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Putting Canted Cosine-Theta To Its First Test
Path to Nb3Sn CCT magnets with fields greater than 10 T
Anticipating future requirements of high-energy colliders, ATAP’s Superconducting Magnet Program (SMP) is developing a high-field dipole based on a hitherto little-used design concept: the Canted Cosine-Theta (CCT) winding geometry. CCT, a concept invented in the late 1960s but little used, turns out to be well adapted to the brittle niobium-tin high-field materials now coming into use.
In May, we achieved another milestone by completing and beginning the testing of the 5-tesla prototype CCT2. This magnet is a technique-development prototype made with ductile niobium-titanium.
CCT2 has a bore of 90 mm and a two-layer design made with nested tubes of Al-bronze with NbTi superconducting cable wound into grooves in each tube. The cables are canted or tilted in opposite directions in each layer to cancel out the solenoid component of the field that each layer would produce by itself.
The magnet structure consists of concentric tubes with G10 insulation between them. The tubes are assembled by pressing the inner tube into the outer and finishing with an aluminum shell.
Left: Final assembly of CCT2 magnet prior to epoxy impregnation. One can see the power leads from each layer plus the two instrumentation leads for quench antennas placed on layer 2. Right: Layer 1 being inserted into layer 2. The cable has not yet been placed in the grooves of layer 2.
Since our group is the first to fabricate coils with the CCT concept, we had to develop materials, tooling, and processes for winding, assembly, and epoxy impregnation. These are necessary to achieve the next goal of a 10-T magnet made with Nb3Sn superconducting cable.
The magnet reached a bore field of 4.6 T at a current of 9,300 A. This current is about 90% of the short sample current limit (SSL) of the cable. It achieved 80% of the SSL in 7 quenches.
Measurements of the static harmonics showed excellent agreement between measured and calculated harmonics for a probe 100 mm long.
Acoustic sensors and quench antennas developed for CCT2 worked as expected and pointed to the quench locations in the coils. These results are still being analyzed and will be reported later.
The next step is to fabricate a 2-layer 10 T class Nb3Sn CCT magnet by September or October of this year. The ultimate goal of this campaign is a 16-T unit made with Nb3Sn.
To Learn More…
The CCT concept and its motivations are detailed in “Can Do on Canted Cosine-Theta,” ATAP Newsletter, April 2015.
The Superconducting Magnet Program is part of the new Berkeley Center for Magnet Technology, announced in the June 2015 special issue of the Newsletter.
The Superconducting Magnet Program page on this site describes the program’s several R&D campaigns.
Testing the First Full Prototype of an LCLS-II Undulator
LCLS-II — the Linac Coherent Light Source-II project being built at SLAC National Accelerator Laboratory by a collaboration that includes LBNL — received Critical Decision 3b approval from the Department of Energy on May 28. This milestone approves long-lead procurements that are necessary to maintain the project schedule, and indicates the importance of the project to BES and the Office of Science. The next major project milestone will be CD-2/3, denoting approval of the project baseline design, cost, and schedule, and go-ahead to begin construction. A CD-2/3 review is being planned for December 2015.
LBNL’s participation in LCLS-II prominently includes design and development of the undulators at the heart of the facility’s free-electron laser. A full prototype LCLS-II undulator, designated HXU32, has been assembled.
HXU32 is a complete prototype of an LCLS-II undulator, including a full set of magnetic modules, mechanical frame, and mechanical drive systems. This prototype will be measured extensively in coming weeks to demonstrate the performance of the integrated systems.
Development of undulators for LCLS-II has resulted in designs and prototypes of magnetic modules offering unique flexibility in aligning magnetic components, along with multiple ways to trim magnetic field errors. These capabilities are integrated with precision mechanical systems that control the position of the magnets to within microns under extreme forces generated by the strong magnets and by thermal effects.
To Learn More…
Both the LCLS-II undulators and the Advanced Photoelectron Experiment (APEX) were featured in the February 2015 edition of the ATAP Newsletter, and the FEL R&D, LCLS-II, and APEX page of this website gives further information on our LCLS-II efforts and their background and context.
Pushing the Envelope — The Long, Narrow Envelope — of Ion-Sputtering Coating
Ion Beam Technology expertise could help ALS Upgrade, other future accelerators realize ultrahigh vacuum in extremely small apertures
Several proposed next-generation accelerators will require much narrower vacuum chambers or “beam pipes” than did their predecessors. Narrower chambers bring the magnets closer to the beam that they manipulate, making it possible to achieve shorter focal lengths and thereby smaller beamsizes, as well as higher undulator performance. Diffraction-limited synchrotron light sources, such as “ALS-U,” the proposed upgrade of LBNL’s Advanced Light Source, call for vacuum chambers potentially as narrow as 4 mm in some straight sections.
For such narrow chambers, the vacuum pumping conductance is greatly reduced, making it extremely difficult to reach the ultrahigh vacuum requirements of storage rings. With non-evaporative getter (NEG) coatings, the surfaces of the vacuum components themselves can trap gas molecules, putting the final touch on the process of evacuating the beam chamber by “gettering” of any additional desorbed gases.
This well established technique is used on many existing accelerators. However, the small inner diameter of ALS-U vacuum chambers makes them challenging to coat with NEG materials. The usual CERN-developed coating process calls for sputtering from transition-metal wires placed along the axis of the to-be-coated chamber, which are traditionally 20 mm or more in inner diameter. As the chambers get narrower, there is not much space left between the wire (sputter target) and the chamber (substrate) to accommodate the discharge plasma for the sputtering process.
Pushing the envelope of sputtering technology, Andre Anders and his group in ATAP’s Ion Beam Technology Program, in collaboration with a team including experts from the Engineering and ALS Divisions, are developing a method using fine wires of Ti, V, and Zr, suspended vertically and with reasonable tension, to put coatings on the inside of 10 mm and even 6 mm diameter tubes. The plasma is produced by a voltage-pulsing technique that allows for greater flexibility than the traditional continuous operation. Observing the Paschen scaling law, the process is done at unusually high pressure for such work to compensate for the unusually small distance between electrodes.
“Coating the inside of a straw” may be understating the challenge of applying smooth, even coatings of NEG materials to the inside of the vacuum chamber for a next-generation synchrotron light source like the ALS Upgrade. The Plasma Applications Group, part of ATAP’s Fusion Science & Ion Beam Technology Program, has made it work in chambers of several-mm diameter and meter-plus length, with further progress expected.
In this R&D campaign, part of a broader effort towards ALS-U supported by Laboratory-Directed R&D funds, Anders and his team have demonstrated NEG coatings of tubes 1.2 m long and only 6 mm in diameter. “It’s like coating a straw, just longer,” someone observed in a project meeting. The preliminary results will be presented at the next meeting of the American Vacuum Society (AVS), to be held in October in San Jose, California.
The work is far from over. Using the Materials Science Division’s ATAP-operated Pelletron accelerator and Rutherford backscattering facility, compositional variations were detected. Such variations can affect the pumping speed and the so-called activation temperature (a little less than 200° C), which is the temperature needed to let surface atoms diffuse inside the coating, thereby cleaning the surface and activating it for “gettering” residual gas atoms.
Anders, with support of graduate student Xue Zhou and the Engineering Division’s Chuck Swenson, is addressing the issue not only by optimizing the wire sputtering approach but also by considering alternative physical or chemical vapor deposition techniques so that ALS-U designers know which approach to NEG coating will be the best.
Volunteer for a Mission to the Adventure Zone
We took many paths to our careers in science and engineering, but chances are, we all realized in childhood that science was interesting, that learning how the world around us works is its own reward. Why not get back in touch with that feeling — and perhaps inspire it in others — as a BLAZES volunteer for the upcoming school year?
BLAZES (Berkeley Lab Adventure Zone in Elementary Science) brings local 5th grade classes (including all Berkeley public school 5th grade classes) to the Lab on a 3.5 hour field trip. Each year between 75 and 80 classes participate! They get to do some hands-on activities exploring the properties of matter, get a brief ALS tour, and enjoy a demonstration with liquid nitrogen. The program includes three hands-on stations where they get to explore dry ice, electrical conductivity, and thermal conductivity. One of the stations is staffed by the person teaching the program, the other two by volunteers like you.
What do the volunteers do? Just before the kids start on the stations, the volunteers introduce themselves and say a couple of sentences about their own work at the Lab. (“Show and tell” is encouraged if you have something cool that’s portable and works in front of a class.) Then each volunteer runs that station while the kids rotate through spending 20 minutes at each station. After the activities, the kids have an opportunity to ask additional questions relating to what they saw and did, or the volunteer’s job.
BLAZES groups usually come Mondays through Thursdays from October through May. A volunteer’s duty typically starts around 10:30.
Many volunteers are scientists, but that is not a requirement. You don’t really need a PhD to understand 5th grade science, after all, and a BLAZES visit is an opportunity for the kids to learn that great science takes a lot of support people whose jobs are interesting and important. If you can convey the idea that science matters to the world and is something they can enjoy learning, that’s the main qualification.
The Lab’s Workforce Development and Education Office, which runs the program, holds regular training sessions for new volunteers. During the session you’ll actually get to perform each of the three activities and get some tips on the scientific points and how best to make them. Please watch Today at Berkeley Lab for announcements of upcoming training sessions.
You can also fill out this form to register your interest in becoming a BLAZES volunteer.
If you would like to know more about the program, please contact the Division’s coordinator for Outreach and Diversity, Ina Reichel (x4341, IReichel@lbl.gov).
Safety: The Bottom Line
Phasing out Job Hazards Analyses and Activity Hazard Documents in favor of WPC
Work Planning and Control (WPC) Activity Manager is now LBNL’s primary database for planning work activities, analyzing hazards, determining controls, and authorizing work. The old Job Hazards Analysis (JHA) and Activity Hazard Document (AHD) systems are being phased out. Since July 15, new people have not been added to the JHA system, and no new AHDs are being created.
ATAP is making good progress in implementing WPC. As of July 17, we have 21 active ATAP activities. Fifty-one people out of 153 have been assigned to at least one Activity and have reviewed and accepted their work assignments.
The challenge ahead is to meet LBNL’s goal of having everyone fully covered by WPC and removed from JHA by September 30, 2015. To meet this goal, we must:
- Determine which work tasks are not currently covered by Activities;
- Finish developing Activities to cover the remaining work;
- Assign the right people to the Activities;
- “Opt out” affiliates who are not currently doing LBNL work; and
- Review and accept the work to which we have been assigned.
With the performance-review cycle now underway, supervisors will incorporate WPC status into discussions with their employees.