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| WEPPC040 | Evaluation of VATSEAL Technology to Seal Waveguide Serving High-field Superconducting RF Cavities | vacuum, SRF, cavity, impedance | 2298 |
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Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. A waveguide flange seal serving a high-field, superconducting, radio-frequency (SRF) cavity ideally possesses several characteristics. Seals must generally be ultrahigh-vacuum leak tight. Seals must also bridge the inner surfaces of connecting flanges for optimum transmission and minimal heating due to trapped modes. In addition, if seal contact areas are minimized, flange seals may serve as convenient thermal impedances. Finally, seals must be easily cleanable and not be prone to generate particulate matter during assembly and disassembly. A unique sealing technology known as VATSEAL may neatly address all of the above requirements. In this paper, we describe our evaluation of VATSEAL technology for use in SRF cavity assemblies. |
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| WEPPC049 | Individual RF Test Results of the Cavities Used in the First US-built ILC-type Cryomodule | cavity, cryomodule, SRF, linear-collider | 2321 |
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Funding: Work supported in part by the U.S. Department of Energy under Contract No. DE-AC02-07CH11359. Eight 1.3-GHz, nine-cell SRF cavities have been installed in a cryomodule intended to demonstrate the ILC design goal of 31.5 MV/m. These cavities all underwent two types of individual RF testing: a low-power continuous-wave test of the “bare” cavity and a high-power pulsed test of the “dressed” cavity. Presented here is a discussion of the results from these tests and a comparison of their performance in the two configurations. |
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| WEPPC094 | Optimizing Centrifugal Barrel Polishing for Mirror Finish SRFCavity and Rf Tests at Jefferson Lab | cavity, SRF, controls, superconductivity | 2435 |
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Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. We performed Centrifugal Barrel Polishing (CBP) on a 1.3GHz fine grain ILC SRF cavity following a modified version of the recipe* originally developed at Fermilab (FNAL)**. We were able to obtain a mirror like surface similar to that obtained at FNAL, while reducing the number of CBP steps. This paper will discuss the change in surface and subsequent cavity performance before CBP on a raw cavity and post CBP, after a 800C bake (no pre-bake chemistry) and minimal controlled electro-polishing (below 10 micron). In addition to Q vs. Eacc thermometry maps with preheating characteristics and optical inspection of the cavity before and after CBP will also be shown. * A. D. Palczewski et al., Proc. of SRF2011, THPO071 (2011). ** C.A. Cooper et al., FERMILAB-PUB-11-032-TD, (May 31, 2011). |
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| WEPPD078 | Progress with PXIE MEBT Chopper | kicker, simulation, vacuum, coupling | 2708 |
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Funding: Fermilab is operated by Fermi Research Alliance, LLC, under Contract No. DE-AC02-07CH11359 with the United States Department of Energy A capability to provide a large variety of bunch patterns is crucial for the concept of the Project X serving MW-range beam to several experiments simultaneously. This capability will be realized by the Medium Energy Beam Transport’s (MEBT) chopping system that will divert 80% of all bunches of the initially 5mA, 2.1 MeV CW 162.5 MHz beam to an absorber according to a pre-programmed bunch-by-bunch selection. Being considered one of the most challenging components, the chopping system will be tested at the Project X Injector Experiment (PXIE) facility that will be built at Fermilab as a prototype of the Project X front end. The bunch deflection will be made by two identical sets of travelling-wave kickers working in sync. Presently, two versions of the kickers are being investigated: a helical 200 Ω structure with a switching-type 500 V driver and a planar 50 Ω structure with a linear ±250 V amplifier. This paper will describe the chopping system scheme and functional specifications for the kickers, present results of electromagnetic measurements of the models, discuss possible driver schemes, and show a conceptual mechanical design. |
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| WEPPR027 | Complete Electromagnetic Design of the ESS-Bilbao RFQ Cold Model | rfq, quadrupole, dipole, simulation | 2991 |
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| In this work, the ESS-Bilbao 352,2 Mhz RFQ Cold Model to be built in the ESS-Bilbao accelerator facility is presented. The Cold Model intends to be a small scale representation of the final 4 meters long RFQ which will be able to accelerate a 75 mA proton beam from 75 keV to 3 MeV. The work shown here covers the complete electromagnetic design process of the Cold Model which will be built in aluminium with a total length of 1 meter. Moreover, in order to find out fabrication tolerances, a longitudinal test modulation in the vane regions similar to the one designed for the final RFQ is included in the Cold Model. This modulation represents also a useful tool in order to test the agreement between measurements and electromagnetic simulations. In addition, a complete parametric study of the RFQ ends and radial matchers is presented as an important design parameter able to adjust the field flatness. Finally, slug tuning rods are also added to be able to test the tuning procedures. A final RFQ Cold Model prototype has been designed and is currently under fabrication. | |||
| THPPC009 | Investigation of the Approaches to Measure the RF Cable Attenuation | controls, insertion, linac, acceleration | 3290 |
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| In the accelerator facilities, many RF cables are used for the various purposes such as the transmission system and the cavity monitor. The knowledge of the power attenuation in those cables is important role to control RF. In general, the cable attenuation is measured from S parameters to use a network analyzer. However, the control system is located far from the place of the cavities, and it difficult to measure by a network analyzer. Then we investigated other methods to measure the RF cable attenuation. | |||
| THPPC027 | Measurement of the Dynamic Response of the CERN DC Spark System and Preliminary Estimates of the Breakdown Turn-on Time | simulation, impedance, vacuum, cathode | 3338 |
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| The new High Rep Rate (HRR) CERN DC Spark System has been used to investigate the current and voltage time structure of a breakdown. Simulations indicate that vacuum breakdowns develop on ns timescales or even less. An experimental benchmark for this timescale is critical for comparison to simulations. The fast rise time of breakdown may provide some explanation of the particularly high gradients achieved by low group velocity, and narrow bandwidth, accelerating structures such as the T18 and T24. Voltage and current measurements made with the previous system indicated that the transient responses measured were dominated by the inherent capacitances and inductances of the DC spark system itself. The bandwidth limitations of the HRR system are far less severe allowing rise times of around 12ns to be measured. | |||
| THPPC061 | A 12 kV, 1 kHz, Pulse Generator for Breakdown Studies of Samples for CLIC RF Accelerating Structures | controls, power-supply, vacuum, RF-structure | 3431 |
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| Compact Linear Collider (CLIC) RF structures must be capable of sustaining high surface electric fields, in excess of 200 MV/m, with a breakdown (BD) rate below 3×10-7 breakdowns/pulse/m. Achieving such a low rate requires a detailed understanding of all the steps involved in the mechanism of breakdown. One of the fundamental studies is to investigate the statistical characteristics of the BD rate phenomenon at very low values to understand the origin of an observed dependency of the surface electric field raised to the power of 30. To acquire sufficient BD data, in a reasonable period of time, a high repetition rate pulse generator is required for an existing d.c. spark system at CERN. Following BD of the material sample the pulse generator must deliver a current pulse of several 10’s of Amperes for ~2 μs. A high repetition rate pulse generator has been designed, built and tested; this utilizes pulse forming line technology and employs MOSFET switches. This paper describes the design of the pulse generator and presents measurement results. | |||
| THPPC080 | The Development of LLRF System at PAL | LLRF, controls, cavity, simulation | 3473 |
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| The Super Conducting Radio Frequency (SCRF) systems will be installed for PLS-II. The PAL has been carrying out the design of the low level radio frequency (LLRF) system for the SCRF control using the digital technologies. The requirements of the LLRF system are to maintain the field stability in a cavity within ±0.75% in amplitude and 0.35° in phase. The LLRF system includes the analog front-end, analog and digital board (ADC, DAC, DSP, FPGA, etc.), clock generation and distribution, and so on. The control algorithm will be implemented by the VHDL. The hardware design of the LLRF for PLS-II, simulation and test results were described in the paper. | |||
| THPPC093 | SRF Cavity Surface Topography Characterization Using Replica Techniques | cavity, SRF, niobium, superconductivity | 3497 |
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Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. To better understand the roll of topography on SRF cavity performance, we seek to obtain detailed topographic information from the curved practical cavity surfaces. Replicas taken from a cavity interior surface provide internal surface molds for fine Atomic Force Microscopy (AFM) and stylus profilometry. In this study, we confirm the replica resolution both on surface local defects such as grain boundary and etching pits and compare the surface uniform roughness with the aid of Power Spectral Density (PSD) where we can statistically obtain roughness parameters at different scales. A series of sampling locations are at the same magnetic field chosen at the same latitude on a single cell cavity to confirm the uniformity. Another series of sampling locations at different magnetic field amplitudes are chosen for this replica on the same cavity for later power loss calculation. We also show that application of the replica followed by rinsing does not adversely affect the cavity performance. |
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| THPPP064 | Project X RFQ EM Design | rfq, simulation, quadrupole, dipole | 3883 |
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| Project X is a proposed multi-MW proton facility at Fermi National Accelerator Laboratory (FNAL). The Project X front-end would consist of an H− ion source, a low-energy beam transport (LEBT), a cw 162.5 MHz radio-frequency quadrupole (RFQ) accelerator, and a medium-energy beam transport (MEBT). Lawrence Berkeley National Laboratory (LBNL) and FNAL collaboration is currently developing the designs for various components in the Project X front end. This paper reports the detailed EM design of the cw 162.5 MHz RFQ that provides bunching of the 1-10 mA H− beam with acceleration from 30 keV to 2.1 MeV. | |||