Injection Energy Review - PowerPoint Presentation

Slide1

Injection Energy Review

D. SchulteSlide2

Introduction

Will review the injection energy

So could answer the following questions:

Which injection energy can be accommodated in the baseline?

To identify the minimum energy that is acceptable with reasonable risk

Requires to identify margins and budgets for effects that have not been considered in detail

Which changes are required to adapt to a given injection energy?

Allows to understand the design and cost impact of different energies if we stay at the same risk level

We can at some level answer with a relative comparisonSlide3

Assumptions Made for Baseline

The main drivers for the injection energy are

Impedance

the main impedance is coming from the

beamscreen

other collective effects are not dominating

Dynamic aperture

we need at least the same beam stay clear as in LHC

in beam sizes

t

he same ratio of top to injection energy as in LHC may ensure the magnet field quality

a tentative choice to deal with the uncertainty of the magnet errors

(Amount of beam that can be transferred in one pulse)Slide4

Lattice Baseline

The goal has been to

minimise

the magnet aperture

This requires to

minimise

the

beamscreen

aperture

Tentative assumptions

Cell design similar to LHC

The shortest cell that reaches the same dipole filling factor as LHC

This

minimises

the average beta-function, which

minimises

the impedance effects

Cell length about 2 times LHC cell lengthSlide5

Tentative Conclusions for Baseline

The injection energy should be at least 3.3

TeV

Tentative assumption is based on magnetic field error consideration

At this energy the

impedance

is the dominating factor for the beam screen aperture, the

beam stay clear

is larger than in LHC

This is opposite to the LHC, where mainly the beam stay clear has been an issue and the impedance less critical

The impedance requires a≈13mm

This translates into 1.8 times more space in the arcs

For the same

emittance

it would be 1.4 timesSlide6

Impedance Effect

Scalings

Coupled-

bunch

impedance

effect

p

er turn scales

as

D. Schulte: Beam pipe kickoff meeting

Local r

esistive

wall impedance

Ratio

of FHC to LHC coupled-bunch effect scale

Exa

mple

at 50K and 25ns spacing at injection

Or: Why was a potential problem to be expected?

Assuming the same fractional tune in FCC and LHCSlide7

Impedances, Instability and Feedback

First, preliminary conclusions from impedance studies:

Beamscreen

resistive wall at injection

Multi-bunch instability rise time is O(25 turns)

Copper layer on

beamscreen

must be 300

m

m thick TMCI threshold is 5x10

11

protons

Pumping holes

TMCI threshold is reduced to 2x10

11

protons Worth to reduce amount of holes (as considered by vacuum team)

Synchrotron radiation slit Little impact on the impedance Beamscreen

and collimation at collision energy TMCI threshold is 1.5x1011

Close to the limit Feedback is of great importance Much better performance than in LHC required Novel solutions? HTS?O. Boine-FrankenheimU. Niedermayer

,B. Salvant, N. MounetX. Buffat, E. MetralThere seems to be little marginCan gain margin by increasing the injection energy initially used as fallback safety margin (assuming LHC as injector)

now have to spell it outHave to be very careful in choosing the stability criteria

e.g. assumptions about chromaticity determining how much margin is required and in which form

Remember two decisions were made in the process:

Fractional tune below 0.5

Give up parameter set for 50ns bunch spacing

=> Check if we still agree with themSlide8

Impact on Injection

Currently assuming that total energy per injected train has to remain below 5MJ

Higher energy means less charge per train

Requires shorter gaps between trains

Requires faster kickers

or more charge per bunch, which we would like to avoid

Check if this is a serious concern or if we can accept shorter rise times for the moment

Also check impact of injection energy on turn-around timeSlide9

Next Steps

Have to determine the minimum injection energy

field errors

dynamic aperture

Have to more precisely determine the impedance limit

include all relevant terms

sometimes with guesses

agree on model of beam stability

chromaticity etc.

include proper feedback models

as transfer functions

include sufficient margin

Since this seems to give the limit we have to really explore the limits

Verify that the other assumptions are OK

i.e. that only dynamic aperture and impedance are important limits

Then have to understand the impact of the other potential injection energies

identify a small set of potential values matching to the injector optionsSlide10

Example for Illustration

Multi-bunch instability example

Assuming:

a=13mm

beamscreen

radius is just right for 3.3TeV

Δ

BS

=

12mm are need between beamscreen and magnet

the cost scales as

Cost goes up 5% at 2TeV and down by 4% at 5TeVSlide11

Beamscreen

Design

Centre of the

beamscreen

is not he centre of the magnet

Need to explore the options to deal with this

The pumping holes are an important part of the impedance

Need to agree on the amount of holes neededSlide12

Conclusion

Much more work to be done to give as precise answers as possible:

Does our rational hold true?

Did we miss something?

Which injection energy can be accommodated in the baseline?

Get full evaluation process in control

Which energy ranges could be provided by each injector?

Pick a limited number of values to limit the study

Which changes are required to adapt to a given injection energy?

To evaluate the cost impact