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| MO3001 | Intense Heavy-Ion Beam Production with ECR Sources | plasma, ion, electron, ion-source | 18 | ||
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An average increase of about one order of magnitude per decade in the performance of ECR ion sources was obtained up to now since the time of pioneering experiment of R. Geller at CEA Grenoble and this trend is not deemed to get the saturation at least in the next decade, according to the increased availability of powerful magnets and microwave generators. Electron density above 1013 cm-3 can be obtained by 28 GHz microwave heating, but only an adequate plasma trap may allow to exploit that plasma for heavy elements ionization. A study about the optimization of the magnetic field and of the other different parameters affecting the ECRIS plasma is presented, with a special emphasis on the coupling of microwaves to plasma. Long-term perspectives are presented finally, with an analysis of the possibilities opened by higher frequency generators, as 60 GHz gyro-TWTs, with the use of moderate confinement trap, by combining the large plasma density with larger escape rates in order to get larger ion beam currents.
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| MOP053 | Construction of a High-Current RFQ for ADS Study | rfq, dipole, vacuum, quadrupole | 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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| MOP064 | Emittance Preservation for the Curved ILC Main Linac | linac, emittance, quadrupole, alignment | 192 | ||
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It is envisaged in Baseline Configuraation Document that the main linear accelerator of ILC will follow the earth curvature instead of being laser-straight. Beam based alignments will be imperative for preserving the small vertical beam emittances through the main linac. Various beam based algorithms have been developed during the last decade. However, most of the simulation studies assumed the straight geometry of the linac. In this work we present the results on single bunch emittance dilution in the curve ILC main linac, using Dispersion Free Steering under the nominal misalignment of the beam line components. We present the comparison of the curve linac with laser stright geometry. We have studied the sensitivity of the DFS to the various misalignments and also considered the effect of incoming beam jitter and quadrupole vibration jitter. Further, robustness of DFS to the failure of corrector magnets or BPM is investigated. The beneficial effect of the dispersion bumps on the emittance dilution performance is also discussed.
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| TUP004 | Intense L-Band Electron Linac for Industrial Applications | linac, electron, impedance, klystron | 250 | ||
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An intense L-band travelling-wave electron linac is under development for irradiation applications. It is capable of producing 10 MeV electron beams of 30 kW average beam power. The operating energy is limited to prevent neutron production. On the other hand, the current is limited by the beam loading effect in the given structure. The accelerating structure operated with 2π/3 mode is constant-impedance and disk-loaded waveguides. We determined the optimum operating parameters by adjusting the duty factor, which is again governed by the available high-power pulsed klystron. The SUPERFISH code was used to design the bunching and accelerating cavities. The PARMELA code gives the result of beam dynamics. We present design details of the intense travelling-wave linac powered by a 1.3 GHz, 25 MW pulsed klystron with a duty factor of 0.21%. We also present cold test results for the prototype cavities.
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| TUP030 | RF Cavity Performance and RF Infrastructure for the ISAC-II Superconducting Linac | linac, controls, power-supply, acceleration | 309 | ||
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The ISAC-II superconducting linac is presently being commissioned. Twenty cavities have been prepared and characterized in single cavity tests before mounting in the on-line cryomodules. The cavities are specified to operate at a challenging peak surface field of 30MV to supply an accelerating voltage of 1.1MV/cavity. The cavity bandwidth of ±20Hz is achieved by overcoupling while a mechanical tuner actively maintains the cavity frequency within this bandwidth. An overview of the rf systems will be given. We will describe the early operating experience and compare the cavity on-line performance with the single cavity characterizations.
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| TUP061 | The HERA RF-Driven Multicusp H- Ion Source | plasma, electron, vacuum, 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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| TUP092 | Emittance Exchange at FNPL | emittance, klystron, electron, pick-up | 478 | ||
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An experiment to attempt the exchange of the transverse emittance with the longitudinal emittance of the Fermilab/NICADD PhotoInjector electron beam is being developed. The emittance exchange occurs by placing a TM110 mode RF cavity in the maximum dispersive region of a magnetic chicane. Properly employed, the cavity's longitudinal shearing Electric field zeros the momentum spread at the cost of generating a non-zero betatron oscillation amplitude. We report on the beam line modeling, beam line design, the RF cavity design, present status as well as the future program.
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| WE2003 | LLRF Systems for Modern Linacs: Design and Performance | controls, feedback, linac, resonance | 498 | ||
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Near-future linac projects put yet unreached requirements on the LLRF control hardware in both performance and manageability. Meeting their field stability targets requires a clear identification of all critical items along the LLRF control loop as well as knowledge of fundamental limitations. Large-scale systems demand for extended automation concepts. The experience gained with present systems as well as dedicated experiments deliver the basis for a design of future systems. Digital hardware has evolved quickly over the past years and FPGAs became common not only in LLRF control. A high degree of digitization in various fields, as for example beam diagnostics, suggests to aim for a convergence of the digital platform designs. Channeling of efforts of different research laboratories may be the key to an affordable solution that meets all requirements and has a broad range of applications.
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| WE2005 | HOM Damping and Power Extraction from Superconducting Cavities | damping, linac, impedance, electron | 506 | ||
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Damping of Higher Order Modes plays an important role in achieving and preserving low emittance and low energy modulation of beams in accelerators based on the superconducting technology. In the overview, various damping schemes and damping devices and their advantages and disadvantages will be discussed.
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| TH1004 | A 70-MeV Proton Linac for the FAIR Facility Based on CH - Cavities | linac, proton, rfq, quadrupole | 526 | ||
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Future Accelerators for fundamental and for applied research will need a significant improvement in injector capabilities. This paper will describe the concept and the status of the 70 MeV, 70 mA proton injector for GSI - FAIR and compare the CH - linac design with traditional DTL concepts. Improvements in the space charge routine of the LORASR code as well as CH - prototype cavity development and cavity grouping with respect to commercial 3 MW rf power amplifiers is reported. Additionally, the potential of robust superconducting low and medium energy high current linac sections will be explained on the basis of experimental results from a first 19 cell s.c. 350 MHz CH - prototype cavity.
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| THP024 | Development of Ultra-fast Silicon Switches and their Applications on Active X-Band, High-Power RF Compression Systems | simulation, plasma, laser, resonance | 619 | ||
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In this paper, we present the recent results of our research on the ultra-high power fast silicon RF switch and its application on active X-Band RF pulse compression systems. This switch is composed of a group of PIN diodes on a high purity silicon wafer inserted into a cylindrical waveguide operating in the TE 01 mode. Switching is performed by injecting carriers into the bulk silicon through a high current pulse. A switch module is composed of the silicon switch, a circular waveguide T with the silicon switch at the center port and a movable short at the other end of silicon switch. The module can tune the S-matrix of on and off states to desired value. Our current design uses a CMOS compatible process and the fabrication is accomplished at SNF (Stanford Nanofabrication Facility). The switch has achieved <300ns on time with ~3% loss on the wafer. The RF energy is stored in a room-temperature, high-Q 400 ns delay line; it is then extracted out of the line in a short time using the switch. The pulse compression system has a achieved a gain of 7, which is the ratio between output and input power. Power handling capability of the switch is estimated at the level of 10MW.
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| THP026 | HIGH POWER TEST OF COUPLER WITH CAPACITIVE WINDOW | vacuum, 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, vacuum, 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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| THP032 | A Variable Directional Coupler for an Alternate ILC High-Power RF Distribution Scheme | polarization, klystron, quadrupole, linac | 643 | ||
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We describe the design and functionality of an RF directional coupler for which the power division between the output ports is mechanically variable. In an alternate power distribution scheme for the ILC, power is delivered to cavities in pairs, through hybrids. Four pairs, or eight cavities, are fed from one waveguide feed, from which one fourth, one third, and one half of the power is coupled out at consecutive directional couplers. Three such feeds are powered by a single 10 MW klystron. Experience suggests that cavities considered useable will display some variation in the operational accelerating gradient they can sustain. With fixed distribution, the klystron power must be kept below the level at which the weakest cavity out of 24 receives its power limit. This problem can be solved by installing variable attenuators, but that means wasting precious power. With adjustable coupling, distribution can be optimized for more efficient use both of available power and of the accelerating cavities. This novel device, feeding cavities paired by similar performance, can provide such benefit to the ILC.
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| THP034 | Effective Standing-Wave RF Structure for Charged-Particle Beam Deflector | RF-structure, linac, simulation, impedance | 649 | ||
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In this report we describe new standing wave pi-mode rf structure for charged particles deflection. For L-band frequency range parameters of the proposed structure are compared with classical TM110 mode deflecting cavity ones. With originating TE11n mode, our proposal has several times higher rf efficiency, one order wider pass-band and smaller (in times) transverse dimensions. The cavity design idea and typical are parameters are presented. Some particularities of the beam dynamics in the proposed structure are pointed out. Preferable field of structure application is discussed.
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| THP040 | New Concept of Small Delay Line Type RF Pulse Compressor Using Coupled Cavities | beam-loading, klystron, simulation, linac | 667 | ||
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I propose a new concept for the RF pulse compressor using the coupled cavities to make a small delay line. This new concept is a hybrid scheme of a cavity type and a delay line type of the RF pulse compressor. The delay line produces the pulse compression outputs through resultant RF beat between two inputs connected both ports of the coupled cavities. The time constant of the beat is matched to the time constant of the power flow of the coupled cavities. Further the special test stand for the coupled cavities was developed to easily adjust the resonant frequency of such high-Q coupled cavities.
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| THP044 | Design and Development of RF Structures for Linac4 | linac, klystron, booster, quadrupole | 679 | ||
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Linac4 is a new 160 MeV H- linac proposed at CERN to replace the 50 MeV Linac2 as injector to the PS Booster, with the goal of doubling its brightness and intensity. The present design foresees after RFQ and chopping line a sequence of three accelerating structures: a Drift Tube Linac (DTL) from 3 to 40 MeV, a Cell-Coupled DTL (CCDTL) to 90 MeV and a Side Coupled Linac (SCL) up to the final energy. The DTL and CCDTL operate at 352 MHz, while in the SCL the frequency is doubled to 704 MHz. Although the injection in the PS Booster requires only a low duty cycle, the accelerating structures are designed to operate at the high duty cycle required by a possible future extension to a high power linac driver for a neutrino facility. This paper presents the different accelerating structures, underlining the progress in the design of critical resonator elements, like post-couplers in the DTL, coupling slots in the CCDTL and bridge couplers for the SCL. Alternative structures to the SCL are analysed and compared. Prototyping progress for the different structures is reported, including the RF design of a DTL tank prototype and results of low and high power tests on a CCDTL prototype.
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| THP047 | Prototyping of a Single-Cell Half-Reentrant Superconducting Cavity | simulation, superconductivity, vacuum, resonance | 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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| THP053 | Simulations and Optimizations of a New Power Coupler for 3.9-GHz Superconducting Cavities at Fermilab | simulation, electron, impedance, cryogenics | 701 | ||
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3.9 GHz third harmonic superconducting cavities have been used to increase the peak bunch current and to compensate for non-linear distortions in the longitudinal phase space due to sinusoidal 1.3 GHz accelerating cavity voltage. The power coupler is one of the important and complicated components of the third harmonic system for the TTF3 project. From electromagnetic, multipacting, and thermal simulations of the power coupler, optimized designs have been achieved, enabling one to minimize or eliminate potential problems in advance. This paper presents our recent work on simulation and optimization of the power coupler.
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| THP058 | Proposed LLRF Improvements for Fermilab 201.25 MHz Linac | linac, beam-loading, feedback, pick-up | 713 | ||
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The Fermilab Proton Plan, tasked to increase the intensity and reliability of the Proton Source for 10 or more years of operation, has identified the Low Level RF (LLRF) system as the critical component to be upgraded in the Linac. The current 201.25 MHz Drift Tube Linac was designed and built over 30 years ago and does not meet the higher beam quality demands required under the new Proton Plan. Measurement data, used to characterize the system, has been collected as input for a new computer model of the system. This model shows what improvements can be made by replacing the LLRF system to improve beam quality. The model includes RF driver amplifiers, a 5 MW 7835 triode power amplifier, the high voltage switch tube modulator, and the drift tube cavity. Complete system gain and bandwidth characterization data has been collected for the 7835 triode power amplifier, modulator and RF driver stages. This model will be a useful analysis tool for present and future Linac system upgrades.
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| THP059 | Coaxial HOM Coupler Designs Tested on a Single-Cell Niobium Cavity | pick-up, vacuum, 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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| THP066 | Lorentz-Force Detuning Analysis for Low-Loss, Re-entrant and Half-Reentrant Superconducting RF Cavities | simulation, linear-collider, collider, superconducting-RF | 734 | ||
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The RF design of a superconducting elliptical cavity requires a trade-off in the optimization of the cell shape between the region of high electric field and the region of high magnetic field. In practice, the cavity performance may be limited not by the RF characteristics, but by detuning due to the Lorentz force, bath pressure fluctuations, or microphonics; Lorentz force detuning is of concern primarily for pulsed accelerators such as the proposed International Linear Collider. Hence the structural properties must also be taken into account in the cavity design. Several new cavity shapes are being developed in which the surface magnetic field is decreased relative to the TeSLA cavity shape, with the goal of reaching a higher accelerating gradient. This study will compare the Lorentz force detuning characteristics of the TeSLA, "low-loss", "reentrant", and "half-reentrant" cavity middle cells, and explore possible methods for stiffening the structures.
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| THP070 | Study of BSNS RFQ Design | rfq, simulation, dipole, quadrupole | 746 | ||
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A new 324MHz RFQ used for the project of Beijing Spallation Neutron Source (BSNS) is being designed. The designed injection and output energy are 50keV, 3.0MeV, respectively. The designed pulsed current is 40mA though the required current of BSNS at its first stage is only 20mA. The pulsed width is 420 s with a 50% chopping ratio and repetition rate is 25Hz. The transverse structure of BSNS RFQ will be basically the same as the former RFQ used for ADS, but the length of 3.62m is shorter comparing to the length of 4.75m of the former. The beam dynamics design and the RF structure design of the RFQ will be presented in this paper.
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| THP081 | Study on Fault Scenarios of Coaxial Type HOM Couplers in SRF Cavities | SNS, electron, radiation, vacuum | 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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| THP090 | Initial Studies of 9-Cell High-Gradient Superconducting Cavities at KEK | pick-up, insertion, superconductivity, higher-order-mode | 794 | ||
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Vertical tests of single cell cavities of the KEK Low Loss "Ichiro" design have established that gradients as high as 51 MV/m are feasible in principle. We have also performed vertical tests of 9-cell cavities. The internal surface was prepared according to the prescription developed in the single cell series test. In this paper we report results on the accelerating gradients achieved so far, an investigation of the possible presence of hydrogen "Q Disease," and other high-field related studies. We also present the measurement of the higher modes of the cavities.
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| THP093 | Polyhedral Cavity for Superconducting Linacs | linac, collider, emittance, brightness | 803 | ||
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A polyhedral cavity structure has been devised for use in superconducting linacs. It has the same ellipsoidal side contour as a TESLA cavity but is configured as a polyhedron in its end view. Each segment of the polyhedron consists of a Nb foil bonded to a Cu wedge that has been machined to the desired ellipsoidal inner contour. There are no welds, and the seams between adjacent segments do not affect the high Q of the accelerating mode but block the azimuthal currents of deflecting modes. The power coupled into deflecting modes can be slot-coupled at the seams into dielectric-loaded waveguides integrated in the copper segments and conveyed to warm termination. The inner surface of each segment is accessible for polishing and characterization. It accommodates application of improved superconducting surfaces, such as the multi-layer thin-film Nb3Sn proposed by Gurevich. Refrigeration can be provided by gun-bored channels within the copper segments. The copper segments provide a rigid assembly that eliminates Lorentz detuning. The talk will discuss the mode properties and coupling strategies, the strategy for Nb/Cu bonding, and plans for building and testing of prototype cavities.
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