The past decade was characterized by an increasing scientific demand for extending towards higher repetition rates (MHz class and beyond) the performance of already operating lower repetition rate ...accelerator-based instruments such as x-ray free electron lasers (FELs) and ultrafast electron diffraction (UED) and microscopy (UEM) instruments. Such a need stimulated a worldwide spread of a vibrant R&D activity targeting the development of high-brightness electron sources capable of operating at these challenging rates. Among the different technologies pursued, rf guns based on room-temperature structures resonating in the very high frequency (VHF) range (30–300 MHz) and operating in continuous wave successfully demonstrated in the past few years the targeted brightness and reliability. Nevertheless, recently proposed upgrades for x-ray FELs and the always brightness-frontier applications such as UED and UEM are now requiring a further step forward in terms of beam brightness in electron sources. In this paper, we present a few possible upgrade paths that would allow one to extend, in a relatively simple and cost-effective way, the performance of the present VHF technology to the required new goals.
MRI magnets and other magnets that have a low current and high self-inductance are passively quench-protected with a system that includes sub-divided coils with resistors and diodes that are in ...parallel with sections of the coils. The primary purpose of coil sub-division is to protect the coil from the high voltages that can occur during a quench. In the event of a lead failure (conventional or superconducting) between the coil and its power supply or its persistent switch, the total current in the coil flows through the diodes and resistors in parallel with the coil. When a lead fails, the current decay time constant for the coil current can be quite long. It is desirable that the coil quench in a time that is short compared to the coil current decay time constant. Experience shows that the heating from the resistors and diodes will eventually quench the magnet. This paper presents methods for shortening the time between a lead failure or a persistent switch failure and the eventual magnet quench.
A solid understanding and accurate analysis of the voltage transients in the quench process of superconducting magnets is the basis for verifying quench protection system design. This paper presents ...an analysis of the voltage spike that triggered a quench in a serially connected set of superconducting solenoid magnets, which are protected by a stack of cold diodes and dump resistors. The voltage development associated with the normal zone growth is analyzed. The magnets were trained close to the full design current and all the terminal voltages of the coils were captured by a specialized quench detection system. In the analyses described in this paper, the different stages of the voltage transient development will be detailed. Comparisons of simulations and the training results are provided to substantiate the mechanism of the quench voltage behavior in this passive protection scheme.
The Muon Ionization Cooling Experiment (MICE) spectrometer solenoid magnets will be the first magnets to be installed within the MICE cooling channel. The spectrometer magnets are the largest magnets ...in both mass and surface area within the MICE cooling channel. Like all of the other magnets in MICE, the spectrometer solenoids are kept cold using 1.5 W (at 4.2 K) pulse tube coolers. The MICE spectrometer solenoid is quite possibly the largest magnet that has been cooled using small coolers. Two spectrometer magnets have been built and tested. This report discusses the results of current and cooler tests of both magnets.
The MICE spectrometer solenoid magnets will be the first magnets to be installed within the MICE cooling channel. The MICE spectrometer solenoids may be the largest magnets that have been cooled ...using small two stage coolers. During the previous test of this magnet, the cooler first stage temperatures were too high. The causes of some of the extra first stage heat load has been identified and corrected. The rebuilt magnet had a single stage GM cooler in addition to the three pulse tube coolers. The added cooler reduces the temperature of the top of the HTS leads, the shield and of the first stage of the pulse tube coolers.
Fabrication status of the MICE RF cavities will be described. Design of a single-cavity vessel to test the cavities will be discussed, along with the plans for processing and testing the cavities.
The key to being able to operate the superconducting solenoids in the Muon Ionization Cooling Experiment (MICE) using cryocoolers running at around 4.2 K is the application of high temperature ...superconducting (HTS) leads. Because the MICE magnets are not shielded, all of them will have a stray magnetic field in the region where the coolers and the HTS leads are located. The behavior of the HTS leads depends strongly on the HTS material used for the leads, the magnetic field and their warm end temperature. A pair of binary leads consisting of copper leads and HTS leads made from oriented multiple strands of BSCCO wires will be used for electrical transfer of the MICE coupling magnet for the purpose of reducing the heat leak through the leads to 4.2 K region. This paper mainly discusses the detailed design of the HTS leads and their cooling. Protection for the HTS leads during a power failure is discussed as well.
The goal of the Muon Ionization Cooling Experiment (MICE) is to demonstrate muon cooling for a future muon collider. In order to quantify this cooling effect with high precision, scintillating fiber ...trackers in a uniform 4 Tesla field are required. The MICE spectrometer solenoids were designed to meet these requirements. Based on superconducting niobium-titanium (Nb-Ti), each of the two MICE spectrometer solenoids consists of five separate coils contained in a vacuum vessel of 2.7 m length and 1.4 m diameter. In this paper, we report on results from first measurements to verify initial magnet performance at the manufacturer site using a portable Hall-probe-based measurement system. A comparison with theoretical expectations based on OPERA simulations will be discussed and design aspects of the measurement system will be presented.
The RF coupling coil (RFCC) module of MICE is where muons that have been cooled within the MICE absorber focus (AFC) modules are re-accelerated to their original longitudinal momentum. The RFCC ...module consists of four 201.25 MHz RF cavities in a 1.4 meter diameter vacuum vessel. The muons are kept within the RF cavities by the magnetic field generated by a superconducting coupling solenoid that goes around the RF cavities. The coupling solenoid will be cooled using a pair of 4 K pulse tube cooler that will generate 1.5 W of cooling at 4.2 K. The magnet will be powered using a 300 A two-quadrant power supply. This report describes the ICST engineering design of the coupling solenoid for MICE.
The Design Parameters for the MICE Tracker Solenoid Green, M.A.; Chen, C.Y.; Juang, T. ...
IEEE transactions on applied superconductivity,
06/2007, Letnik:
17, Številka:
2
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
The first superconducting magnets to be installed in the union ionization cooling experiment (MICE) will be the tracker solenoids. The tracker solenoid module is a five coil superconducting solenoid ...with a 400 mm diameter warm bore that is used to provide a 4 T magnetic field for the experiment tracker module. Three of the coils are used to produce a uniform field (up to 4 T with better than 1 percent uniformity) in a region that is 300 mm in diameter and 1000 mm long. The other two coils are used to match the muon beam into the MICE cooling channel. Two 2.94-meter long superconducting tracker solenoid modules have been ordered for MICE. The tracker solenoid will be cooled using two-coolers that produce 1.5 W each at 4.2 K. The magnet system is described. The decisions that drive the magnet design will be discussed in this report.
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