RF Issues with Configuration Options Project X retreat Nov 2, 2010 Brian Chase, Julien Branlard, Gustavo Cancelo, Warren Schappert, Yuriy Pischalnikov ProjX Retreat Nov 21RF Issues B. Chase

Outline Current results of resonance control tests Some answers to posed question Simulation results for Pulsed linac Exploring options Conclusions ProjX Retreat Nov 22RF Issues B. Chase

Parameter Space ProjX Retreat Nov 23RF Issues B. Chase

Forward and reflected power The PI control is an effective regulator as long as there is enough RF power available and the RF operates in the linear region. A cavity detuned by 500Hz (~2 half bandwidths) requires 4 times more power. Pfor/Pref crosstalk Pref not zero because QL not matched ProjX Retreat Nov 24RF Issues B. Chase

300Hz 10Hz PIEZO OFF PIEZO ON (Vp-p=90V) 44% extra Power C1(AES04)- FNAL/Blade Tuner Cavity Eacc=27MV/m, RF feedback ON by FNAL Piezo Control System Provided by Warren Schappert & Yuriy Pischalnikov ProjX Retreat Nov 25RF Issues B. Chase

Beam parameters for injection Need to accumulate 26 mA-ms of beam in the Recycler every 0.75 sec. Below is the possible beam parameter space to meet this requirement: – Foil stripping: Beam current 1 mA, beam-ON pulse 2 ms, 20 Hz, 14 pulses. – Foil stripping: Beam current 1 mA, beam-ON pulse 4.2 ms, 10 Hz, 6 pulses. – Foil stripping: Beam current 2 mA, beam-ON pulse 2 ms, 10 Hz, 7 pulses. – Laser stripping: Beam current 1 mA, beam-ON pulse 26 ms, 1.5 Hz. – Laser or foil stripping: Beam current 2 mA, beam-ON pulse 13 ms, 1.5 Hz. ProjX Retreat Nov 26RF Issues B. Chase

Configuration Choices Does not include power for resonance control Work in progress Chart provided by Vyacheslav Yakovlev ProjX Retreat Nov 27RF Issues B. Chase

Comparison of proposals – For the 3-8 GeV section Pros and cons of these three scenarios: – 1mA, 4ms flat 10 Hz » A reasonable compromise – lowest cost 3 to 8 GeV solution – 1mA, 2ms flat 20 Hz » Average power and cryo power are up » Lowest RF energy per pulse – 2mA, 2ms flat 10 Hz (or 4ms flat 5 Hz) » Most of LFD happens in the 2-3 first ms of flat top » QL ~ 5e6 are preferable » Higher cryo load for 20 Hz (pulse is 10 msec out of 50) – 26 ms flat top, 1.33Hz » Eliminates RR and maybe 6 to 8 GeV section » Highest RF energy per pulse – 13 ms flat top, 1.33Hz » Elimiates RR and maybe 6 to 8 GeV section » Lowest average power » lowest cost overall? All these scenarios will require piezo resonance control Need better PZT control than anything we have achieved so far Need new tuner/cryomodule design for in situ repair ProjX Retreat Nov 28RF Issues B. Chase

Open Questions – For the 1 GeV CW section What are the effects of a 500  sec gap in beam current at Hz? – No large issue for RF vector control as LLRF can switch drive current quickly – No issue for resonance control as LFD is not driven – No large issue for HLRF as power is just reduced during gap – May excite other cavity passband modes but not likely to be a big issue What are the issues associated with switching from 1mA to 2 mA with a few percent duty factor? – LLRF - No problem for vector or resonance control as cavity field remains almost constant – HLRF – If Q l is setup for 2 mA, then reflected power at 1mA is 20% higher than a perfect match. Somewhat higher operating costs – Higher peak power means some cost increase for RF system (no easy answers, not a linear problem ) ProjX Retreat Nov 29RF Issues B. Chase

What are the effects of pulse width and rep rate? Explore 1mA - 10Hz, 4.2 ms FT vs. 20Hz 2ms FT At 60kW forward power, the fill time to 25 MV/m at a Ql of 6E6 is 2ms – For these short flattop lengths, does a higher Q make sense? LLRF - LFD induced cavity ringing for the present 1300 MHz cavity design reaches a max excursion at about 2 ms – no fundamental difference for 2 or 4 ms FT – Current tests suggest Hz LFD control Loaded Qs of 6E6 are realistic HLRF – total pulse energy is higher for 4 ms (50%) while average power is lower for 4 ms, 10 Hz – Power efficiency is poor due to the fill to flattop ratio 20Hz cryo load is higher due to fill and decay At 20 Hz cavity ringing will have half the damping time of 10 Hz – We will probably get pulse to pulse effects ProjX Retreat Nov 210RF Issues B. Chase

Slow fill Long pulse Phase track off 4 ms fill 13 ms flattop Phase tracking on Q l = 1e7 Cavity phase rolls away from drive vector during fill. ProjX Retreat Nov 211RF Issues B. Chase

Slow fill Long pulse Phase track on 1mA 4 ms fill 13 ms flattop Phase tracking on Q l = 1e7 32kW Phase trajectory programming with a slow fill allows cavity to detune without ringing ProjX Retreat Nov 212RF Issues B. Chase

Slow fill Long pulse Phase track on 2 mA 4 ms fill 13 ms flattop Phase tracking on Q l = 1e kW Perfect power match at 2mA Twice the beam power for an additional 20kW ProjX Retreat Nov 213RF Issues B. Chase

Power Overhead for Control 1mA 60 kW RF max Hitting Pmax 75kW/ cavity Is conservative power target ProjX Retreat Nov 214RF Issues B. Chase

Harmonic Numbers in MI IF we inject directly into the Main Injector – &IF The injection energy = GeV Kinetic – &IF We change the Harmonic number of MI to 605 – &IF We can develop long pulse RF systems – Then the MI injection frequency = MHz =162.5 MHz / 3 – Then we has synchronous RF transfers and get rid of: 2 GeV of expensive Linac Complex chopping patterns (may allow for resonant chopper) Many beam loading spectral spurs in Linac (less chance to excite passband modes and HOMS) Complex injection loading patterns in MI (straight forward injection) Clock generation issues (no meta-stable states) – Harmonic # 604 works at GeV ProjX Retreat Nov 215RF Issues B. Chase

What R&D is needed for the pulsed linac? The dominant RF control issue for long pulse, low current operation is Lorentz Force Detuning The approaches to controlling this are: – stiffer cavities The KEK cavities have much higher mechanical frequencies Warren and Yuriy are not convinced this helps – Piezo fast tuners Recent FNAL test show control at the 50Hz level for long pulses, 10 Hz for 1msec FT short pulse – Other fast tuners Electromagnetic solenoid ? Some work has been done at TD ProjX Retreat Nov 216RF Issues B. Chase

What can we test here at FNAL? 325 MHz – HTS: Microphonic compensation, IOTs 650 MHz – IOT test stand: Dynamic power tests, optimization of power tube tuning 1300 MHz – NML CM1: vector sum control and multi-cavity resonance control proof of principle – Fully characterize mechanical models of cavities – Understand the spread in parameters – Lifetime study on Piezo Failure mode analysis -> improve design – Limited in pulse length by modulator and klystron – A0 CC1: transients due to beam current change – HTS: high QL (up to 1.6e7) and long pulses operation ProjX Retreat Nov 217RF Issues B. Chase

Conclusions The “best” configuration is not obvious and we need: – More information – Parametric analysis Some things are becoming clear – For CW linac Limit Qs to 2E7 for microphonics Lowering Qs in 650 MHz section to 1E7 -> 20% reflected power Limit gradient to 15 or 16 MeV/m for cryo and reliability Some increase over 1 mA for pulsed operation will come at a small cost, at some point there may be a discrete jump ProjX Retreat Nov 218RF Issues B. Chase

Conclusions For pulsed linac Limit Qs to 6E6 or slightly higher for vector control in the presence of Lorentz FD Risetimes are at least 2msec and no-beam power required is probably 35 kW Short pulses are – good to reduce RF energy per pulse – Bad for average RF power – Bad for cryo load Long pulse and injection into MI may be interesting – Shorter linac – Synchronous RF ProjX Retreat Nov 219RF Issues B. Chase

Backup Slides ProjX Retreat Nov 2RF Issues B. Chase20

Issues with Circulators For solid state amplifiers and IOTs, manufactures have repeatedly suggested that we may not need circulators as both of these devices will handle high VSWR. Gysel Combiner design replaces circulator / 2 RF distribution will reflect the cavity impedance to the power device – Reduce cost – Improved efficiency when running over-coupled cavities ProjX Retreat Nov 221RF Issues B. Chase

Open questions for pulsed linac What is a reasonable maximum Q? – 8E6 based on 50 Hz regulation What is a reasonable minimum power overhead? – 25kW based on 50 Hz regulation What is the level of open loop regulation per cavity? – 3% 3 deg Will FVMs be required? – Not unless better regulation is needed Are there modifications to the cavity design we recommend? – The stiffer, the better as long as tuners can still control Are piezo tuners required for cavity operation? – Yes, but can they be designed to meet operational reliability requirements? – Should piezos be repairable in the tunnel? ProjX Retreat Nov 222RF Issues B. Chase

R&D The possible study locations are: – HTS (long pulse but limited power) HTS allows for testing of multiple cavities and tuner assembles Schedule conflicts with cavity production – CC2 (same as HTS) Should have lots of study time Single cavity with DESY style tuner – CM1 (pulse length unknown)?? 8 cavities with reasonable study periods – Main Injector Deceleration studies to 6 GeV ProjX Retreat Nov 223RF Issues B. Chase