parameters represent relatively conservative operating points resulting from optimiza- tion subject to the constraints imposed by the various accelerator sub-systems.
2.3
The Compact Linear Collider (CLIC)
The Compact Linear Collider (CLIC) is a high-energy and high-luminosity e+e−collider project under development by the world-wide CLIC collaboration. The design was pre-
sented in the Conceptual Design Report (CDR)[53] after years of a large number of
simulation studies and R&D tests. The nominal collision energy is 3 TeV. CLIC is based on a novel two-beam acceleration technique with acceleration gradients at the level of 100 MV/m. Recent implementation studies for CLIC have converged towards a staged approach offering a unique physics programme covering two decades. In this scheme, CLIC would provide high-luminosity e+e− collisions within a centre-of-mass
energy range from 380 GeV to 3 TeV [45]. 4 CLIC staging baseline
(c)FT TA BC2 delay loop 2.5 km decelerator, 25 sectors of 878 m 540 klystrons 20 MW, 148 µs CR2 CR1 circumferences delay loop 73 m CR1 293 m CR2 439 m BDS 2.75 km IP TA BC2 delay loop 2.5 km 540 klystrons 20 MW, 148 µs
drive beam accelerator
2.4 GeV, 1.0 GHz CR2 CR1 BDS 2.75 km 50 km CR combiner ring TA turnaround DR damping ring PDR predamping ring BC bunch compressor BDS beam delivery system IP interaction point
dump
drive beam accelerator
2.4 GeV, 1.0 GHz Drive Beam Main Beam booster linac 2.86 to 9 GeV e+ main linac e– main linac, 12 GHz, 72/100 MV/m, 21 km e+ injector 2.86 GeV e+ PDR 389 m e+ DR 427 m e– injector 2.86 GeV e– DR 427 m BC1
Figure 19: Overview of the CLIC layout at ps = 3 TeV.
Year
0
5
10
15
20
]
1
Luminosity per year [fb
0
200
400
600
800
1000
Luminosity per yearTotal 1% peak
0.38 TeV 1.5 TeV 3 TeV
Figure 20: Luminosity per year in the considered staging scenario. Years are counted from the start of beam commissioning. This figure includes luminosity ramp-up of four years (5%, 10%, 25%, 50%) in the first stage and two years (25%, 50%) in subsequent stages.
values for two modes corresponding to short (“waiting for beam”) and long (“stop”) beam interruptions. 973
At any stage, the power consumption has a large volatility, allowing CLIC to be operated as a peak- 974
shaving facility for the electrical network, matching not only seasonal, but also daily fluctuations of 975
the demand. This particular feature constitutes a strong asset towards optimal energy management, a 976
Draft: 09.04.2016 – 03:01 34
Figure 2.2: Overview of the CLIC layout at√s= 3 TeV based on the updated staging
baseline document [45].
2.3.1
CLIC stages
The CLIC project presents an ambitious long-term programme, with three energy stages lasting 7, 5 and 6 years, respectively to achieve the integrated luminosity goals, interrupted by 2-year upgrade periods. The total duration of the three-stage pro- gramme is about 22 years from the start of beam commissioning. The operating scenario currently planned for the complete CLIC programme is outlined in Figure2.3
2.3. The Compact Linear Collider (CLIC) 37 4 CLIC staging baseline
(c)FT TA BC2 delay loop 2.5 km decelerator, 25 sectors of 878 m 540 klystrons 20 MW, 148 µs CR2 CR1 circumferences delay loop 73 m CR1 293 m CR2 439 m BDS 2.75 km IP TA BC2 delay loop 2.5 km 540 klystrons 20 MW, 148 µs
drive beam accelerator
2.4 GeV, 1.0 GHz CR2 CR1 BDS 2.75 km 50 km CR combiner ring TA turnaround DR damping ring PDR predamping ring BC bunch compressor BDS beam delivery system IP interaction point
dump
drive beam accelerator
2.4 GeV, 1.0 GHz Drive Beam Main Beam booster linac 2.86 to 9 GeV e+ main linac e– main linac, 12 GHz, 72/100 MV/m, 21 km e+ injector 2.86 GeV e+ PDR 389 m e+ DR 427 m e– injector 2.86 GeV e– DR 427 m BC1
Figure 19: Overview of the CLIC layout at ps = 3 TeV.
Year
0 5 10 15 20
]
1
Luminosity per year [fb
0 200 400 600 800
1000 Luminosity per year
Total
1% peak
0.38 TeV 1.5 TeV 3 TeV
Figure 20: Luminosity per year in the considered staging scenario. Years are counted from the start of beam commissioning. This figure includes luminosity ramp-up of four years (5%, 10%, 25%, 50%) in the first stage and two years (25%, 50%) in subsequent stages.
values for two modes corresponding to short (“waiting for beam”) and long (“stop”) beam interruptions. 973
At any stage, the power consumption has a large volatility, allowing CLIC to be operated as a peak- 974
shaving facility for the electrical network, matching not only seasonal, but also daily fluctuations of 975
the demand. This particular feature constitutes a strong asset towards optimal energy management, a 976
Draft: 09.04.2016 – 03:01 34
(a) Luminosity per year
DRAFT
4 CLIC staging baselineYear 0 5 10 15 20 ] 1 Integrated luminosity [fb 0 1000 2000 3000 4000 Integrated luminosity Total 1% peak
0.38 TeV 1.5 TeV 3 TeV
Figure 21: Integrated luminosity in the considered staging scenario. Years are counted from the start of beam commissioning. This figure includes luminosity ramp-up of four years (5%, 10%, 25%, 50%) in the first stage and two years (25%, 50%) in subsequent stages.
Table 9: CLIC estimated power consumption for the updated staging scenario. Values at the 1.5 TeV and 3 TeV centre-of-mass energy stages are taken from the CDR [1].
ps [TeV] Pnominal[MW] Pwaiting for beam[MW] Pstop[MW]
0.38 252 168 30
1.5 364 190 42
3.0 589 268 58
necessary approach in view of the large values of power consumption of the CLIC complex during 977
nominal operation. 978
Estimating yearly energy consumption from the power numbers requires an annual operational scenario 979
(Figure 23). In any “normal” year, i.e. once CLIC will have been fully commissioned and operates in
980
cruise mode, we consider a 90-day annual shutdown, and an additional 50 days of scheduled maintenance 981
stops (typically 1 day per week and 2 weeks every 2 months). Out of the remaining 225 days, we assume 982
80% availability, i.e. 45 days of fault-induced stops. This leaves 180 days for operation, of which 55 days 983
are allocated to machine development and tuning runs, thus yielding 125 days for physics data taking 984
(“luminosity runs”). This is the assumption used for estimating the build-up of integrated luminosity 985
inFigure 21. 986
For energy consumption, one also has to consider reduced operation in the first years at each energy 987
stage, similar to what was done in the CDR [1]. For example, at 380 GeV centre-of-mass energy a single 988
positron target is used for the first three years (-10 MW with respect to nominal). 989
At each centre-of-mass energy stage and during the first year, we consider the 180 days of operation to 990
be composed of three periods of 60 days each. In the first period, a bunch train is formed in order to 991
commission the drive-beam generation complex, and then to commission each decelerator in turn, one at 992
Draft: 09.04.2016 – 03:01 35
(b) Integrated luminosity
Figure 2.3: The luminosity is increase each year (5%, 10%, 25%, 50%) in the first four-years stage and two years (25%, 50%) in subsequent stages.
The duration of each stage is defined by the integrated luminosity targets of 500 fb−1
at 380 GeV, 1.5 ab−1 at 1.5 TeV and 3 ab−1 at 3 TeV collision energy. During the
first stage a top threshold scan will be performed near 350 GeV. For this scan an additional integrated luminosity of 100 fb−1 will be collected during a few months of CLIC operation. The high-energy programme would be adapted depending on new discoveries at LHC or “elsewhere”.
2.3.2
Machine parameters and accelerator
The conceptual layout of CLIC at 3 TeV is shown in Figure 2.2. The main compo-
nents are:
• Polarized electron source
The CLIC polarized electron source consists of a DC-photo gun, a 1 GHz bunch- ing system, and a 2 GHz accelerator. The electrons are accelerated up to 200 MeV before injection into the common injector linac. A spin-rotator in front of the pre-damping ring orients the spin vertically in the rings. The electron source produces spin-polarized electrons with a degree of polarization of 80% or higher. • Positron source
The baseline design for the CLIC positron source provides only unpolarized positrons. The source consists of a conventional primary electron-beam linac with energy of 5 GeV, followed by hybrid tungsten targets, a positron capture section, and a pre-injector linac to accelerate the positrons to 200 MeV.
• Pre-damping and Damping rings
The main purpose of the CLIC damping rings is to ‘cool’ the incoming electron and positron beams to the very small emittances needed for collisions. This goal
2.3. The Compact Linear Collider (CLIC) 38 is achieved with four rings, a pre-damping and a main damping ring for each particle species. A pre-damping ring (PDRs) is needed to damp the large input emittance, particularly of the positrons, at the high repetition rate of 50 Hz. • Booster Linac
The booster linac accelerates the beam to the main linac injection energy of 9 GeV. The same linac is shared by electrons and positrons.
• Ring to Main linac transport (RTML)
The RTML connects the damping rings and the main linacs. It consists of beam lines for the transport of the beams from the central injector site, which is close to the surface, to the outer ends of the main linac, which is about 100 m underground. It includes sections for longitudinal bunch compression and spin rotation. The two RTMLs for electrons and positrons each have a total length of approximately 27 km.
• Drive-beam accelerator (DBA)
The DBA consists of 24 short bunch trains of 244 ns length, which follow each other at about 6 µs intervals. DBAs generate then 142 µs long drive-beam pulses and accelerate them to a final energy of 2.4 GeV. For that purpose, normal conducting fully-loaded accelerating structures with an RF frequency of 1 GHz are used. The two DBAs are identical and have a total length of 2.6 km, including injectors and bunch compressors, and provide Drive-Beam pulses for the positron and the electron main linacs in order to achieve the challenging accelerating gradient of 100 MV/m.
• Delay loops and combiner rings (CR)
The time compression of the drive-beam pulses takes place in the Delay Loops and Combiner Rings (CR1 and CR2). An RF deflector operating at the bunch frequency will deflect subsequent 244 ns long trains alternately into the loop or along the straight path. If the flight time of the electrons between the two paths exactly matches the length of the train, the bunches of the delayed train will be placed between the bunches of the following train using a second deflector. The combined train therefore has twice the bunch repetition frequency and twice the peak current. These trains are then injected into the combiner rings, where the bunch repetition frequency is increased to 12 GHz and the peak current to 101 A, reducing the bunch length to 1 mm.
• Main linacs
The two main linacs, one for positrons and one for electrons, accelerate the beams from an initial energy of 9 GeV to the final value of 1.5 TeV using nor- mal conducting accelerating structures with an RF frequency of 12 GHz and a gradient of 100 MV/m. The linac design is identical for electrons and positrons and the linacs are each about 21 km long.
2.4. The International Large Detector (ILD) 39