Project X Reference Design Overview

Project X Reference Design Overview

Sergei Nagaitsev

April 12, 2011

Reference Design

Apr 12, 2011 - S. Nagaitsev Page 2

Reference Design Capabilities

• 3 GeV CW superconducting H- linac with 1 mA average beam current.– Flexible provision for variable beam structures to multiple users

• CW at time scales >1 msec, 15% DF at <1 msec– Supports rare processes programs at 3 GeV– Provision for 1 GeV extraction for nuclear energy program

• 3-8 GeV pulsed linac capable of delivering 300 kW at 8 GeV – Supports the neutrino program– Establishes a path toward a muon based facility

• Upgrades to the Recycler and Main Injector to provide ≥ 2 MW to the neutrino production target at 60-120 GeV.

• Day one experiment to be incorporated utilizing the CW linac

Þ Utilization of a CW linac creates a facility that is unique in the world, with performance that cannot be matched in a synchrotron-based facility.


Reference DesignProvisional Siting


Pulsed Linac

CW Linac

Pulsed 3-8 GeV Linac based on ILC / XFEL technology


Reference design: accelerator scope

• Warm cw front end 162.5 MHz, 5 mA (H- ion source, RFQ, MEBT, chopper)

• 3-GeV cw SCRF linac (325, 650 MHz), 1-mA ave. beam current

• Transverse beam splitter for 3-GeV experiments

• 3-8 GeV: pulsed linac (5% duty cycle), 1.3 GHz

• Recycler and MI upgrades

• Various beam transport lines

5% du

ty cy

cle

Pulsed dipole

Changes to the reference design since Sep 2010

• Eliminated a 1.3-GHz section from the CW linac (Nov 2010)– Larger aperture, lower stripping losses, fewer cavities, cost neutral

• Changed the RFQ frequency to 162.5 MHz (Jan 2011)– Easier chopper, lower RFQ power, larger aperture

• Introduced a LEBT chopper (Nov 2010)

• Ion source operates at a constant current, 5 mA max (Nov 2010)

• Limit the max. cryo loss per cryomodule to 250 W (2K) (Nov 2010)– Per cavity – 25 W

• Established pulsed 1.3 GHz linac configuration (Nov 2010)– 25 MV/m gradient– 1 mA beam current in 4.3 ms pulses– 1 Klystron per 16 cavities (2 CM)– 8 ms, 10 Hz



Linac beam current

• Linac beam current has a periodic time structure (at 10 Hz) with two major components.

0 2 4 6 8 10

Pulseddipole

OFF

ON

Beamcurrent, mA

0

1

Time, ms

4.3 ms flattop

Choppingfor injection

Choppingfor 3-GeV program

100

0

20

40

60

80

100

120

140

160

180

200

-10-8-6-4-20246810

Matching

DC switch dipole to Experimental Area

Pulsed switch dipole to RCS

DC dipole

ARC ARC

DC dipole

Linac Dump

Momentum Dump

Momentum Dump

Buried Beam Pipe

CollimationCollimation

Beam to Recycler

Chopping for injection

• RF frequency at injection into the Recycler : ~50 MHz

• Chopper needs to provide a kicker gap (~200 ns per 11 µs) and needs to remove bunches that fall into “wrong” phase of ring rf voltage.

– 50% of bunches are removed ( ion source at 2 mA)– 80% of bunches are removed ( ion source at 5 mA)

Apr 12, 2011 - S. Nagaitsev Page 80 1 2 3 4 5 6 7 8 9 102-

1-

0

1

2

f t( )

g t( )

h t( )

t

Recycler RF

162 MHz bunches to be removed


Chopping and splitting for 3-GeV experiments

1 msec period at 3 GeVMuon pulses (16e7) 81.25 MHz, 100 nsec at 1 MHz 700 kWKaon pulses (16e7) 20.3 MHz 1540 kWNuclear pulses (16e7) 10.15 MHz 770 kW

Separation scheme

Ion source and RFQ operate at 4.2 mA75% of bunches are chopped at 2.5 MeV after RFQ

Transverse rf splitter0

2

4

6

8

10

12

14

16

18

0.0 0.1 0.3 0.4 0.5 0.6 0.7 0.9 1.0 1.1 1.2 1.4 1.5 1.6 1.7 1.9 2.0

Num

ber

of io

ns p

er b

unch

, (e7

)

Time, us

Beam after splitter


0

2

4

6

8

10

12

14

16

18

0.0 0.1 0.3 0.4 0.5 0.6 0.7 0.9 1.0 1.1 1.2 1.4 1.5 1.6 1.7 1.9 2.0

Num

ber

of io

ns p

er b

unch

, (e7

)

Time, us

0

2

4

6

8

10

12

14

16

18

0.0 0.1 0.3 0.4 0.5 0.6 0.7 0.9 1.0 1.1 1.2 1.4 1.5 1.6 1.7 1.9 2.0N

umbe

r of

ions

per

bun

ch, (

e7)

Time, us

0

2

4

6

8

10

12

14

16

18

0.0 0.1 0.3 0.4 0.5 0.6 0.7 0.9 1.0 1.1 1.2 1.4 1.5 1.6 1.7 1.9 2.0

Num

ber

of io

ns p

er b

unch

, (e7

)

Time, us

10 MHz bunches

20 MHz bunches

1 MHz pulses


Ion source: TRIUMF-typeH- DC ion source

Delivery expected: May 2011LBNL + FNAL will test emittance etc.


Proposed LEBT configuration

• LEBT will likely have a chopper to provide 0.5 ms gaps, needed for a switching magnet at 3 GeV

RFQ (162.5 MHz)

CW RFQ:

Several design

studies by LBNL

Good experience at ANL and LBNL



MEBT design: 5 mA at 162.5 MHz beam

=0.25 ∙μm; z,n=0.3 ∙μm

325 MHz warm bunching cavities

MEBT chopper


RT Bunching CW cavities


Effect of longitudinal emittance (L/=0.52)


Bunch Length (3) vs. Synch. Phase

SSR0

MEBT


Prelim Conclusions: Front End

• Transverse rms (norm) emittance 0.25 mm-mrad

• Range of acceptable longitudinal emittances is close to equipartition, z/ ≈ 0.8-1.2, =0.25 ∙μm

• No need for using 162.5 MHz cavity (copper) in MEBT.

• SSR0 section at 325 MHz works for 162.5 MHz RFQ option

• Unanswered issues:– Chopper driver– Beam absorber (10 kW)– Absorber sputtering and blistering rates

SRF LinacTechnology Map

Apr 12, 2011 - S. Nagaitsev

b=0.11 b=0.22 b=0.4 b=0.61 b=0.9

325 MHz2.5-160 MeV

b=1.0

1.3 GHz3-8 GeV

650 MHz0.16-3 GeV

Section Freq Energy (MeV) Cav/mag/CM Type

SSR0 (bG=0.11) 325 2.5-10 18 /18/1 SSR, solenoid

SSR1 (bG=0.22) 325 10-42 20/20/ 2 SSR, solenoid

SSR2 (bG=0.4) 325 42-160 40/20/4 SSR, solenoid

LB 650 (bG=0.61) 650 160-460 36 /24/6 5-cell elliptical, doublet

HB 650 (bG=0.9) 650 460-3000 160/40/20 5-cell elliptical, doublet

ILC 1.3 (bG=1.0) 1300 3000-8000 224 /28 /28 9-cell elliptical, quad

CW Pulsed

Page 19

325 MHz spoke cavity families

20

cavity type βGFreq MHz

Uacc, max

MeVEmax

MV/mBmax

mTR/Q,

ΩG,Ω

*Q0,2K

109

Pmax,2K

WSSR0 β=0.114 325 0.6 32 39 108 50 6.5 0.5SSR1 β=0.215 325 1.47 28 43 242 84 11.0 0.8SSR2 β=0.42 325 3.34 32 60 292 109 13.0 2.9

Parameters of the single-spoke cavities

SSR0 – design,

prototyping

SSR1 – prototyping, testing

SSR2 - design


21

Focusing Periods in SSR sections:

800 mm Focusing Period:SSR0: (sol+cav) = 610 mmSSR1: (sol+cav) = 800 mmSSR2: (sol+cav+cav+60 mm) = 1600 mm


650 cavities

• 650 MHz, 5-cell cavity:– Similar length as for ILC-type cavity;– About the same maximal energy gain per cavity;– The same power requirements;

• Benefits compared to 1.3 GHz ILC-type cavity:– Higher accelerating efficiency smaller number of cavities and RF sources:– Beam dynamics

• 2-fold frequency jump instead of 4-fold easier transition• Smaller beam losses;• Less effect of cavity focusing (~1/ λ)

• Trade-offs: – more serious problem with microphonics, but still may be manageable;– Larger diameter (comp to 1.3), higher cost per cavity;– additional rf frequency -> infrastructure.

Page 22Apr 12, 2011 - S. Nagaitsev

650 MHz cavities

Parameter LE650 HE650β_geom 0.61 0.9R/Q Ohm 378 638G-factor, Ohm 191 255Max. Gain/cavity (on crest) MeV 11.7 19.3Acc. Gradient MV/m 16.6 18.7Max surf. electric field MV/m 37.5 37.3Max surf. magnetic field, mT 70 70Q0 @ 2°K 1010 1.5 2.0P2K max [W] 24 29

650 MHz: β=0.61 650 MHz: β=0.9

Page 23Apr 12, 2011 - S. Nagaitsev

Apr 12, 2011 - S. Nagaitsev 24

LE Cryomodules

11325.12

8878.49

CMs lengths are shown from the first cavity iris to the last cavity iris.

HE Cryomodules3238.09

3282.03


650 MHz Cryomodule (Tesla Style-Stand Alone, 250 W @ 2K)

End PlateBeam

Vacuum VesselCold mass supports (2+1)

Power MC (8)


Cavity string & 300mm pipe

CW linac: Envelopes


Energy Gain per Cavity


• Single cavity per power source

– Solid State, IOT

3 GeV CW LinacCryogenic Losses per Cavity

• ~42 kW cryogenic power at 4.5 K equivalent

Apr 12, 2011 - S. NagaitsevPage 29

Solenoid Magnetic Field



Quadrupole (doublet) Gradient

35 0 100

35 0

Doublet (FD)


Errors and misalignments

• Misalignments ±1 mm for all elements (specification ±0.5 mm )• RF jitter of 0.5 ° x 0.5 % in the front-end & 1 ° x 1% RF jitter in the

high-energy part was implemented. • 100 seeds and 1 million macro-particles per seed. • 1 corrector, 1 BPM per solenoid/douplet/quad; BPM resolution=30 μm• Beam centroid is corrected to ±1mm; Emittance increase < 20%. • The uncorrected seeds predict losses above 100 W/m; corrected – no

losses

The red curves are the 100 seeds without correction and the blue curves are the 100 seeds corrected

Beam Centroid off-set Beam Transverse Emittance


H- stripping Summary• Stripping on residual gas is < 0.1 W/m if pressure is better than 10-8

Torr - Assuming gas contains 50% H2, 25% O2, 25% N2

• Magnetic stripping is well below 0.1 W/m even for unrealistic 5 mm beam offset.

• Stripping on blackbody radiation is not an issue for SC linac.

• Intra-beam stripping is ~0.1 W/m


3 – 8 GeV acceleration

• Pulsed linac based on the ILC technology– 1.3 GHz, 25 MV/m gradient, ≤5% duty cycle – considering 8-30 ms pulse length– ~250 cavities (28 ILC-type cryomodules) needed.– Simple FODO lattice– 1 Klystron per 2 CM’s


Cavity Energy Gain

Eacc = 25 MV/m: L=1.038m


Envelopes (sigma)


Summary of studies for pulsed linac• Beam losses are smaller than for CW linac

- Intra-beam stripping is well below 0.1 W/m- Magnetic stripping is small for reasonable beam displacement (<20mm)

• LLRF control- Simulated for scheme with 1 klystron feed 2 CM- VS control at the level below~0.5 % and 0.5 deg (individual cavity error

~10% and 10 deg) allows to keep energy jitter at 8 GeV below 10 MeV. (needed for injection)

Injection

• Need to accumulate 26 mA-ms protons in the MI/Recycler

• For a stationary foil, a single 26-ms pulse would destroy the foil.

• 6 pulses at 10 Hz give enough time for radiative cooling between pulses


Foil efficiency


Recycler injection


Alternative injection scheme

• A possibility to inject in a single 26-ms pulse is highly desirable.– Eliminates the need for Recycler (as an accumulator)– Potentially allows for a lower linac energy (6-7 GeV)– Requires long-pulse linac operation


Recycler parameters


Number of particles 1.7×1014

Longitudinal emittance 0.6 eV sMomentum spread (100%) ±2.5×10-3

Transverse emittance (100%) h=v

25 mm·mrad

Harmonic number 588Number of bunches 548Main RF Frequency 52.811 MHzMain RF Voltage 750 kVSecond Harmonic RF Voltage 375 kVBetatron tunes Qh/Qv 20.45/20.46

Betatron tune chromaticity -20Synchrotron tune (maximum) 0.0067Transverse acceptance 40 mm·mradMomentum acceptance ±3.2×10-3

Phase-space painting


Motivation– Gaussian beam G =3– Single RF harmonic at 53 MHz B =5

DQ= -0.3

– Uniform beam G =1– Longitudinal painting B =2

DQ= -0.04

BGN

N

b

320

14

2r-Q

mrad mm25107.1

D

Longitudinal painting

• Linac long. emittance: 1.3e-4 eV-s

• Recycler long. emittance: 0.6 eV-s

Apr 12, 2011 - S. Nagaitsev Page 44B=2.2

0 1 2 3 4 5 6 7 8 9 102-

1-

0

1

2

f t( )

g t( )

h t( )

t

Recycler RF

162 MHz bunches to be removed

Transverse painting

• Transverse painting is designed to:– Minimize the number of secondary passages and foil heating– To make correlated x-y painting (K-V distribution) with radius increase

for each next pulse

• Injected beam does not move on foil

• Closed orbit describes almost a quarter of circle (forward and back)


Recycler modifications

• New rf systems:– 53 MHz and 106 MHz (fixed frequency)

• New injection system

• Possibly TiN vacuum pipe coating to mitigate electron cloud


MI modifications

• New RF systems– 53 MHz and 106 MHz (with freq. sweep for acceleration)– 2.7 MV/turn at 36-degree synch phase

• γt jump system• Possibly TiN vacuum pipe coating to mitigate electron cloud


Summary

• Project X design concept is well developed and has been stable for more than 1 year.

• We have an RD&D plan to take us through CD2. Key R&D issues (among others)

– Chopper section

– Recycler injection

– SRF cavities


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