Empfehlung einer Strategieschoning/... · A (second) laser or a particle beam creates strong...

A.Schöning 1 Accelerator Physics WS 2015/16

Accelerator Physics

Lecture 12

New Technologies Superconducting RF CLIC Technology Plasma Wakefield Accelerators


Electron-Positron High Energy Collider

LEP: P ~ 100 MW s = 200GeV

LEPX: P ~ 63 GW s = 1000GeV

~63 nuclear plants!!!

International Linear Collider (successor of the TESLA project)


from E.ElsenRF-Acceleration Concepts

● Resonator required for➔ longitudinal component E

z

➔ adjustment of phase velocity

Two concepts● wakefields

➔ bunch acquires energy whilewave amplitude attenuates

● Standing wave➔ bunch is accelerated by

mean field gradient;field amplitude is hardly affected

E z=E0 cos(ϕ)

E z=E0sin (ω t+ϕ)sin (k z )


from E.ElsenRF-Generation Concepts

● Klystron➔ velocity and densitiy modulation of electrons generates RF-field➔ electrical field is coupled out

● Wakefied➔ field of compact moving electron bunches generate RF-field in cavitites which are coupled out


Cavity Basics

∣Z−1∣=∣1

1iωC

+iω L+R∣=ω/L

((ω2−ω0

2)2+ω

2Γ2)1/2

02=

1LC

= = R / L

with series resistor

C L

R

Quality factor:

Q0 =0

=1R LC Ohmic resistor determines quality factor!

104 – 105 normal conducting> 109 superconducting

High frequency oscillator:

cavity circuit

resoncance frequency: bandwidth:


Superconducting Cavity ILC (TESLA)

f = 1.3 GHz

Niobium

Advantage SC-RF:no electrical resistance!no power losses!


Superconductor

Meißner-Ochsenfeld Effect

Limitation:

critical magnetic field Hc

H c T ≈H c 01−T2/T c

2

need low temperatures!

Superconductor of first kind


TESLA Cavity

TESLA TDR

A superconductor in a HF field has a surface resistance RS

B fieldHF field

superconducting

penetration depth(London parameter)

~100 mT~30 MV/m

Superheating: for a short time (HF) magnetic field may exceed critical temperature!

Rs surface resistance


Superconducting Cavity

Technical problems● thermal instabilities● field emissions

caused by● weld splatters● cracks ● dust

Therefore very clean surface required electro-polishing

strong em. field → heating

maximum acceleration field 35-40 MV/m


FabricationMaterial niobium Tc=9.2 K

single-crystal (no welding)

small impurities!

careful processing:

high power

water pressure rinsing

heating

chemical polishing


Yield of CavitiesILC goal: 31.5 MV/m (average)

Yield


Future Ideas

H0 = 324mTHi = 150mT

d

figures from Elmar Vogel (DESY)

Coating of surface coating reduces magnetic fieldin superconducter and surface resistance (A. Gurevich)

B0

thin layer


Superconducting MaterialsTask: Find superconductor with high H

C

Problem: Most “high temperature” superconductors are of second kind(incomplete Meißner effect → flux tubes)

flux tubes

HF: walking flux tubes absorb energy!

need SC of 1st kind!


CLIC

The wakefield accelerator

the bigger the boat → the faster runner


CLIC from E.ElsenThe CLIC Concept

● high gradient > 100 MV/m➔ compact collider;

total length < 50 km for 3 TeV➔ acceleration in normal

conducting elements @ 12GHz

● Acceleration field generated by parallel high intensity beam

➔ field generated only during acceleration➔ efficient generation of high intensity beam


CLIC from E.Elsen


CLIC

from E.Elsen


Plasma Wakefield Accelerators

A revolutionary technology...


Plasma Wakefield Accelerators

Driving Beams:● Laser● electron beam● proton beam

E.g.: Proton Driven Plasma Wakefield Accerator:

Use 7 TeV LHC proton beam to transfer energy to

an electron beam of 7 TeV or even higher, fantastic!

F.S.Tsung et. al.


Acceleration in Plasma

Principle: Plasma is created either by using strong

Lasers or by heating

A (second) laser or a particle beam creates strong electric fields which lead to charge density fluctutations in the plasma

The mobility of ions is given by its mass → electrons move

Charge density fluctutation create strong fields which can be used for acceleration

E field = c me0 p = c n p e

2

0me

electrical field: Plasma frequency:

density fluctutation np = plasma density

F.S.Tsung et. al.


Plasma Wakefield by Electron Beam

Sketch:


Proton Driven Plasma Wakefield

electrical field density fluctutation

Simulation (A.Caldwell et. al.):

witness bunch!

long. E-field

2 GeV/m !!!!


SLAC Result with Electron Beam:

driving beam

accelerated electrons

energy more than doubledin plasma !


Simulation of 1 TeV Proton Beam

Could be experimentally studied at SPS (E=450 GeV)

protons electrons

However, proton bunches are usuall long ~ 10cm

(A.Caldwell et. al.)


Microbunching and Self Modulationof Proton Beams

red/blue electrical field black plasma density

(N.Kumar et. al.)

plasma is also modulated using long proton bunches!

Self Modulation


The Future: Proton Driven Plasma Accelerator at LHC?

A.Caldwell et al. Nature (2009)

1km linear TeV accelerators with large acceleration gradients are possible, in principle!


AWAKE Collaboration @ CERN

Empfehlung einer Strategieschoning/... · A (second) laser or a particle beam creates strong...

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