Download - Peter Spiller, GSI, ICFA workshop, 17.10.2004 Optimization of SIS100 Lattice and Dedicated Collimation System P. Spiller, GSI ICFA 2004 Bensheim 18.10.04.

Peter Spiller, GSI, ICFA workshop, 17.10.2004

Optimization of SIS100 Lattice and Dedicated Collimation System

P. Spiller, GSI

ICFA 2004

Bensheim 18.10.04


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) Dx = 2.5 m

Six superperiods (space for large tune spread and long storage time)


U28+ : Reference Ion of the FAIR Project

Present Intensity in SIS12/18

2.5 x 109 U73+ -ions /cycle

Planned Intensity in SIS12 Booster Operation

2.5 x 1011 U28+ -ions /cycle

Planned Intensity in SIS100/300

1 x 1012 U28+ -ions /cycle

The step to highest heavy ion beam intensities requires medium charge states.


History of U28+ operation at GSI

<2001 Life time measurements at low intensities (108)

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


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.


Residual Gas Pressure Dynamics

Fast variations (time scale s) Slow variations (time scale s)


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


Loss Mechanism Location Time scale Angle Energy

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)

Seconds Envelope 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)

mrad Injection energy

RF capture losses Everyywhere 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 mrad Full energy range

Ionization and e. loss in septum wires

behind e-septum Spill time >25 mrad Final energy

Loss Mechanisms


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 (U29+) 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 U29+-ions.

No additional load for the UHV system during beam operation


4. The collimation efficiency for U29+ - 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


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


Multiple Ionisation

R. Olsen et.al., HIF04

SIS100 injection energy

SIS18 injection energy

E [MeV/u]

Average num

ber of proj. loss electrons

SIS18 experimental

LEAR

P = 3.67x10-11 P = 2.87x10-11

H2 – 81.87 %

CH4 – 11.86 %

CO – 3.02 %Ar – 3.25 %

H2 – 83.18 %

He – 2.36 %CH4 – 10.38 %

CO – 1.73 %N2 – 1.38 %

Ar – 0.97 %

Cross section interpolationMultiple ionization reduces the collimation efficiency


Charge Separator Lattice and Collimation

wedge collimator at 80 K

cold, pumping secondary chamber at 4.5 K

About 10 collimators per arc


Collimation Efficiency

80%

82%

84%

86%

88%

90%

92%

94%

96%

98%

100%

1,0 1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 1,9 2,0

Distance from Beam Axis [ n*Rbeam]

Col

limat

ion

Effi

cien

cy

Acceptance CDR

CDR-lattice

Acceptance 3 Dipole DF

3 Dipole DF

coll = Ncoll/Ntotal

at injection energy


Storage Mode Lattice

Collimator distance from beam axis

Col

limat

ion

effic

ienc

y

SIS100 Lattice


Vergleich alle Lattices

55%

60%

65%

70%

75%

80%

85%

90%

95%

100%

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2

Abstand von Strahlachse / n*R(k-v-Verteilung)

Ko

llim

atio

nse

ffiz

ien

z

CDR (TR_DFD_4Dipole3.0Grad2.0T_08_Ausgelagert)TR_DFD_3Dipole2.9Grad2.0T_09TR_DFD_3Dipole3.0Grad2.0T_09_AusTR_DFD_3Dipole3.0Grad2.0T_10_AusgelagertTR_FDF_3Dipole2.9Grad2.0T_09TR_FDF_3Dipole3.0Grad2.0T_09_AusgelagertTR_FDF_3Dipole3.0Grad2.0T_10_AusgelagertDOFO_2Dipole3.0Grad2.0T_17DP_DF_2Dipole3.0Grad2.0T_13_TuneDP_DF_2Dipole3.0Grad2.0T_13_AusgelagertDP_DF_2Dipole3.0Grad2.0T_13_Aus_TuneDP_DF_2Dipole3.0Grad2.0T_14DP_DF_2Dipole3.0Grad2.0T_14_TuneDP_DF_2Dipole3.0Grad2.0T_14_AusgelagertDP_DF_2Dipole3.0Grad2.0T_14_Aus_TuneDP_DF_2Dipole3.0Grad2.0T_15DP_DF_2Dipole3.0Grad2.0T_15_AusgelagertDP_DF_2Dipole3.0Grad2.0T_15_Aus_TuneDP_DF_2Dipole3.0Grad2.0T_15_Aus_T2DP_DF_2Dipole3.3Grad1.9T_13_AusgelagertDP_DF_2Dipole3.3Grad2.0T_13DP_DF_2Dipole3.3Grad2.0T_13_AusgelagertDP_DF_2Dipole3.3Grad2.0T_14DP_DF_2Dipole3.3Grad2.0T_14_AusgelagertDP_DF_3Dipole2.7Grad2.0T_11_AusgelagertDP_DF_3Dipole2.9Grad2.0T_11DP_DF_3Dipole2.9Grad2.0T_12DP_DF_3Dipole3.0Grad1.9T_11_AusgelagertDP_DF_3Dipole3.0Grad2.0T_11_AusgelagertDP_DF_3Dipole3.0Grad2.0T_12_AusgelagertDP_DF_3Dipole3.3Grad2.0T_11DP_DF_3Dipole3.3Grad2.0T_12DP_FD_2Dipole3.0Grad2.0T_15DP_DF_2Dipole3.0Grad2.0T_16_Aus_11/2_TuneDP_DF_2Dipole3.0Grad2.0T_16_Aus_11/2DP_DF_2Dipole3.0Grad2.0T_16_Aus_11/2_19_17DP_DF_2Dipole3.0Grad2.0T_16_Aus_11/2_28_16DP_DF_2Dipole3.0Grad2.0T_16_Aus_11/2_28_20

Lattice Choice and Optimization


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.


t [s] t [s]

N, p[m

bar]

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)


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


Summary

1. A promising concept for the high current U28+ 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.


Acknowledgements:

group BEN and project group SIS100/300