Status of the 805 MHz Modular Cavity Effort Fabrication Ongoing - PowerPoint PPT Presentation

Status of the 805 MHz Modular Cavity Daniel Bowring Introduction Simulation/Design Status of the 805 MHz Modular Cavity Effort Fabrication Ongoing Work Planned Daniel Bowring Experiments Conclusion Lawrence Berkeley National Laboratory Supplemental MAP 2013 Collaboration Meeting

Status of the 805 Background MHz Modular Cavity Daniel Bowring Introduction Simulation/Design Effort Fabrication Ongoing Work Planned Experiments Conclusion ◮ Strong magnetic fields reduce Supplemental the maximum achievable surface electric field in vacuum RF cavities. ◮ RF breakdown → damaged cavities, reduced gradients. Figure: D. Huang et al. , ◮ This is a challenge to building PAC09, Vancouver, Canada, TU5PFP032. an ionization cooling channel.

Status of the 805 RF breakdown in magnetic fields: Open MHz Modular Cavity Questions Daniel Bowring Introduction Simulation/Design ◮ Does pulsed heating / cyclic fatigue play Effort a role? Fabrication Ongoing Work ◮ Can we mitigate this problem via clever Planned material choices? Experiments ◮ What role does the coupler play? Conclusion Supplemental ◮ Does measurement order (0 T vs. 3 T) play a role? The modular cavity addresses these questions. This talk presents the design and fabrication status of the modular cavity.

Status of the 805 The 805 MHz modular cavity in one slide MHz Modular Cavity Daniel Bowring Introduction Simulation/Design Effort Fabrication Ongoing Work Planned Experiments Conclusion Supplemental ◮ End goal: A functioning ionization cooling channel. ◮ f = 805 . 00 MHz, Q 0 = 20500, β = 1 . 3 ◮ Power coupled in through the equator. Everything fits in the 44 cm diameter Lab G solenoid. ◮ Modular design: test different materials (Cu vs Be), surface treatments, gap lengths. ◮ Under fabrication now. ◮ Delivered to MTA by the end of FY’13.

Status of the 805 21 people at 5 institutions are involved in this MHz Modular Cavity effort. Daniel Bowring Introduction LBNL FNAL SLAC Simulation/Design Effort ◮ A. Bross ◮ C. Adolphsen ◮ D. Bowring Fabrication ◮ D. Kaplan ◮ L. Ge ◮ A.J. DeMello Ongoing Work ◮ A. Moretti ◮ A. Haase ◮ A.R. Lambert Planned Experiments ◮ M.A. Palmer ◮ K. Lee ◮ D. Li Conclusion ◮ R.J. Pasquinelli ◮ Z. Li ◮ S. Virostek Supplemental ◮ Y. Torun ◮ D.W. Martin ◮ M. Zisman U. Miss. BNL ◮ T. Luo ◮ R.B. Palmer ◮ D. Summers

Status of the 805 Zenghai Li has already discussed the simulation MHz Modular Cavity effort. Daniel Bowring Introduction Simulation/Design Effort Fabrication Ongoing Work Planned Experiments Conclusion TEM3P thermal analysis. Omega3P eigenmode modeling. Supplemental Track3P multipacting studies. G4beamline simulation of scattering in Be.

Status of the 805 Exploded view of the modular cavity MHz Modular Cavity Daniel Bowring Introduction Simulation/Design Effort Fabrication Ongoing Work Planned Experiments Conclusion Supplemental Copper components, narrow waveguide, retaining rings, coolant channels, instrumentation ports.

Status of the 805 Working on the assembly now. MHz Modular Cavity Daniel Bowring Introduction Simulation/Design Effort Fabrication Ongoing Work Planned Experiments Conclusion Supplemental

Status of the 805 Working on the assembly now. MHz Modular Cavity Daniel Bowring Introduction Simulation/Design Effort Fabrication Ongoing Work Planned Experiments Conclusion Supplemental Parts fabrication is almost done. Assembly has begun!

Status of the 805 Timeline MHz Modular Cavity Daniel Bowring Introduction Simulation/Design Effort Task When? Fabrication All parts at SLAC for final assembly mid-July Ongoing Work Planned Assembly / cold testing July & August Experiments Final assembly August Conclusion Supplemental Ship to FNAL September Unpacking, inspection FY’13 High-power testing October 2013

Status of the 805 We’ll test different surface finishes, materials. MHz Modular Cavity Daniel Bowring Cu surface at 10X magnifi- Introduction cation, no surface treatment. Simulation/Design What emitter density can we Effort expect from this surface? Fabrication Ongoing Work Planned Experiments Conclusion Buttons from 805 MHz pillbox. Supplemental Be may be more resistant than Cu to breakdown damage. ◮ Compare different Cu surface treatments: as-received, baked, chemically polished. ◮ Cu vs. Be walls: Be has longer radiation length, higher melting point.

Status of the 805 Future work: Vary cavity length to study dark MHz Modular Cavity current impact energy Daniel Bowring Introduction Simulation/Design Effort Fabrication Ongoing Work Planned Experiments Conclusion ← → ← → Supplemental 10.44 cm 14.50 cm ◮ What effects from cavity length? ◮ Transit time factor affects FE impact energy. ◮ Stored energy may influence BD damage extent. ◮ Modular cavity is 10.44 cm long. We can test a 14.5 cm version to evaluate these effects.

Status of the 805 Future work: Button variations MHz Modular Cavity ◮ Measure FE Daniel Bowring currents. Introduction 1. Induce field Simulation/Design Effort emission Fabrication Ongoing Work Planned Experiments ◮ Decouple cyclic Conclusion Supplemental 2. Button/anti- fatigue, FE. button tests ◮ Map local 3. Photoemission variations of β , tests φ .

Status of the 805 Thanks for your attention! MHz Modular Cavity Daniel Bowring Introduction Simulation/Design Effort Fabrication ◮ We expect to begin high-power testing of the modular Ongoing Work cavity in the MTA in October 2103. Planned Experiments ◮ With Cu and Be end plates + variations, we expect to Conclusion address most of the open questions involving RF Supplemental breakdown in magnetic fields.

Status of the 805 MHz Modular Cavity Daniel Bowring Introduction Simulation/Design Effort Fabrication Ongoing Work Supplemental Slides Planned Experiments Conclusion Supplemental

Status of the 805 Damage Analysis MHz Modular Cavity Daniel Bowring Introduction Simulation/Design Effort Fabrication Ongoing Work Planned Experiments Conclusion Supplemental We’re developing computer Damage spot size distribution vision tools to automate may describe breakdown current density. cavity surface inspection. Red circles (above) are 1 mm breakdown spots tagged by J.E. Daalder, IEEE Trans. Power. computer. App. Syst. 93 (1974) p. 747.

Status of the 805 Field Emission MHz Modular Cavity Daniel Bowring Considering the Fowler-Nordheim equation: Introduction Simulation/Design � j � = 5 . 7 × 10 − 12 · 10 4 . 52 φ − 0 . 5 − 6 . 53 × 10 9 · φ 1 . 5 Effort � � ( β E s ) 2 . 5 exp Fabrication φ 1 . 75 β E s Ongoing Work Planned Experiments ◮ φ is the work function of the metal, measured in eV. Conclusion ◮ β is the geometric field enhancement factor of an Supplemental emitting surface feature. Very roughly, β ∼ h / r . ◮ For Cu, φ ≈ 4 . 5 eV on average. ◮ Recent work suggests that variations in φ are important for FE analysis. See H. Chen et al. , PRL 109 204802 (2012).

Status of the 805 � j � vs. φ MHz Modular Cavity The average work function of copper is ≈ 4 . 5 eV. Daniel Bowring Introduction Simulation/Design 15 10 Effort β = 1 13 β = 5 10 Average FE current density (A/m 2 ) Fabrication β = 10 11 10 β = 50 Ongoing Work β = 100 9 10 Planned Experiments 7 10 Conclusion 5 10 Supplemental 3 10 1 10 -1 10 -3 10 0 2 4 6 8 10 Work Function φ (eV) Figure: Average FE current for varying work function, using five different values of β . E = 50 MV/m.

Status of the 805 Photoemission studies to map β , φ on cathode MHz Modular Cavity surface Daniel Bowring Introduction Simulation/Design Effort Fabrication Ongoing Work Planned Experiments Conclusion Supplemental