# Presentation: 371594

## SNS Mini-workshop, June 25, 2001

Masanori Ikegami
KEK

and other stuffs of the linac group of the KEK/JAERI joint project

- 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:					400 MeV
- Peak current:				50 mA
- Macro pulse duration:			0.5 msec
- Repetition:				25 Hz (50 Hz)
- Duty factor:				1.25 % (2.5 %)
- Chopping ratio:				56 %
- Average current before chopping:		0.625 mA (1.3 mA)
- Average current after chopping:		0.35 mA (0.7 mA)
- Average beam power after chopping:	140 kW (280 kW)
- Frequency:				324 MHz for < 190 MeV
- 					972 MHz for > 190 MeV

- ( ): in future

## Layout

## Brief history

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

## Outline

- 190-400 MeV part
- Overview of ACS option
- Design strategy for SCC option
- A preliminary design for SCC option
- 400 MeV transport (L3BT)

## Project member (ACS, SCC, L3BT)

- 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)
- L3BT	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 p/p of less than 0.1 % in “full” width for RCS injection
- Unnormalized “100 %” emittance of less than 4 ・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:	972 MHz		Number of tanks:		46
- Input energy: 	190 MeV 		Number of cells per tank:	15
- Output energy: 	400 MeV 		Number of Klystron:		23
- E0:		4.3-4.4MV/m	Total length:	108 m
-  Lattice:		Q doublet

## Layout of an SCC module

- Input energy:	190 MeV
- Output energy:	400 MeV
- Frequency:	972 MHz
- Lattice:		Q doublet
- Total length:	87 m

- Num. of cells per cavity:		9
- Num. of cavities per cryomodule:	2
- Num. of Klystrons per cryomodule:	1
- Num. of modules:			18

## Cavity specifications

- Frequency:	972 MHz 		Operating temp.:	2 K
- Material:		Niobium 		Geometrical :	0.56-0.71
- Thickness:	3.8 mm 		Coupling strength:	4.0-2.9 %
- Equator radius:	140-139 mm	Esmax/Eacc:	4.55-3.14
- Bore radius:	45 mm 		Esmax:		> 40 MV/m
- (K. Mukugi)

## Beam dynamics issues for SCC option

- Large phase slip ← beta grouping
- Transition ← beta grouping
- Non-equipartition & longitudinal-transverse coupling resonance ← strong longitudinal focusing
- RF control in pulsed operation ← Lorentz detuning

- Possible source of problems in SC option from beam dynamics point of view:

## Comparison with model linacs (I)

- 			SCC type	ACS type
- Num. of tanks		34		46
- Num. of cells per tank	9		15
- Num. of  groups		4		46
- Total length (m)		80.1		109.2
- Structure length (m)	29.9		68.2
- E0 (MV/m)		8.9-12.6		4.29

**Parameters for model linacs**

- CCLINSAC simulations for 2 types of model linac with RF errors
- 9600 simulation particles
- nx 0.24 mm・mrad  nz 0.46 MeV・deg (normalized, rms)

- T. Kato

## Comparison with model linacs (II)

- SCC type (E21P11)                    T. Kato

- ACS type (E21P11)

## Comparison with model linacs (III)

- Energy deviation (E11P11)

## “Smooth” design

- Different geometrical g for a different module (two cavities in one module).
- Three spare modules with typical three g.
- 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.
-  x0 < 90°to avoid the structure resonance.
-  x > z to avoid the longitudinal-transverse coupling resonance at x ~ z .
- Esmax is lowered to ~ 30 MV/m to achieve x > z .

## A preliminary design (I)

- Main parameters

- Number of cells in a cavity:		9
- Number of cavities in a module:	2
- Number of modules:		18
- Number of  groups:		18
- Number of cryomodule types:	3
- Lattice:				Warm Q doublet
- Focusing Period:			4.63-5.07 m
- Esmax:				28-30 MV/m
- Esmac/Eacc:			4.55-3.14
- Synchronous phase:		-30°
- Egain per module:		7.8-15.4 MeV
- Total length:			86 m

## A preliminary design (II)

- Initial emittance:
- nx = 0.24 mm•mrad
- nz = 0.42 mm•mrad
- normalized, rms, 190 MeV

- 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
- nx = 0.24mm・mrad nz = 0.42mm・mrad (normalized, rms)
- K. Hasegawa / K. Mukugi

## A preliminary design (IV)

- PARMILA (modified by
- K. Hasegawa)
- 10,000 particles
- Distribution type-2
- nx = 0.24mm・mrad
- nz = 0.42mm・mrad
- (normalized, rms)
- No error
- No excess drift space in
- warm section
- K. Hasegawa / K. Mukugi

## Layout of L3BT

- 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 0.1mm thickness

- (M. Matsuoka / K. Yamamoto)

## Beam dynamics issues in L3BT

- Longitudinal and transverse halo collimation
- Debunching & energy correction to realize		 p/p < 0.1 %
- Combined effect of space charge and dispersion in the arc section

- Codes:
- Lattice design: 		MAD, Transport, Trace3D
- Particle simulation:	PARMILA, Simpsons
- Collimator:		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mm・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 kW.
**Aperture radius:**
- Collimator: 50 mm / Secondary collimator: 55 mm / Beam pipe: 65 mm
**Initial distribution**
- Transverse collimation:
- 	Transverse: 3-Gaussian with 100% emittance of 10mm・mrad
- 	Longitudinal: parabolic distribution within p/p=±0.1%
- Longitudinal collimation:
- 	Transverse: 3-Gaussian with 100% emittance of 4mm・mrad
- 	Longitudinal: parabolic distribution within p/p=±0.2%
- 						K. Yamamoto

## Halo collimation (II) 

- Halo collimation (II)

- Calculated with
- STRUCT
- No space-charge
- K. Yamamoto

## Summary

- SC option
- SC option has been considered for 190-400 MeV part.
- A preliminary design is determined.
- The “smooth” design is adopted.
- Esmax is lowered to make z lower than x.
- We will continue this work to make use of the outcome for the 400-600 MeV SCC design.

## Summary (continued)

- L3BT
- Urgent tasks
- Code validity check
- Establishment of energy correction scheme
- Space-charge correction for achromat bend
- Halo collimator optimization with space-charge