DB long transfer line- a first pass -

B. Jeanneret

CLIC Dynamics ABP, 4th July 07

Acknowledments:Hans for many discussionsAlessandra Lombardi for permanent magnet issuesStephane Fartoukh for optics issues

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Outline

• Optics

• Magnets

• Ions

• Other

• Further work

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Optics• Requirements

– Connect last combiner ring to every turnaround in the Main Linac

– Keep emmitance • Entrance : 1.e-4 m rad• Decelerator : 1.5e-4• most of the margin : for the turnaround/compression

(see with Frank Stulle next in 10 days)

– Be cheap• One option is to use permanent magnets • This implies that not many correctors are needed (or none,

only quadrupoles?)CR2

… 26 x

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Regular FODO cell, no dipoles

• Thin lens limit can be treated analytically

• Use phase advance/cell of pi/2 to see

• Skip a few steps :

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Transport over 20 km• Match to a turnaround every 800 m

– ~10/20 m, while large / long cells more economical

• Do we need a chromatic correction ? p = 0.01

L cell [m] N cell max [m] [mm] (0) / 2 (0.01) / 2

10 2000 17 0.6 500 6.3

50 400 85 1.3 100 1.27

100 200 170 1.9 50 0.63

• Yes, otherwise full filamentation after any kick (even static) – need your feed-back

• Need a dispersion wave (close/open at every turnaround ?)• Need more work, and a error/tolerance analysis

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Quadrupoles

• L_cell = 100 m G lq = 0.25 T/m x m

– Usual iron shaped field – not studied here– Cos 2 coil, ~allowed by low gradient– Permanent magnets

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Cos 2 coil - I

• For L_cell=100m• 11 wires• I = 30 A• S_wire =2mm^2• P=400W• 400 Q / Linac• V_tot = 5000V

A bit limit, if shorter cell.Need more work (on-going with help fromAT/MCS)

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Cos 2 coil - II

• No lamination• No glue• Maybe only two external

weldings• Hopefully no cooling• Sextupole doable as well

Insulator with printed or incrusted copper

Aluminium shell with surface insulation

Iron cylinder to increase fieldand minimize stray field, shrinkeverything

External diameter < 100mm

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Permanent magnets• Small series under way for Linac IV (A.Lombardi)

• Two cylinders of CoSm rods in Al matrix

• Inner radius 10mm, length 40mm

• G = 60 T/m, dG/G = 0.5%, dB/B_nonlin<1%• Tc = 1500 C (weaker field species ~3000 C)

• Price 2300Eu per piece for 100 ordered

• G = 5 T/m , lq = 0.05m Glq = 0.25 T/m m

• Use simpler prismatic geometry cheaper (2000 Q x 1000Eu = 2MEu – add sextupoles …)

• Large enough w.r.t. to pipe to keep away from beam losses and keep good field quality

• Combine permanent with Cos 2 for adjustment– Low power one power supply per station ?

We need less gradient :

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Logistics in the tunnel

• Survey team and Carlo worry about space at the tunnel roaf

• Quad with small transverse size : better• Proposal to adopt the same cell length for Main-

beam and DB Single support Single survey system

• Imply similar technology for MB and DB thinkable ?

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Ion production and counter-effect on the beam

• The electron beam ionises the residual gas

• Electrons are repelled rapidly (light objects)

• Ions are attracted (or focused) by the beam and can be trapped inside (so called ‘neutralisation’ of the beam’)

induces tune-shift & tune spread

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Ion data

Mean free path for electrons to produce a ion :

One DB train , Ne = 1.78e14, p=10-8 T : lit = 1.11e7 ion/m

Coherent tune-shift : (copied from HAPE, FZ p.128)

= 100 m : = 0.15

But coherent tune is not the whole story,and there is another issue,see below

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Ion trapping

• Atomic numbers > Atrap are trapped

• Inside train, Ne = 5e10, L = 2.5e-2 mAtrap = 1.3e-4 CO is trapped

• Train-train, Ne = 1.8e14, L = 1500 mAtrap = 4e5 CO fully untrapped

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Ion motion - I

• Nice continuous focusing inside the train

• Note the central accumulation at the end of the train

Initial ion distribution:-Beam profile + thermal speedTracking :- Motion : in exact field for round+ gaussian beam-enough slices for smooth motion

X [m]

Time [s]

Train length

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Ion motion - II

• Soon after the train passed, ions are projected to the wall

• Good : no accumlation between trains

• Less good : desorption at impact on the wall (see below)

Train Gap

Time [s]

X [m]

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Transverse ion distribution

• Beam & initial ion distribution• Ion at the end of the train

Coherent tune-shift applies only for very small amplitudes

• Does tune-shift formula consider the sharpening of the ion profile?

• Most likely not (only appears)• 3 = 0.45 ?

– Between small and large (> – Between head and trail of train

NEED DEEPER STUDY

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Desorption and pressure rise

• Static density at 10nT : rgas,lin = 5e19 mol/m• Ion production per meter :

• dn/dt = ion,train Ntrain fr x ISD = 10e11 atom/s (with ISD = 5 at 1KeV on unbaked ss

• Marginal if pumping time ~< 1month …

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Open issues

• Optics :– chromatic correction– Dispersion bumps, stregth and longitudinal granularity– Sensitivity to misalignment, ground motion, correction schemes– Similar issues for 9 GeV MB line ?

• Matching to turnaround – ‘matching sections’ in turnaround or in transfer line

• More work needed with ions to say if p=10nT OK– Otherwise : better inner surfaces (gold) or getter/bake-out (Eu ..)

• Yet untouched :– resitive wake-fields– Beam loss issues

• Integration and cost