Proton Driver Conceptual Design at RAL

ISIS Accelerator DivisionJohn Thomason

Reference IDS Neutrino Factory Design

• Supply protons to target to produce pions

High Power Proton Driver

• Basic specifications:- 4 MW proton beam power- Proton kinetic energy 5 – 15 GeV- RMS bunch length 1 – 3 ns- 50 Hz repetition rate- Three bunches, extracted > 80 µs apart

• Linac based (SPL) proton driver at CERN – the most advanced

• Synchrotron(s)/FFAG based proton driver (green field solution) – under study at RAL

• Project X based solution at Fermilab • Solution based on synergy between neutron spallation source (ISIS MW upgrade) and NF – idea shared by many people

• Other solutions (multiple FFAGs, NS-FFAGs, etc.) – in the state of ideas

Current Options for NF Proton Driver

Green Field Solution

• Lower injection energies provide smaller bucket area in the ring and the small longitudinal emittance needed for final ns bunch compression. Studies show that 180 MeV is a realistic energy for NF

• Separate booster ring designed for low loss phase space painting for beam injection and accumulation. Synchrotron moving buckets give flexibility to capture all of the injected beam

• Separate main ring with optics chosen for ns bunch compression. Could be FFAG (cheaper but insufficiently developed) or a synchrotron (reliable, tried and tested)

• Special achromat for collimation (longitudinal and transverse) and momentum ramping for injection

• Compressed bunches need to be held and sent totarget at intervals of ~100 μs. Possible in FFAG and also synchrotron with flat top

Proton Driver for a Neutrino FactoryChris Prior, Grahame Rees,Shinji Machida ( )

• High intensity ~1014 protons– Achieved with phase space painting in RCS booster

• 50 Hz rep rate• Booster circumference 400 m• Bunch area (h = 3) 1.1 eVs• ns bunch compression

– Achieved with FFAG accelerator– 1.3 MV per turn for 3.0 ns RMS, improved by higher harmonic component to 1.9 ns– FFAG circumference ~800 m

• Delayed extraction of bunches to meet requirements of muon accelerators and decay rings

– May be easier with FFAG than synchrotrons

10 GeV ns-FFAG Proton Driver

10 GeV ns-FFAG Proton Driver

ns-FFAG chosen for:• Lower RF accelerating fields• Ability to hold compressed bunches at top energy• Metallic vacuum chambers (c.f. ceramic with RF shields for RCS)• Uses h = 24, 1.3 MV per turn for 3.0 ns bunch compression

Pumplet (Grahame Rees)

• Non-linear, combined function magnets with exit-entry faces parallel• Tunes per cell νx = 4 , νy = 3 ; 66 cells, Qx = 20 4 , Qy = 15 3

• Zero chromaticity at each reference energy orbit• Large dynamic aperture

13 13

13 13

• High intensity ~1014 protons– Achieved with phase space painting in RCS booster

• 50 Hz rep rate• Booster circumference 400 m• Bunch area (h = 3) 1.1 eVs• ns bunch compression

- Achieved with RCS accelerator

(h = 24)

- 1.3 MV per turn for 3 ns RMS

compression

- RCS circumference same as for

FFAG (~800 m)

• Finemet, rather than ferrite, could be

used for rf cavities

10 GeV RCS Proton Driver

3 GeV RCS Booster

0.2 GeV H− linac

RCS Main synchrotron

10 GeV RCS Proton Driver

10 GeV RCS:• Circumference ~800 m; γt ~20 • Doublet cells to provide long dispersion-free straights• Uses h = 24, 1.3 MV per turn for 3.0 ns bunch compression• Voltage mid-cycle reduced through use of dual harmonic magnetic guide field,

B(t) = B0 – B1cos2πft + B2cos4πft

3 GeV Booster RCS• 50 Hz RCS preferred to FFAG; more efficient H− injection • 7 triplet cells in four superperiods, long (10.6 m) free straight sections• Separate superperiods for collimation, RF and extraction• Injection in 8º low field dipole (~0.055 T) with Dx/√βx = 1.9 m½ for horizontal phase space painting, using RF steering and momentum ramping; vertical painting with conventional bump magnets – avoids need for injection chicane

• Beam power in booster is 1.2 MW – higher than for any existing RCS • Over 100 m provided for RF system• Booster uses h = 3, 0.85 MV per turn for 1.1 eVs bunches• Foil heating from stripping and subsequent proton traversals is a concern

Achromat and Collimation Beam Line

• Beam prepared for injection in achromatic arc between Linac and booster ring• Combined function magnets, 8 with +45º bends, 4 with -45º bends• Length 41.6 m normalised dispersion D/√β = 5.1 m½

• Horizontal and vertical beam loss collimators, cavities for momentum spread reduction and correction• Stripping foils for momentum collimation

ISIS Upgrade + NF Solution

0.24 MW ISIS

• Assumes an optimised 2RF system giving 300 µA in the synchrotron• 4/5 pulse pairs to TS-1 (192 kW) and 1/5 pulse pairs to TS-2 (48 kW)• Must keep beam to TS-2 for the foreseeable future

Further developments of the ISIS accelerator and target stations are possible with each stage giving of order a factor 2 enhancement of the neutron source characteristics

0) Linac and TS1 refurbishment

1) Linac upgrade leading to ~0.5 MW operations on TS1

2) ~3.3 GeV booster synchrotron: MW Target

3) 800 MeV direct injections to booster synchrotron: 2 – 5 MW Target

4) 800 MeV direct injections to booster synchrotron + long pulse mode option

overlap with NF proton driver

ISIS MW Upgrade Scenarios

2) Based on a ~3.3 GeV RCS fed by bucket-to-bucket transfer from ISIS 800 MeV synchrotron (1MW, perhaps more)

3) RCS design also accommodates multi-turn charge exchange injection to facilitate a further upgrade path where the RCS is fed directly from an800 MeV linac (2 – 5 MW)

1) Replace ISIS linac witha new ~180 MeV linac (~0.5MW)

ISIS MW Upgrade Scenarios

2) Lattice and high intensity studies for a ~3.3 GeV booster synchrotron and associated beam lines: ISIS, ASTeC and Imperial College staff.

 - This upgrade would make ISIS competitive (in terms of raw beam power) with the facilities now being commissioned at SNS in the USA and JPARC in Japan. - A full physics design, integrated with the 800 MeV Linac design below, would follow on from that for the upgraded ~180 MeV Linac, and is scheduled to be carried out in 2011/2012, ready for engineering and costing input and the design of a new target station.- Much of the necessary development and benchmarking of simulation codes, upgrade of computing power and study of key high intensity phenomena on ISIS will overlap with that required for the ~180 MeV Linac upgrade.- All MW upgrade designs will incorporate TS2 running at its full capacity.- If possible will remain compatible with UKNF proton driver plans.

Possible ~3.3 GeV RCS Rings Grahame Rees ( )Chris Warsop, Dean Adams, Ben Pine,Bryan Jones, Rob Williamson ( )

Energy 0.8 – 3.2 GeV

Rep Rate 50 Hz

C, R/R0 367.6 m, 9/4

Gamma-T 7.2

h 9

frf sweep 6.1-7.1 MHz

Peak Vrf ~ 750 kV

Peak Ksc ~ 0.1

εl per bunch ~ 1.5 eV s

B[t] sinusoidal

5SP RCS Ring

3) 800 MeV high intensity Linac design – ASTeC Intense Beams Group and FETS Collaboration staff. - This addition to the facility would allow direct injection into the ~3.3 GeV booster synchrotron, giving 2 – 5 MW of beam power.- Beam dynamics studies for this upgrade can be carried out in parallel with the upgraded ~180 MeV Linac and ~3.3 GeV booster synchrotron, giving a full, integrated physics design by 2012.- Engineering and costing are only sensible at the point when funding for a ~3.3 GeV booster synchrotron has been approved, unless these options are to be considered together as a stand alone facility, separate from the present ISIS.- This high intensity Linac design could also be the basis for an additional long pulse mode option in the future.

Beam power for 2 MW, 30 Hz, 3.2 GeV RCS 0.5 MW

Beam pulse current before MEBT chopping 43.0 mA

Beam pulse current after MEBT chopping 30.0 mA

Number of injected turns for 370 m RCS ~500 turns

Beam pulse duration at the 30 Hz rep rate ~730.0 μs

Duty cycle for the extent of the beam pulse ~2.2 %

MEBT(in) normalised rms emittances 0.25, 0.375 (π) mm mr

MEBT(out) normalised rms emittances 0.30, 0.42 (π) mm mr

Cell equipartition transv/long phase shift ratios 1.40

800 MeV, Hˉ Linac Design ParametersGrahame Rees,Ciprian Plostinar ( )

• All options have the same 324 MHz, 74.8 MeV stage 1:

IEBTDTLMEBTRFQ 74.8 MeV

Options F (MHz) Stage 2 Stage 3 Stage 4

1 648 ScL 1 ScL 2 ScL 3

2 648 CCL ScL 2 ScL 3

3 (324) 972 (ScL a) ScL b ScL c~200 MeV 800 MeV

Design Options

H

V

Δφ

ScL1 ScL2 ScL3

Debunching line

Beam Sizes in 800 MeV Linac & Beam Line

ISIS MW upgradeAdditional RCS

• Requires additional RCS machine in order to meet the power and energy needs of the Neutrino Factory

• Both facilities can have the same ion source, RFQ, chopper, linac, H− injection, accumulation and acceleration to 3.2 GeV

Common Proton Driver for the Neutron Source

and the Neutrino Factory• Based on MW ISIS upgrade with 800 MeV Linac and 3.2 (~3.3) GeV RCS

• Assumes a sharing of the beam power at 3.2 GeV between the two facilities

• 3 bunches will be transfered from the booster RCS at 3.2 GeV and 2 MW

• Acceleration by a factor of 2 is needed to get the necessary 4 MW (to 6.4 GeV)

• Some beam parameters at injection: - longitudinal emittance 1.8 eVs - total bunch length 110 ns - intensity 2.6x1013 protons/bunch - 3 bunches

• Options for the bunch compression to 1 – 3 ns RMS bunch length: - adiabatic compression in the RCS - ‘fast phase rotation’ in the RCS - ‘fast phase rotation’ in a dedicated compressor ring

Summary of Assumptions for theCommon Proton Driver

Number of superperiods 6Circumference 708.788 mHarmonic number 6

RF frequency 2.4717-2.5289 MHzBetatron tunes ( QH, QV) (7.81, 7.78)Gamma transition 7.9056Beam power at 6.4 GeV 4 MW for 2 bunchesBunch area 1.8 eVs

Δp/p at 3.2 GeV 5.3 10-3

Injection / extraction energy

3.2 / 6.4 [10.3] GeV

Repetition rate 50 Hz

Max B field in dipoles 1.2 T ( at 10.3 GeV)

Length of long drift 12 m

• Lattice may allow for flexibility in gamma transition choice (even with beam)• Ring is overdesigned in order to allow for 10.3 GeV• Optimised solution for 6.4 GeV is in preparation!

Parameters of 6.4 (10.3) GeV RCS

Preliminary design of the second RCSJaroslaw Pasternak( , )

• Fast phase rotation in the dedicated compressor ring (most economic from the RF point of view, but another ring is needed)• Bunches will be extracted one by one from the RCS• Compressor ring works above transition, but the rotation is very fast• The bunches in the RCS will wait uncompressed for 200 µs• We do not have a design for the compressor ring at the moment, but CERN design can be adopted

RCS3.2 GeV50 Hz

800 MeV H- linac

Compressor ring

NF target4 MW

3 bunches

Neutrontarget, 2.6 MW

RCS6.4 GeV50 Hz

Alternative Proton Driver Layout

• Parameters needed for the Neutrino Factory Proton Driver are still evolving (pulse length, energy?), but this will not change too much in the design

• Several solutions are advancing well to be able to meet the goal • A common proton driver compatible with the ISIS MW upgrade is a very attractive solution to create a cost effective multi-user facility, but careful attention must be given to potential conflicts of interest between the neutron and neutrino communities.

• More work is needed on the bunch compression scenarios.

Summary and Future Plans

• High power front end (FETS)• RF Systems• Stripping Foils• Diagnostics• Targets• Kickers• etc.

To realise ISIS MW upgrades, UKNF and generic high power proton driver development, common hardware R&D will be necessary in key areas:

• In the neutron factory context SNS and J-PARC are currently dealing with many of these issues during facility commissioning and we have a watching brief for all of these• Active programmes in some specific areas

Necessary R&D

NF on RAL/HSIC Site

Norsaq

x