Cold versus Warm contribution to the discussion on energy and luminosity

Giorgio Bellettini, Seul ITRP meeting, August 11, 2004,

Premise, disclaimer

I am aware that my job is to comment on the merits of major technical, scientific, intellectual endeavors. The quality of the people involved and of their work is outstanding. In no way my comparisons should be interpreted as a criticism or a lack of appreciation and respect for the supporters of the disfavored technology.

I would like to quote a sentence from a letter of Jonathan:“…Clearly, the proponents of each technology felt that they can meet the goals…. Our committee can argue about each element and try to decide which machine has a better chance of meeting the ILCSC goals”.

It is in this spirit that I have tried to indicated elements of distinction.

“ENERGY”

Linacs have no intrinsic energy limitation in as much as they have no intrinsic length

limitation.

What do we expect below 500 GeV?

1) The t-tbar pairs at s 260 GeV, sure

2) A light Higgs with MH < 400 GeV likely

3) Some new particle at 205 < s < 500 GeV plausible

4) (a comment on precision measurements follows)

If SUSY is there beyond the SM

At least one SUSY Higgs, gauginos, sleptons…A Linear Collider can measure detailed properties of several supersymmetric particles:• masses• quantum numbers• lifetimes• decays

AN ENORMOUS PROGRAM even below 500 GeV

Significance of the proposed energy step

If the LC ranges up to s 1 TeV:

From the SLC to the LC, factor ~ 10From LEP2 to the LC, factor ~ 5

Compare with past experience:

From PETRA to LEP2, factor ~ 5From the ISR to the SpS Collider, factor ~ 10From the SpS Collider to the Tevatron Collider, factor ~ 3From the Tevatron collider to the LHC, factor ~ 7

We would be fully consistent with past experience.

Among us even if not sexy enough for politicians: discoveries can be made through precision

From precision at LEP the number of (light) neutrino families:N = 2.994 0.012

Conclusion: let`s trust the LC as a Giga-Z factory and as a great tool to study WW interactions!

© J. Illana

Enough for us!But: is s ~1 TeV enough for selling the LC?

Wise man comment: our road maps to future discoveries will not be dictated by our ambition. They will be dictated by facilities that we are able to get funded.

IF by ~2010 new physics below the TeV will be confirmed by LHC, it will be impossible for any opponent to question the physics case and we will fight for construction funds. If we succeed a sub-TeV LC will be built. It will be made as long and extendable in energy as funds will allow.

IF NOT, the construction of any LC will inevitably be delayed until a multi-TeV machine can be reliably designed.

Insisting now on possible machine upgrades would be seen as if we were not convinced of the 500 GeV LC and we would try to get a “small” machine approved while planning to ask very soon for more. I would stay far away from this danger. In particular, I would not dare mentioning an empty tunnel.

“LUMINOSITY”The luminosity which matters is that part

which is delivered stably, reliably and under clean experimental conditions. That

luminosity provides useful data for physics.

The new machine must be a solid facility to be used by a world-wide community.

I consider luminosity as vital parameter whose risk should be minimized

Alignment of COLD and WARM

Installation requirements:

Offset of quads from survey line: TESLA ~300 , NLC ~50 (*)

Structure to structure offset: TESLA ~300 , NLC ~25

Structure tilt : TESLA ~240 rad, NLC ~ 33 rad

Installation alignment simpler in Cold.

Final accurate alignment based on BPM`s is crucial to preserve luminosity in Warm and Cold. However: Dynamical realignment of mechanical elements to correct for the slow ground motion is expected to be needed hourly in warm, while only dispersion corrections every ~ 10h should be sufficient in Cold.(**)

(*) Accuracy in the installation of Fermilab magnets is ~250 (**) Answers to question 7

Long term stability in Tesla

Preserving luminosity in COLD and WARM(s = 500 GeV)

Design L = 3,4.1034 cm-2s-1 in TESLA, L = 2,5.1034 cm-2s-1 in NLC

Transverse kicks by wake fields ~ Na-3 N = bunch population ~ 2.00.1010 in TESLA (*) N ~ 0,75.1010 in NLC a = iris diameter ~1/f , a(TESLA)/a(NLC) ~9 Na-3 ~ 200 times larger in Warm than in Cold. Extremely efficient damping and detuning of structures will be vital for Warm.

Bunch to bunch orbit correction would be possible in Cold during the 337 ns inter-bunch time. It will only be possible every ~35 bunches (~50 ns) in Warm. Any fluctuation in bunch-bunch overlaps at crossing would reduce L.

(*) ILCTRC Second Report (2003), megatable 7.19

TESLA NLC CLIC irises

Wake fields induced by misalignments

Final comment on luminosity

One more consideration:A superconducting linac is shielded from stray fields by the cryostat and is protected against sudden catastrophic beam losses by its thermal capacity.

In conclusion:the cold technology has a better chance to be able to deliver stable luminosity for physics.

Backup slides next

Emitt. growth due to system. struct.& quad mis-alignment in 500 GeV LC accord. to Bane model TESLA NLC CLIC

Linac injection/final energy, Ei/Ef (GeV) 5/250 2/250 2.4/250

Bunch Charge Ne (nC) 3.2 1.2 0.64

# structures/quads per linac, Ns / Nq 10296/350 6096/233 3636/300

Length of structures, Ls (m) 1.036 0.9 0.5

Initial, av. / av. FODO length, 0 / LFODO (m) 64/80 12/48 5/15

Trans. m-bunch wake-pot. <S> (V/pC/m/mm) 0.003 0.7 1.4

Struct.-to-struct. misalign for 1% (m-rms) 250 12 20

Quad-to-beam offset for 25% (m-rms) 15.2 0.74 1.5

radm

EE

EENSLNee

f

fsrmsrmsss

2

3

0

00

22224 1

Bane/Adolphsen/Kubo/Thompson model:Bane/Adolphsen/Kubo/Thompson model:

radm

EE

EESLN

LNNe

f

frmsrmsqss

FODOqeq

2

3

0

0220

24 1

2

Wake-Fields and Emittance DilutionWake-Fields and Emittance Dilution

500 GeV LC Table – Beam Emittances and Alignment Tolerances500 GeV LC Table – Beam Emittances and Alignment Tolerances

rms beam size parameters at IP TESLA JLC/NLC

CLIC

Horizontal/vertical N in IP (mm-mrad) 10/0.03

3.6/0.04 2.0/0.01

Hor./vert. rms IP beam size bef. pinch (nm)

554/5 243/3 202/1.5

Longitudinal rms beam-size z* at IP (m)

300 110 35

rms alignment tolerances to remain within ~ 50-100% emittance budget

Quadrupole to beam offset (m) 20 2 10

Structure to structure offset (m) 300 30 10

Structure tilt (rad) 240 30 ?

Quad BPM offset / resolution (m)* ?/10 10/0.3 10/0.1

Time to restore vertical emittance, cold

TESLA answer to question 7

Time to restore vertical remittance, warm

JLC/NLC answer to question 7