| Paper | Title | Page |
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| MOP81 | Analysis of the Qualification-Tests Performance of the Superconducting Cavities for the SNS Linac | 210 |
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| Thomas Jefferson National Accelerating Facility (Jefferson Lab) is producing superconducting radio frequency (SRF) cryomodules for the Spallation Neutron Source (SNS) cold linac. This consists of 11 medium-beta (β=0.61) cyomodules of 3 cavities each, and 12 high-beta (β=0.81) cryomodules of 4 cavities each. Before assembly into cavity strings the cavities undergo individual qualification tests in a vertical cryostat (VTA). In this paper we analyze the performance of the cavities during these qualification tests, and attempt to correlate this performance with cleaning, assembly, and testing procedures. We also compare VTA performance with performance in completed cryomodules. | ||
| MOP82 | SRF Cavity and Materials R&D at Fermilab | 213 |
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| Two 3.9 GHz superconducting RF cavities are under development at FNAL for use in the upgraded Photoinjector Facility. A TM110 mode cavity will provide streak capability for bunch slice diagnostics, and a TM010 mode cavity will provide linearization of the accelerating gradient before compression for better emittance. The status of these two efforts and a review of the FNAL infrastructure development will be given. | ||
| MOP84 | First Cryogenic Tests with JLab's new Upgrade Cavities* | 216 |
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| For the upgrade of CEBAF to 12 GeV two types of 7-cell cavities have been developed: the High Gradient type (HG) has been optimized with respect to the ratio of Epeak/Eacc and for the Low Loss (LL) type the shunt impedance has been maximized. Each cavity type features four DESY type coaxial HOM couplers and a waveguide input coupler. Design goals for these cavities have been set to Eacc = 20 MV/m with a Q-value at 2.05 K of Q0 = 8·109. A niobium prototype of each cavity has been fabricated at JLab and in a first test the HG cavity has been evaluated at cryogenic temperatures after appropriate buffered chemical polishing. Data for Q(E) were taken at several temperatures after R(T) was measured during initial pump down. In addition the pressure sensitivity as well as the Lorentz force detuning were evaluated. The damping of approximately 20 High Order Modes was measured to verify the room temperature data. Measurements on the LL prototype are in progress. We present in this contribution a summary of measured results of tests we performed on the new proposed shapes of the upgrade cavities. | ||
| MOP85 | Influence of Ta Content in High Purity Niobium on Cavity Performance: Preliminary Results* | 219 |
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In a previous paper* a program designed to study the influence of the residual tantalum content on the superconducting properties of pure niobium metal for RF cavities was outlined. The main rationale for this program was based on a potential cost reduction for high purity niobium, if a less strict limit on the chemical specification for Ta content, which is not significantly affecting the RRR–value, could be tolerated for high performance cavities. Four ingots with different Ta contents have been melted and transformed into sheets. In each manufacturing step the quality of the material has been monitored by employing chemical analysis, neutron activation analysis, thermal conductivity measurements and evaluation of the mechanical properties. The niobium sheets have been scanned for defects by an eddy current device. From three of the four ingots—Ta contents 100, 600 and 1,200 wppm—two single cell cavities each of the CEBAF variety have been fabricated and a series of tests on each cavity with increasing amount of material removal have been performed. This contribution reports about the results from different tests and gives an analysis of the data.
*T. Carneiro et al; http://conference.kek.jp/SRF2001/ |
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| MOP86 | Cold Test Results of the ISAC-II Medium Beta High Gradient Cryomodule | 222 |
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| Many proposals (RIA, Eurisol, ISAC-II) are emerging for a new generation of high gradient heavy ion accelerators. The ISAC-II medium beta cryomodule represents the first realized application that encorporates many new techniques to improve the performance over machines presently being used for beam delivery. The machine lattice, compatible with multi-charge acceleration, uses high field (9T) superconducting solenoids with bucking coils for active fringe field compensation. The bulk niobium quarter wave medium beta cavity produces 6 MV/m over an effective length of 18cm with a peak surface field of ~30 MV/m. TRIUMF has developed a mechanical tuner capable of both coarse (kHz) and fine (Hz) frequency adjustments of the cavity. The demonstrated tuner resolution is better than 0.1 μm (0.6 Hz). A new rf coupling loop has been developed that operates at 200 Watts forward power with less than 0.5 Watt of power being added to the helium load. Cold alignment in ISAC-II has been done with rf pick-ups using a stretched wire technique. Finally all cryomodule and testing has been done in a clean environment. The alignment cryogenic, solenoid and rf performance will be presented. | ||
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Transparencies | |
| MOP87 | Conceptual Layout of the European X-FEL Linear Accelerator Cryogenic Supply | 225 |
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| As a source for the European x-ray free electron laser (European X-FEL project) at DESY a superconducting linear accelerator will deliver a pulsed electron beam of about 20 GeV. A conceptual layout for the cryogenic supply of the linac is presented. The linac will consist of about 1000 superconducting niobium 1.3 GHz 9-cell cavities, which will be cooled in a liquid helium bath at a temperature of 2 K. Eight cavities and one superconducting magnet package will be assembled to a cryomodule of 12.2 m length. The cryomodules are equipped with two thermal shields at a 5 K and 80 K temperature level respectively. The linac of about 1.6 km length will be divided in 10 cryogenic sub units. Each sub unit will consist of 12 cryomodules. In addition to the main linac, two injector sections have to be supplied separately by means of helium refrigerators and a related helium distribution system. | ||
| MOP88 | RF Coupler Design for the TRIUMF ISAC-II Superconducting Quarter Wave Resonator | 228 |
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| An RF Coupler for the ISAC-II medium beta (β=0.058 and 0.071) superconducting quarter wave resonators was designed and tested at TRIUMF. The main goal of this development was to achieve stable operation of superconducting cavities at high acceleration gradients and low thermal load to the helium refrigeration system. The cavities will operate at 6 MV/m acceleration gradient in overcoupled mode at a forward power 200 W at 106 MHz. The overcoupling provides ±20 Hz cavity bandwidth, which improves the stability of the RF control system for fast helium pressure fluctuations, microphonics and environmental noise. Choice of materials, cooling with liquid nitrogen, aluminum nitride RF window and thermal shields insure a small thermal load on the helium refrigeration system by the Coupler. An RF finger contact which causedμdust in the coupler housing was eliminated without any degradation of the coupler performance. RF and thermal calculations, design and test results on the coupler are presented in this paper. | ||
| MOP89 | A Wire Position Monitor System for the ISAC-II Cryomodule Components Alignment | 231 |
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| TRIUMF is developing ISAC-II, a superconducting (SC) linac. It will comprise 9 cryomodules with a total of 48 niobium cavities and 12 SC solenoids. They must remain aligned at liquid He temperatures: cavities to ±400 μm and solenoids to ±200 μm after a vertical contraction of ~4 mm. A wire position monitor (WPM) system based on a TESLA design has been developed, built, and tested with a prototype cryomodule. The system is based on the measurement of signals induced in pickups by a 215 MHz signal carried by a wire through the WPMs. The wire is stretched between the warm tank walls parallel to the beam axis providing a position reference. The sensors, one per cavity and two per solenoid, are attached to the cold elements to monitor their motion during pre-alignment, pumping and cool down. A WPM consists of four 50 Ω striplines spaced 90° apart. A GaAs multiplexer scans the WPMs and a Bergoz card converts the RF signals to DC X and Y voltages. National Instruments I/O cards read the DC signals. The data acquisition is based on a PC running LabVIEW. System accuracy is ~7 μm. The paper describes system design, WPM calibration and test results. | ||
| MOP92 | Simulation of the RF Coupler for TRIUMF ISAC-II Superconducting Quarter Wave Resonators | 234 |
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| The inductive RF coupler for the TRIUMF ISAC-II 106 MHz superconducting accelerating quarter wave resonators was used as a basis for the simulation model of stationary transmission processes of RF power and thermal fluxes. Electromagnetic simulation of the coupler was done with ANSOFT HFSS code. Transmission line theory was used for electromagnetic wave calculations along the drive line to the Coupler. An analogy between electric and thermal processes allows the thermal calculations to be expressed in terms of electrical circuits. The data obtained from the simulation are compared to measured values on the RF coupler. | ||
| THP16 | Engineering and Cryogenic Testing of the ISAC-II Medium Beta Cryomodule | 630 |
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| The medium beta section of the ISAC-II Heavy Ion Accelerator consists of five cryomodules each containing four quarter wave bulk niobium resonators and one superconducting solenoid. A prototype cryomodule has been designed and assembled at TRIUMF. The cryomodule vacuum space contains a mu-metal shield, an LN2 cooled, copper, thermal shield, plus the cold mass and support system. This paper will describe the design goals, engineering choices and fabrication and assembly techniques as well as report the results of the initial cold tests. In particular we will summarize the alignment procedure and the results from the wire position monitoring system. |