Transcript Some Comments to the Wise Guys - LNL-INFN

Bejing 2004: the Choice of Cold Technology
Giorgio Bellettini
International Workshop on
Thin films Applied to Superconducting RF: Pushing the Limits of RF
Superconductivity
Legnaro INFN National Laboratory, October 9, 2006
Content
1) Charge of the International Technology
Recommendation Panel
2) Linear Collider options
3) ITRP methods of work
4) Scientific, technical, social issues
5) Recommendation
Charge: Tesla versus JLC/NLC
“The International Technology Recommendation Panel (the Panel) should
recommend a Linear Collider (LC) technology to the International Linear
Collider Steering Committee (ILCSC). “
“On the assumption that a linear collider construction commences before
2010 and given the assessment by the ITRC that both TESLA and JLCX/NLC have rather mature conceptual designs, the choice should be
between these two designs. If necessary, a solution incorporating C-band
technology should be evaluated.”
The ITRP interpreted this charge as being to recommend a technology, not a
design. However, for comparison purposes the parameters of the existing
designs were used.
The 5.7 GHz RF warm machine design (C-band) was not found superior to
the JLC/NLC design (at 11.4 GHz) and was not influential in the global
technology comparison.
A description of CLIC was heard but that option was not considered.
ITRP method of work
A large amount of written material was studied
ITRP visited DESY, SLAC, KEK
Each Panel Member interacted personally with
members of the community
A matrix of evaluation parameters was built on
which each Panel Member expressed his view.
Evaluation Matrix
Matrix parameters which turned out to be more important:
Scientific issues
Technical issues
Physics operation issues
Schedule issues
Social impact of the LC
It was agreed that cost of either machine could not be
reliably assessed. Cost was removed from the matrix.
Scientific issues: machine luminosity
CHARGE:
“Luminosity and reliability of the machine should allow
the collection of approximately L = 500 fb**(-1) in the
first 5 years of running”
The design luminosity of both machines
L = 3,4.10**34 (cm-2.s-1) in TESLA,
L = 2,5.10**34 (cm-2.s-1) in NLC
was found to be adequate.
Scientific issues: machine energy
CHARGE: “The machine should allow for an energy range between
200 and 500 GeV and allow for energy scans in this range with
operation as dictated by physics”.
“Both technologies were found to offer this flexibility”
CHARGE: “The maximum c.m.s. energy should be 500 GeV”.
“The machine will be designed to begin operation at 500 GeV,
with a capability for an upgrade to about 1 TeV, as the physics
requires. This capability is an essential feature of the design. ”
Significance of the proposed energy step
If the LC ranges up to s  1 TeV:
From the SLC to the LC, factor ~ 10
From LEP2 to the LC, factor ~ 5
Compare with past experience:
From PETRA to LEP2, factor ~ 5
From the ISR to the SpS Collider, factor ~ 10
From the SpS Collider to the Tevatron Collider, factor ~ 3
From the Tevatron collider to the LHC, factor ~ 7
We would be fully consistent with past experience.
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
Energy reach versus operation reliability
CHARGE: “The Panel will make its recommendation based on its
judgment of the potential capabilities of each conceptual design for
achieving the energies and the peak and integrated luminosities
needed to carry out the currently understood scientific program”.
“The warm technology allows a greater energy reach for a fixed
length, and the damping rings and positron source are simpler.
The Panel acknowledged that these are strong arguments in
favor of the warm technology.
The superconducting technology has features, some of which
follow from the low RF frequency, that the Panel considered
attractive and that will facilitate the future design.”
Some TESLA/ NLC Parameters (500 GeV)
TESLA
NLC
3.4
2.5
5
120
No. of Bunches per Pulse
2820
192
Bunch Separation (nsec)
337
1.4
Bunch Train Length (msec)
950
0.267
Loaded gradient (MeV/m)
23.8
50.0
Two-Linac-Length (km)
30
13.8
Total Site AC Power (MW)
140
195
Plug to Beam Efficiency (%)(*)
(*) Includes estimated loss in couplers and
HMO absorbers
23.3
8.8
Design Luminosity (·1034cm-2sec-1)
Linac Repetition Rate (Hz)
RF Parameters (500 GeV)
TESLA
JLC/NLC
RF Frequency (GHz)
1.3
11.4
Loaded Gradient (MV/m)
23.8
50
Klystron Peak Power (MW)
9.7
75
RF pulse length (ms)
1370
0.4
Filling Time (ms)
420
0.120
Bunch Train Length (msec)
950
0.27
Tesla linac layout
1500 ms, 5Hz,
TESLA: one 10 MW klystron driving 36
one meter long cavities (= 3 cryomodules a 12 cavities) with 230 kW/m.
130 kV, 150 A
20 m
TESLA
2820 bunches/train, 337 ns apart, 5 Hz,
head-on collisions
NLC linac layout
NLC: 8 x 75 MW klystrons, supplying (after pulse compression) a peak
power of ~100 MW/m.
1.6 ms, 120Hz,
500 kV, 2.12kA
192 bunches/train, 1.4 ns apart, 120 Hz,
requires X-angle
Accelerating power
TESLA has 572 Klystrons, ~ 1 Klystron/GeV
The NLC has 4064 klystrons, ~ 8 Klystrons/GeV
TESLA transfers the power to the beam in
1 millisecond, and the JLC/NLC in 0.3 microsecond.
Over 3 orders of magnitude higher peak power in
JLC/NLC.
Space density of power on beam : TESLA 0.226
MW/meter, NLC ~100 MW/meter after bunch
compression. About 500 times larger density in JLC/NLC
Time structure of beams
LC pulses are trains of bunches.
1 ms long trains are separated by 200 ms in Tesla (5 Hz)
0.3 microsecond trains are separated by 8.3 ms in NLC (120 Hz)
Within trains, bunches are separated by 337 ns in Tesla
Within trains, bunches are separated by 1.4 ns in NLC
Adequate intra-bunch time helps to preserve luminosity.
If some bunches miss the collision one has time to react within a
Tesla train and ridirect later bunches.
If malfunctioning is signaled by front of train one can abort the rest.
ITRP comment on beam time structure
“The long bunch interval of the cold machine
permits inter-bunch feedback and may enable
increased beam current”.
TESLA NLC CLIC Iris diameter
In Tesla, iris diameter is
a = 70 mm.
Transverse wake potentials
are proportional to a**-3,
must align cavity to within
0.5 mm.
Aligment required to
within 10-100 micron in
NLC
(Note: even 5 mm are
hard to get at the Tevatron)
Installation tolerances in TESLA and NLC*
(s = 500 GeV)
Quad to survey offset:
TESLA ~300m, NLC ~50m**
Structure to structure offset:
TESLA ~300m, NLC ~25m
Structure tilt :
TESLA ~240mrad, NLC ~ 33 mrad
 Installation alignment simpler in TESLA. Final emittance preservation
based on BPM`s easier in TESLA.
Dynamical realignment of elements based on BPM`s is planned hourly
in NLC.
•ILCTRC Second Report (2003), megatable 7.19
•** At Fermilab present accuracy in magnet alignment at installation is ~250 m
Alignment issue
Luminosity stabilization (jitter
in beam size and axis, final
focus vibration) very
challanging for all LC.
Re-alignment every some
months required in any LC to
correct for slow ground motion.
Continous re-alignment
required in NLC to correct for
frequent minor motion.
ITRP comment on beam alignment
“The large cavity aperture of the cold machine
reduces the sensitivity to ground motion”
Importance of a system test
DESY will build XFEL and pave the way to a
cold ILC by clearing a number of issues,
including components reliability and linac cost.
This will provide for free a testbed for the ILC.
“The construction of the superconducting XFEL free
electron laser will provide prototypes and test many
aspects of the linac”
Social issues
The large electrical bill of a multi-MW research
facility will raise running budget questions and
might face popular criticism.
Total site AC power at 500 GeV is:
Tesla 140 MW,
NLC 195 MW
luminosity/power is 1.9 times larger in Tesla.
“The use of superconducting cavities significantly
reduces power consumption”
Rational of ITRP reccomandation
• The superconducting technology has features, some of which
follow from the low rf frequency, that the Panel considered
attractive and that will facilitate the future design:
• The large cavity aperture and long bunch interval simplify
operations, reduce the sensitivity to ground motion, permit interbunch feedback, and may enable increased beam current.
• The main linac and rf systems, the single largest technical cost
elements, are of comparatively lower risk.
• The construction of the superconducting XFEL free electron
laser will provide prototypes and test many aspects of the linac.
• The industrialization of most major components of the linac is
underway.
• The use of superconducting cavities significantly reduces power
consumption.
Oversimplified rational and recommendation
“The main linac and rf systems, the single
largest technical cost elements, are of
comparatively lower risk.”
“We recommend that the linear collider be
based on superconducting rf technology. This
recommendation
is
made
with
the
understanding that we are recommending a
technology, not a design.”
CONCLUSIONS
• It was a hard decision, with heavy and far reaching
consequences
• The detailed design of a cold ILC being addressed
is drifting appreciably from the TESLA design and
indicating how difficult the real job will be
• We judged that it would be less difficult. However,
the cold ILC will be by no means an easy machine.
The future of HEP depends to a large extent on its
success.