Beam dynamics design for the KEKJAERI proton linac

Beam dynamics design for the KEK/JAERI proton linac SNS Mini-workshop, June 25, 2001 Masanori Ikegami KEK and other stuffs of the linac group of the KEK/JAERI joint project

Main parameters Energy: Peak current: Macro pulse duration: Repetition: Duty factor: Chopping ratio: Average current before chopping: Average current after chopping: Average beam power after chopping: Frequency: 400 Me. V 50 m. A 0. 5 msec 25 Hz (50 Hz) 1. 25 % (2. 5 %) 56 % 0. 625 m. A (1. 3 m. A) 0. 35 m. A (0. 7 m. A) 140 k. W (280 k. W) 324 MHz for < 190 Me. V 972 MHz for > 190 Me. V ( ): in future

Layout

Brief history • In the original plan, the output energy of the linac was 600 Me. V (190 -400 Me. V: ACS, 400 -600 Me. V: SCC, 400 Me. V injection to RCS). • The output energy is reduced to 400 Me. V (400 -600 Me. V part → 2 nd phase). • Esmax of more than 40 MV/m has been achieved. • Consideration of SC option for the 190 -400 Me. V part was started (March, 2001). • It was decided to adopt NC structure for the 190 -400 Me. V part (June, 2001).

Outline • 190 -400 Me. V part – Overview of ACS option – Design strategy for SCC option – A preliminary design for SCC option • 400 Me. V transport (L 3 BT)

Project member (ACS, SCC, L 3 BT) • • • Accelerator group leader Y. Yamazaki (KEK) Dynamics design – ACS M. Ikegami, T. Kato (KEK) – SCC K. Mukugi*, K. Hasegawa (JAERI), M. Ikegami, T. Kato (KEK) – L 3 BT M. Matsuoka**, F. Noda***, K. Yamamoto, K. Hasegawa (JAERI) Cavity design – ACS N. Hayashizaki (TIT), H. Ao (JAERI), V. Paramonov (INR), S. C. Joshi (CAT), M. Ikegami (KEK) – SCC S. Noguchi, K. Saito, E. Kako (KEK), N. Ouchi, K. Mukugi*, H. Ao, M. Matsuoka** (JAERI) Supported by other staffs of the accelerator group for the KEK/ JAERI proton accelerator * also Mitsubishi Electoric Co. ** also Mitsubishi Heavy Industries, Ltd. *** also Hitachi Ltd.

Requirements • Momentum spread Dp/p of less than 0. 1 % in “full” width for RCS injection • Unnormalized “ 100 %” emittance of less than 4 p･mm ･mrad for the transverse direction for RCS injection • Uncontrolled beam loss of less than 0. 1 W/m

Layout of an ACS module Frequency: Input energy: Output energy: E 0: Lattice: 972 MHz 190 Me. V 400 Me. V 4. 3 -4. 4 MV/m Q doublet Number of tanks: Number of cells per tank: Number of Klystron: Total length: 108 m 46 15 23

Layout of an SCC module Input energy: Output energy: Frequency: Lattice: Total length: 190 Me. V 400 Me. V 972 MHz Q doublet 87 m Num. of cells per cavity: Num. of cavities per cryomodule: Num. of Klystrons per cryomodule: Num. of modules: 9 2 1 18

Cavity specifications Frequency: Material: Thickness: Equator radius: Bore radius: 972 MHz Niobium 3. 8 mm 140 -139 mm 45 mm Operating temp. : Geometrical b: Coupling strength: Esmax/Eacc: Esmax: 2 K 0. 56 -0. 71 4. 0 -2. 9 % 4. 55 -3. 14 > 40 MV/m (K. Mukugi)

Beam dynamics issues for SCC option Possible source of problems in SC option from beam dynamics point of view: • Large phase slip ← beta grouping • Transition ← beta grouping • Non-equipartition & longitudinal-transverse coupling resonance ← strong longitudinal focusing • RF control in pulsed operation ← Lorentz detuning

Comparison with model linacs (I) CCLINSAC simulations for 2 types of model linac with RF errors 9600 simulation particles enx 0. 24 pmm･mrad enz 0. 46 p. Me. V･deg (normalized, rms) Parameters for model linacs Num. of tanks Num. of cells per tank Num. of b groups Total length (m) Structure length (m) E 0 (MV/m) SCC type 34 9 4 80. 1 29. 9 8. 9 -12. 6 ACS type 46 15 46 109. 2 68. 2 4. 29 T. Kato

Comparison with model linacs (II) SCC type (E 21 P 11) ACS type (E 21 P 11) T. Kato

Comparison with model linacs (III) Energy deviation (E 11 P 11)

“Smooth” design • Different geometrical bg for a different module (two cavities in one module). • Three spare modules with typical three bg. • Three types of cryomodule to enable spare module installation, which needs excess drift space in a cryomodule. • Excess drift space in warm section for smooth change in focusing period.

Concept of smooth design

Pros & Cons for smooth design • Pros: – Small phase slip ← ~± 4° – No transition • Cons: – Longer total length ← ~ 2. 7% increase – Manufacturing cost ← ~ negligibly small – Large phase slip in spare modules ← Only in emergency

Transverse focusing configuration • Warm Quadrupole doublet focusing. • Equipartition condition is not imposed. • sx 0 < 90°to avoid the structure resonance. • sx > sz to avoid the longitudinal-transverse coupling resonance at sx ~ sz. • Esmax is lowered to ~ 30 MV/m to achieve sx > sz.

A preliminary design (I) • Main parameters Number of cells in a cavity: Number of cavities in a module: Number of modules: Number of b groups: Number of cryomodule types: Lattice: Focusing Period: Esmax: Esmac/Eacc: Synchronous phase: Egain per module: Total length: 9 2 18 18 3 Warm Q doublet 4. 63 -5. 07 m 28 -30 MV/m 4. 55 -3. 14 -30° 7. 8 -15. 4 Me. V 86 m

A preliminary design (II) Initial emittance: enx = 0. 24 pmm • mrad enz = 0. 42 pmm • mrad normalized, rms, 190 Me. V K. Mukugi

A preliminary design (III) PARMILA (modified by K. Hasegawa) No excess drift space in warm section 10, 000 particles Distribution type-2 No error enx = 0. 24 pmm･mrad enz = 0. 42 pmm･mrad (normalized, rms) K. Hasegawa / K. Mukugi

A preliminary design (IV) PARMILA (modified by K. Hasegawa) 10, 000 particles Distribution type-2 enx = 0. 24 pmm･mrad enz = 0. 42 pmm･mrad (normalized, rms) No error No excess drift space in warm section K. Hasegawa / K. Mukugi

Layout of L 3 BT 90 degree achromat bend 2 debunchers (972 MHz) 1 momentum collimator 8 transverse collimators (4 horizontal and 4 vertical) 1 secondary collimator (absorber) just after the momentum collimator Collimator: carbon foil with 0. 1 mm thickness (M. Matsuoka / K. Yamamoto)

Beam dynamics issues in L 3 BT • Longitudinal and transverse halo collimation • Debunching & energy correction to realize Dp/p < 0. 1 % • Combined effect of space charge and dispersion in the arc section Codes: Lattice design: Particle simulation: Collimator: MAD, Transport, Trace 3 D PARMILA, Simpsons STRUCT

Debunching Calculated with TRANSPORT No space-charge correction for achromat bend No error M. Matsuoka

Halo collimation (I) STRUCT calculation Halo is defined as particles which locate outside 4 pmm･mrad ellipse in transverse phase space or which have momentum deviation of larger than 0. 1 %. Total amount of halo is assumed to be 2 k. W. Aperture radius: Collimator: 50 mm / Secondary collimator: 55 mm / Beam pipe: 65 mm Initial distribution Transverse collimation: Transverse: 3 s-Gaussian with 100% emittance of 10 pmm･mrad Longitudinal: parabolic distribution within Dp/p=± 0. 1% Longitudinal collimation: Transverse: 3 s-Gaussian with 100% emittance of 4 pmm･mrad Longitudinal: parabolic distribution within Dp/p=± 0. 2% K. Yamamoto

Halo collimation (II) Calculated with STRUCT No spacecharge K. Yamamoto

Summary • SC option – SC option has been considered for 190 -400 Me. V part. – A preliminary design is determined. – The “smooth” design is adopted. – Esmax is lowered to make sz lower than sx. – We will continue this work to make use of the outcome for the 400 -600 Me. V SCC design.

Summary (continued) • L 3 BT – Urgent tasks • Code validity check • Establishment of energy correction scheme • Space-charge correction for achromat bend • Halo collimator optimization with space-charge