X-ray Booster IR Linac Harmonic RF RF Systems for NSLS-II J. Rose, A. Blednykh, N. Towne With help from many others at BNL and other institutions

Beam Energy3 GeV Beam Current500 mA Energy loss/turn2 MeV  p/p acceptance 3 % Power to Beam1 MW X-RAY Ring RF requirements RF parameters Frequency500MHz Cavity Voltage4.9 MV Momentum compaction Synchrotron frequency ~35kHz

Baseline CESR-B Cavity Beam energy gain/cav >2.4 MV Eacc>8 MV/m Unloaded Q >7  10 8 Standby (static) losses <30 W Dynamic + static losses <120W Operating Temperature 4.5 K Max. beam power/cavity <250 kW Frequency500 MHz SCRF chosen for lower R/Q, highly damped HOM’s, lower operating cost and comparable capital cost CESR-B has well established commercial production. Units 15 and 16 now being produced by ACCEL. In operations at Cornell (4), CLS(2), Taiwan (2). Being commissioned at Diamond (3). Ordered for ASP(?)

1500MHz “Bessy” cavity Voltage/cavity 0.5 MV Eacc>5MV/m Unloaded Q >7  10 8 Static losses <6W Dynamic + static losses <12W Operating T. 4.5 K Frequency 1500 MHz Harmonic Cavity for Bunch Lengthening required for 3% Momentum acceptance: 1500MHz requires 3 cavities Work continues on effect of bunch train transients on bunch lengthening N. Towne

X-Ray Ring Layout MHz cavities (1MW req’d and 250kW/coupler) MHz cavities At 1500MHz and 0.5MV/cav) Stray magnetic fields at cavities must be << 0.5 Gauss at cooldown !

IR Ring Requirements Vacc >2.5MV Beam current =1.0A (1.5) Beam power <10 kW 1 SCRF module (1M$ cavity, 0.2M$ RF + cryoplant) Low beam power means either matching stubs or adjustable coupling Benefits from Antennae Coupler ! Fwd. and Rev. Power vs. I

Thales 310kW transmitter costed, one per 2.3M$ ea CPI 800 kW klystron exists if dual or high power coupler adopted (can be optimized for 600kW) Option: Combine 50 kW IOT’s from broadcast industry (times 6 or 12 does not seem attractive,will study Diamond’s results) Will use IOT’s for Booster, IR ring RF Power Source Options TH2161B installed at CLS

Booster Ring Requirements Energy loss per turn = 1MeV, Vacc = 2MeV for 0.9% RF acceptance Negligible Energy gain per turn ~29 keV for 300ms ramp Beam current = ~3mA (~6mA for IR) Beam power 3-6 kW 2 “Petra” type cavities and 2 -50kW IOT’s (1.5M$ cavities + 0.4M$ RF) OR 1 SCRF module kW IOT (1M$ cavity, 0.2M$ RF + cryoplant)

Cavity Modeling with GdFdl GdfidL vs. CFISH Benchmark ferrite losses, superconductor surface resistance GdfidL vs. measurements Confirm ferrite properties Full Cavity results are now being calculated to be used to analyze CB instability Next is coupler analysis, Cavity pair with spool piece Alexei Blednykh

MOTIVATION Reduces # X-ray cavities from 4 >2 which reduces ring impedance Adjustable coupling to minimize IR ring, Booster rf power req’d. Lower static cryo-losses Frees up 6m straight ! R&D roadmap for power coupler R&D needs: RF transmitter Coupler development Coupler test stand Cryo-test facility Cavity prototype FOR NSLS-II: Dual antennae coupler design most appealing ! 250kW/coupler has been demonstrated, 500kW/cavity low technical risk. Adjustable coupling allows better matching for low power requirements of Booster, IR rings: need only one coupler: lower cost Road to upgrade: Add HOM to IR ring 2nd coupler port?

Cryo-Plant Requirements X-ray -4.9MV4 Cavities2 cavities Cavity V1.23 MV2.45 MV Static load30W ea Dynamic load26 W ea98 W ea Valve box~30W* total Harmonic 15 W +1W/m transfer lines 100 W *75 W* IR Ring(30Static +98Dynm.+30VB) W Booster(30Static +62Dynm.+30VB) W Total K K * Not sure how many VB’s needed, how many meters of transfer line

Frequency GHz Length 5.2 m Shunt imp.51 M  /m Q14000 Filling time0.74  s Energy gain 12.6*sqrt(P MW ) Attenuation  = 0.55 Np GHz Linac Picture courtesy of ACCEL Energy gain 80MeV/tank for 40MW power input (no-load) 1 Klystron TH2100 (45MW) per accelerating tank Solid state modulator to drive klystron

Low Level RF Emphasis to date has been on cavity choices and high power systems which have immediate impact on beam dynamics, ring layout, and have longer lead times. Unlike the cavities and high power systems the LLRF is likely to be upgraded throughout the life of the project. Take advantage of the flexibilty of new digital RF systems and direct IQ modulation at 500 and 2998MHz. Unlike the high power systems LLRF is not available commercially, and skills need to be in-house. Digital RF requires additional skill set (e.g., the rf programmer)

Conclusions RF requirements for NSLS-II can be met with existing technology, often from commercial sources Development of high power and/or dual antennae coupler would reduce number of cavities from 4 to 2 in X-ray ring, reducing impedance, freeing up ID straight. Allows more efficient low power operation in Booster, IR rings. Upgradeable, not locked in to existing performance. Need to continue work on cavity modeling and impedance calculations, analysis of bunch lengthening with harmonic RF in the near term, and later on systems analysis and LLRF