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Plasma Source Development at MPP

Plasma Source Development at MPP. Erdem Öz, Patric Muggli. M ax P lanck Institute for P hysics . Overview. Heat Pipe Oven. Heat Pipe Oven: main parts are assembled at Max-Planck Delivery of the heaters expected by the end of 2012

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Plasma Source Development at MPP

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  1. Plasma Source Development at MPP Erdem Öz, Patric Muggli Max Planck Institute for Physics

  2. Overview Heat Pipe Oven • Heat Pipe Oven: main parts are assembled at Max-Planck • Delivery of the heaters expected by the end of 2012 • Field Ionizing Laser to be purchased in early 2013 • Vapor Cell: Biggest challenge is valves. • Fast special valves are being designed in collaboration with VAT Inc. • Diagnostics are developed to study the effect of fast valves on uniformity Vapor Cell E. Oz: AWAKE Meeting, CERN, October 2012

  3. Vapor Cell vs. Heat Pipe • Heat Pipe Oven WHY BUILT? • Has been built before MAIN ISSUE • The %0.1 uniformity is not certain yet. • Vapor Cell WHY? Better uniformity MAIN ISSUE • Engineering Challenge E. Oz: AWAKE Meeting, CERN, October 2012

  4. Plasma Formation • Photon ionization is not preferred non-uniform laser spot would cause non-uniform plasma • Plasma formed by field ionization Field ionization probabity* (W) is a strong function of electric field (E) It’s a threshold process • Above threshold we ionize % 100 Plasma density = Vapor Density • We use alkali metals because of their low ionization potential (I) The laser threshold power scale as** E. Oz: AWAKE Meeting, CERN, October 2012 *M. V. Ammosov et.al. Sov. Phys. JETP, 64:1191–1194, 1986. **S. August et. al. Phys Rev Lett. 1989 Nov 13;63(20):2212-2215.

  5. Why the %0.X Uniformity for the vapor? • Because of scaling (Ewake~ ) we need shorter proton drivers • Producing short proton bunches not possible today w/o major investment. Not an option for the short term • Using transverse two-stream instability (Self modulation instability) • microbunches are naturally spaced at the plasma wavelength, and act constructively to generate a strong plasma wake. Investigated both numerically and theoretically (N. Kumar, A. Pukhov, and K. V. Lotov, Phys. Rev. Lett. 104, 255003 (2010)). • This resonance effect (<%2) ans electron acceleration (% 0.2 )and therefore it requires a highly uniform plasma* • This requirement scales inversly with the number of oscillators • 1/(Number of Microbunches) E. Oz: AWAKE Meeting, CERN, October 2012 * K.V.Lotov et. Al. “Effect of plasma inhomogeneity on plasma wakefield acceleration driven by long bunches” 2012, http://arxiv.org/abs/1205.3388v1

  6. Fast Valve • 1-10 ms or faster,many thousands of recycling time (every 30s x few hours a day x few weeks),work under hostile alkali metal enviroment, at temperatures 140 Co (1014 cm-3)to 250 Co (1015 cm-3) Rb and 520-610 Co for Li • To the best of our knowledge, none of the off the self valves satisfies these requirements • For example: fast closing safety shutters (gate valves) provided by VAT Only close fast (10-20 ms)and 2000-5000 cycles they need to be serviced, also they do not satisfy temperature requirement • How about literature? We found 2 articles describing ms order fast valves. Series 75 and 77 shutters E. Oz: AWAKE Meeting, CERN, October 2012

  7. a Fast Valve from Literature • W van Toledo et. al. Meas. Sci. Techology,471-474, 1992, A fast shutter valve for use in plasma diagnostics 1-Shutter Blade (0.4 mm stainless steel) 2-Entrance Slit (30mmx3mm) 3-Armco iron cores 4-Electromagnetic Coils 5-Fe 360 Tubes Distance between aliminum bronze Plate and blade: 50 m • Shutter speed 0.3 mm/ms 1 mTorr H2 • We will be working VAT Inc. for making a similar desing • That will satisfy all our requirements • We are meeting with their engineers • next week in their Switzerland Headquarter E. Oz: AWAKE Meeting, CERN, October 2012

  8. Another Fast Valve from Literature A.X. Chen et. al., Nuclear Instruments and Methods in Physics Research A 670 (2012) 45–48 . Fast mechanical shutter for pulsed ion beam generation. • A fast valve without the other reuirements can be used to study the effect of valve on the density non-uniformity • Valve speed 1mm/ms • If our initial leak tests with Teflon are satisfactory at Max-Planck, • we are looking into building such a valve within next months to study effect of the valves E. Oz: AWAKE Meeting, CERN, October 2012

  9. Neutral Gas Density Diagnostics:to study effect of valves • Note that the vapor cell is a static system and P=nkT, therefore initially when the valve is closed we can measure the temperature with Calibrated Platinum Resistor (PT100) or even uncalibrated DT-670 Slicon Diode Sensors to get accuracy of % 0.1 for Dn/n0 • To our best knowledge the most accurate pressure sensors at this pressure range: Capacitance gauges % 0.15 percent accuracy for example CMR 373 (we have one at max planck) • Non-local, does not work at high temperature and response too slow ~20 ms. • Therefore We are looking two other diagnostics: Piezzo Resistive Sensor, Electron Beam Fluorscence E. Oz: AWAKE Meeting, CERN, October 2012

  10. Piezoresistive silicon pressure sensor • Assuming a constant excitation current Ie in the Wheatstone bridge circuit diffused onto the thin diaphragm (figure 5(b)), the output signal voltage depends strongly on the pressure applied on the diaphragm, and weakly on temperature.* • B. Rollinger et. al. Review of Scientific Instruments 83, 065002 (2012) • High temperature fast response pressure probe for use in liquid metal • droplet dispensers, Laboratory for Energy Conversion, ETH Zurich, 8092 Zurich, Switzerland • 0.1 ms response, works up to 255 Co in alkali metal • environment • Resolution is questionable but we are in contact • with them on possiblity of using their probe E. Oz: AWAKE Meeting, CERN, October 2012 *P. Kupferschmied et. al. Meas. Sci. Technol. 11 (2000) 1036–1054

  11. Chracterization of Density Non-Uniformity Caused by Valves :Electron Beam Fluoresence* • For low densities fluorescence yield is constant, • i.e. radiation-free, collision-quenching processes are negligeble E-Gun 250 eV Fast Valve Fast Valve Cell Shunt Resistor (e-charge) • Assuming valve opening is reproducible Narrow band H a filter Combined Uncertainty ~% 0.25 Gated-Intensified 16 bit camera • This will also be studied by using • (DSMC) Direct Simulation Monte Carlo *Measuring the density of a molecular cluster injector via visible emission from an electron beam D.P. Lundberg et al, Princeton Plasma Physics Laboratory Rev. Sci. Instrum. 81, 10D707 (2010);

  12. Steady State Solution Roddam Narasimma* • Note also that back reflection from the walls gives a negligeble correction. *Narasimha, R., “Orifice Flow at High Knudsen Numbers,” Journal of Fluid Mechanics, vol. 10, no. 3, 1961, pp. 371–384. **Gas Flux and Density Surrounding a Cylindrical Aperture in the Free Molecular Flow Regime", George C. Soulas http://ntrs.nasa.gov/search.jsp?R=20110009985

  13. PLANS AND FUTURE WORK • Finish 1-m long heat-pipe • Build an intermediary fast valve • Study effects of this valve on uniformity with diagnostics and simulations • Start initial design for the vapor • Start the actual valve designs with VAT Thank you for listening. Any questions?

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