High power RF capabilities From Two 50 MW Klystrons Variable iris Variable Delay line length through variable mode converter Gate Valves Two experimental stations inside the enclosure, one with compressed pulse and the other without the benefit of the pulse compressor. With two 50MW XL4 klystrons ASTA can produce: 1.5 μs --> 63 ns at X-band and feed two experimental outputs in the enclosure. Courtesy of Valery Dolgashev

components to support the experimental facilities Tee for variable iris Bends for low loss transmission and reliable RF systems Dual moded delay lines with variable delay for a flexible pulse width Courtesy of Sami Tantawi Gate valve

SRS 60 Hz AFG TWTK K llrf configuration I&Q MIXER I&Q MIXER SRS DG645 4 port combiner no SLED SLED Power meters Dark current signals DUT FE/RE Klystron RE Vacuum

Pulse compression and pulse shaping Each bin of has independent I&Q modulation via two channel AFGs Forward power RF signals are I&Q demodulated and can be used in pulse shape feedback Delay line tuning is handled by feedback Pulse compressor forward power

Breakdown rates vs gradient forward power reflected power faraday cup 1 faraday cup 2 Faraday cup signals register breakdowns and inhibit further pulses Gradient is calculated. Several weeks for typical structure characterization GS/s acquisition rates Breakdown traces are saved Automated processing Breakdown rate vs. pulse length for C10-VG ns 130 ns

Accelerating structures RF power PETS Main beam Drive beam Courtesy of Alessandro Cappelletti Peak power Avg power Energy BD CERN CLIC PETS3 Testing 133 ns 266 ns

Revised: April 7, 2010 Jake Haimson Recirculation Implementation

Some ongoing and planned HG studies

Test of a Vacuum Brazed CuZr and CuCr Structures High Gradient Structures--AAC 2010 Page 11 Normal copper

Diffusion bonding and brazing of copper zirconium are being researched at SLAC. Clamping Structure for testing copper alloys accelerator structure The clamped structure will provide a method for testing materials without the need to develop all the necessary technologies for bonding and brazing them. Once a material is identified, we can spend the effort in processing it. Furthermore, it will provide us the opportunity to test hard materials without annealing which typically accompany the brazing process Clamped Structure

Test of Hard Copper Hard Copper showed an observable improvements of annealed brazed structures Clamped Structure with Hard Copper cells High Gradient Structures--AAC 2010 Page 13

Cryogenic RF material testing at SLAC Test bed for novel SRF materials – Finding materials with higher quenching RF magnetic field Leading to higher gradient in SRF accelerator structures Samples in different forms, thin film or bulk, multilayer, etc – Unique X-band system with compact size and short pulses, resulting lower pulsed heating – Quick testing cycles with small samples – Surface resistance characterization

Cavity design High-Q cavity under TE013 like mode Q 0,4K =~224,000 Q 0,290K =~50,000 (measured from bulk Cu samples) F res, design =~11.399GHz F res, 290K =~11.424GHz F res, 4K =~11.46GHz Q 0,4K =~350,000 (Estimated for zero resistivity samples, using measured Cu sample results) Sample R=0.95” Tc~3.6µs(using Q value for copper at 4K) Qe~310,000 High-Q hemispheric cavity under a TE 013 like mode – Zero E-field on sample – Maximize H-field on the sample, peak on bottom is 2.5 times of peak on dome – Maximize loss on the sample, 36% of cavity total – No radial current on bottom Copper cavity body – Stable, no transition or quenching – Higher surface impedance – Coupling sensitive to iris radius Nb cavity body being designed – Lower loss for more accurate surface impedance characterization – Q ext is much higher with smaller iris H E

Selected test results: MgB 2 on Sapphire

Experimental Evaluation of Magnetic Field role in Breakdown Rate Experiments with short standing wave structures and specifically with structures where magnetic field is increased due input slots or field-confining rods (PBG) showed that magnetic field plays an important role in determining the gradient limit. Before we studied effect of rf magnetic fields on rf breakdown high-magnetic-field and low-magnetic-field waveguide tests (V.A. Dolgashev, S.G. Tantawi, RF Breakdown in X-band Waveguides, EPAC02) Here we suggest a test that separately controls electric and magnetic fields using the TE01 and the TM02 modes

A standing wave accelerator cell with iris dimensions similar to standing wave accelerator structure Electric Field along the surface TM 02 Mode with resonance frequency GHz Feed with TM 01 mode converter S. Tantawi

A standing wave accelerator cell with iris dimensions similar to standing wave accelerator structure Feed with TE 01 mode converter Magnetic Field along the surface TE 01 Mode with resonance frequency GHz S. Tantawi

Rf Breakdown at Cryogenic Temperatures at ASTA We plant to test hypotheses that connect statistical properties of rf breakdowns to dislocation dynamics in metals: this dynamics dramatically changes at cryogenic temperatures Single-Cell-SW structure TM01 input waveguide S. Tantawi et al. Cryostat “Cold head” of refrigerator

Crystal migration due to pulse heating ―Interferometer ―High resolution microscopy Pulse temperature measurement by High-Speed Radiation Thermometer Particles observation by Laser scattering In-Situ Observation of Metal Surface (KEK, SLAC) SW structure New pulse heating cavity

Future plans for ASTA EPICS for remote monitoring and control Spectrometer to measure gradient Phase measurements and breakdown localization 24 hour unattended operation Move cryostat to ASTA Thanks for your attention