МЕЖДУНАРОЛНЫЙ ЛИНЕЙНЫЙ КОЛЛАЙДЕР

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МЕЖДУНАРОЛНЫЙ ЛИНЕЙНЫЙ КОЛЛАЙДЕР

Сессия Секции ядерной физикиИТЭФ, 26/11/2008А.Н.Скринский,

ИЯФ, Новосибирск

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3FFTB

SLC

SLAC long history !

VLEPP (Novosibirsk)!(Published proposal 1978)

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@ DESY

Shift to SC RF technology:

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Super-conducting option accepted for

ILC !

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International Performance Specification

– Initial maximum energy of 500 GeV, operable over the range 200-500 GeV for physics running.– Equivalent (scaled by 500 GeV/√s) integrated luminosity for the first four years after commissioning of 500 fb-1.– Ability to perform energy scans with minimal changeover times.– Beam energy stability and precision of 0.1%.– Capability of 80% electron beam polarization over the range 200-500 GeV.– Two interaction regions, at least one of which allows for a crossing angle enabling γγ collisions.– Ability to operate at 90 GeV for calibration running.– Machine upgradeable to approximately 1 TeV.

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Superconducting RF Cavities

High Gradient Accelerator35 MV/meter -- 40 km linear collider

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LINAC Gradient (3/5)

LL = low lossRE = ré-entrante

(J. Sekutowicz)

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A TESLA nine-cell 1.3 GHz superconducting niobium cavity.

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SCRF Cryomodules.

Left: an 8 cavity TESLA cryomodule is installed into the FLASH linac at DESY.

Right: design for the 4th generation ILC prototype cryomodule, due to be constructed at Fermilab National Laboratory.

11Basic design parameters for the ILC (values at 500 GeV center-of-mass energy).

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Nominal and design range of beam parameters at the IP.

The min. and max. columns do not represent consistent sets of parameters, but only indicate the span of the design range for each parameter.

(Nominal vertical emittance assumes a 100% emittance dilution budget from the damping ring to the IP.)

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RF unit layout.

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Cutaway view of the linac dual-tunnel configuration.

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The principal challenges in the main linac are:

• Achieving the design average accelerating gradient of 31.5 MV/m. This operating gradient is higher than that typically achievable today and assumes further progress will be made during the next few years in the aggressive program that is being pursued to improve cavity performance.

• Control of emittance growth due to static misalignments, resulting in dispersion and coupling. Beam-based alignment techniques should be able to limit the single-bunch emittance growth.

• Long-range multibunch effects are mitigated via HOM dampingports on the cavities, HOM absorbers at the quadrupoles, and HOM detuning. Coupling from mode-rotation HOMs is limited by splitting the horizontal and vertical betatron tunes.

• Control of the beam energy spread. The LLRF system monitors the vector sum of the fields in the 26 cavities of each RF unit and makes adjustments to flatten the energy gain along the bunch train and maintain the beam-to-RF phase constant.

(Experience from FLASH and simulations indicate that the baseline system should perform to specifications.)

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Schematic View of the Polarized Electron Source.

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Overall Layout of the polarized Positron Source.

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• The most challenging elements of the positron source are:the 150 m long superconducting helical undulator, which has a period of 1.15 cm and a K-value of 0.92, and a 6 mm inner diameter vacuum chamber.• The Ti-alloy target, which is a cylindrical wheel 1.4 cm thick and 1 m in diameter, which must rotate at 100 m/s in vacuum to limit damage by the photon beam.

(But liquid lead curtain ??!)• The normal-conducting RF system which captures the positron beam, which must sustain high accelerator gradients during millisecond-long pulses in a strong magnetic eld, while providing adequate cooling in spite of high RF and particle-loss heating.

The target and capture sections are also high-radiation areas which present remote handling challenges.

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Pictures were made on the 11th of July 2005 after about 400 h continues run of the cogwheel pump based system. Total pump operation time is around 1200 h. Liquid lead flux is about 0.25 liter/s. Alloy contains 90% Pb and 10% Sn, and has operating temperature of 300 C. (NOVOSIBIRSK)

{+ mercury target studies in several labs}

Liquid

Lead

Target

(p r e - p r o t o t y p e)

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Scheme of the prototype of liquid lead positron production target.

Driving motor

Rotating vacuum feedthrough

Vacuum pump

Vacuum tank of the system

Cog-wheel pump

Liquid lead transport tubes

Target head

Still not in operation

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The principal challenges in the damping rings are:

• Control of the electron cloud effect in the positron damping ring. This effect, which can cause instability, tune spread, and emittance growth, has been seen in a number of other rings and is relatively well understood. Simulations indicate that it can be controlled by proper surface treatment of the vacuum chamber to suppress secondary emission, and by the use of solenoids and clearing electrodes to suppress the buildup of the cloud.

• Control of the fast ion instability in the electron damping ring. This effect can be controlled by limiting the pressure in the electron damping ring to below 1 nTorr, and by the use of short gaps in the ring ll pattern.

• Development of a very fast rise and fall time kicker for single bunch injection and extraction in the ring. For the most demanding region of the beam parameter range, the bunch spacing in the damping ring is 3 ns, and the kicker must have a rise plus fall time no more than twice this. Short stripline kicker structures can achieve this, but the drive pulser technology still needs development.

22Examples of DESY nine-cell cavities achieving 35 MV/m.

23Recent result from Jefferson Lab of nine-cell cavity achieving 40 MV/m.

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World Record Eacc

= 46.4 MV/m, CW

Pulsed = 47 MV/m= 1800 Oe

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ICHIRO single-cells being prepared for

testing at KEK.

World-record performance from novel shape single-cells

(ICHIRO and Cornell's reentrant cavity).

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But there is a lot of work in physics and technology on this way to the optimized ILC.

One example in my view: I consider these full length “storage rings” as far from optimum (for example, beams are on the space charge basic limitation).

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Schematic layout of the ILC complex for 500 GeV CM.

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Beam Delivery System tunnels for 2x14 mrad(Valencia)

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Photon-Photon and Electron-Photon collisions

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ωmax~0.8 E0

Wγγ, max ~ 0.8·2E0

Wγe, max ~ 0.9·2E0

αc ~25 mrad

~1-2 mm

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Laser system

The cavity includes adaptive mirrors and diagnostics. Optimum angular

divergence of the laser beam is ±30 mrad, A≈9 J (k=1), σt ≈ 1.3 ps, σx,L~7 μm

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One example. View of the detector with the laser system (the pumping laser is in the building at the surface)

For easier manipulation with bridge crane and smaller vibrations it may be better to hide the laser tubes under the detector. If IR depth is large, the laser room is needed somewhere underground.

K.Monig, et al, Zeuthen

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Possible upgrade 14 mr (e+e-) to 25 mr ( • For transition from e+e- to γγ one should shift the

detector by about 0.0055*600=3.3 m as well as to shift 600

m of the upstream beam line or (better) to construct an additional final transformer and doublet, in any case the final doublet should be different.

In that case the transition between e+e- and γγ modes will be faster.

• Two extra 250 m tunnels for γγ beam dump.• Somewhat wider experimental hall. Different

position of doors.• Tunnel in FF area may need to be wider

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There are three classes of costs:

• site-specic costs, where a separate estimate was made in each of the three regions;

• conventional costs for items where there is global capability - here a single cost was determined;

• costs for specialized high-tech components (e.g. the SCRF linac technology), where industrial studies and engineering estimates were used.

1 ILC Unit = 1 US 2007$ (= 0.83 Euro = 117 Yen).

ILC-accelerator cost @ the Reference Design is 4.79 Billion

The cost scale for the two detectors envisioned for the ILC is about10% of the cost of the machine.

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The GDE together with the leaders of the particle physics community will continue to work with the regional funding agencies and governments to begin construction of this project in the early part of the next decade.

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На стр. 2 кратко изложен статус фотонного коллайдера, который более-менее прояснился на IRENG07, на котором я еще раз сформулировал требования к конфигурации ILC и предложенные изменения были в целом приняты. Это включает некоторое расширение тоннелей вблизи места встречи для того, чтобы можно было увеличить угол встречи с 14 до 25 мрад, а также два дополнительных 250 м тоннеля для beamdumps. Также потребуется дополнительные beamlines (частично те же) на последних 600 м. Размеры экспериментального холла и положение защитных стен немного изменятся виду сдвига детектора на 3-4 м. Также нужно будет предусмотреть место для лазерной комнаты и подвода лазерных пучков к детектору.

На стр. 2-3 приложено письмо от Jeff Gronberg (US gg convener), который представлял фотонный коллайдер на последующем Beam Delivery System Kick-off meeting, который состоялся через 20 дней после IRENG07. Он излагает (как он понял из общения с EDR managers), на что в основном будет нацелена работа по фотонному коллайдеру в рамках EDR.

Более детальную информацию и рисунки можно найти в двух моих докладах (перекрывающихся) на IRENG07: telnov-ireng07-WG-D.ppt - первое выступлениеtelnov-ireng07-discuss-A-C.ppt - второе, на plenary discussion session

Также прилагаю большой доклад “Introduction to the photon collider”,который сделал в июле 2007 на Photon2007:файл telnov-intr.ppt

Комментарии

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О статусе фотонного коллайдера в проекте ILC (В.И. Тельнов)

Базовые документы по ILC рассматривают Фотонный коллайдер как “option”(наряду с е-е-, поляризацией позитронов, работе на энергии Z бозона и WW пороге). Эти возможности должны быть предусмотрены в конструкции ILC. В ILC Reference Design фотонный коллайдер рассматривался в разделах Физика и Детекторы, но был опущен в разделе Ускоритель (как и все другие “Options”), поскольку основной задачей этого проекта была оценка минимальной стоимости ILC (только e+e-, 2E=500 GeV). В RDR (2007 г.) принят вариант с одним местом встречи под углом 14 мрад и двумя детекторами, работающими поочередно. Данная конфигурация несовместима с фотонным коллайдером, для которого требуется угол встречи25 мрад (необходимо для вывода пучков из детектора). Решено, что на этапе Инженерного проекта (EDR), будут учтенытребования, предъявляемые фотонным коллайдером: угол 25 мрад, специальный beamdump, место для лазерной системы, необходимая модификация детектора. Работы в этом направлении уже начаты. Таким образом, фотонный коллайдер рассматривается как вторая очередьILC, к которой необходимо готовиться с самого начала. Окончательные планы по фотонному коллайдеру (как и по ILC в целом), будут сформулированыпосле получения результатов с LHC.

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(from Jeff Gronberg’s letter to photon collider colleagues about passed Beam Delivery System Kick-off meeting Oct.11-13, 2007)

..At Hamburg we have discussed that a plan had to be in place for the photon

collider in the ILC baseline to prevent making decisions that would preclude this option in the future. Valery was invited to give a talk on the photon collider option at the IRENG07 meeting and I was asked to talk about the needed work to quantify the photon collider option at the BDS kick-off meeting. It appears that this argument has been accepted to a certain extent. The direction from EDR management is that work should focus on value engineering. This means quantifying both the value and cost of various options rather than just finding a minimum cost for the baseline. It appears that physics options will be an official work package in the BDS WBS. It will not have the same priority as baseline work and only work that is necessary to define the required facilities and their associated costs will receive any priority. It should also be noted that the EDR management has no resources to allocate and collaborators are expected to bring their own resources to apply to work that they wish to contribute to. However, it will be possible to claim that photon collider work is ILC work. (continue on next page)

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Valery's proposal for a 5mr extra bend at 700m upstream of the IR seems to be what we will use as a cost basis for the extra tunnels needed for gamma-gamma. The Conventional facilities people were insistent that the extra tunnels would need to be included in the baseline and could not be retrofitted after initial operations. So for the first time there is going to be a real cost quantified for keeping photon collider as an option. Marc Ross mentioned that he would be looking for feedback from the HEP community and project management on the value and priority of supporting the options. I suspect that this means that we should be ready to present the physics case to a Jeju style panel sometime in the next year and the BDS group will probably have a 20% number for the cost of the extra tunnels on that time scale.The BDS group has already done some work. Mark Woodley provided an optics deck and Fred Asiri loaded it into his CAD model of the tunnel. The pictures he produced are attached.

I think this is a step forward for photon collider in ILC.