X-Band Klystron Development at SLAC Slide 1
The Beginning X-band klystron work began at SLAC in the mid to late 80 s to develop high frequency (4x SLAC s-band), high power RF sources for the linear collider designs under consideration at that time. The first of these development tubes was the XC series. Slide 2
XC Series Design Parameters Frequency 11.424 GHz. Pk. Output Power 100 MW RF Pulse Width 1 µs. Beam Voltage 440 KV Beam Current 520 A Beam areal Compression 190:1 Max. Gun Surface Gradient 308 KV/cm Cathode diameter 8.9 cm (3.5 ) Focusing Field 6kG Slide 3
XC1 The XC Series 5 cell Klystron with single cell reentrant output cavity. Reached 65 MW at 30-40 ns but suffered from RF breakdown at wider pulse widths. XC2 2 cell coupled cavity output 72 MW at 100 ns Thin windows (.8 mm), later rebuilt with thick windows (3.7 mm) XC3 2 cell coupled cavity output Improved magnetic profile over XC2 Similar performance to XC2 Slide 4
XC1,2 Performance 80 70 Power Measurements (1/92) XC1 XC2 60 50 40 30 20 10 0 200 400 600 800 1000 1200 RF pulse width Slide 5
XBT Diode The XC Series Diode to study improved magnetic entrance design (floating inner polepiece) and reduced beam convergence (area compression 110:1) Had four electrically isolated drift sections of decreasing diameter to measure beam loss along tunnel Slide 6
XBT Diode Slide 7
XC4 2 cell coupled cavity output The XC Series Reduced convergence gun Had Be drift tunnel inserts to protect against beam erosion Built with internal RF loads (no windows) Still had RF breakdown, found damage in the coupling irises between cells XC5,7 4 cell TW output 52 MW at 1µs Slide 8
XC4 Slide 9
XC6 The XC Series 2 cell uncoupled cavity output feeding four output windows 90 MW at 200 ns XC8 4 cell SW output Oscillated, lead to the incorporation of external loss cavities in the output waveguide in subsequent tubes Slide 10
The XC Series Output Circuits Slide 11
The XL Series Drawing on the XC experiences the XL series was launched to produce RF sources for the NLCTA Reduced peak power to 50 MW Reduced μperveance to 1.2 Used TE 01 output windows Used multi-gap outputs (SW and TW) Slide 12
XL Series Design Parameters Beam Voltage Beam Current Peak Output Power RF Pulse width Cathode Diameter 440 KV 350 A 50 MW 1.5µs 71.4 mm Beam areal compression 125:1 Peak Cathode loading 12.8 A/cm 2 Magnetic field µperveance 1.2 0.47 T December 1-4, 2008 Workshop X-Band on RF X-band Structure RF & Technology Beam Dynamics for FELs Workshop- Cockcroft Institute, UK Slide 13
XL Diode μperveance- 1.2 99.5% Transmission Slide 14
The XL Series Slide 15
XL1 Three cell SW output The XL Series 58 MW at 250 ns, 50 MW at 1.5 μs 17 GHz oscillation due to equal gap penultimate cavities HV seal puncture, rebuilt with gun ion pump, used on all subsequent XL tubes XL2 Same as XL1 with modified penultimate cavities 67 MW at 200 ns Slide 16
XL3 XL4 The XL Series Four cell TW output, wider bandwidth for better pulse compression Some high frequency instabilities Stainless steel drift tubes between penultimate cavities to kill high frequency instabilities 90 MW at 100 ns, 50 MW at 1.5 μs Slide 17
The XL Series Output Power vs Beam Voltage for the XL4 Klystrons 100 80 XL4-2 (1.5 microsec) XL4-1 (1.5 microsec.) XL4-1 (1.2 microsec.) (100 ns.) 60 40 20 0 250 300 350 400 450 500 Beam Voltage (KV) aev-3/24/97 Slide 18
XL4 This is our current work horse x-band RF source 15 tubes built to date (not counting rebuilds) Four in use in the KTL to feed the ASTA bunker and HGB experiments at TS-2 and TS-4 Seven sockets in ESB, five for NLCTA and a two-pack socket (not all occupied currently) One tube and spare for LCLS linearizer, more contemplated for transverse structure installation and future injector(s) Incremental design improvements Larger TE 01 output windows from PPM tube work Large radius coupling cell irises from XL5 work Slide 19
The PPM Series For the large RF systems under consideration for linear colliders, it was clear that the high DC power demand of the XL series solenoids had to be eliminated. This lead us to investigate PPM (or more accurately PCM) focused klystrons. Slide 20
The PPM Series XL-PPM, 50 MW, 1.5 μs, μk=.6 Integral drift tunnel/magnetic circuit (iron pp s monel spacers) SmCo magnets Five cell TW output cavity Two TE 01 output windows Beam diode attained 99.9% beam transmission at 490 kv, 2.8 μs pulse length, 120 Hz PRF Klystron exhibited non-monotonic gain attributed to multipactor in the drift tube, cured with TiN coating 50 MW at 2.4 μs 120 Hz for two minute bursts (heating and x-ray limited) Basis of initial industrialization effort for the NLC Two tubes bought from industry with limited success Slide 21
The PPM Series Slide 22
XL-PPM Gain Curve Slide 23
XP1 XL-PPM success encouraged us to increase power to 75 MW with.75 μp Design features Larger diameter drift tunnel Smooth SST drift tunnel bore NdFeB magnets All PM focusing (no matching coils) Performance Magnet quality plagued us 1.4 GHz (gun) and 20 GHz (tailpipe) oscillations, fixed with lossy ceramics 79 MW at 2.8 μs, limited to 10 Hz due to body heating Slide 24
XP3 A DFM device with better cooling capability Design features Water cooled clamp-on magnet structures Smooth SST drift tunnel bore NdFeB magnets Matching coils return New compact gun design Slide 25
XP3 Design Parameters Output Power 75 MW Beam Voltage 490 KV Beam Current 257 A Perveance 0.75 Pulse Length 3.2 µs PRF 120 Hz. Average RF Power 27 KW Gain 55 db min. Efficiency 60% No. Output Windows 2 Slide 26
Performance Diode XP3 Gun oscillations, cured with lossy ceramics on gun stem XP3-1 11.7 GHz Output oscillation due to incorrect loss cavity position XP3-2 CPI built RF circuit and magnet structure Gun oscillation broke HV seal XP3-33 Added another gun loss ceramic 75 MW at 1.6 μs, 120 Hz Slide 27
Performance (cont.) XP3-4 XP3 Integral polepiece drift tunnel for reduced transverse field Increased coupler iris radii Air cooled 75 MW at 1.62 μs pulse length, 120 Hz 1.3% beam interception (very good) XP3-5 Similar to 75XP3-4 Suspected window breakdown Slide 28
XP3-1 Slide 29
XP3 Gun Stem Slide 30
75XP4 Design incorporating the best of the XL- PPM, XP1, and XP3 designs Large gun from XL-PPM/XP1 Integral polepiece Anode matching coils Good cooling Not finished due to NLC->ILC re-aligment Slide 31
XL5 During 2008 and 2009 MOUs were established between SLAC and three European labs (CERN, PSI, and ST) for the development and fabrication of a 50 MW 12 GHz klystron scaled from the XL4 (total of five tubes) Slide 32
Design features XL5 Use XL4 beam optics (same gun, solenoid, collector) Keep XL4 cavity spacing to allow reuse of more parts Scale cavities and other frequency dependent parts only (output, mode converter, windows) Slide 33
XL5 Components Slide 34
XL5 Performance Expectations 60 55 50 45 40 35 30 25 0 200 400 600 800 1000 Gain (purple) and MW out vs input (blue) - AJDSK runs of the XL5 design at 420kV and MAGIC (yellow) Slide 35
XL5 and XL4 Design Comparison 80 70 60 XL5-380kV XL5-400kV XL5-420kV XL4-13A @ 420kV, 1.5us XL4 sim at 420kV XL5-440kV output MW 50 40 30 20 0 200 400 600 800 1000 1200 Drive W Slide 36
Acknowledgements Many thanks to those who have worked on the KMD x- band program(s) over the years (in no particular order): Ed Wright, Sami Tantawi, Daryl Sprehn, Richard Schumacher, Chris Pearson, Terry Lee, Andrew Haase, W.R. Fowkes, Ken Eppley, George Caryotakis, Richard Callin, Karen Fant, Bob Phillips, David Martin, Lisa Laurent, John Eichner, Saul gold Particular thanks to Arnald Vlieks whose X-Band RF Structure & Beam Dynamics Workshop talk I borrowed heavily from Slide 37