1. 100 MeV- 1 GeV Proton Synchrotron for Indian Spallation Neutron Source Gurnam Singh Beam Dynamics Section CAT, Indore CAT-KEK-Sokendai School on Spallation Neutron Sources, 2004

2. BASIC LAYOUT OF INDIAN SPALLATION NEUTRON SOURCE 100 MeV Linac Linac to PS Transfer Line PS to Target Transfer Line 100 MeV – 1 GeV PROTON SYNCHROTRON (PS) TargetTarget H- Source RFQ 4.5 MeV

3. Outline: 1.Preliminary design aspects of Rapid Cycling Proton Synchrotron 2.Linac to Synchrotron Transfer Line

4. Preliminary design aspects Of Rapid Cycling Proton Synchrotron

5. Key parameter in a spallation source Beam Power P beam = q.N p.E.R =I.E P beam :Beam power (W) at target q :Charge on proton (C) N p :No. of protons in ring E:Final proton energy (eV) R:Repetition rate (Hz) I:Average current at target (A)

6. To increase the beam power Two Ways Increase beam energy  Large machine, big cost Increase beam Current  Severe space charge  Collective beam instabilities Choose optimum energy & current

7. Accelerator choice Full Energy Linac & Accumulator Ring Linac & RCS High power achievable but high cost High injection energy means very tight beam loss control at injection High injection energy, so more heating of injection foil Low injection energy, thus more space charge problem Rapid acceleration, means powerful RF systems Ceramic chamber

8. Indian Spallation Neutron Source 100 MeV Linac & RCS based Beam power:100 kW Final energy of the beam: 1 GeV Average current: 100  A [@ 25 Hz Repetition Rate]  2.4  10 13 protons in synchrotron

9. Design Considerations 1. Injection energy 100 MeV The first estimation of current in the synchrotron is made by space charge tune shift. => For the required N, the tune should not cross any dangerous resonances. Thus tune should have sufficient room for movement. In our design, allowable tune shift taken as 0.2.

10. For decreasing the tune shift (for enhancing the average current handling capability of the synchrotron) * Increase the injection energy => Increase the cost of Linac. * Decrease the N and increase the repetition rate, so that average current remains same => Constraints from technology and frame overlap in time of flight type experiments. *Increase the bunching factor at injection => Deciding factor of RF programme of the machine.

11. 2. Beam loss control Beam loss control is of major concern in the high intensity machines. 1W/m is the allowable limit of uncontrolled loss for hands on maintenance. => @ injection, average beam power 10 kW Uniform loss on whole length of ring gives the upper most limit: 2% allowed uncontrolled loss. => Thus for controlled loss, betatron and momentum collimators needed.

12. 3. Sufficient space Large dispersion free straight sections are needed for 1) RF systems. 2) Betatron collimators 3) Injection systems 4) Extraction system Apart from these, other systems which should be accommodated in the ring are diagnostic devices, vacuum pumps, correctors etc. 4. High tune for working well below the  transition

13. Options for the lattices Many lattice configurations can fulfill these requirements:  For making an arc with achromatic conditions 1. FODO with Missing dipole scheme (IPNS, KEK-JAERI etc.) 2. Achromat design (eg. SNS)  Obtaining the long straight dispersion free sections 1. FODO 2. Doublet/ Triplet structures

14. Lattice for the ISNS  FODO structure: Simple, smooth variation of beta function means less prone to errors.  Missing dipole for the dispersion matching  Four superperiods The four long straight sections will be used for the injection system, collimators (beam collimatoss), RF- system and extraction system respectively. Four superperiods have better stability for structure resonance than the three period structure.

16.  One period Qf2Qd2Qf1 Qd1Qf1 Qd1Qf3 ARC SECTION Half-cell length of FODO: 4.425 m Total cells in arc:4 (one period) Total straight section cells:2 (one period) Quadrupole families:5 (3f & 2d) Length of the period:53.1 m Length of long straight:4  3.875=15.5 m

17.  Choice of tune 90  phase advance per cell requires a tune of 6.0, so the tune of the machine is kept near 6.0. In horizontal plane, it is higher than the 6.0 and in vertical plane it is on the lower side. But it has wide tunability range and it can be operated at split and un-split working points.

18.  Structure & half integer resonance diagram ( upto 4 th order) Shaded region is the space for different tune options y x 56 7 8 4 5 6 7 3 X =20 X +2 y =20 X +2 y =16 2 X +2 y =24 2 X - y =8 3 X - y =12 3 X + y =28 X +3 y =24 5.5 6.5 (6.88, 5.88) X - y =1 X - y =0 (7.3, 6.3) (6.3, 6.3)

19. * Further selection depends on imperfection resonance The lattice can have various tune points in these regions. Primarily selected tune is 6.88 and 5.88 [other options are 6.3, 6.3 and 7.3, 6.3 (higher tunes)]. Tune is far away from resonance up to 3 rd order. Tune drift of –0.2 (due to space charge) does not hit any resonance up to 3 rd order.

20.  Lattice parameters

21. Preliminary tracking results with sextupoles (without error) Horizontal phase space, 5000 turns Vertical phase space, 5000 turns Initial co-ordinates are chosen corresponding to maximum displaced particle in both the planes with 1%  p/p.  Further optimization needed in sextupoles for vertical plane.

22. H - Injection  500  s ( 300 turns ) pulse length of H - ions from 100 MeV linac to be injected through a stripping foil.  Constraints imposed by Liouville’s theorem on conventional multi-turn injection  do not apply in this case.  possible to inject a large number of turns.

23. Goals Of Injection   To fill transverse acceptances (  x =  y = 300  mm mrad) in K-V distribution  uniform filling  avoid excessive space charge forces  referred as injection painting

24. Injection Paintings Horizontal Phase Space : Variable Bump by four bump magnets located in a long straight section  Angle of Injection  Peak of the bump at the stripping foil  Minimum number of traversal of beam through the foil

25.  Partially stripped particles H 0 do not pass through high magnetic field ( centre of QD )  Sripped H - (Magnetic field)  unwanted halo formation around circulating particles

26. Layout of the injection system of ISNS

27. Time Dependence of Four Kick Bump Angles

28. Orbit Bump and its Slope at the Location of Stripping Foil (Injection Point) vs Injection Turn Number

29. Bending Angle with Injection Turn Number

30. Amplitude of Betatron Oscillations of Injected Particles with Turn Number During Injection

31. Painting in vertical normalized phase space

32. Spatial distribution of nearly 350 injected turns

33. Striping Foil Thickness of the foil: (High stripping efficiency ) At 100MeV 60  g cm -2 is adequate Foil materials: Polyparaxylene,carbon or Aluminium oxide

34. Beam loss and Collimators  The lattice should accommodate the collimators (betatron and momentum) for controlled loss. At injection only 2% particle loss is allowed (if distributed uniformly all over the length) in the ring.  Key parameter in collimator design: Phase advance between primary and secondary collimators and their apertures

35.  Collimators remove the Halo from the beam at the predefined locations.  The first collimator scatters the halo particles, with low impact parameter. Due to scattering, the amplitude increases and these are collected at secondary collimator, which is placed at a proper phase advance.

36. Proper phase and critical kick is given by n 1 and n 2 are the apertures of primary and secondary in terms of beam size. The critical kick is Phase difference between primary and secondary collimator X – Plane: 158  and n 2 /n 1 =1.08 Y – Plane: 144  and n 2 /n 1 =1.20

37.  Material choice in collimators  Two Effects:  When a proton traverse through a primary collimator, it loses energy. If this loss is high, particle may be out of bucket or longitudinal acceptance. (Acceptance of ring 1%)  The primary collimator has to give a large kick, so protons hit the secondary collimator with large impact parameter. This kick is largely imparted through the multiple Coulomb scattering.

38. The first effect demands a very thin collimator, which does not cause the much energy loss. The second effect demands a high Z material. Thus choices are among Pt, W etc. Other requirements are good thermal conductivity, high melting point, good polishing capability, radiation damage. As high Z has the shower effects, which is drawback. Therefore, for proper choice of material and optimization of its thickness, simulation studies are essential.

39.  Tentative locations of betatron collimators In next period to injection. y-plane x-plane Phase difference between primary and secondary collimator X – Plane: 158  and n 2 /n 1 =1.08, beam sizes at the collimators: 4.2cm, 3.8 cm, 3.2 cm Y – Plane: 144  and n 2 /n 1 =1.20, beam sizes at the collimators: 3.8cm, 5.6 cm, 3.6 cm

40.  Tentative locations of momentum collimators Phase difference between primary and secondary collimator X – Plane: 150  and n 2 /n 1 =1.15 In arc next to injection system.

41. Preliminary beam diagnostic requirements  48 Beam position monitors ( one @ each quadrupole).  Beam loss monitors distributed all over the ring.  Beam profile monitors.  Current monitors (Average and Pulse).

42. ParameterValue Beam power100 kW Energy0.1 – 1.0 GeV Repetition Rate25 Hz Circumference (m)212.4 Periodicity4 No. of bending magnets24 Bending angle 15  per magnet Bending Magnet Field0.207 - 0.789 T Bending radius (m)7.1626 No. of quadrupoles48 Maximum gradient (T/m)4.5 Nominal tune point6.88, 5.88  x,max,  y,max (m) 16.4, 16.4 No. of sextupoles16 (two families 8F and 8D)  Parameters of Synchrotron

43. ParameterValue D max (m)2.4896 Chromaticity-8.954, -7.640 Momentum compaction0.031989  -transition 5.591 Dispersion free straights 4  3.874=15.5 m / period Straight with dispersion 2  3.875=7.75 m / period  RF (MHz) 1.21 – 2.47 for h = 2 Revolution Time1.65 – 0.81 µs Peak energy gain per turn60 keV Beam size (max) 9.6 cm @ 1%  p/p @ Qf1 Emittance after painting 300  mm.mrad after injection in both planes Peak RF voltage120 kV

44. Parameters of Linac (injector) ParameterValue Energy100 MeV Pulse length 500  s Pulse current25 mA Energy spread0.3 % Emittance (normalized) 0.23  mm mrad

45. Magnet apertures Magnet Max  (m) Max D (m) Strength (m -2 ) Good field radius (mm) Qf116.42.6-0.67120 Qd116.12.50.56100 Qf216.10.0-0.64100 Qd216.40.00.61100 Qf313.22.5-0.67120 BM~8~20.8 T100, 100

46. Linac to Synchrotron Transfer Line

47. Design Philosophy To match the beam parameters from the linac output to synchrotron injection point. To provide the adequate space for installation of various components, as 1.RF cavity for energy jitter correction. 2.Diagnostic elements (Profile monitors, Current monitors, Beam position monitors and Beam loss monitors). 3.Dump line. 4.Bumpers for injection painting. To install collimators for control of beam loss.

48.  Optics parameters of Transfer Line Matching section 4 Quads 2 FODO Achromat 1 FODO Matching section 4 Quads

49. Primary collimator Secondary collimator X Secondary collimator Y RF Cavity

50. ParameterValue Length62.95 m No. of quadrupoles21 (11 F & 10 D) Maximum strength (m -2 )6.1 No. of dipoles2 Bending field (T)0.65  x,max,  y,max (m) 27.6, 15.8  x,inj,  y,inj, D inj (m) 0.99, 1.95, 0.00  x,ext,  y,ext, D ext (m) 13.0, 2.5, 0.0

51. Conclusions Only preliminary linear studies have been carried out. Studies to be carried out 1. Non-linear behavior and sextupole scheme 2. Detailed studies of Longitudinal dynamics with space charge and deciding the RF program 3. Space charge issues and beam loss control 4. Detailed studies of injection and extraction 5. Design of transfer lines 5. Transverse and Longitudinal instabilities

53. Exact formulation of Tune Shift (including the image terms)

54. y x 56 7 8 4 5 6 7 3 X =20 X +2 y =20 X +2 y =16 2 X +2 y =24 2 X - y =8 3 X - y =12 3 X + y =28 X +3 y =24 5.5 6.5 (6.88, 5.88) X - y =1 X - y =0 (7.3, 6.3) (6.3, 6.3)