Recent DRFS and Related CFS Issues KEK　Fukuda Contents Tunnel Layout Review LCWS and DRFS DRFS in Kamaboko Tunnel DRFS and 5.7m Dia. Single Tunnel Heat Dissipation DRFS vs RDR 2011/10/12 CFS-Tsukuba11 (Fukuda)

Tunnel Layout Review 2011/10/12 CFS-Tsukuba11 (Fukuda)

CFS Issues for DRFS In the middle of May, CFS team will have a presentation of newly proposed NATM tunnel. Two candidates: 5.7m dia TBM method tunnel and NATM tunnel. Single tunnel plan for DRS and concerned issues: Current configuration of DRFS in 5.7m diameter tunnel shows the high density components layout. Space consideration will be necessary by changing the specifications of modulator/power supply. Shielding issues are still concerned Heat dissipation issues are discussed FNAL team started to developing the drawing of 5.7m dia. Tunnel of DRFS NATM tunnel plan was proposed, which was an advantage for mountain site, and DRFS was developed based on this proposal. 2011/10/12 CFS-Tsukuba11 (Fukuda)

Previous 5.7m dia. Single tunnel plan Single tunnel plan of 5.7m diameter in which cryomodule is on the floor is based on the presentation in BAW1 in Tsukuba in Sep. 8 2010. Alcove for local electricity is eliminated and each P/S accepts 6.6kV directly and changes to 420V. Low voltage line is generated locally. Radiation shield is changed to wall-like and height limitation in P/S room disappeared. Parts of klystrons are installed in bunch to make the maintenance space and consequently PDS became more complicated. Due to the acceptance of cavity field variation, average power increased. In order to consist to SB2009 and low energy scheme, Average power increased due to the longer pulse width in BAW2 in Tsukuba in Jan. 18 2011. Revised layout was sent to FNAL in July 2011. Recently 8+8+8 cavities scheme was proposed and it has the merit in this layout from space consideration. Air Ventilation Radiation Shield Bunched klystrons and PDS Cooling Water 2011/10/12 CFS-Tsukuba11 (Fukuda)

Model Compared Circle/Twin T Circle/Single T Circle/J. Single T Bullet/J. Single T Wagon Roof/Single T 2011/10/12 CFS-Tsukuba11 (Fukuda)

Benefits of Wagon-Roof Type Tunnel Cost Benefit in the Mountain Region such as Japanese Site Some Cases Reasonable Construction Period comparing with TBM Wider Cross Section of the Tunnel comparing with TBM Case-8 was adopted to new DRFS application 2011/10/12 CFS-Tsukuba11 (Fukuda)

Newly Proposed Tunnel Plan (Kamaboko Tunnel) CFS team consider the another construction method of the tunnel, i.e. NATM, which is especially effective in mountain region and we started to develop the consistent layout configuration for this method. We (Japanese) want to name this tunnel as “Kamaboko” tunnel. Kamaboko is a Japanese traditional food, which is made from fresh fish’s paste, and very delicious. Cross-section of tunnel is actually just the shape of kamaboko! 2011/10/12 CFS-Tsukuba11 (Fukuda)

LCWS11 and DRFS 2011/10/12 CFS-Tsukuba11 (Fukuda)

TDR Parameter Change of DRFS for New Situation Consistent Scheme Model from Low Power Option to Full Scheme. Cryomodule with 8+8+8 from 9+8+9 Cryomodule numbers, DC power supplies and MA modulators increase 8.3%. Klystron and PDS numbers remains same. Accepting cavity gradient variation of 31.5MV/m+-20% and Cavity gradient sorting Power increase is required and follows to the table shown in BAW2. DRFS klystron output power increase to 800-850kW. Introducing circulator and variable hybrid to accept the cavity degradation when cavities are installed. Components numbers of circulators and variable hybrid change and layout is also changing. NATM type single tunnel for DRFS; elimination of back-up unit Layout of DRFS in Kamaboko tunnel change like slide-11. Back-up module for “hot swappable” is eliminated and average heat dissipation decreases. Basic feature is described above and detailed number will be presented soon. 2011/10/12 CFS-Tsukuba11 (Fukuda)

Same units Increase units Consistent Scheme for 3 operation mode Low Energy 10Hz, SB2009 and Full scheme and DRFS Layout (1) Low energy 10Hz operation: 250GeV, 4.5mA, 10Hz All units have a capability of 2.3ms pulse width, 10Hz. Facility requires 144% power capability. Numbers of active klystrons are 50% to 70% depending on the sorted kly. group. (2) Reduced bunch operation: 500GeV, 4.5mA, 5Hz All units have a capability of 2.3ms pulse width, 5Hz. Facility requires 144% power capability. Numbers of active klystrons are same in sorted kly. group. Same units (3) Full energy operation: 500GeV, 9mA, 5Hz Increase units Old units have same capability, and new units with 1.8ms pulse width. Facility for new units requires 113% power capability. 2011/10/12 CFS-Tsukuba11 (Fukuda)

A Proposal Revised (By Akira) Akira Yamamoto 888 Cavity Strings A Proposal Revised (By Akira) 9 4 + Q +4 9 9 8 8 Q 8 8 4 + Q +4 8 Keep the concept of 8 cavity string unit, to be simplified Accept two types of Cryomodules (from Cryomodule manufacturing) 2011/10/12 CFS-Tsukuba11 (Fukuda)

888 Cavity Strings Effects from 9+8+9 to 8+8+8 From the acceptance of cavity gradient acceptance of 31.5MV/m+-20%, more rf power is possibly required for RDR configuration if 9+8+9 strings are kept. More than 10MW output MBK may be required. For DRFS, 8+8+8 scheme is simpler than 9+8+9 and smooth transition from low energy option to full energy scheme is performed. There expected other good effects in LLRF control since 8+8+8 combination is multiple of even and convenient for digital control. This modification results in costing up, but less than the factor of 26/24 in DRFS. Costing-up is come from the increase of the number of cryomodule and RF power supply. Since numbers of cavities remain same, numbers of klystron & PDS remain same in DRFS. Power supplies follows to the unit configuration of cryomodule and increase the number. In RDR, Klystron and modulator numbers are also increased by 26/24. 2011/10/12 CFS-Tsukuba11 (Fukuda) 12

888 Cavity Strings Comparison between 888 & 989 in DRFS In DRFS, layout for the reduced bunch operation and low energy operation becomes simple. There are no RF unit to feed powers to the cavities in the different cryomodule. Modification from low energy/current option to full energy option is straight forward and simple. Cost-up factors; Since numbers of cavity remains same, numbers of klystron are also same. Numbers of DC power supply and MA modulator increase and cost up of about 3% of HLRF is expected. (cf. In RDR, 6% of HLRF) 2011/10/12 CFS-Tsukuba11 (Fukuda)

Cavity Degradation Issue Cryomodule Gradient Spread D. Kostin & E. Kako Cavity Degradation Issue Cryomodule Gradient Spread FLASH: 3 PXFEL cryomodules PXFEL-1 PXFEL-2 PFEL-3 NML-CM1 (Fermi)　In progress S1-Global　＠　KEK 2011/10/12 CFS-Tsukuba11 (Fukuda)

Fraction of Degradation Cavity Degradation Issue Current statistics on cavity gradient degradation Current degradation estimation (By A. Yamamoto) Poor Statistics Now (see right table) Select cavities which decreased more than 20%: High rate of ~12/40, which leads to ~30%. This is too high, and efforts of improving is required. How improved? Maybe up to ~10%. (acceptable?)　 Sorting after vertical test is planed in DRFS. Furthermore 10% decrease of gradient is likely occurred and this reality should included at the construction plan. This effect also results in cost-up. Numbers of cavities and rf units must be increased if total acceleration is short and it is not compensated by the overhead. Since DRFS employs one rf unit feeds powers to 2 or 4 cavities without using circulator, and therefore cavity gradient sorting is inevitable, effect of unexpected cavity gradient degradation is larger than other scheme such as RDR and KCS. Operational experiences now Institute Project Fraction of Degradation DESY/FLASH PXFEL Prototype-1 2/8 PXFEL Prototype-2 PXFEL Prototype-3 1/8 Fermi Lab CM-1 4/8 KEK S1-Global 3/8 Total 12/40 2011/10/12 CFS-Tsukuba11 (Fukuda)

One RF unit feeds power to sorted 2 cavities without circulators. Cavity Degradation Issue Influence for DRFS due to the Cavity Gradient Degradation (I) Assumption; Fraction of total numbers of 10% degrades cavity gradient from vertical value. Amount of degradation from vertical measured value is 20% in average. Full DRFS case; One RF unit feeds power to sorted 2 cavities without circulators. 　　　-> Normal cavity which is a pair with 20% deteriorated cavity must be operated in 20% lower level. # of cavities which is operated in lower level is 20% instead of 10%. 　　 -> Decrease of energy gain 80%*1 (Normal) +20%*0.8 (Field Degradation amount) =96% 　　　　 cf. In the system with PkQl, decrease of energy gain is 10%. 　　　　　　　 90%*1 (Normal) +10%*0.8 (Field Degradation) =98% if circulators and VTO are added in DRFS, energy gain is same as 98%. In each scheme, it is necessary to compensate the numbers of cavity and rf source by amount of decreased rate. Difference between DRFS and other scheme is 2%. Cost up for adding circulators and VTO is less than 1.0% in total cost, then adding circulators and VTO in DRFS has a merit. 2011/10/12 CFS-Tsukuba11 (Fukuda) 16 16

Influence for DRFS due to the Cavity Gradient Degradation (2) Low Power/Energy Option DRFS; ->One RF unit feeds power to sorted 4 cavities without circulators and disadvantage due to the cavity gradient degradation becomes worse. Numbers of 10% deteriorated cavity forces other 30% normal cavity to operate in the lower level. 　　 -> Decrease of energy gain 90%*90%*90%* 90%(All 4 normal)+(1- 90%**4) (any of 1 in 4 degrade) *0.8 (Field degradation amount) =93% 　　　　cf. In the system with PkQl, decrease of energy gain is 10% of all cavity. 　　　　　90% (Normal) +10%*0.8 (Field Degradation amount) =98% Difference between DRFS in low energy/current option and other scheme increase larger. if circulators and VTO are added in DRFS, energy gain is same as 98%. In each scheme, it is necessary to compensate the numbers of cavity and rf source by amount of decreased rate. Difference between DRFS and other scheme is 2%. Cost up for adding circulators and VTO is less than 1.0%*(1/merit figure of low power option) in total cost, and adding circulators and VTO in DRFS has bigger merit the case of full energy case. 2011/10/12 CFS-Tsukuba11 (Fukuda)

Solution=Introduce circulator and variable hybrid in DRFS Cavity Degradation Issue Solution Against Cavity Gradient Degradation in DRFS In Low Current/Energy Operation, decrease of energy gain due to the cavity gradient degradation in DRFS is predominant and become serious. On the other hand, cost increase for introducing circulators and variable hybrids is expected to be less than 1.0% of total cost. Cost of circulator is pure increase. Cost of variable hybrid is the cost of introducing variable mechanism. Cheep variable hybrid was already used and evaluated in S1-global test in KEK. For the cavity gradient degradation of 10% numbers of averagely 20% deterioration or worse, introducing circulators and variable hybrids results in cheaper cost effect. In this case, degree of energy gain drop is the same as RDR/KCS. Solution=Introduce circulator and variable hybrid in DRFS 2011/10/12 CFS-Tsukuba11 (Fukuda)

DRFS in Kamaboko Tunnel 2011/10/12 CFS-Tsukuba11 (Fukuda)

New Features of DRFS in New Tunnel Plan(1) Based on Japanese CFS Tunnel Plan, new configuration of DRFS was presented at SCRF meeting in June 1, 2011. This is based on the NATM method of tunnel excavation and Japanese mountain cite employs this configuration. 2011/10/12 CFS-Tsukuba11 (Fukuda)

New Features of DRFS in New Tunnel Plan(2) For the CFS view points, there are lots of merit features comparing to previous 5.7m dia. single tunnel plan. Therefore we are now designing DRFS based on this new scheme. RDR configuration is also reassessed in this scheme. Both cases, if work during the acceleration is possible due to thick shield, we can eliminated the backup module. Central shield thickness of more than 4m satisfies this condition. In this configuration, there are lots of advantageous features for DRFS; radiation problem, maintainability and availability, possible revision of redundancy Recently 8+8+8 cavities scheme was proposed and it has the merit in this layout from space consideration. 2011/10/12 CFS-Tsukuba11 (Fukuda)

New Features of DRFS in New Tunnel Plan(3) In Kamaboko tunnel, there are two areas, accelerator area and service area like RDR two tunnel. In service tunnel, DRFS klystrons are installed on the intermediate floor of 2.34m high and WR650 waveguides penetrate the central wall through the hole at 2.925m high. Under the intermediate floor, HV cables of 70kV are delivered near the wall. Water headers are also expected to be set there (not determined in detail). There are enough access pass which is used for the equipment installation. Basically there are no alcoves for each 4 RDR units. 2011/10/12 CFS-Tsukuba11 (Fukuda)

New Features of DRFS in New Tunnel Plan(4) In Kamaboko tunnel, there are lot of spaces in longitudinal direction if back-up unit of power supply is eliminated. If central radiation shield wall is efficiently thick enough, personnel can access in the tunnel during the beam operation for the maintenance. MTBF of power supply is long and overhead unit covers the failure unit, backup can be eliminated. For slow neutron dose, more study is necessary. DRFS Klystrons are equally distributed on the intermediate floor. Water header is set at the place where there are no equipment or rack. Basically there are no alcoves for each 4 RDR units and 6.6kV line is directly connected to the local VCB in each unit. This configuration is basically same as previous 5.7 dia. Tunnel plan. Birdseye View of DRFS Side view of DRFS 2011/10/12 CFS-Tsukuba11 (Fukuda)

New Features of DRFS in New Tunnel Plan(5) 2 RDR Units Kamaboko-tunnel doesn't need back-up. Birdseye View of DRFS Side view of DC P/S Backup VCB is not necessary 2011/10/12 CFS-Tsukuba11 (Fukuda)

New Features of DRFS in New Tunnel Plan(6) New scheme revisions should be all reflected to the DRFS scheme of Kamaboko tunnel, but not yet completed. 888 cavity strings change: Total numbers of cryomodule, power-supply and MA modulator is increased by the amount of 8% in ML, while total capacity of electricity and water keep same. From the cavity degradation consideration, DRFS abandons the circulator-less system but it gives miner effect to CFS. Adopting the cavity sorting scheme or not is still the issue because sorting expects to give small change of PkQl manipulation. Increase of power capability and heat dissipation required to low power/low current option and acceptance of cavity gradiate of 31.5MV/m+-20% is still alive and basically same as before. . Side view of DC P/S 2011/10/12 CFS-Tsukuba11 (Fukuda)

Electricity Distribution (Q):What is the interface point between the DRFS equipment for one RF unit and the CFS electrical distribution system. (A):Yes, comparing with RDR layout, in DRFS scheme we eliminated the alcoves of CFS electricity after the discussion with Atsushi and CFS group to save the cost. (KEK: CFS Review June 10, 2010) 6.6 kV line is directly introduced to two VCBs of two power supplies (P/S) respectively. So electrical interface points is sub-electric center which has the transformers of 66kV to 6.6 kV in every 4.5km distance. (A):In every front end of the electricity of P/S makes a low voltage line such as AC100V and AC200 V for the control and low voltage electricity. Center:275kV 275kV->66kV 66kV->6.6kV in each 4.5km apart 2011/10/12 CFS-Tsukuba11 (Fukuda)

DRFS and 5.7m Diameter Single Tunnel 2011/10/12 CFS-Tsukuba11 (Fukuda)

Previous 5.7m dia. Single tunnel plan Single tunnel plan of 5.7m diameter in which cryomodule is on the floor is based on the presentation in BAW1 in Tsukuba in Sep. 8 2010. Alcove for local electricity is eliminated and each P/S accepts 6.6kV directly and changes to 420V. Low voltage line is generated locally. Radiation shield is changed to wall-like and height limitation in P/S room disappeared. Parts of klystrons are installed in bunch to make the maintenance space and consequently PDS became more complicated. Due to the acceptance of cavity field variation, average power increased. In order to consist to SB2009 and low energy scheme, Average power increased due to the longer pulse width in BAW2 in Tsukuba in Jan. 18 2011. Air Ventilation Radiation Shield Bunched klystrons and PDS Cooling Water 2011/10/12 CFS-Tsukuba11 (Fukuda)

Layout of DRFS in 5.7m Single Tunnel I believe Auto-cad data had already been sent by Miyahara before and basically almost same as before. Today I just show you 2-D PDF data, because layout comprises of lots of drawings. If you couldn’t read Auto-cad drawing, we are ready to send them again or 2-d DWG file. Today I show yu 2-D PDF data to explain you the DRFS. 2011/10/12 CFS-Tsukuba11 (Fukuda)

Layout 1/3 2011/10/12 CFS-Tsukuba11 (Fukuda)

Layout 2/3 2011/10/12 CFS-Tsukuba11 (Fukuda)

Layout 3/3 2011/10/12 CFS-Tsukuba11 (Fukuda)

Layout of Power Supply 2011/10/12 CFS-Tsukuba11 (Fukuda)

Electricity Distribution (Q):What is the interface point between the DRFS equipment for one RF unit and the CFS electrical distribution system. (A):Yes, comparing with RDR layout, in DRFS scheme we eliminated the alcoves of CFS electricity after the discussion with Atsushi and CFS group to save the cost. (KEK: CFS Review June 10, 2010) 6.6 kV line is directly introduced to two VCBs of two power supplies (P/S) respectively. So electrical interface points is sub-electric center which has the transformers of 66kV to 6.6 kV in every 4.5km distance. (A):In every front end of the electricity of P/S makes a low voltage line such as AC100V and AC200 V for the control and low voltage electricity. Center:275kV 275kV->66kV 66kV->6.6kV in each 4.5km apart 2011/10/12 CFS-Tsukuba11 (Fukuda)

Switching from Failure one to STB unit(Q1) (A) ; This 1 STB unit is some sense hot, but some sense not hot. It is keep alive but it is not connected to the real load (DFRS klystrons) and not fully powered. (these loads are common for P/S and STB P/S). If P/S has a fault and STB P/S is necessary, once VCB is off and connection change from previous P/S to new (STB) P/S is performed in low voltage and then STB VCB is on and gradually up to the rated voltage. This is done because of real hot swappable turn on and off is difficult due to the HV relay’s specification. Failed This sequence is same for the case of MA modulator 2011/10/12 CFS-Tsukuba11 (Fukuda)

Heat dissipation In following slides, complete revisions due to the design change of LCWS11 are not yet done. 2011/10/12 CFS-Tsukuba11 (Fukuda)

Heat Loss of STB Unit Valid for 5.7m tunnel Heat Loads of STB Modules are included In the previous table　 Indicated by spare or Back-up. Red and blue circle are required in Kamaboko tunnel scheme. Heat load to LCWater is Not available. To air. 2011/10/12 CFS-Tsukuba11 (Fukuda)

Power Increase Requirement(1) At BAW-2 held in SLAC in Jan. 18-22,2011, SB2009 and low energy 10Hz operation were discussed and we required to increase the power to match to the cavity condition to accelerate 4.5mA in DRFS. Mainly this situation is come from the requirement of pulse width expansion. At the same time, accepting the cavity gradient variation of 31.5MV+-20% was discussed. This also resulted in the increase of power requirement. In this case, cavity sorting on 5 group gradient was proposed in DRFS to balance the power between cavities fed by the same klystron. Due to the Ql mismatch, it I s necessary to prolong pulse width and peak power increase. In full energy scheme: For units for maximum power requirement, Gradient of 31.5MV, 9mA, 5Hz, then pulse width of 1.565ms (Original) Highest gradient group =31.5*120%, 9mA, 5Hz, then pulse width of 1.8ms Required klystron power 850kW (13% overhead) and required power increase of 27% In SB2009 and 10 Hz operation: Gradient of 31.5MV, 9mA, 5Hz, then pulse width of 1.565ms (Original) Highest gradient group =31.5*120%, 4.5mA, 5Hz, then pulse width of 2.3ms Required klystron power 850kW (13% overhead) and required power increase of 44% RF sources used in this operation are kept used in full energy operation. New rf sources have a capability mentioned above. 2011/10/12 CFS-Tsukuba11 (Fukuda)

Power Increase Requirement(2) Considering cavity gradient degradation, energy gain is decreases by amount of numbers of degraded cavity and average gradient degradation. Assume that fraction of total numbers of 10% degrades cavity gradient from vertical value and amount of degradation from vertical measured value is 20% in average, then totally 2% of power should be compensated from the previous slide. 2011/10/12 CFS-Tsukuba11 (Fukuda)

Power table for full energy scheme (need to revise) It is not determined to use cavity sorting or not in PkQl –DRFS scheme. 888 cavity strings are not reflected in this table. Cavity degradation requires 2% up of power/water. This table has back-up unit. 2011/10/12 CFS-Tsukuba11 (Fukuda)

2011/10/12 CFS-Tsukuba11 (Fukuda)

Power Table of Full Energy Case (need to revise) Data of Power table about DRFS is revised. New table includes the effect of cavity gradient variation. For each group of sorting, power data is different, but averaging all group is same as median group. Pulse width is increased to 1.8ms and output power from klystron is increased to 850kW. RF Load heat table increases considering imperfect mismatching of cavity. Collector loss power is calculated in the case of efficiency of 5% lower and then it increases. Interpretation using average Total Heat Load = 194.3 KW per RF Heat from Racks =11.65/RF Beam Power = 37 .12KW / RF Total RF Power per RF (excluding Racks)~ 219.78 KW No of RF =560 (RDR) + 24 (RTML gave to ML during SB2009) = 584 So Total Plug Power = 219.78 x 584 = 128.3 MW Cavity degradation requires 2% up of power/water. 888 system changes the number of a unit. 2011/10/12 CFS-Tsukuba11 (Fukuda)

Power table for reduced bunch operation (need to revise) It is not determined to use cavity sorting or not in PkQl –DRFS scheme. 888 cavity strings are not reflected in this table. Cavity degradation requires 2% up of power/water. This table has back-up unit. 2011/10/12 CFS-Tsukuba11 (Fukuda)

2011/10/12 CFS-Tsukuba11 (Fukuda)

Power Table of Reduced Bunch Operation (need to revise) Data of Power table about reduced bunch operation is revised based on BAW-2. New table includes the effect of cavity gradient variation. For each group of sorting, power data is different, but averaging all group is same as median group. Pulse width is increased to 2.3ms and output power from klystron is increased to 850kW. RF Load heat table increases considering imperfect mismatching of cavity. Collector loss power is calculated in the case of efficiency of 5% lower and then it increases. Interpretation using average Total Heat Load = 169.82 KW per RF Heat from Racks =11.65/RF Beam Power = 18.86KW / RF Total RF Power per RF (excluding Racks)~ 177.04 KW No of RF =560 (RDR) + 24 (RTML gave to ML during SB2009) = 584 So Total Plug Power = 177.04 x 584 = 103.3 MW Cavity degradation requires 2% up of power/water. 888 system changes the number of a unit. 2011/10/12 CFS-Tsukuba11 (Fukuda)

DRFS vs RDR 2011/10/12 CFS-Tsukuba11 (Fukuda)

New Tunnel Scheme and DRFS/RDR New Tunnel Plan with NATM has a cutaway view of bread shape (a Kamaboko shape) and is particularly mating for the mountain site ILC. Follows are advantageous features. Complete single tunnel plan is possible and fit for DRFS. It is possible to have a wider space comparing with the single tunnel plan with 5.7m diameter TBM plan. Original DRFS plan (completely distributed RF system) is possible. It is possible to introduce thick shield wall and concerned radiation influence on the electric circuit maybe predominantly reduced. If thick radiation shield enables us to enter the tunnel, maintenance work during the operation is possible. In DRFS, it is possible to eliminate the “hot” swappable back-up unit. (Big cost-cutting!) New Tunnel Plan with NATM gives the same merits to single tunnel RDR plan. Cost of RDR is cheaper than DRFS, and evaluation and assessment between RDR and DRFS is necessary. 2011/10/12 2018/11/21 CFS-Tsukuba11 (Fukuda) 47

High Availability @ DRFS S. Michizono/LCWS08 High Availability @ DRFS Assumption: There is a 0.4% stand-by cavities (1/250:corresponding to roughly 1 rf unit in baseline and 26 units in single cavity driver). Reliability 0.4% STB p: each rf unit reliability Ptotal: total reliability Baseline: N=250,m=1 Single drive: N=250*26=6,500, m=26 If component has an availability of 99.8%, total reliability becomes 99.96% incase of 26cav.STB. 2011/10/12 CFS-Tsukuba11 (Fukuda)

High Availability @ DRFS(2) S. Michizono/LCWS08 High Availability @ DRFS(2) Each rf unit has a reliability of 99.8%? Maybe yes. : 99.8% corresponds to 20 min./week, 5 hrs/yr (5,000 hrs op.) From the experience of KEKB injector linac (60 units, 7,000 hrs operation/yr.), the downtime of the unit is<5min./week. In addition, we can neglect one cavity failure in DRFS. (because its energy contribution is negligibly small (0.015%). -> We can make some diagnostics even during luminosity operation! -> Exception handling becomes quite simple. (Fast recovery of beam energy is not necessary even when quench or rf failure happen.) Operation flexibility is expected since there are many RF sources being operated independently. 2011/10/12 CFS-Tsukuba11 (Fukuda)

for listening my presentation! Thank you for listening my presentation! 2011/10/12 CFS-Tsukuba11 (Fukuda)