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PEP Super-B High Power RF Peter McIntosh SLAC Super-B Factory Workshop in Hawaii 20-22 April 2005 University of Hawaii Stanford Linear Accelerator Center Outline RF Requirements Cavity Limitations Voltage Power Klystrons 1.2 MW 2.4 MW Circulators HVPS System System Configurations Conclusions Stanford Linear Accelerator Center RF Requirements 3 cavity solutions being investigated: R/Q = 5, 15 and 30 W (see S Novokhatski’s talk). The RF power required for L = 7e35 and 1e36 varies as a function of cavity option as the R/Q impacts primarily the HOM losses: As R/Q goes up cavity HOM losses go up! The R/Q also impacts the cryogenic losses which affect the Total AC power required: As R/Q goes up cavity cryogenic losses go down! For the cavity options being investigated, the net difference in Total AC power is almost zero! Assuming the cavity to be used lies somewhere between 5 – 30 W we can see that …… Stanford Linear Accelerator Center RF and AC Power (5W) Stanford Linear Accelerator Center RF and AC Power (30W) Increased Reduced Stanford Linear Accelerator Center RF and AC Power Summary To define the number of cavities required, have assumed that 1 MW can be supplied to each RF cavity (see later). For L = 7e35 using R/Q = 5 W cavity: LER = 21.7 MW HER = 16.2 MW For L = 7e35 using R/Q = 30 W cavity: LER = 22.1 MW HER = 16.2 MW For L = 1e36 using R/Q = 5 W cavity: LER = 39.8 MW HER = 24.9 MW For L = 1e36 using R/Q = 30 W cavity: LER = 42.0 MW HER = 25.0 MW Cavity HOM losses increase by 2.2 MW in the LER at 1e36. Total AC cryogenic power however reduces considerably for the 30 W cavity by 50% for both luminosity options compared to the 5 W cavity. Net AC power difference is comparable (to within 2%) for each cavity option at each luminosity. Stanford Linear Accelerator Center R/Q=15W Solution Stanford Linear Accelerator Center Cavity Limitations - Voltage Practical achievable voltage/cell depends upon: Cavity Qo Niobium purity Cryogenic operating temperature Cryogenic load For the R/Q = 5, 15 and 30 W cavities: Required voltage per cell Vc = 1.25 MV, requiring Qo = 3e9, 1e9 and 1e9 respectively. For feedback stability R/Q = 5 W preferable lowest detuning (see D. Teytelman’s talk) For cryogenic reasons R/Q = 30 W preferable (see later). Number of cavities required is the same for each @ L =7e35. At L = 1e36, the cavity HOM losses in the LER require more RF cavities (2) at R/Q = 30 W. What cavity voltage can we expect to reach …. Stanford Linear Accelerator Center Voltage for R/Q = 5 W Cavity Stanford Linear Accelerator Center Voltage for R/Q = 30 W Cavity Stanford Linear Accelerator Center Voltage for R/Q = 15 W Cavity Stanford Linear Accelerator Center Cavity Epk and Hpk Parameters S Novokhatski Stanford Linear Accelerator Center Voltage Overhead (for 30W) Theoretical Quench Limit for Nb (Hpk = 1700 Oe or 135.281 kA/m) Field Emission Onset (Epk > 10 MV/m) Stanford Linear Accelerator Center Voltage Overhead (for 5W) Theoretical Quench Limit for Nb (Hpk = 1700 Oe or 135.281 kA/m) Field Emission Onset (Epk > 10 MV/m) Stanford Linear Accelerator Center Voltage Overhead (for 15W) Theoretical Quench Limit for Nb (Hpk = 1700 Oe or 135.281 kA/m) Field Emission Onset (Epk > 10 MV/m) Stanford Linear Accelerator Center Cavity Limitations - Power To minimize the number of RF cavities per ring: Based on what has been achieved at ~ 500 MHz for both KEK-B and CESR: 1 MW total RF input power per cavity has been chosen! Cavity will employ dual RF feeds, each providing up to 500 kW. RF breakdown investigations need to be performed to identify a system that can meet this power requirement at 952 MHz. Coaxial coupler arrangement more compact. Is this power level realistically achievable? Stanford Linear Accelerator Center Cavity Input Couplers CESR (fRF = 500 MHz): Aperture waveguide coupled Operate typically up to 300 kW Operated up to 360 kW (through) Superconducting Damped Cavity for KEKB T. Furuya DOOR KN OB TRAN SFOR MER INPU T COUPL ER KEK-B (fRF = 508 MHz): Biased coaxial coupler Operate typically up to 350 kW For Super-KEKB hope to reach 500 kW Tested up to 800 kW (through) GATE VAL VE L He GATE VAL VE F REQU ENCY TUN ER HOM DAMPER ( SBP) HOM DAMPER (LBP) Nb CAV ITY ION PUMP N 2 SHIEL D 0 0.5 1m Stanford Linear Accelerator Center Klystrons – 1.2 MW SLAC already produces 1.2 MW tubes at 476 MHz for PEP-II. Each powered by a 2.5 MVA DC HVPS. Tube operates at 83 kV and 24 A with perveance of 1.004. Maintaining these beam parameters for Super-B @ 952 MHz would enable the same HVPS system to be used. Scale the cavity frequencies, drift tube spacing, gap lengths, drift pipe and beam radii. Magnetic field increases by factor of 2 existing 476 MHz tube focus coil adequate. Stanford Linear Accelerator Center 1.2 MW Klystron – Small Signal Stanford Linear Accelerator Center 1.2 MW Klystron – Large Signal Stanford Linear Accelerator Center 1.2 MW Klystron Specification Parameter Gun Collector (Full power) Frequency (MHz) 952 Beam Voltage (kV) 83 Beam Current (A) 24 Perveance 140.0 Accelerating Cavities RF Output (WR975) Value 1.004 Bandwidth (MHz) 10 Gain (dB) 47 Efficiency (%) 70 Stanford Linear Accelerator Center Klystrons – 2.4 MW Doubling in RF power means that the existing 2.5 MVA HVPS can no longer be used now need a 4 MVA HVPS. Beam power characteristics increase up to 125 kV and 29.2 A with drop in perveance to 0.6607. Higher beam voltage increases cavity spacing and gap lengths accelerating section ~ 20% longer than the 1.2 MW tube. Magnetic field comparable to that of the 1.2 MW tube. Thermal loading of the output circuit requires more detailed investigation. Suspect will most likely require a dual output to minimize thermal loading at the RF windows. Stanford Linear Accelerator Center 2.4 MW Klystron – Large Signal Stanford Linear Accelerator Center 2.4 MW Klystron Specification Gun Collector (Full power) 160.0 Accelerating Cavities Parameter RF Output (WR975) Value Frequency (MHz) 952 Beam Voltage (kV) 125 Beam Current (A) 29.2 Perveance (A/V3/2) 0.6607 Bandwidth (MHz) 8* Gain (dB) 49.8 Efficiency (%) 70 * Needs further optimization Stanford Linear Accelerator Center Klystron Option Footprints 1.2 MW @ 476 MHz 83 kV and 24 A Perveance = 1.004 210.07 1.2 MW @ 952 MHz 83 kV and 24 A Perveance = 1.004 140.0 2.4 MW @ 952 MHz 125 kV and 29.2 A Perveance = 0.6607 160.0 Stanford Linear Accelerator Center 2.4 MW AFT Circulator Layout Stanford Linear Accelerator Center Circulators Spec 1.7% 1 dry load, 1 water load Full Reflection! Klystron would see 2.4 kW in beam abort x 4 increase c.f. 1.2 MW 476 MHz unit Stanford Linear Accelerator Center HVPS Originally designed for a depressed collector klystron. Existing 2.5 MVA HVPS has a primary SCR-controlled rectifier operating at the existing site-wide distribution voltage of 12.47kV: control provides for fast voltage adjustment and fault protection. Rectifier configuration prevents the dump of filter capacitor stored energy into the klystron in the event of a klystron arc. 12.47kV enters the circuit breaker and manual load disconnect switch and provides a safety lock and tag disconnect for maintenance. Remote turn-on and turn-off is by a full, fault-rated vacuum breaker used as a contactor. A 12-pulse rectifier reduces power line harmonic distortion to industrial standards. Stanford Linear Accelerator Center PEP-II/SPEAR3 2.5 MVA HVPS FILTER RESISTORS 500 OHMS 1KW CAPACITORS 8uFD 30KV RECTIFIERS 30KV 30A -90KV TERMINATION TANK T2 FILTER RECTIFIERS 30KV 3A AVE -77KV RECTIFIER TRANSFORMER T2 CROWBAR 100KV 80A 12.47KV 3PH 3000 KVA -52KV THYRISTOR CONTROLED RECTIFIER 40KV 80A DISCONNECT & BREAKER T1 PHASE SHIFTING TRANSFORMER -26KV FILTER INDUCTOR SPEAR 3 KLYSTRON POWER SUPPLY T1 GRN KLYSTRON UP TO 90KV UP TO 27 AMPS Stanford Linear Accelerator Center Super-B HVPS Options 1.2 MW Klystron: Existing 2.5 MVA HVPS system compatible. No development overhead. 2.4 MW Klystron: Same 2.5 MVA HVPS design, with larger transformers to reach 4 MVA: Applicable transformers are commercially available. Higher voltage required (125 kV): Makes HV connections more difficult/expensive. Anticipate a 20 – 30% size and cost increase over the existing 2.5 MVA unit. Stanford Linear Accelerator Center System Configuration 1 1.2 MW Klystron Single 952 MHz RF Cavity 1.2 MW Circulator WR975 Waveguide Stanford Linear Accelerator Center System Configuration 2 2.4 MW Klystron 2.4 MW Circulator Dual 952 MHz RF Cavities WR975 Waveguide Stanford Linear Accelerator Center System Configuration 3 1.2 MW Circulator Dual 952 MHz RF Cavities 2.4 MW Klystron 1.2 MW Circulator Stanford Linear Accelerator Center Conclusions RF requirements for L=7e35 and L=1e36 identified need up to 190 MW site AC power! Low R/Q cavities needed for stability control. Cavity voltage and RF power limits identified how far can we push these?!? High power klystrons (> 1 MW) at 952 MHz look to be achievable. High power circulators appear to be available from industry. HVPS systems for Super-PEPII klystrons are available now at 1.2 MW, but require development at 2.4 MW. Watch this space! Thank You Stanford Linear Accelerator Center RF Parameters Summary