injection, extraction and protection of the clic damping rings

Injection, extraction and protection of the CLIC damping rings

R. ApsimonTE-ABT-BTP

CLIC Workshop 201330th January 2013

CLIC Workshop 2013 2

Design requirements

• Primary goal:– Minimise length of injection & extraction insertions• Minimises beam instability due to collective effects

– Must respect physical limitations of elements• Maximum field in kicker and septum magnets

– Homogeneity and stability requirements• Aperture constraints

• Secondary goal:– Protect machine from injection/extraction failures

30/01/2013


Damping ring requirements

• Keep equilibrium emittance small– Relies on high degree of symmetry• Injection & extraction cells must be symmetrical

– Kicker and septa orders swapped between injection and extraction

– Identical design for both systems– Injection emittance larger than extraction• More kicker length required• Longer cell length• Injection system more critical for design

30/01/2013


Kicker and septum magnet parametersParameter Injection Extraction

Aperture (mm) 12*Repetition rate (Hz) 50

Vacuum (mbar) 10-10

Pulse voltage per stripline (kV) ±12.5Stripline pulse current [50Ω load] (A) ±250

Rise and fall times (ns) 1000Pulse flat top duration (ns) ~160

Flat top reproducibility ±1x10-4

Stability ±2x10-3 ±2x10-4

Field homogeneity (%) ±0.1 ±0.01

Parameter Thin septum Thick septumGap height (mm) 5 5

Septum thickness* (mm) 5 / 10 20 / 25Pulsed mode DC DCLength (m) ~ 0.85 ~ 2.00

Injection stability ±2x10-4 ±2x10-5

Extraction stability ±2x10-5 ±2x10-6

Deflection angle (mrad) 17 190Gap field (T) 0.19 0.91

Coil current (kA) 0.76 3.60

Kicker parameters Septa parameters

Kicker and septa designs are optimised for their geometries to provide the maximum field, without exceeding their respective stability requirements.

For the optimisation of the injection and extraction optics, their lengths are the only parameters which will varied.

* The kicker aperture for the baseline design is 20mm; 12mm is used for the injection cell optimisation. This is the aperture of the long straight sections and is near optimal.

30/01/2013


Parameterisation of injection systemLcell

Lthick Lthin Ldr1 Ldr2 Lkick

Optimisation parameter

System constraint Beam constraints

Cell symmetry 6σ beam < aperture

Minimise Beam to fit d-quad

Clear thin septum blade Beam to fit kicker ap

Clear thick septum blade Match beam after cell

Clear quad radius

Turns out matching cell is required after injection cell to meet aperture constraint.

Extraction system is identical but septum and kicker orders reversed.

30/01/2013

Septum magnets

Stripline kicker


Injection/extraction parametersSepta in vacuum Septa not in vacuum

Kicker parametersAperture 12 mm 12 mmVoltage ±12.5 kV ±12.5kV

Kicker length 2.4 m 2.6 mThin septum parameters

Gap field 0.2T 0.2T

Length 0.9 m 0.9 m

Thick septum parameters

Gap field 1T 1T

Length 2.0 m 2.0 m

Inj/ext cell length 7.9 m 9.4 mMatching cell length 2.4 m 3.1 m

Total length 10.3 m 12.5 m

30/01/2013


Failure modes

• Fast failures– Particles hit aperture within few turns• E.g. injection and extraction kicker failures

– Passive protection needed (collimators, absorbers)• Slow failures– Failure slow enough to abort/dump beam before

it hits aperture • E.g. magnet power supply failure

– Use extraction system to remove beam

30/01/2013


Injection kicker failure modes

• Inductive adder level failure– 20 levels: supply ~700V each (See J. Holma’s talk)– Consider up to 3 levels failing simultaneously

• Assumed to be caused by failure of FETs on level• ~8σ event, so realistic worst-case scenario.

• Total inductive adder failure• Likely to be due to a trigger timing error• ALL particles considered dangerous and hit aperture shortly

downstream of injection• Injection collimator designed to capture full 6σ beam (+

tolerances)

30/01/2013


Collimator considerations [1]

• Number of σ that can pass through aperture

Region A1/2 (mm) H-plane V-plane H-plane V-planeLSS 12 ≥13.3 ≥65.3

Arc 20 ≥33.7 ≥126.1

Injection cell Extraction cell

1st quad 20 17.1 246.5 17.1 246.5

Septum - 7.1 242.7 9.3 110.8

Kicker 12 9.9 263.0 8.7 119.9

δ = alignment tolerance = 2mmA1/2 = physical half-aperture

Acceptance calculations at injection emittance, assuming there is a pre-damping ring

30/01/2013


Collimation considerations [2]

• Beam aperture critical in injection/extraction regions– Use absorbers to protect septa (fixed position)– Collimators to protect rest of machine (moveable)

• Collimation scheme depends on whether septa are in vacuum or not– Dependence on injection trajectory

30/01/2013


Septa in vacuum: H-plane

30/01/2013

Quad

Septum

Kicker

Collimation absorbers

Matching cell


Septa not in vacuum: H-planesteeper angle

30/01/2013

Quad

Septum

Kicker

Collimation absorbers

Matching cell


Comments on collimator plots

• Beam envelope– 6σ envelope ± 2mm tolerance

• First collimator– Needed to stop particles hitting aperture before

reaching second collimator• Second collimator– Designed to completely capture beam for total

kicker failure• Scattering + secondary particles not yet considered

30/01/2013


Comparison of schemes

• Septa in vacuum• Smaller beams; good aperture clearance• >4 m reduction in total length of DR

– This is almost entirely drift length

• Septa not in vacuum• Efficient collimation• Simpler septum design and operation

30/01/2013

Tracking simulations• Tracking done for failure of 3 inductive adder levels– 1000 particles for 100 turns

• Uniform random number generators: 6σ ± 2mm phase space• Polar coordinates to create oval beams

– 340 “dangerous” particles• Exceed 6σ ± 2mm phase space of nominal orbit• ~3.45% loss for Gaussian beam

Turn number % absorbed

At injection 37.4%

1 turn 52.1%

2 turns 92.4%

3 turns 95.9%

4 turns 97.4%

10 turns 99.1%

All particles captured by absorbers + collimators; no losses in kickers or elsewhere.

Remaining 0.9% of particles on edge of phase space limit and survive for many turns.


Emittance estimates

• Taken from tracking data– After 100 turns

Horizontal Vertical

@ Injection 4.5 x 10-8 1.1 x 10-9

Nominal orbit 1.2 x 10-7 1.2 x 10-9

Poorly injected 2.9 x 10-7 3.1 x 10-9

30/01/2013


Phase space: no collimationPhase space plot at second injection collimator

30/01/2013


Phase space coverage: 1 turn

Blue: phase space of nominal orbitGreen: Phase space of poorly injected beam (3 levels failed) without collimationRed: Phase space of poorly injected beam (3 levels failed) with collimationBlack: Phase space confined by collimation

30/01/2013


Phase space coverage: 2 turns


30/01/2013




30/01/2013


Dump system considerations

• Latency– How many turns before beam can be dumped?

• Location and space constraints

30/01/2013


Breakdown of latency

• Signal time of flight to dump kicker• ~1μs

• Latency of electronics• <1μs

• Kicker rise time• ~1μs

• Time for 1 turn of ring (circumference: 400-450m)• 1.3-1.5μs

• ~2-3 turns of ring required to dump beam

30/01/2013


Location + space constraints

• Avoid– Regions with synchrotron radiation– High dispersion regions• Near injection or extraction only suitable places.

• Dedicated dump cell?– Would add ~10m in each straight section• Unacceptable increase in length

– Can extraction cell be used as dump system?

30/01/2013


Technical challenges

• Kicker must fire in two modes– Extraction mode (±12.5kV)– Dump mode (±17.5kV)• Need to extract beam with injection emittance

• Separate dumped beam from extracted

30/01/2013


How to achieve 2 kicker modes

• Separate inductive adder into 2 banks of levels– “Bank 1” contains 20 levels– “Bank 2” contains 8-10 levels– Extraction trigger discharges Bank 1– Dump trigger discharges Banks 1 and 2

• Triggering system likely to be challenging– Need to test reliability of 2-mode trigger

30/01/2013


Kicker triggering

Bank 1 Bank 2

Trigger select

“Extract”

Bank 1 Bank 2

Trigger select

“Dump”

30/01/2013


Kicker failure modes

• Extraction mode– Both banks fire: beam dumped → safe– Bank 1 fires: beam extracted → safe– Bank 2 fires: beam absorbed by septum absorber and collimator → safe– Neither bank fires: beam remains in ring

• Dump mode– Both banks fire: beam dumped → safe– Bank 1 fires: beam extracted → NOT SAFE– Bank 2 fires: beam absorbed by septum absorber and collimator → safe– Neither bank fires: beam remains in ring

30/01/2013


Separate extracted and dumped beams

• Start of extraction line– Kicker gives larger deflection to dumped beam– Use defocussing quad to further separate beams

• Septum magnet to separate extraction and dump lines– Use same septa design as in extraction system

30/01/2013


Current design: h-plane

30/01/2013

Dumped beam

Extracted beam

Septum magnets

Dipole


Consideration of damping time [1]

• Time needed to damp beam:– Injection: 54 μm rad (x), 1.3 μm rad (y)– Extraction: 500 nm rad (x), 5 nm rad (y)– Equilibrium: 470 nm rad (x), 4.8 nm rad (y)

t

eqinjeq et

30/01/2013


Consideration of damping time [2]

• ~8.5 damping times to reach design emittance– 17ms (injection period 20ms)

• How long to charge inductive adder?– Currently unknown: If not sufficient then…• Add levels in Bank 2 to compensate missing charge?• Reduce storage time by ~1 damping time?

– 4% increase in extraction emittance; acceptable?• Reduce damping time?

– New wiggler design reduces damping time to 1.8ms– Increases equilibrium emittance slightly; net gain?

30/01/2013


Comments on design

• Septa in vacuum?– Easier if extraction septa NOT in vacuum• More lever-arm; less length needed to separate beams• Twiss parameters more controllable

• Final quad needed in dump line– Control spot size at dump block

30/01/2013


Radiation length

• Need minimum 5 rad. lengths for 2.86 GeV e-

– Use 10 rad. lengths for dump block– Use 5 rad. lengths for absorbers and collimators

Material Density (kg m-3)

Radiation length (m) ΔTinst (Inj)(K)

ΔTinst (Ext)(K)

Beryllium 1.84 X 103 0.353 0.002 4.9

Carbon 2.25 X 103 0.188 0.006 15.0

Titanium 4.50 X 103 0.036 0.007 18.1

Copper 8.93 X 103 0.014 0.01 24.2

Tungsten 19.3 X 103 0.0035 0.025 60.2

Higher density means more back scattering, but shorter radiation length

30/01/2013


Material choice

• In DR, space is limited– short radiation length and low back-scattering• Use titanium: ~20cm for collimators and absorbers

• Dump block– Space not limited• Use carbon for dump block• Surround block in higher mass material (e.g. concrete)

to contain radiation.

30/01/2013


Conclusions

• Injection and extraction optics– Fully optimised for both septum magnet designs• Septum outside vacuum seems better

• Machine protection– Injection• Tracking simulations show DR collimation is sufficient

– Extraction• Combined dump looks promising; needs further studies

30/01/2013

injection, extraction and protection of the clic damping rings

Documents

kicker aperture

injection cell optimisation

rings injection

kicker orders

extraction optics

injection stability2x1042x10

beam730012013clic workshop

design30012013clic workshop