Proton Driver Main Linac Parameter Optimization

G. W. Foster

Proton Driver General Meeting

Jan 19, 2005

OPTIMIZATION

• The Proton driver is mainly eight repetitions of the TESLA RF unit:– One Klystron– 36 Cavites~ 1 GeV of Beam Energy

• Optimization of the main linac means mainly optimization of this basic RF unit, subject to the constraints of the Proton Driver

Nov 18, 2004 G.W.Foster - Proton Driver

0.5 MW with TESLA Frequencies & SCRF F.E.

R F QR F Q

Modulator

H -

B=0.47 B=0.47 B=0.61 B=0.61 B=0.61 B=0.81 B=0.81 B=0.81 B=0.81 B=0.81 B=0.81 B=0.81

Modulator

"Pulsed RIA" SCRF Linac 325 MHz 0 - 120 MeV

B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1

Modulator Modulator

12 Klystrons (2 types) 11 Modulators 20 MW ea. 1 Warm Linac Load 54 Cryomodules~550 Superconducting Cavities

8 GeV 0.5 MW LINAC

8 Klystrons288 cavites in 36 Cryomodules

2 Klystrons96 cavites in 12 Cryomodules

B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1

Modulator Modulator

B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1

Modulator Modulator

B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1B e t a = 1

Modulator Modulator

Modulator

48 cavites/ Klystron

36 cavites/ Klystron

TESLA Klystrons1300 MHz 10 MW

"Squeezed TESLA" Superconducting Linac1300 MHz 0.087 - 1.2 GeV

"TESLA" LINAC 1300 MHz Beta=1

S S RS S RS S RD S RD S RD S R

Multi-Cavity Fanout at 10-20kW/cavityPhase & Amplitude Adjust via Fast Ferrite Tuners

TESLA Klystrons1300 MHz 10 MW

325 MHz Klystrons1.5 MW

SRF Linac Parameters

Table 1- Comparison of the 8 GeV Linac with other SCRF Pulsed Linacs

8 GeV Injector

SNS (Spallation Neutron Source)

TESLA-500 (w/ FEL)

TESLA-800

Linac Energy 8 GeV 1 GeV 500 GeV 800 GeV Particle Type H-, e+, or e- H- e+, e- e+, e- Beam Power 2 MW 1.56 MW 22.6 MW 34 MW AC Power (incl. warm FE) 12 MW ~15 MW 97 MW 150 MW Beam Pulse Width 1 msec 1 msec 0.95 msec 0.86 msec Beam Current(avg. in pulse) 26 mA 26 mA 9.5 mA 12.7 mA Pulse Rate 0.6 – 10 Hz 60 Hz 5(10) Hz 4 Hz # Superconducting Cavities 384 81 21024 21852 / 2 # Cryomodules 48 23 1752 1821 # Klystrons 41 93 584 1240 # Cavities per Klystron 8 – 12 1 36 18 Cavity Surface Fields (max) 45 MV/m 35 MV/m 46.8 MV/m 70 MV/m Accel. Gradient (max) 22.5 MV/m 16 MV/m 23.4 MV/m 35 MV/m Linac Active Length 692 m 258 m 22 km 22 km

Proton Driver Beam Power Upgrade Scenario

Initial scenario with 0.5 MW Stand-alone 8 GeV Beam Power and 12 Klystrons

(looks a lot like TESLA…)Ultimate scenario with 2 MW Stand-alone

8 GeV Beam Power and 36 Klystrons(looks a lot like the SNS…)

Both scenarios support 2 MW of 120 GeV Beam Power out of the Main Injector

Proton Driver Upgrade Scenario

The attempt to display a CAD-rendered movie of the PD Linac Upgrade Scenario was a fiasco, with the best result being the laptop displaying the movie on it’s local screen, while the projector simultaneously displayed the Windows Media Player outline and controls on the big screen except the media player frame was blank… sigh.

However, these movies and others are available at:http://protondriver.fnal.gov

What are the Input Parameters ?Particle Type H-

Linac Energy 8 GeV (kinetic)

Charge per pulse 1.5E14 PPP (25uC)

Beam Pulse Width 3 msec *

Linac Rep Rate 2.5 Hz *

Operating Frequencies 1300 MHz / 325 MHz

Accelerating Gradient 25 MV/m

CopperSCRF transition 15-85 MeV* for the PD linac with 0.5 MW 8 GeV Beam Power

Why is this an H- Linac?

• H- stripping foil injection allows:– cheating Liouville with multi-turn injection (~100)– spreading out the energy-per-pulse over a longer

time interval

• In principle, you could do one-turn injection of Protons– The Booster was originally run this way– The linac beam current would be 2 Amps and the

peak RF power (=Klystron power) required would be (2 amps) x (8 GeV) = 16 GigaWatts

What are the Derived Parameters ?

1. Beam Energy Per Pulse2. Average Beam Power3. Peak Beam Current4. Average Beam Current5. Peak RF Power 6. Number of Klystrons7. RF Coupler Power8. Cavities Per Klystron9. Average RF Power10. Klystron Duty Factor11. Modulator Charging Supply Power12. Number of Cavities13. Cryogenic Operating Power14. AC Wall Power15. Number of turns of H- Injection16. Circulating Current in Main Injector17. RF Power in Main Injector

Technological Limitationsmust beRespectedon both Inputand DerivedParameters!

Examples of Derived Parameters

Energy Per Pulse = Charge * Beam Energy= 25 uC * 8 GeV = 200kJ

Average Power = (Rep Rate) *(E/pulse)

= 2.5 Hz * 200kJ = 0.5MW

Beam Current = Charge / Pulse Length= 25uC / 3 msec = 8.5 mA

More Derived ParametersPeak RF Power = Beam Energy * Current

= 8 GeV * 8.3 mA = 67MW

Naïve Klystron Count: (10 MW TESLA MBK’s)= 67 MW / 10 MW/klystron

= 6.7 Klystrons

Actual Klystron Count = 12(reflects overheads, waveguide losses, etc)

Some Parameters non-Negotiable

Modulator Capacitor Bank Size x Fractional Discharge of Cap Bank (~40%) x Efficiency of Klystron (~60%) x Efficiency of RF Distribution (80%) x (1-fraction of energy left in cavity) (70%)= Linac Energy Per Pulse

But you still get to chose how often to recharge the capacitor bank and re-fire the linac

Reconfigurable Klystron Modulators

Pulse Transformer& Oil Tank

IGBT Switch & Bouncer

CAP

BANK

10 kV115 kVCharging

Supply

300kW

4.5 msecx 2.5 Hzx 12 Stations

0.5 MW Beam Power

Klystron

1300 MHz TESLA MBK

or 325MHz JPARC

10kV

Pulse Transformer& Oil Tank

IGBT

Switch

&

Bouncer

CAP

BANK

10 kV115 kVCharging

Supply

300kW

Klystron

1300 MHz TESLA MBK

or 325MHz JPARC

10kV

Pulse Transformer& Oil Tank

IGB

T S

wit

ch

&

Bo

un

cer

CA

P B

AN

K

10 kV115 kVCharging

Supply

300kW

Klystron

1300 MHz TESLA MBK

or 325MHz JPARC

10kV

3 msecx 5 Hzx 24 Stations1MW Beam Power

1.5 msecx 10 Hzx 36 Stations

2 MW

Reconfigure & add new modulators for 3, 2, or 1 msec beam pulse widths for upgrade scenarios

Modulators can be reconfigured & parts re-used for RF power upgrade scenarios

Technological Limitation: Klystron Duty Factor

The Klystron (and other RF components) have Duty Factor Limitiations from average heating: ~1.5% for TESLA RF

The prohibits, for example, just turning up the Repetition rate for the (long 3 msec pulse) initial scenario to obtain 2MW

No substitute for Average klystron power!

Technological Limitation:Coupler Power & Gradient

If we are aggressive simultaneously on both beam current (25 mA) and SCRF gradient (40 MV/m) then we can get into trouble on RF coupler power:

(40 MV/m)*(1m cavity)*(25 mA) = 1 MW/cavity

This is at or beyond the present state of the art for reliable power couplers.

ILC faces same problem when considering superstructures (~2m cavities)

Long or Short Pulse Length(from Ch 4 of 2003 PD Linac Design Report)

CONSIDERATION

FAVORED PULSE

LENGTH

REASONS

Klystron count Long Lower beam current allows fewer Klystrons with fan out to more cavities per klystron

Peak Power in RF distribution components

Long Peak power proportional to beam current

Klystron Duty Cycle Limitations Short SNS Klystrons OK at up to ~10% Duty Factor but TESLA MBK needs changes above ~1.5% D.F.

H- Injection turns Short 90 injection turns per msec of Linac pulse width Cryogenic Dynamic Wall Power Short Cryo Losses Proportional to RF pulse length Cryogenic Static Wall Power Long Lower power coupler designs have lower heat leak Cavity Filling Losses in SCRF - Cavity filling energy is lost once per pulse Modulator Capacitor Bank Size - Cap Bank Energy = Beam Energy + Filling Losses Charging Supply (RF Wall power) - Only depends on average power Resistive Power in RFQ/DTL Short Only ~ 6% of total RF power in baseline design Sensitivity to Microphonics Short Easier with high beam current, lower loaded Q Emittance Dilution for non-painted beams

Short Reduce number of injection turns and foil scattering

RF Distribution Losses - (perhaps small effect in ferrite tuner) Main Injector Cycle time - Pulse length is small contributor to cycle time Linear Collider Application ~1 msec Want to be close to TESLA linac parameters 8 GeV Neutrino Short Minimize cosmic ray backgrounds 8 GeV Proton Fixed Target Long Many experiments want high duty factor 8 GeV Electron Fixed target ? Depends on experiment XFEL ? Depends on experiment

Conclusions

1. This subject is longer than a half-hour talk

2. The SNS and TESLA linacs are reasonably optimized point designs, and the Proton Driver is operating in an intermediate parameter space where it does not appear we get into trouble.