Peter Spiller, GSI, ICFA workshop, Optimization of SIS100 Lattice and Dedicated Collimation System P. Spiller, GSI ICFA 2004 Bensheim

Peter Spiller, GSI, ICFA workshop, Lattice Optimization - General CDR triplet lattice with 4 dipoles per cell (Acceptance : 100 x 55 mm mrad) Doublet lattice with 2 dipoles per cell (Acceptance : 170 x 50 mm mrad )  Maximum beam acceptance („small“ aperture magnets for fast ramping)  Dispersion free straight sections (no transv.-longit. coupling in rf systems)  Low dispersion in the arcs (momentum spread during compression) D x = 2.5 m  Six superperiods (space for large tune spread and long storage time)

Peter Spiller, GSI, ICFA workshop, U 28+ : Reference Ion of the FAIR Project Present Intensity in SIS12/ x 10 9 U 73+ -ions /cycle Planned Intensity in SIS12 Booster Operation 2.5 x U 28+ -ions /cycle Planned Intensity in SIS100/300 1 x U 28+ -ions /cycle The step to highest heavy ion beam intensities requires medium charge states.

Peter Spiller, GSI, ICFA workshop, History of U 28+ operation at GSI  <2001 Life time measurements at low intensities (  10 8 )  2001 First observations of time dependend life time and fast pressure variations within single SIS18 cycles  2002/2003 Proposal and installation of a dedicated collimator for the controle of desorption gases in SIS18  2003 Report on analysis and first modelling of the observations  2003/2004 Desorption rate measurements at the GSI test stand  2004 Optimization off SIS100/300 lattice structure with respect to collimation efficiency  2004 First time dependend modelling including primary losses, collimation efficiency, pumping properties, target and projectile (mulitple) ionization and desorption

Peter Spiller, GSI, ICFA workshop, Life Time and Vacuum Instability Beam losses induced by a dynamic vacuum or a vacuum instability is the most crucial item for achieving the goals of the new facility.

Peter Spiller, GSI, ICFA workshop, Residual Gas Pressure Dynamics Fast variations (time scale  s) Slow variations (time scale s)

Peter Spiller, GSI, ICFA workshop, Vacuum Stabilization – General  Short cycle time and short sequences SIS12 :10 T/s - SIS100 : 4 T/s (new network connection in preparation)  Enhanced pumping power, optimized spectrum (Actively cooled magnet chambers 4.5 K, NEG coating (local and distributed)  Localization of losses and controle of desorption gases Prototype desorption collimator installed in S12  Low-desorption rate materials Desorption rate test stand in operation wedge collimator increased pressure ion beam cryo pump

Peter Spiller, GSI, ICFA workshop, Loss MechanismLocationTime scaleAngleEnergy Tails and Halo due to Resonances, non-linear dynamics etc. (higher order dynamics) Everywhere but mainly on acceptance limiting devices (in straight sections) (both sides) SecondsEnvelope angle (<5 mrad) + some  rad Full energy range Closed orbit distortions, injection losses, tracking errors (1. order dynamics) Everywhere but mainly on acceptance limiting devices (in straight sections (both sides) Max. ms (untill beam fits into acceptance) mradInjection energy RF capture lossesEveryywhere but mainly on acceptance limiting devices (inner side) Envelope angle (<5 mrad) + some  rad Injection energy Losses due to momentum spread jump (at compression) Mainly in the arcs (both sides) (  250  s) max. ¼ synchrotron osc. Envelope angle (< 5mrad) + some  rad Final energy Ionization in residual gas Mainly in the arcs (inner side) Full cycle and during SE <25 mradFull energy range Ionization and e. loss in septum wires behind e-septumSpill time>25 mradFinal energy Loss Mechanisms

Peter Spiller, GSI, ICFA workshop, Design Concept for Medium Charge State Uranium Beams 1 1. From all loss mechanisms, only particles which are further stripped by collisions with the residual gas atoms are able to reach the beam pipe within one lattice cell ! 2.Each lattice cell must be designed as a charge separator. The „stripped“ beam (U 29+ ) must be well separated from the reference beam. The low dispersion function in the SIS100 arcs complicate this issue. 3. The main lattice structure optimization criteria is the collimation efficiency for U 29+ -ions. No additional load for the UHV system during beam operation

Peter Spiller, GSI, ICFA workshop, The collimation efficiency for U ions must be 100%. 5. Mainly single (no multiple) ionized ions shall be generated. 6. The 100% collimation efficiency must be achieved with collimators at maximum distance from the beam edge. No significant acceptance reduction shall be caused by the collimator system. 7. No ionization beam losses shall occure on cold and NEG coated surfaces. 8. By an optimued design, the effective desorption rate of the collimators shall be almost zero. Design Concept for Medium Charge State Uranium Beams 2

Peter Spiller, GSI, ICFA workshop, Wedge collimator + secondary chamber + cryo pump The collimation system must controle the desorption gases (  eff = 0) SIS18 Prototype Desorption Collimator Desorption gases are generated in secondary chamber

Peter Spiller, GSI, ICFA workshop, Multiple Ionisation R. Olsen et.al., HIF04 SIS100 injection energy SIS18 injection energy E [MeV/u] Average number of proj. loss electrons SIS18 experimental LEAR P = 3.67x P = 2.87x H 2 – % CH 4 – % CO – 3.02 % Ar – 3.25 % H 2 – % He – 2.36 % CH 4 – % CO – 1.73 % N 2 – 1.38 % Ar – 0.97 % Cross section interpolation Multiple ionization reduces the collimation efficiency

Peter Spiller, GSI, ICFA workshop, Charge Separator Lattice and Collimation wedge collimator at 80 K cold, pumping secondary chamber at 4.5 K About 10 collimators per arc

Peter Spiller, GSI, ICFA workshop, Collimation Efficiency  coll = N coll /N total at injection energy

Peter Spiller, GSI, ICFA workshop, Storage Mode Lattice Collimator distance from beam axis Collimation efficiency SIS100 Lattice

Peter Spiller, GSI, ICFA workshop, Lattice Choice and Optimization

Peter Spiller, GSI, ICFA workshop, Simulation Code Development Integrated time resolved loss and pressure calculation must comprise:  Initial residual gas composition  Initial systematic beam losses (e.g. multi turn injection)  Projectile and target ionization cross sections and resulting ionization degree and multiple ionization degree  Collimation efficiency for the generated ionization degrees  Effective desorption rate of the collimation system  Realistic pumping power for the different residual gas consitutents and UHV conductivity  Desorption coefficients and assumptions for the desorped masses.  Desorption created by target ionization.

Peter Spiller, GSI, ICFA workshop, t [s] N, p[mbar] Time Resolved Simulation of Losses and Pressure First step: Evaluation of a single SIS18 cycle Second step: Evaluation of a high repetition mode (booster) Recent results indicate the importance of initial losses (MTI)

Peter Spiller, GSI, ICFA workshop,  The collimation system is designed for uranium operation.  The collimation efficiency for other ion species is lower (lower max. intensity).  Some amount of additional pressure load can not be avoided.  Therefore chambers of the s.c. magnets shall be cold and act as cryopumps. ( Without active cooling, the dipole chamber temperature was about 50K. )  Cooling channels must be foreseen at least in the drift- and quadrupole chambers. ( about 700 m of the chambers will be cold and act as cryo pumps )  NEG coating of SIS100/300 magnet chambers is not possible since baking would be required.  NEG coating will be considered for the straight drift chambers (200 m). (Present ) Limits of the Concept

Peter Spiller, GSI, ICFA workshop, Summary 1.A promising concept for the high current U 28+ operation has been developed. 2.The situation of the SIS12 booster operation is more critical since the lattice is not optimized for collimation and multiple ionization is more probable. 3.The collimation efficiency for other heavy (e.g. Au, Pb) ions is lower and the fractions of the beam which may be lost uncontrolled is higher. 4. The ionisation cross section drop for lighter ions and life time is longer.

Peter Spiller, GSI, ICFA workshop, Acknowledgements: group BEN and project group SIS100/300