gradient ion beam acceleration at high line charge density. We report experimental results on beam neutralization, neutralized focusing, neutralized drift compression from a series of experiments. We also report energy gain and beam bunching in the first beam dynamics validation experiments exploring the PLIA.
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| TH2001 | High-Power Couplers for Linear Accelerators | linac, emittance, impedance, simulation | 531 | ||
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High power input couplers are a fundamental component of the linear accelerating structures and in particular of the superconducting structures. In fact, in this case, the power couplers function is not only the power transfer and the vacuum separation but includes also the thermal transition and the integrity of the cavity cleanliness. A lot of activity has been recently worked out in the framework of different project on both CW (KEK and Cornell) and pulsed (SNS and TTF) power couplers. Particular attention has been devoted to the design phase to take care about the thermo mechanical and electromagnetic performances, the multipacting thresholds, the preparation procedures and, last but not least, the cost that in the case of high energy linacs is a fundamental parameter. In this framework not only the design phase but also the conditioning of the couplers has stimulated different studies. Partial reviews of the existing designs and of the couplers characteristics will be presented taking into account the different challenges.
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| THP021 | Study of Vacuum Insulator Flashover for Pulse Lengths of Multi-Microseconds | plasma, cathode, electron, diagnostics | 610 | ||
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We have studied the flashover of vacuum insulators for applications where high voltage conditioning of the insulator and electrodes is not practical and for pulse lengths on the order of several microseconds. The study was centered about experiments performed with a 100-kV, 10-μs pulsed power system and supported by a combination of theoretical and computational modeling. The base line geometry for the experiments was a cylindrically symmetric, +45° insulator between flat electrodes. In the experiments, flashovers or breakdowns were localized by operating at field stresses slightly below the level needed for explosive emissions with the base line geometry. The electrodes and/or insulator were then seeded with an emission source, e.g. a tuff of velvet, or a known mechanical defect. Our study differs from most vacuum insulator studies in that our emphasis was on flashovers originating at the anode triple junction as well as bulk breakdowns within the insulator. Various standard techniques were employed to suppress cathode-originating flashovers/breakdowns. We present the results of our experiments and discuss the capabilities of modeling insulator flashover.
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| THP026 | HIGH POWER TEST OF COUPLER WITH CAPACITIVE WINDOW | coupling, linac, linear-collider, collider | 625 | ||
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New type of coupler with capacitive-coupling inner conductor is designed in KEK. This coupler has a module structure, which is convenient for mass-production, assembling and repairing. Four samples of couplers were made and two of them were tested at high power level. The main parameters of the couplers and test results are presented in this paper.
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| THP029 | Development of an RFQ Input Power Coupling System | rfq, coupling, SNS, simulation | 634 | ||
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An RF input coupler system is designed, manufactured, and tested for future upgrade of the coupling system of the RFQ in the SNS linac. The design employs two coaxial loops in vacuum side of two coaxial ceramic windows through coaxial transmission lines that are connected to a magic-T waveguide power splitter for 402.5 MHz operation. The couplers will be used with up to total 800 kW peak power at 8% duty cycle. RF properties of the system and fabricated structure along with vacuum and thermal properties are discussed. Two couplers are joined together through an evacuated bridge waveguide for high power RF processing. Result of the high power conditioning that is performed in the RF test facility of the SNS is presented.
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| THP030 | Investigation of Ferroelectrics for High-Power RF Phase Shifters in Accelerator Systems | impedance, simulation, SNS, klystron | 637 | ||
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High power vector modulators enable independent control of RF power to each accelerating cavity, allowing a fan-out configuration to be used to power many cavities from a single high-power klystron. Previously, ferrite materials have been used in high-power phase shifters and vector modulators. It is shown that ferroelectric materials such as barium-strontium titanate (BST) can also be used in such tunable structures. Since ferroelectrics are controlled by an electric, rather than magnetic field, tuning can be faster than tuning a ferrite-loaded device. A BST-loaded coaxial structure is investigated theoretically and experimentally. Good high voltage performance is critical since DC biasing voltages of up to 80 kV can be impressed on the BST sections for tuning. It can also be seen that matching structures around the BST can improve performance over a wider range of amplitudes and phases.
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| THP038 | Normal Conducting High-Gradient Studies at KEK | linear-collider, collider, acceleration, extraction | 661 | ||
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Normal-conducting high field studies have been pursued at XTF, a high power X-band RF facility of KEK developed for linear collider. Three traveling-wave structures developed for X-band linear collider were studied in high field of more than 70MV/m level. High-field characteristic such as field emission properties and trip rate, etc. are studied carefully as the processing proceeds. Operation at 50MV/m level was found very stable while breakdowns happened once an hour or so at more than 70MV/m, indicating the approach to some critical point. This characteristics is discussed in conjunction with various author’s trials to make a scaling law of severe breakdowns among power, pulse width and so on. Further basic studies on field/power limitation or robustness against breakdowns in various materials are planned using narrowed waveguide configuration. Unique features related to this study is also described.
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| THP043 | The RF System of the Sparc Photo-Injector @ LNF | klystron, gun, linac, controls | 676 | ||
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The S-band linear accelerator SPARC is in advanced phase of installation and test at the INFN Frascati Laboratories. The purpose of the machine is to produce low emittance, high peak current electron beams to drive a SASE-FEL experiment. The SPARC RF system consists of an RF gun followed by 3 S-band room-temperature accelerating structures, supplied by 2 pulsed high power klystrons. The use of waveguide power attenuators and phase-shifters is foreseen to adjust independently the accelerating structures field amplitude and phase; this will be helpful for tuning the linac working point in the initial machine set-up. This paper reviews the experience in installation, RF conditioning, and commissioning of the normal conducting linac accelerating structures and RF subsystems.
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| THP047 | Prototyping of a Single-Cell Half-Reentrant Superconducting Cavity | simulation, superconductivity, resonance, coupling | 685 | ||
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As superconducting niobium cavities achieve higher gradients, it is anticipated they will reach a performance limit as the peak surface magnetic field approaches the critical magnetic field. "Low loss" and "reentrant" cavity designs are being studied at CEBAF, Cornell, DESY, and KEK, with the goal of reaching higher gradients via lower surface magnetic field, at the expense of higher surface electric field. At present, cavities must undergo chemical etching and high-pressure water rinsing to achieve good performance. It is not clear whether this can be done effectively and reliably for multi-cell low loss or reentrant cavities using traditional techniques. A "half-reentrant" cavity shape has been developed with RF parameters similar to the low loss and reentrant cavities, but with the advantage that the surface preparation can be done easily with existing methods. Two prototype single-cell half-reentrant cavities are being fabricated at 1.3 GHz; the non-reentrant wall angle is 8 degrees, the beam tube radius is 29 mm, and the cell-to-cell coupling is 1.47%. The half-reentrant cavity design and the results and status of the prototyping effort will be presented.
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| THP051 | Status of 3.9-GHz Superconducting RF Cavity Technology at Fermilab | superconducting-RF, controls, linac, higher-order-mode | 695 | ||
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Fermilab is involved in an effort to design, build, test and deliver 3.9 GHz superconducting RF cavities with a goal to deliver one 'third harmonic' cryomodule containing four cavities in early 2007 for use at the DESY TTF III Project. The design gradient of these cavities is 19 MV/m. This effort involves design, fabrication, intermediate testing, assembly, and eventual delivery of the four cavity cryomodule. We report on all facets of this enterprise from design through future plans. Included will be early test results of single 9-cell cavities, lessons learned, and other findings.
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| THP052 | Tests Results of Beta 0.12 Quarter-Wave Resonator for the SPIRAL2 Superconducting Linac | linac, cryogenics, controls, heavy-ion | 698 | ||
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New developments and tests have been carried out, at IPN-Orsay, on high β = 0.12, 88 MHz superconducting Quarter Wave Resonators. These resonators will be installed in the high beta section of the LINAC driver. RF tests results of the prototype cavity are reported. The fabrication of 2 pre-series cavities and their cryomodule is in progress in order to be ready for high power RF tests at 4.2 K at the beginning of 2007.
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| THP054 | Spoke Cavity Developments for the EURISOL Driver | proton, cryogenics, linac, diagnostics | 704 | ||
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EURISOL is the next generation of Radioactive Ion Beam (RIB) facility which aims at the provision of high intensity beams of radioactive nuclei with variable energy, from a few keV to greater than 100 MeV per nucleon, at an intensity several orders of magnitude higher than those currently available. The driver of EURISOL has to accelerate protons at a final energy of 1 GeV and 5 mA current, but also deuterons at 200 MeV (total energy). For the intermediate energy part of the driver, a solution based on superconducting (SC) spoke cavities is under study at the IPN Orsay laboratory. In this paper are presented the results of beam dynamics simulations for the linac, experimental results on the β = 0.15 spoke cavity, as well as achievements on the power coupler and cold tuning system. A new horizontal cryostat for performing a test of a fully equipped spoke cavity is detailed and an optimized design for a new β ~0.35 spoke prototype is also presented.
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| THP056 | Design of 325-MHz Single and Triple Spoke Resonators at FNAL | linac, proton, pulsed-power, target | 707 | ||
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We present the design of two 325 MHz superconducting single spoke resonators at β=0.22 and β=0.4 and a 325 MHz superconducting triple spoke resonator at β=0.62 for the front end of a 2 MW proton linac. We describe the optimization of the spoke resonator electromagnetic performance and how the resonator structural integrity and shape is ensured. We describe the mechanical design of the slow tuner mechanism and, via a coupled ANSYS-MWS analysis, how the mechanism adjusts the resonator operating frequency. The RF design of the power coupler is also presented
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| THP057 | Design of Normal Conducting 325-MHz Crossbar H-Type Resonators at Femirlab | linac, lattice, focusing, impedance | 710 | ||
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The warm section of the proposed High Intensity Neutrino Source at Fermilab is designed to accelerate H- ions and protons from 2.5 MeV to 10 MeV (β=0.0744 to β=0.1422). After the ion source, the beam will travel through a radio frequency quadrupole, a medium energy beam transport (two buncher cavities and a chopper) and finally 16 normal-conducting resonators, all separated by superconducting solenoids in individual cryostats. Over 10 MeV the design uses superconducting resonators and solenoids in common cryomodules. In this paper the electromagnetic design and optimization of all the 325 MHz Crossbar H-type normal-conducting resonators is presented. The mechanical design, performance and fabrication of the first prototype (β=0.0744) is presented in detail. The design of the prototype for the input coupler that will be used in the resonators is included.
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| THP059 | Coaxial HOM Coupler Designs Tested on a Single-Cell Niobium Cavity | coupling, pick-up, simulation, damping | 716 | ||
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Coaxial higher order mode (HOM) couplers have been developed for HERA cavities and are used in TESLA, SNS and Jlab upgrade cavities. The principle of operation is the rejection of the fundamental mode by the tunable filter of the coupler and the transmission of the HOMs. It has been recognized recently that inappropriate thermal designs of the feed through for the pick-up probe of the HOM coupler will not sufficiently carry away the heat generated in the probe tip by the fundamental mode fields, causing a built-up of the heating of the niobium probe tip and subsequently, a deterioration of the cavity quality factor has been observed in cw operation. An improvement of the situation has been realized by a better thermal design of the feed through incorporating a sapphire rf window [1]. An alternative is a modification of the coupler loop (“F” – part) with an extension towards the pick-up probe. This design has been tested on a single cell niobium cavity in comparison to a “standard TESLA” configuration. by measuring the Eacc behavior at 2 K. The measurements clearly indicate that the modified version of the coupler loop is thermally much more stable than the standard version.
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[1] C. Reece et al; http://accelconf.web.cern.ch/accelconf/, paper TPPT082 |
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| THP060 | Capture Cavity II at Fermilab | klystron, resonance, instrumentation, cryogenics | 719 | ||
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Capture Cavity II is a 9-cell high gradient TESLA Superconducting cavity intended to upgrade the existing Fermilab Photoinjector electron beam energy from 15MeV to 40Mev. DESY provided the cavity which performed to 33MV/m. Beam tube component preparation and installation onto the cavity was completed at DESY. The cavity was shipped to FNAL under vacuum. Installation and testing of this cavity has provided an opportunity to demonstrate Fermilab’s SCRF High Power Testing infrastructure. We report on the high power RF tests performed with Capture Cavity II at both 4.5K and 1.8K, Cryogenic System Performance, Piezo Electric based fast tuner, and low level RF control.
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| THP063 | First High-Power ACS Module for J-PARC Linac | linac, pick-up, ion, resonance | 725 | ||
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J-PARC Linac will be commissioned with energy of 181-MeV using 50-keV ion source, 3-MeV RFQ, 50-MeV DTL and 181-MeV SDTL (Separated DTL) on December 2006. It is planed to be upgraded by using 400-MeV ACS (Annular Coupled Structure), in a few years from the commissioning. The first high-power ACS module, which will be used as the first buncher between the SDTL and the ACS has been fabricated, and a few accelerating modules are also under fabrication until FY2006. Detail of cavity design and tuning procedure has been studied with RF simulation analysis and cold-model measurements. This paper describes RF measurement results, fabrication status, and related development items.
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| THP064 | Tuning a CW 4-Rod RFQ | rfq, resonance, acceleration, pick-up | 728 | ||
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A 4-Rod RFQ has been built, which operates cw and will accelerate 5mA D beams up to 3 MeV. The length of the structure is 3.8 m, the power consumption as high as 250 kW. The tuning of a 4-Rod RFQ with 30 rf-cells at the frequency of 175 MHz is difficult, so procedures have been developed, to facilitate this work. The properties of the RFQ accelerator, the tuning procedure and the status of the project will be discussed.
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| THP067 | Status of the Tuner for the 19-Cell Superconducting CH Prototype Cavity | simulation, cryogenics, radio-frequency, linac | 737 | ||
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The radio frequency tuning of the multi-cell superconducting CH structure for beta equal to 0.1 is investigated for a 19-cell niobium cavity operated at liquid helium temperature. By applying external mechanical forces the deformation of the structure is studied and the resulting change in frequency is analysed. The ruling equations of elasticity and the electromagnetic eigenvalue problem are solved by using commercial finite element tools. The quantitative results form the basis of an optimized tuning device. In order to guarantee a long lifetime of the cavity, fracture criteria are defined to avoid mechanical damage. Wherever possible the results are compared with experimental data obtained from measurements performed on the first CH prototype developed at the Institute of Applied Physics at Frankfurt. In addition a fast piezo device will be integrated into the slowly acting mechanical tuner. The whole system will operate in an existing horizontal cryostat for testing purposes.
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| THP072 | Fabrication and Low-Power Measurements of the J-PARC 50-mA RFQ Prototype | rfq, laser, linac, pick-up | 749 | ||
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In the Japan Proton Accelerator Research Complex (J-PARC) project, the beam commissioning of the H- linac will be started with a 30mA peak current. A 30mA type RFQ, which is developed for the former Japan Hadorn Facility (JHF) project, is used for the day-1 operation. However, it is required to accomplish the peak current of 50mA as soon as possible. For this purpose, we have developed an RFQ for the 50mA peak current, which is a four vane type RFQ and resonant frequency of which is 324MHz, same as the 30mA RFQ. In the R&D of this RFQ, we have adopted laser welding to join oxygen free copper blocks to be a cavity structure. The heat load of the laser welding can be more localized than that of the brazing, and the copper is not annealed, therefore, we think, it is possible to obtain more mechanical accuracy. We have developed a longitudinally 1/3 prototype cavity of the J-PARC 50mA RFQ. In this cavity, the distortion of the vane tips is measured to be less than 30 micro-meters, and the field uniformity of within 1% is obtained in a low power measurement after tuning. In this paper, we discuss about the fabrication and the low power measurement of this prototype cavity.
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| THP073 | High-Current Elliptical Cavity Design and Prototyping | pick-up, simulation, linac, injection | 752 | ||
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Beam instabilities due to undamped higher-order modes (HOMs) in the cavities can limit the performance of high-current superconducting accelerators, such as energy recovery linacs. If the accelerator is designed such that the bunch frequency is equal to the accelerating mode frequency and the beam pipe radius is chosen such that the cutoff frequency is less than twice that of the accelerating mode, all of the monopole and dipole HOMs that can be driven by the beam can be well-damped. A 6-cell elliptical cavity for speed-of-light particles and a 2-cell elliptical injection cavity have been designed for high-current accelerator applications. Both cavities have an aperture 29% larger than the TeSLA cavity, at the expense of peak surface fields about 10% higher for the same gradient. The injection cavity has a geometric β of 0.81 and was designed to accelerate electrons from 50 keV to 1 MeV, and the 6-cell cavity has a geometric β of 1 for further acceleration. Both cavities are designed for the purpose of accelerating hundreds of milliamps without HOM-induced beam breakup and to operate at 2.45 GHz. The cavity designs and prototype injection cavity results will be presented.
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| THP075 | RF Performance of a Superconducting S-Band Cavity Filled with Liquid Helium | pick-up, superconductivity, radiation, controls | 755 | ||
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Copper RF cavities filled with hydrogen gas at high pressure have been studied recently by Muons, Inc. and IIT for simultaneous acceleration and ionisation cooling of a muon beam. A further step in this direction would be a superconducting RF cavity filled with liquid helium. One might imagine that this would make the cavity less vulnerable to thermal breakdown, field emission, and multipacting. A disadvantage is that magnetostatic focussing of the beam could not be done simultaneously. Preliminary RF testing has been done on a 2.45 GHz single-cell elliptical cavity filled with liquid helium. Low-field results indicate little or no increase in the power dissipation, consistent with predictions and measurements in the literature. The frequency shift with pressure for a cavity filled with saturated liquid is about 100 times greater than for a cavity under vacuum, consistent with published values of liquid helium permittivity as a function of temperature. Investigation of the high-field performance of a liquid-filled cavity is in progress.
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| THP076 | Prototyping of a Superconducting Elliptical Cavity for a Proton Linac | proton, linac, SNS, radiation | 758 | ||
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A superconducting cavity has been designed for acceleration of particles travelling at 81% the speed of light (β = 0.81). Possible applications include the proposed Fermilab Proton Driver Linac. The cell shape is similar to the β = 0.81 cavity for the Spallation Neutron Source Linac, but the resonant frequency is 1.3 GHz rather than 805 MHz and the beam tube diameter matches that of the 1.3 GHz cavity for the TeSLA Test Facility. Six single-cell prototypes are being fabricated and tested. Three of these cavities are being formed from standard high purity fine grain niobium sheet. The rest are being fabricated from large grain niobium, following up on the work at Jefferson Lab to investigate the potential of large grain material for cost savings and/or improved RF performance. The fabrication of two 7-cell cavity prototypes (one fine grain, one large grain) is planned. A status report on this prototyping effort will be presented.
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| THP077 | A High-Gradient Test of a 30-GHz Copper Accelerating Structure | electron, linac, pick-up, acceleration | 761 | ||
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The CLIC study is investigating a number of different materials at different frequencies in order to find ways to increase achievable accelerating gradient and to understand what are the important parameters for high-gradient operation. So far a series of rf tests have been made with a set of identical-geometry 30 GHz and X-band structures in copper, tungsten and molybdenum. A new test of a 30 GHz copper accelerating structure has been completed in CTF3 with pulse lengths up to 100 ns. The new results are presented and compared to the previous structures to determine dependencies of quantities such accelerating gradient, material, frequency, pulse length, power flow, conditioning rate, breakdown rate and surface damage.
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| THP078 | High-Gradient Test of a Tungsten-Iris X-Band Accelerator Structure at NLCTA | linear-collider, collider, RF-structure, impedance | 764 | ||
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The CLIC study group at CERN has built two X-band accelerating structures to be tested at SLAC in NLCTA. The structures consist of copper cells with insert irises made out of Molybdenum and Tungsten, clamped together and installed in a vacuum tank. These structures are exactly scaled versions from structures tested previously at 30 GHz and with short pulses (16 ns) in the CLIC Test Facility at CERN. At 30 GHz these structures reached gradients of 150 MV/m for Tungsten and 195 MV/m for Molybdenum. These experiments were designed to provide data on the dependence of rf breakdown on pulse length and frequency. This paper reports in particular on the high-gradient test of the tungsten-iris structure. At a pulse length of 16 ns a gradient of 125 MV/m was reached at X-band, 20 % lower than the 150 MV/m measured at 30 GHz in the CLIC Test Facility. The pulse length dependence and the dependence of the break down rate as a function of gradient were measured in detail. The results are compared to data obtained from the Molybdenum-Iris experiment at X-band which took place earlier as well as to 30 GHz data.
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| THP079 | High-Power Test of a 57-MHz CW RFQ | rfq, acceleration, pick-up, linac | 767 | ||
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High power heavy-ion drivers require a CW low-frequency RFQ for initial acceleration. The technique of high-temperature furnace brazed OFE copper cavities has proven to be very reliable for the production of high-quality CW accelerating structures. By appropriate choice of the resonant structure for the RIA driver RFQ we have achieved moderate transverse dimensions of the cavity and high quality accelerating-focusing fields required for simultaneous acceleration of multiple charge state ion beams. In our application the RFQ must provide stable operation over a wide range of RF power levels. To demonstrate the technology and high-power operation we have built an engineering prototype of one-segment of the 57-MHz RFQ structure [1]. The RFQ is designed as a 100% OFE copper structure and fabricated with a two-step furnace brazing process. The brazing process was successful and the cavity was shown to be vacuum tight. The errors in the tip-to-tip distances of the vanes average less than 50 microns. The RF measurements show excellent electrical properties of the resonator with a measured unloaded Q equal to 95% of the simulated value. Currently high-power tests are being performed.
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*J. W. Rathke et al., Preliminary Engineering Design of A 57.5 MHz CW RFQ for the RIA Driver LINAC. Proc. of the LINAC-2002, p. 467. |
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| THP081 | Study on Fault Scenarios of Coaxial Type HOM Couplers in SRF Cavities | SNS, electron, coupling, radiation | 770 | ||
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Coaxial type couplers are adopted in many superconducting radio-frequency (SRF) cavities to suppress higher order modes for beam dynamics and cryogenic loads issues. HERA (Hadron-Electron Ring Accelerator) and TTF (Tesla Test Facility) are equipped with this type coupler and showed successful performances. It is, however, under suspicion that a limitation or a fault could be initiated from this type of coupler at certain combinations between cavity operating conditions and engineering designs of the coupler. Some possible scenarios are summarized and also some observations in the SNS (Spallation Neutron Source) SRF cavities are also reported.
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| THP082 | Industrialization of TESLA-Type SRF Technology at ACCEL | cryogenics, controls, electron, monitoring | 773 | ||
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In the last 15 years the worldwide TESLA collaboration under the leadership of DESY performed successful developements of SRF technology for possible use in a future international linear collider (ILC). Today this technology is also the baseline for other demanding projects like the European X-FEL at DESY site, 4GLS at Daresbury, BESSY FEL, Cornell-ERL, FEL at Peking University and others. Through all these years ACCEL has followed and supported this tremendous developement by producing and processing SRF cavities, couplers and complete accelerator modules. The current ability and future prospects of ACCEL for manufacturing and processing such key components as well as turnkey SRF modules with guaranteed performance for such projects are described.
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| THP086 | Mitigation of Power Loss Due to Skin Effect by Thin-Layered Film | resonance, controls, electromagnetic-fields | 785 | ||
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The AC current flows only on the metal surface, which is known as skin effect. The current concentration on the surface increases power loss. This results higher transmission loss of cable and degradation of Q in cavities. Skin effect on a metal film that is thinner than a skin depth is investigated starting from general derivation of skin depth on a bulk conductor. The reduction of the skin effect power loss with layered conductor films is reported and discussed.
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