The Introduction to CSNS Accelerators Oct. 5, 2010 Sheng Wang AP group, Accelerator Centre,IHEP, CAS

2 Outline  A Brief Introduction to CSNS  The Status of CSNS  The RCS/CSNS Design Related Issues

3 CSNS Layout and primary parameters PhaseIUpgrade potential Beam power on target [kW] Beam energy on target [GeV]1.6 Ave. beam current [  A] Pulse repetition rate [Hz]25 Protons per pulse [10 13 ] Ion Source typePenningRF Volume Linac energy [MeV]81250 Linac RF freq. [MHz]324 Max. space charge tune shift Target number11 Number of spectrometers318

4 The Status of CSNS  Small budget for R&D from 2006; IS, DTL, Dipole, Quadrupole, Vacuum chamber, PS, ……  The site of the project has been decided in Guangdong province;  Land prepare has begun from May 2010;  Official start will be at the beginning of 2011;  Beam commissioning will be started around the end of 2015;  ……

5 The RCS/CSNS Design Related Issues

6 Lattice design － 4-fold Structure Separated-function design The collimation can be performed in a individual straight section. The superperiodicity of 4 is better for reducing the impact of low-order structure resonance than superperiodicity of 3.

7 Lattice design Lattice consists of 16 triplet cells, with a gap in the middle of arc, and with long free space in dispersion free straight section. Four-fold symmetry － Separated functions Triplet structure － Small magnet aperture Dispersion-free long uninterrupted straight － For collimation & injection/extraction Straight at arc with large dispersion － high efficiency mom. collimation The all-triplet structure is not good for chromaticity correction and dynamic aperture

8 The main parameters of lattice Circumference (m) Superperiod 4 Number of dipoles 24 Number of quadrupoles 48 Lattice structure Triplet Total Length of long drift (m) 3.85*8+11*4 Nominal Betatron tunes (h/v) 4.82/4.80 Nature chromaticity (h/v) -4.3/-9.2 RF Freq. (MHz) ~ RF Voltage (kV) 165 Trans. acceptance (  m.rad) 540 Momentum acceptance 1% Effective length of dipoles(m) 2.1 Dipole gap (mm) 160 Max. quadrupole aperture (mm) 265 Number of dipole power supplies 1 Number of quadrupole power supplies 5

9 Tune Diagram for 4-fold Structure red ： 1 st order structure resonance golden ： 2 nd 1st order structure resonance blue ： 3 rd order structure resonance green ： 4 th order structure resonance gray ： 3 rd deference structure resonance pink ： coupling resonance

10 Chromaticity correction Powered with DC power supply 2 families power supplies Designed for low beam density - for commissioning

11 The layout of the transverse collimation system

12 Impedance and instabilities The impedance of RCS comes from the wall of chamber, bellows, kickers, RF cavities, BPM, collimators, steps space charge. The impedance of these components has been calculated for both injection energy and extraction energy.  the space charge impedance dominates in the broad band impedance,  wall impedance mainly comes from the stainless steel chamber.

13 There is about 0.3% addational beam loss when sextupoles are used in the simulation. The combined effects of sextupoles and space charge (1)

14 The tune spread with and without sextupoles With sextupolesWithout sextupole The combined effects of sextupoles and space charge (2)

15 Beam injection H- stripping and painting method are used to match the small emittance beam from linac to large emittance beam in RCS. The injection is performed in a 11 m long straight section, Four horizontal painting magnets (BH), four vertical painting magnets (BV), and four shift orbit bump magnets (BC). Shift bump magnets works in DC mode.

16 Extraction Two 1.6GeV proton bunches are extracted by one-turn extraction from RCS in each RCS cycle. The beam is vertically kicked by a series of kicker to a horizontal bending Lambertson type septum. The bunch length is about 70~100ns, and the space between two bunch is about 330~360ns. The rise time of kicker is required to be less than 250ns and with flat top field more than 550ns.

17 Extraction from RCS

18 Thank you for your attention!