Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
High Gradient and High Q R&D Topics • 1- Explore Q > 1010 for TESLA parameter flexibility – higher luminosity through higher rep rate, longer rf pulse… • 2- Improve geometry of TESLA cavity to increase accelerating field – reduce peak magnetic field by 10% – allow peak electric field to rise 20% • 3- Understand gradient limitations related to dark current and voltage breakdown in copper for NLC Gradient Related R&D con’t • 4 - Study gradient vs rf pulse length – Can we get 45 MV/m for 100 msec instead of 30 MV/m for 1000 msec? • 6- Streamline TESLA cavity production and preparation – Heat treat stack of half-cells,electropolish half-cell (instead of 9-cell structure) – Spin entire 9-cell structure out of one tube (done for copper) 21,000, 9-cell cavities Item 1: Potential Q improvements can lead to Q from 1010 to 1011 Achieved in single cells already, Need to achieve in 9-cells Explore Improved TESLA Cavity Shape Proposed New Geometry 10% higher Eacc for same Hpk Simulations show that new shape will not be prone to multipacting Better Surface Treatments Lead to High Gradients in TESLA Cavities Module 5 cavities. Vertical test results. 10 Q0 10 C45 AC60 AC61 AC65 AC66 AC79 AC78 AC62 10 9 0 5 10 15 Eacc [MV/m] 20 25 30 Denis Kostin, DESY, MHF/SL 100 mm More surface studies needed to show how to get to 40 + MV/m? Dark Current and Voltage Breakdown Studies Important for Warm NLC J. Wang 1995 Eacc = 65-75 MV/m R. Kirby/SLAC Individual Sparks Craters not harmful Reduce dark current (condition ing) SLAC DS2 1.8 m long structure - Cell 8, Downstream Side AFTER RF But Sustained Sparks Cause Too many craters=> surface erosion=> cavity detuning Previous Studies Show Many Common Features between RF and DC Breakdown • DC single breakdown events are very fast (few ns) like in cavities • Cause few isolated craters (not harmful) emission halted! (processing) • But multiple breakdown events can be long and cause severe surface damage (erosion) Copper Single Breakdown Event 1 mm Digital Video of Spark CERN Diamond Machined Copper cathode, HPR Craters from single breakdown event ? Ion bombardment Starburst region 20 um Sustained Spark at 170 MV/m QuickTime™ and a DV - NTSC decompressor are needed to see this picture. SEM 50 microns 20 microns Contaminants are one source of field emission and breakdown 1) Diamond Machined Cu, as for cavities 2) Mn Particles found After furnace brazing 3) Sparked 4) Mn particles Were here Now craters Mn particles Were here Now empty craters Mn particles outside starburst survived the spark Intentional V particle: Strong emitter On copper surface SEM 70 MV/m Spark 10 microns 20 microns Starbursts present on copper are carbon depleted areas due to ion bombardment Vanadium from Auger Auger Detection can find residue of original emitter Simulation Results • Modelling of breakdown has started • But could benefit from more effort More Needed Gas Distribution - starts by surface desorption -or melting of emitter tips - builds up by ion bombardment - may be ultimately dominated by cathode material Electrons Gas Electrons Ions Ions 50 microns Resources Needed for First Year Existing RAs and SRA 3 - 4 Graduate Students - 130 K 2 Technician support 150 K Equipment 150 K Materials and Supplies 100 K Outside Contracts 100 K Total 630 K