Injection and extraction systems for the CLIC DR - PowerPoint Presentation

Slide1

Injection and extraction systems for the CLIC DR

R ApsimonSlide2

Content

Cell design and parameterisation

Optimisation methods and comparison

Constraints and limitations of parameter space

Summary of optimised parameters

MADX matching and tracking results

Failure modes

Severity and machine protectionSlide3

Cell design and parameterisation

L

kick

L

drift

L

sep

1

L

sep2

The lengths defined on the above diagram are the variables used to minimise the extraction cell length.

Quad strengths in

ext

cell and matching cell used to match Twiss parameters at end of

ext

cell (5 quads in total).

Fixed parameters

The length of the

quadrupoles

and the a space either side of the kicker and septa (

L

gap

) are considered to be unchangeable.

L

gap

is required for bellows and diagnostics (

eg

. BPMs).Slide4

Matching vs. analytical approach

Before: Parameterisation and optimisation done with MADX.

Incrementally reduce cell length and match constraints to minimise length.

Now: Solved analytically with

Mathematica

Beam trajectory calculated through cell elements.

Constrained to septa thicknesses and quad radius.

Cell length minimised analytically.Slide5

Comparison

Advantages (analytical over matching):

Processing time greatly reduced (

hrs

→ seconds)

Optimum solution always found

MADX matching can converge to non-optimal solution

DisadvantagesQuad strengths + Twiss parameters approximateUseful for investigating parameter space before optimising in MadXSlide6

Comparison (cont.)

Approximation for quad strengths begins to diverge. Though still <10cm effect on cell length.

Cell length (m)

Kicker aperture (m)Slide7

Constraints and limitations of

parameter

space

Cell length

Injection and extraction cells must be same length or DR won’t close!

Use injection cell parameters for both systems

Kickers

Voltage fixed at ±12.5kV for stability reasonsAperture must match local apertureWiggler aperture = 12mm; reduce kicker aperture from 20mm →12mmSlide8

Constraints and limitations of

parameter

space (2)

Septum magnets

Minimise septum thickness

Increased current density needs more cooling

Cooling pipes limit minimum septum thickness

Maximise B-fieldMore current, more cooling, thicker septum…Put septa in vacuum?No beam pipes → 5mm reduction in septum thickness

Increased stray fields but large reduction in cell lengthSlide9

Constraints and limitations of

parameter

space

(3)

Kicker length

Length limited by beam deflection

Kicker aperture

Can 10σ beam (at injection) fit through aperture?As I will show, this is a serious limiting factor…Slide10

Constraints and limitations of parameter space

(4)

“Full” optimisation → FODO cell asymmetric

Kicker half-cell shorter than septa half-cell

Breaks 2-fold rotational symmetry of DR

Causes severe instabilities in the DR

Emittance blow-up, beta beating, dispersion, etc…

Dynamic aperture reduced to ~ 1σ!Optimise for symmetric

FODO cellSlide11

Comparison of cell optimisation

Blue curves are

for symmetric cells.

Red curves are for

asymmetric cells.

Green

curves are for

cells neglecting aperture limits.

Thick solid lines are for the septum magnets not in vacuum.Dashed

lines are for the septum magnets in vacuum.

Mechanical and closed orbit tolerances = 1.0mmSlide12

Comparison of cell optimisation

Blue curves are

for symmetric cells.

Red curves are for

asymmetric cells.

Green

curves are for

cells neglecting aperture limits.

Thick solid lines are for the septum magnets not in vacuum.Dashed

lines are for the septum magnets in vacuum.

Mechanical and closed orbit tolerances = 0.5mmSlide13

Aperture considerations

Blue

curve is beam size with tolerances = 1.0mm

Blue curve is beam size with tolerances =

0.5mm

Green line is kicker apertureSlide14

Summary of design parameters

Septum type

Not in vacuum

In vacuum

Cell

type

Asymmetric

Symmetric

Asymmetric

Symmetric

Kicker voltage

±12.5kV

Kicker aperture12mm

Kicker length

2.89m2.89m2.75m

2.89m

Drift

length 1

n/a

1.09m

n/a

0.60m

Drift length 2

1.79m

1.07m

1.05m

0.60m

Sept.

1 B-field

0.2T

Sept.

1 length

0.81m

0.78m

0.82m

0.80m

Sept.

2 B-field

1.0T

Sept. 2 length

1.90m

1.90m

1.92m

1.92m

Cell

length

8.39m

8.73m

7.55m

7.76mSlide15

Matching in MADX: Beta x

Large beta needed at start of injection and extraction cells to preserve the twiss parameters at the end of the cells.

Beta appears out of phase after ~200m because new DR slightly longer than old one.Slide16

Matching in MADX: Beta ySlide17

Matching in MADX: Delta x

Oscillations in long straight sections because “radiate” enabled in the BEAM module when creating Twiss file for old DR sequence.Slide18

Tracking results: H-plane

Blue: No stray fields from septum magnets

Red: Stray fields includedSlide19

Tracking results: V-plane

Blue: No stray fields from septum magnets

Red: Stray fields includedSlide20

Matching and tracking summary

Beam parameters almost unchanged

Checked

equil

. emittance etc.

Tracking shows little effect of stray fields

Both cases, dynamic aperture ~9

σSlide21

Problem with aperture

Original cell length = 4.7m

Too short to extract beam

New cell length = 7.8m - 8.8m

Longer cell → larger

β

to conserve Twiss parameters for rest of DR

Dynamic aper (~9σ) > geometric aper

(~7.5σ)Assume gaussian beam1 particle lost every ~12 injections

4.07e9 particles per bunch, 312 bunchesSlide22

Failure modes: kickers

HV produced by inductive adder (1 for each strip)

20 levels add ~700V each

2 redundant levels

If level fails during kicker pulse

5% drop in stripline voltage → 2.5% reduction in kick

>1 level failure at same time unlikely

Unless power surge damages all levels… DC power supply failureMultiple PS in parallel as redundancy

Slow failure modeMonitor and interlock beam to protect systemSlide23

Failure modes: septum magnets

Short circuit between coil winding

Significant loss in B-field

2 turns for thin septum: 50% loss

4 turns for thick septum: 25-75% loss (depends on coils)

Slow failure mode

Monitor and interlock

Power supply failureSame as for kicker: redundancy, monitor and interlockDamage from septum magnet failures avoidable

Overall risk is small Slide24

Considerations for injection

Total inductive adder failure

50% reduction in kick

Likely to hit beam pipe at start of wiggler section

Difficult to protect against

Slow failure

Interlock and abort both kicker pulses

Add short drift length + absorber just downstream of kicker1 level fails2.5% reduction in kickBeam still in dynamic aperture, so not lost

Emittance increases by factor of 2 (no radiation in tracking)Dump beam after extractionSlide25

Considerations for extraction

Total inductive adder failure

Beam hits thin septum

Absorber in front of septum edge

1 level fails

Beam still able to extract

Collimator in extraction line to capture beamSlide26

Conclusions

Injection and extraction systems

Parameters optimised and matched

Magnets in vacuum good if feasible

Matched DR looks

good

More thorough study of aperture/acceptance

Failure modes + machine protectionNeed to start work on thisLook more into possible machine protectionBoth cells need ~10cm for absorbers