*High Intensity Neutrino Source Two Devices for HINS* Robyn Madrak Accelerator Physics Center (APC) Part I: Fast Chopper Part II: Vector Modulators

HINS - Purpose 2Robyn Madrak - FNAL APT Seminar - 12/16/ MeV Linac under construction at Fermilabs meson building R&D Linac which will demonstrate novel technologies used for the first time Technical feasibility proof of (front end) for 8 GeV Linac, Project X, etc. High intensity proton source for neutrino physics/ muon storage ring experiments

Unique Aspects/Challenges Solenoidal focusing cleaner, axisymmetric beam Use of SC spoke resonators Fast ferrite phase shifters will allow multiple cavities (and RFQ) to be driven by a single 2.5 MW, 325 MHz klystron => cost savings Fast Beam Chopper 3Robyn Madrak - FNAL APT Seminar - 12/16/2008

4 Parameters * full un-chopped 3 msec pulse at klystron-limited 20 mA

FNAL HINS Ion Source (H - ) RFQ MEBT Room Temperature 16-Cavity, 16 SC Solenoid Section =0.4 SSR 11-Cavity, 6-Solenoid Cryostat Two =0.2 SSR 9-Cavity, 9-Solenoid Cryostats 2.5 MeV 50 KeV 10 MeV 20 MeV 60 MeV 30 MeV 5Robyn Madrak - FNAL APT Seminar - 12/16/2008

HINS Chopper – Part I Should the HINS be extended to an 8 GeV Linac, output beam would be transferred to Fermilabs Main Injector, with 53 MHz RF frequency HINS Linac Bunches are spaced by 325 MHz (3.1ns) In MI, RF frequency is ~53 MHz (~19ns) Dont want bunches in the 53 MHz separatrix Chop out ~1 of every 6 bunches Additional complication: 325 n G 53 Sometimes chop 1, sometimes 2 6Robyn Madrak - FNAL APT Seminar - 12/16/2008

Traveling Wave Chopper Structure beam is deflected by traveling pulse (electric field) (beam)=0.073 => must slow down pulse Use traveling wave meander structure: - 50 cm long - 16 mm between chopper plates kV per plate - deflection of 6mm at end of plates 6 mm Ω 20 mm thick substrate ( = 9.6) =0.073 d = 16mm V = +2.4 kV V = -2.4 kV ~6ns =0.073 chopper plates (meanders) deflection = 24mRad Pwid < 6 ns 7Robyn Madrak - FNAL APT Seminar - 12/16/2008

Chopper in MEBT length of chopper plates: 50 cm drift space downstream: 30 cm RFQ 2.5 MeV solenoids chopper buncher cavities 8Robyn Madrak - FNAL APT Seminar - 12/16/2008

Deflection length of chopper plates: 50 cm drift space downstream: 30 cm plate separation: 16 mm p, d E L d [m]= E L 2 /2p [10 9 Vm/(GeV/c)] = tan -1 (EL/p ) E = 2 X (1.9kV)/16 mm = 2 X (C 2.4 kV)/16 mm coverage factor d(L=50 cm ) = 6 mm (L=50 cm )X30 cm = 7 mm 24mRad 9Robyn Madrak - FNAL APT Seminar - 12/16/2008

Pulser Development 10Robyn Madrak - FNAL APT Seminar - 12/16/2008 We need Two pulsers to drive the ~50 Ω meanders: +/- 2.4 kV Max ~5.5 ns pulse width (including rise and fall time) 53 MHz rep rate burst of or Programmable pulse width (may sometimes chop 1 bunch, sometimes two) Specs do not lead to an obvious solution

11 Similar Choppers CERN-SPL LANL-SNS CERN-SPLLANL-SNSRAL/ESSFNAL HINS Beam Energy3 MeV2.5 MeV Electrode Length2 X 40 cm35 cm34 cm50 cm Electrode Gap20 mm18 mm14 mm16 mm Deflection Angle5.3 mRad18 mRad16 mRad24 mRad Electrode Voltage±0.5 kV±2.35 kV±2.2kV±2.4kV Pulse Rise Time< 2ns10 ns2 ns< 2ns Pulse Durationmin 8ns300 ns12 ns< 5.5 ns Pulse Rep Rate44MHz1 MHz2.4 MHz53 MHz Bunch Frequency352 MHz402.5 MHz280 MHz325 MHz Burst Duration0.6 ms945 ns1.5 ms3ms, 1ms Burst Rep Rate50 Hz60 Hz25 Hz2.5, 10 Hz Chop Description3/8 bunchesOn 300,off 645 ns1 or 2/6 bunches

~60 V pulse 3.9 ns Combining lower voltage pulses? scope: sees ¼ of ~120V signal (25Ω/100Ω) Fet A (~60V) Fet B (~60V) 75Ω 50Ω 100Ω ferrite 50Ω t_rise =1.4 ns t_fall = 2.2ns width = 4.1ns 2.5ns/div repeat for 10ms Polyfet SP204 Basic Concept: Two 60V50 pulses Combined to One 120 V100 pulse scope 12Robyn Madrak - FNAL APT Seminar - 12/16/2008

Kentech 500V Pulser pulse control cards PSU pulse cards trigger and power dist cards output before fully assembled: one side of combiner: five 25 Ω semirigid cable in parallel, with ferrite 25 Ω semirigid cable 13Robyn Madrak - FNAL APT Seminar - 12/16/2008

~520 V pulse 5.5 ns w/53 MHz rep rate: 1 ms of 53 MHz 3 ms of 53 MHz 500V Pulser Output 10Hz) 2.5Hz) June 06 14Robyn Madrak - FNAL APT Seminar - 12/16/2008

Pulser output 200V/div 5ns/div 3ms burst 200V/div 400 s/div 1.2 kV Pulser Nov 07 15Robyn Madrak - FNAL APT Seminar - 12/16/2008

Kentech Pulsers 500 V Pulser was a success Subsequent 1.2 kV pulser was a success Plan: two (1.2kV50 Ω) into one (2.4kV100 Ω) output This requires a combiner and a meander with 100 Ω impedance 16Robyn Madrak - FNAL APT Seminar - 12/16/2008

Microstrips in General phase velocity and impedance are determined by effective dielectric constant: Delay time ( ) and Z 0 may be adjusted by Adjusting d, W, and also meander pathlength Using only one trace or two in parallel Adding an air gap beneath the dielectric (changes e ); can be used to tune 17 view from end view from top

FNAL Fabricated Meanders We have pursued the following: 1.Use double meander design with air gap between meander and ground plane (50 Ω w/no gap, 100 Ω /w gap) 2.Using single meander Material: Rogers TMM10i, Cu clad; =9.8, 18 long (46 cm) Meander is formed by routing out traces double meander single meander 20mm 40mm 78 mm 18Robyn Madrak - FNAL APT Seminar - 12/16/2008

Chopper Meanders Important Aspects 1.Material: Outgassing? 2.Impedance (avoid reflections) 3.Delay time (match beam ) 4.Pulse Behavior along length (dispersion) 5.Coverage Factor 20mm 40mm 19Robyn Madrak - FNAL APT Seminar - 12/16/2008

Meander Substrate Meander traces are generated by routing out traces on Rogers TMM10i, Cu clad Cheaper, faster than paste/firing/electrochemical deposition Test indicates acceptable vacuum properties Terry 8E-08 torr 0.63 L/s (with final surface area) bakeout begins nitrogen backfill 20Robyn Madrak - FNAL APT Seminar - 12/16/2008

Double Meander, Impedance 101 Ω : with spacers Impedance measurements from 1 – 500 MHz 55 Ω : with no spacers 21Robyn Madrak - FNAL APT Seminar - 12/16/2008

Double Meander, Delay 22Robyn Madrak - FNAL APT Seminar - 12/16/2008 spacingt delay (ns) Want = to match beam speed Measure pulse delay in meander: Varying distance between meander and ground plane shows sensitivity input pulse output; delayed ~100 Ω 50 Ω

Single Meanders: Impedance and Delay Meander 1: 95 MHzMeander 2: MHz input pulse nominal 0.010shims t delay=20.8ns t delay=20.24ns 23Robyn Madrak - FNAL APT Seminar - 12/16/2008

Dispersion input pulse beginning half way end single meander 2 single meander 1 low dispersion input pulse beginning half way end double meander Meanders are 18 long Look at pulse behavior along length using high f scope probe 2 ns/div 24Robyn Madrak - FNAL APT Seminar - 12/16/2008

Coverage Factor V -V d chopper plates E = C * 2V/d (electric field) coverage factor The electric field between the chopper plates is less than that for a structure in which the entire surface is conducting This must be accounted for in the chopper design when determining the voltage needed for the desired kick conductor dielectric 25Robyn Madrak - FNAL APT Seminar - 12/16/2008

Coverage Factor Measurements High frequency probe Tip is at top ground plane xy stage for position dependent measurements meander Ground; top ground plane at beam height above meander network analyzer port 1 network analyzer port 2 26Robyn Madrak - FNAL APT Seminar - 12/16/2008

input end Coverage Factor Normalization ground planes Normalize to stripline with wide trace Use geometry for 50 Ω – convenient For striplines Z = /8(ln2 + w/4h)* Use w = 25mm, 2h = 16mm * R. Collin, Foundations of Microwave Engineering Probe pickup signal (S 21 ), 50 – 150 MHz 27Robyn Madrak - FNAL APT Seminar - 12/16/2008

All Measured Coverage Factors typeDouble 50 Double 100 Single 1 (low dispersion) Single 2 (high coverage) Coverage factor 71%87%48%74% 28Robyn Madrak - FNAL APT Seminar - 12/16/2008

Position Dependence beam RMS size100% x 29Robyn Madrak - FNAL APT Seminar - 12/16/ mm = 0.79

3 ms pulse combined output input 50Ω cable V 1 50 Ω 50Ω cable MN60 ferrite: three 11 OD, 4.5 ID, 1 thick cores 58 turns of ¼ superflex cable ferrite 1 ms pulse Expect behavior to be better than this: currently we have extra unneeded cable length matching resistors (100 Ω to scope 50Ω) add extra inductance Combiner 75Ω 50Ω 2V Ω Test combiner by splitting and recombining (using our 500V pulser): V out = 95% V in scope 30

input ferrite 46 turns of superflex around five 1 MN60 cores 1700 V V pulse V pulse 50 combiner 100 meander structure Kanthal 100 High f probe, away Combiner Optimized 200 s/div 1ms pulse 5ns/div, 1600 V 31Robyn Madrak - FNAL APT Seminar - 12/16/2008

Heating in Meander Minimal heat sinking: Meander sits on SS stand (not clamped) Equilibrium Temperature 1ms, 10 Hz, 50A 1ms, 10Hz, 41 A 3ms, 2 Hz, 50 A T (near trace)83 C58 C44C T (on trace)65C Current in meander will be 2.4 kV/100 = 24 A Need to test heat/current handling capacity Use 1ms/3ms pulses: (24A) 2 x x 5.3 = I 2 test I test = 32 A actual pulsed current chopping DF Skin depth factor 50 A thermocouple 180A, 3ms pulse 32Robyn Madrak - FNAL APT Seminar - 12/16/2008

Chopper: Summary We have built prototypes for the necessary components for the chopper: the pulser, meander structures, and combiner The prototype pulsers from Kentech performed to specs; For a complete chopper system we need 3 more We have built a combiner suited for combining these fast pulses We have explored different layouts for the chopper plates (meander structures). The higher coverage factor single meander is the best candidate. For more details, see proceedings of Linac08 : R. Madrak et al., A Fast Chopper for the Fermilab High Intensity Neutrino Source (HINS) 33Robyn Madrak - FNAL APT Seminar - 12/16/2008

Aside: Application of Chopper R&D to the current accelerator Initially explored the option of using a few fast, 1 kV FETs from DEI for Chopper pulser Realized these could be used for notching in the 750 keV line: create a notch for booster kicker rise time (minimize losses) This effort was begun initially in collaboration with Doug Moehs (first attempt was chopping in the source) 34Robyn Madrak - FNAL APT Seminar - 12/16/2008

Combining three DEI FETs from DEI/IXYS RF Use the same scheme as HINS pulser, combining three ~1kV 16.7 signals (x 30 = 50 ) ~40ns pulses 2.2 s spacing Burst of 15 pulses, repeat at 15 Hz Two pulsers: ±1.9kV 1.9 kV, ~40 ns wide pulse (on test bench w/60 dB atten) 35Robyn Madrak - FNAL APT Seminar - 12/16/2008

Plates: 0.9 spacing W1 36 Notching Plates in 750 keV line (H - )

In Linac after tank 2 V plates = 2.9 kV ~100 ns wide notch 50 ns/div 20 ns/div In Linac after tank 2 V plates = 3.8 kV ~100 ns wide notch In booster ~40 ns wide notch In booster Notching Study ~40 ns wide notch B. Pellico, R. Tomlin 400 ns/div40 ns/div 37

38Robyn Madrak - FNAL APT Seminar - 12/16/2008 Part II – Vector Modulators

HINS 325 MHz RF Pulse Transformer & Oil Tank IGBT Switch & Bouncer CAP BANK 10 kV 110 kV Charging Supply 300kW MODULATOR 325 MHz 2.5 MW or Hz WR2300 Distribution Waveguide IQMIQM IQMIQM IQMIQM IQMIQM IQMIQM Fast Ferrite Vector Modulators RF Couplers IQMIQM IQMIQM IQMIQM IQMIQM IQMIQM IQMIQM 500kW IQMIQM IQMIQM IQMIQM IQMIQM IQMIQM IQMIQM 10kV 50 kW circulator MEBT R F Q SSRSSRSSRSSR H- Medium Energy Beam Transport Copper Cavities Radio Frequency Quadrupole Cryomodule #1Cryomodule #2 TOSHIBA E3740A independent phase and amplitude control in each cavity 39Robyn Madrak - FNAL APT Seminar - 12/16/2008

How it Works In a coaxial line filled with some dielectric ( v = c/ We vary and thus v and phase by varying H applied to the ferrite. H I ferrite outer conductor inner conductor slot in outer conductor supplied by solenoid 40Robyn Madrak - FNAL APT Seminar - 12/16/2008

41Robyn Madrak - FNAL APT Seminar - 12/16/2008 Operates in full reflection mode (end is shorted) Use solenoid along with shifters: phase of reflected wave determined by of ferrite ( depends upon applied H Field) Ferrite is Al doped Yttrium Iron Garnet (YIG) – TCI Ceramics AL-400 Required rate: 1º/ s Power Rating: ~50kW (Room Temp Cavities) or ~500kW (RFQ) Fermilabs Ferrite Phase Shifter

Modulates phase and amplitude independently: With = ( )/2 = ( )/2 90 Degree Quad Hybrid Input (split between ports 2 and 3) Output (Cavity ) 2 3 circulator Vector Modulator: Output power ~ cos 2 ( ) Phase shift ~ Phase Shifter s shorted end solenoid flux return slot 42Robyn Madrak - FNAL APT Seminar - 12/16/2008

Two Phase Shifter Types For Cavities (~75 kW): 1.5 OD X 0.65 ID X 5 long garnet For RFQ (~500 kW): 3 OD X 0.65 ID X 5 long garnet 43Robyn Madrak - FNAL APT Seminar - 12/16/2008

Shifter Design Details Center conductor: shrink fit during assembly Use quarter wave matching section (for 50) Outer conductor has slot (length = 9) to reduce eddy currents (gives faster response) solenoid (12 awg wire around G10) flux return 44Robyn Madrak - FNAL APT Seminar - 12/16/2008

Other VM Parts hybrid for 1 vm: Dielectric circulator for 1 vm: Ferrit-Quasar circulator load: 5kw CW water cooled Altronics 6 hybrid for RFQ vm: MCI Filled with SF 6 to prevent sparking 45Robyn Madrak - FNAL APT Seminar - 12/16/2008

useful phase shift range ~120 deg. (loss < -0.2 dB) Gyromagnetic resonance 2.8 MHz/Oe Phase vs. Applied Field 325 MHz Low Power meas: 46Robyn Madrak - FNAL APT Seminar - 12/16/2008

Small Signal Frequency Response Open loop bandwidth: 15 kHz > 35 kHz w/feedback 47 Response (mixer) solenoid I Program, 10 kHz 0.1 ms 30 deg.

Slew Rate Single Shifter Reflected Phase ~30 deg/div solenoid bias Current 50A/div 20 s/div Phase Shifter Slew Rate: (above resonance) 6 deg/ s Current risetime limited by supply output, solenoid inductance Fast 300A power supply thanks to Brad Claypool, Steve Hays, Howie Pfeffer 48Robyn Madrak - FNAL APT Seminar - 12/16/2008

49Robyn Madrak - FNAL APT Seminar - 12/16/2008 Beam Loading - Simulation Cavity 6 Starting and stopping the compensation 4 usec prior to beam arrival time Beam current 26 mA phiS = -45 deg Results courtesy Julien Branlard

Meson Building Test Facilities 325 MHz RF Test Cage Please do not feed the animals 2.5 MW klystron First room temperature cavity vector modulator 50Robyn Madrak - FNAL APT Seminar - 12/16/2008

Meson Building Test Facilities Testing the RFQ vector modulator Testing the 1 vector modulator 51Robyn Madrak - FNAL APT Seminar - 12/16/2008

Power Capabilities phase ~ ( + )/2 here, both shifters solenoids driven by one power supply = 52Robyn Madrak - FNAL APT Seminar - 12/16/2008

400 s/div 1 Vector Modulator Output: 2 ms pulse 25 kW50 kW Power Capabilities 1 VM for cavities : good to >75 kW Shifters alone could be used in a 200 kW VM if used with oil in ferrite part of coax line (higher power quad hybrid & circulator would be needed) RFQ VM Shifters and Hybrid filled with SF6: Good to > 500 kW Current hybrid is 6 Stripline 500 kW Circulator failed: Getting a new one from Ferrite 53Robyn Madrak - FNAL APT Seminar - 12/16/2008

Vector Modulators: Summary The 1 vector modulators can operate well up to 75 kW (more than needed for the RT cavities) The RFQ vector modulator elements: phase shifters good to ~600 kW hybrid good to ~600 kW initial circulator failed; new Ferrite model on order The speed of the response for the cavity shifters is 6X as fast as the original spec bandwidth > 35 kHz for a first attempt at feedback For more details, see proceedings of Linac08 : R. Madrak and D. Wildman, High Power 325 MHz Vector Modulators for the Fermilab High Intensity Neutrino Source (HINS) 54Robyn Madrak - FNAL APT Seminar - 12/16/2008

55Robyn Madrak - FNAL APT Seminar - 12/16/2008 Conclusions HINS is a key part of Fermilabs Accelerator R&D program, and likely a key part of its future physics program We have demonstrated the workability of two of its more challenging components

Backup Slides 56Robyn Madrak - FNAL APT Seminar - 12/16/2008

Kentech 500V Prototype Pulser Scheme 10 pulse cards: 50V5 Ω 5 FETS/card (in parallel) each FET drives 25 Ω center conductor outer conductor 5Ω5Ω 5Ω5Ω 5Ω5Ω5Ω5Ω5Ω5Ω 5Ω5Ω 5Ω5Ω 5Ω5Ω5Ω5Ω 5Ω5Ω 25Ω pulse control cards output: 500V50 Ω 25 Ω semirigid cable with ferrite five 25 Ω semirigid cable in parallel, with ferrite 57Robyn Madrak - FNAL APT Seminar - 12/16/2008

Coverage Factor, Meanders single meander signal to 500 MHz double meander (100 Ω )around 100 MHz single meander (100 Ω ) around 100 MHz Which gives*: 58Robyn Madrak - FNAL APT Seminar - 12/16/2008 typec double87% Single 148% *Relative to normalization measurement; After correcting for impedance difference and reflected power

Heating in Meander Final Pulse: 2.4 kVZ= 100, or Chop 30% Meander Traces: 70 m thick, R(DC) = 2.7 Dont have 2.4 kV pulser, use test pulse of 1 or 3ms (low freq) Estimate I factor for RF 100 MHz(skin depth): 2.6 in/f = 6.6 m Skin depth factor = 35 m/6.6 m = 5.3 (24A) 2 x x 5.3 = I 2 test I test = 32 A actual pulsed current chopping DF Skin depth factor - Or - Measure power spectrum of pulses; normalize to (2.4kV) 2 /100 x x 0.01 = 192W Convolute with S 21 thru meander; this give Pdiss = 46 W I 2 test x DF test x 2.7 = 46W I test = 41 A actual pulsed power chopping DF 10Hz With safety factor, test at 50 A low power, spectrum analyzer 59Robyn Madrak - FNAL APT Seminar - 12/16/2008

Notching Study + pulsetop plate60 dBscope 50 ohms - pulsebottom plate 60 dBscope 50 ohms +1.9 kV -1.9 kV 60Robyn Madrak - FNAL APT Seminar - 12/16/2008

Using one or two single power switches: from DEI/IXYS RF min width 20ns/div 1ms/div cannot get to a narrow enough pulse … With two switches: Pulses are narrower, but Still not narrow enough 4ns/div 61Robyn Madrak - FNAL APT Seminar - 12/16/2008

Using one or two single power switches: The DEI FETS can be used to make a very narrow pulse by charging cable in the drain But in this case we cannot attain the desired 53 MHz rep rate 20ns/div 4ns/div With a slightly lower current version of the switch: 62Robyn Madrak - FNAL APT Seminar - 12/16/2008

Doug Moehs 20 pulses single pulses DEI FETS were useful for beam notching in H source for the current linac ~40ns pulses 2.2 s spacing Burst of 15 pulses, repeat at 15 Hz Two pulsers: ±800V toroid response shows notched beam trigger signal (time offset) DEI FETS for H Source 63Robyn Madrak - FNAL APT Seminar - 12/16/2008