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Update on SLAC experiments with High Gradient Accelerators and RF Components M.Franzi, V.A. Dolgashev, S. Tantawi June 6, 2016.

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Presentation on theme: "Update on SLAC experiments with High Gradient Accelerators and RF Components M.Franzi, V.A. Dolgashev, S. Tantawi June 6, 2016."— Presentation transcript:

1 Update on SLAC experiments with High Gradient Accelerators and RF Components
M.Franzi, V.A. Dolgashev, S. Tantawi June 6, 2016

2 RF polarizer and new SLED cavity commissioned at LCLS
Outline RF polarizer and new SLED cavity commissioned at LCLS Breakdown studies Cryogenic temperature X and S-band experiments Full structure experiments mm-wave accelerating structures 100 GHz wakefield accelerator (E204 at FACET) 110 GHz standing wave accelerator cavity (MIT/SLAC)

3 Motivation for new SLED design
RF polarizer and new SLED cavity Motivation: Replace SLED-I device with a single compact resonator Commission new SLED on X-band deflector at LCLS

4 High power RF polarizer for use in new SLED cavity at SLAC
RF polarizer and single High-Q spherical resonator for new X-band SLED system : Input TE10 at WR 90 input waveguide Equal coupling to the TE10 and TE20 modes Isolation of the opposite port Each rectangular waveguide mode excite a TE11 mode Excitation in quadrature produces quasi circularly polarized wave TE11 modes excite degenerate TE114 modes of spherical resonator TE20 and TE10 emitted/reflected from the cavity cancel at input port

5 Formulation of Scattering Matrix for RF Polarizer
The Polarizer RF network is broken down into 4 sub-networks. Two 3-port networks (n=1,2) A shorted tuning stub 𝑠 𝑠ℎ𝑜𝑟𝑡 = 𝑒 −2𝑖 𝜓 𝑒 −2𝑖 𝜓 2 A single 4 port matched input network 𝑆 𝑖𝑛𝑝𝑢𝑡 = 𝑒 𝑖 𝜓 𝑎 𝑒 𝑖 𝜓 𝑏 𝑒 𝑖 𝜓 𝑎 𝑒 𝑖 (𝜓 𝑏 +𝜋) 𝑒 𝑖 𝜓 𝑎 𝑒 𝑖 𝜓 𝑏 𝑒 𝑖 𝜓 𝑎 𝑒 𝑖( 𝜓 𝑏 +𝜋) Cascaded scattering matrix defines viable ranges for subnetwork parameters 𝑆 𝑛 = − cos 𝜃 𝑛 − 𝑒 −𝑖 𝜙 𝑛 −cos 𝜃 𝑛 + 𝑒 −𝑖 𝜙 𝑛 sin 𝜃 𝑛 −cos 𝜃 𝑛 − 𝑒 −𝑖 𝜙 𝑛 −cos 𝜃 𝑛 − 𝑒 −𝑖 𝜙 𝑛 sin 𝜃 𝑛 sin 𝜃 𝑛 sin 𝜃 𝑛 cos⁡( 𝜃 𝑛 ) TE10 TE20 Perfect-H Boundary Perfect-E Boundary Port-3 Mode-1 Port-2 Port-1 Mode-2 Operating point of each mode in final design

6 Testing of the RF Polarizer and SLED Assembly
Cold Test: Polarizer Cold Test: Polarizer with SLED High Power Test -45 dB match between port:1 and port:2 TE114 @ TE014 @ Input power 35 MW Peak power 207 MW M. Franzi, J. Wang, V. Dolgashev, S. Tantawi et al., Physical Review Accelerators and Beams Accepted (June-2016).

7 XTCAV with SLED @ 85 MV (4-12-2016)
Commissioning of SLED at LCLS and doubled timing resolution of the X-band deflector (XTCAV) XTCAV no 44 MV ( ) Bunch Charge: 175 pC Bunch Energy: GeV X-ray energy: mJ XTCAV with 85 MV ( ) Bunch Charge: 186 pC Bunch Energy: GeV X-ray energy: mJ Timothy Maxwell, Yountao Ding, Valery Dolgasev, Juwen Wang

8 Breakdown studies of cryogenic temperature X and S-band experiments
Motivation for breakdown studies of copper structures at cryogenic temperatures Breakdown studies of cryogenic temperature X and S-band experiments Motivation: Characterize accelerating gradient and breakdown rate of single cell cold copper accelerating cavities

9 Testing of normal conducting X-band (3-Cell) structure in ASTA at cryogenic tempertures
For low breakdown rates gradients and peak electric fields significantly larger than at room temperature. V.A. Dolgashev, A. Cahill

10 Cryogenic normal conducting copper tests: understanding Q0 at low and high power
Measured total Q of 8,150, and coupling β=1.5. Q0=20,500 According to Cold test should be Q0=36,075 Measurements made with 400 ns 500 kW pulses. Forward Reconstructed Reflected Reflected Reflected Reconstructed Reflected V.A. Dolgashev, A. Cahill

11 Reproduction of low power CW measurements with sub-MW Klystron Pulses
Performed sweep of input power to characterize influence of pulse heating. Scan klystron power from kW Measured total Q remains unchanged (~8150) Performed frequency scans from GHz to GHz to measure S-parameters Reflected power measured using input pulse 800 ns at 7 K. Frequencies match network analyzer data, but coupling does not. In process of building precise model of whole circuit Down Mixers PPM data Cold Test PPM data V.A. Dolgashev, A. Cahill

12 Breakdown properties S-Band normal conducting copper structures at cryogenic temperatures
Now expanding our work into S-Band Conceptual design of RF circuit is completed Fabrication anticipated to begin Fall 2016 SUPERFISH simulation of “single” cell accelerating mode HFSS simulation of Rect. WG to Cyl. WG quadrupole-free mode launcher. Fields for 50 MW input rf power. V.A. Dolgashev, A. Cahill

13 Breakdown studies of room temperature full accelerating structures
Motivation for breakdown studies of copper structures at cryogenic temperatures Breakdown studies of room temperature full accelerating structures Motivation: Characterize conditioning of CLIC TD 24 accelerating structure using real time controller Demonstrate high gradient operation of new Distributed Coupling accelerating structure

14 Testing of Traveling Wave X-Band Structure: CLIC TD24
CERN-SLAC Gradient (MV/m) # of BD (x10) Power (MW) ΔT (C) Pulse Length (10 ns) Scaled Gradient (E0 τ(1/6) BDR(-1/30) (250ns : 10E-7 bpp/m)) Gradient (MV/m) PXI Controller Based on xbox-II architecture CLIC Accelerating Structure TD 24 Installed at ASTA M.Franzi, V. Dolgashev

15 Distributed Coupling Accelerator Enables Doubling RF to Beam Efficiency and Ultra-High-Gradient Operation. Optimize individual cell shape for maximum gradient and shunt impedance without cell-to-cell coupling constraint (Patent filed by Stanford) Requires only 66 MW/m for 100 MV/m gradient compared to 200 MW/m for a typical X-band structure 2016 2015 2017 High power RF testing in ASTA Breakdown and conditioning studies Structure moved to NLCTA High power tests with beam Wakefield characterization Applications Waste-water treatment accelerator Incorporate into an energy recovery system. Fold into future TeV collider S. Tantawi

16 Distributed coupling standing wave accelerating structure
-S11(dB) Field amplitude (a.u.) Phase (degrees) -30 11.3 Frequency (GHz) 11.41 Position (cm) Position (cm) Reflected signal from accelerating structure has one single resonance instead of 20 individual resonances S.Tantawi

17 S. Tantawi, C. Limborg, A. Cahill, M. Nasr
Split Structures accelerates beam and operates at high demonstrate high gradient while demonstrating the predicted shunt impedance 87.5MeV 85.6MeV 89.4MeV 26 cm structure installed at XTA The structure added 24 MeV energy gain by beam 16.5 MW of input power with 300 ns pulse length filling time is 140 ns (expected) The structure is being processed at XTA to go beyond 120 MV/m S. Tantawi, C. Limborg, A. Cahill, M. Nasr

18 Goals of the E204 experiment
mm-wave accelerating structures Motivation: Determine statistical properties of rf breakdown in metal structures, accelerating gradient and pulse length at 100 GHz and 200 GHz frequencies

19 Beam excited mm-wave structure - list of experiments
Solid model of the 100 GHz accelerating structure Experimental setup with copper accelerating structure TOP HALF 1 mm Electron beam Regular cell BOTTOM HALF Coupler iris # Date Type Material Frequency Charge Bunch Length 1 Jun Standing wave Cu 100 GHz 2.7 nC 50 um 2 Mar Travelling wave 3.2 nC 3 May S. Steel 3 nC 4 Mar 5 Apr 25, 200 GHz 6 May Cu-Ag 1.6 nC 25 um 7 Nov Nov = Nov M. Dal Forno, et al., Physical Review Accelerators and Beams 19.1 (2016): M. Dal Forno, et al., Physical Review Accelerators and Beams 19.5 (2016):

20 Results from the experiments at 100 GHz
Achieved gradients and pulse length: # Eacc Emax, (fund. Mode) Emax, (all. Modes) τp latt [GV/m] [ns] [mm] 1 0.1 0.35 2.45 91 2 0.3 0.64 1.5 2.38 3 0.19 0.52 0.33 3.5 Standing wave copper f = 100 GHz, q = 2.7 nC, σz = 50 um Travelling wave copper f = 100 GHz, q = 3.2 nC, σz = 50 um Travelling wave S. Steel f = 100 GHz, q = 3 nC, σz = 50 um 1 2 3 4,7 2012 2014 2015 On next slide Low-transmission coupler ( -30 dB) Filter external interference. No RF breakdowns detected Used crystal and pyro detector. Installed motorized stages Change the gap of the structure. Matched coupler to improve SNR Isolated each half of the structure Used current monitor to detect breakdown Automated scans of motorized stages EPICS control

21 Results from the experiments at 100 GHz (2015)
M. Dal Forno, et al., Physical Review Accelerators and Beams 19.5 (2016): Experiment # 4 : Travelling wave Cu, f = 100 GHz, q = 3.2 nC, σz = 50 um Experiment # 7: Travelling wave Cu-Ag, f = 100 GHz, q = 3.2 nC, σz = 25 um Centroid MAX deflection: ~0.3 mm Simulated with CST studio Measured Measured the deflecting voltage by observing the displacement of the 20 GeV FACET electron beam on a diagnostic screen. Confirmation of simulated values of the deflecting and accelerating gradients. Gap f τp nC Eacc 1 mode @2.7 nC Emax 1 mode [mm] [GHz] [ns] [MW] [MV/m] [GV/m] 0.3 136.27 2.36 0.77 224 0.51 0.5 130.3 2.37 2.48 169 0.47 0.7 126.01 4.03 4.23 127 0.43 0.9 122.66 2.35 5.47 97 0.41 1.1 119.93 1.57 6.42 76 0.32 1.3 117.59 1.15 6.85 59 0.30 200 GHz results will be in V. Dolgashev presentation…

22 Planned high power (110 GHz) structure testing at MIT
Demonstrate realizable mm-wave accelerating structure Power with stand-alone RF source MIT) Direct comparison with breakdown studies at x-band Single Cell: Standing Wave Accelerating Structure Iris Braze Test in Progress Full RF Structure 110 GHz Gyrotron Pulse Accelerating Gradient E. Nanni, V. Dolgashev, J. Neilson

23 E. Nanni, V. Dolgashev, J. Neilson
Planned high power (110 GHz) structure testing at MIT Large diameter window to reduce surface power density Quasi-optical launcher converts guassian mode to TE01 feeding the cavity W-band output coupler with crystal detector for power diagnostics E. Nanni, V. Dolgashev, J. Neilson

24 Conclusion SLAC has numerous ongoing experiments: New SLED embodiment
Single spherical resonator with RF polarizer Successful implementation at LCLS Breakdown studies: Cryogenic temperature single cell cavities In progress of characterizing full RF circuit Full accelerating structure Conditioning of CLIC structure is ongoing Distributed coupling accelerator is being tested with beam at XTA mm-wave structure testing Wakefield accelerator First series of mm-wave breakdown experiments Standing wave single cell accelerating structure Conceptual design completed


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