1. DRFS and Low Energy 10 Hz Option
S. Fukuda
KEK
Dec
10 Hz Cost Review Webex

2. Introduction(1)
There proposed derivative scenarios in ILC due to the limitation of construction cost.
Important scenarios are (1) low energy 10 Hz option and (2) SB2009.
We had proposed the DRFS scheme for both scenarios, while we haven’t presented final consistent schemes and cast profiles for them.
For (1), good efficiency operation is possible by changing the klystron operation point ( change the klystron perveance and external loading for klystron output cavity).
For (2), due to the change of QL between half current and full current, DRFS uses longer pulse width of 2.2ms instead of 1.7ms, and efficiency and cost is not 50 % of RDR.
Main reasons of inconsistent scheme proposal are as follows:
We can propose the adequate scheme for each scenario independently, but we need the possible ILC scenario including the beam operation and construction/upgrade to make a consistent DRFS schemes from low energy operation to full energy operation.
Dec
10 Hz Cost Review Webex

3. Introduction(2)
For coming BAW-2, we assume (or confirm) possible ILC construction and operation scenario and present the DRFS scenario which is consistent for the ILC scenario.
Dec
10 Hz Cost Review Webex

4. Review: DRFS Plan for derivative option
Boundary condition
Smooth transition to full energy scheme with minimum loss.
Basic scheme : kW from DRFS Klystron
65-67kV applied voltage
pulse width of 1.56ms, 5 Hz repetition
Cavity gradient acceptance: 31.5MV/m+-20% or 25-38MV/m
Cavity gradient sorting results in 105% cost up
In order to keep these RF requirements, SB2009 of DRFS prefers to the beam current of 4.5mA so the pulse width is longer to 2.2 ms.
Low energy 10Hz operation is realized by change of klystron operation point.
Dec
10 Hz Cost Review Webex

5. Test of Low-energy 10Hz Operation
Operation Point Shift
Klystron voltage
64kV-> 59kV
Klystron micro-Perveance
1.2 -> 0.8
Klystron efficiency
62%->60%
External Q
Relative Q : 1 ->2.2
These are realized by tapping off VKM /VKA and loading the iris in PDS.
DRFS required the system revision to eliminate the loaded iris.
Tap-off ---cost up
Dec
10 Hz Cost Review Webex

6. PS system for DRFS (one unit)
Voltage tap-off is introduced
Capacitor Bank
VCB
MA modulator
Oil Tank
Oil Tank
(0V)
Klystron（１3） LC
Bouncer
Circuit
50kW
Switching PS
4 units
Switch
Drive
circuit
Spark Gap Switch HV
(-68kV)
-2kV
Bias PS MA HK
Heater PS H
6.6kV/420V TRNS
6.6 kV 3ø
Main AC Line
Control System
HV Relay CT
Dec
10 Hz Cost Review Webex 6

7. ILC Construction/Operation Scheme and DRFS
We need some periods to eliminate loaded iris in PDS. (4000 pieces)
relatively short term is OK
If longer pulse scheme of 2.2ms is introduced, also this scheme must be used
In low-energy 10 Hz option, since DC/PS system must have mated to the
requirement of power consumption and sag compensation. This is loss for 10Hz
Scenario since this is over-specification.
RDR mode (full energy mode) must keep using this over-spec power supply and
Costly not effective.
Dec
10 Hz Cost Review Webex

8. Configuration for Low-energy with 10 Hz
Two 50 kW Switching PSs for 7 Klystrons
Back-up PS
DC PS
Capacitor Bank for 7 Klystrons
Bouncer Capacitors for 7 Klystrons
Low-energy
with 10 Hz
MA Modulator for 13 Klystrons
9 Cell Cavities
9 Cell Cavities
8 Cell Cavities
9 Cell Cavities
Full Power Option
Four 50 kW Switching PSs for 13 Klystrons
DC PS
9 Cell Cavities
9 Cell Cavities
8 Cell Cavities
9 Cell Cavities
Dec
10 Hz Cost Review Webex

9. New DRFS Scenario consistent for derivative option
In SB2009, over-coupling scheme is introduced to shorten the pulse width.
pulse width of nearly 1.6ms is kept by choosing the suitable coupling
coefficient b.
Over coupling generally required more power and total plus minus is not clear. While DRFS employs the cavity sorting and power shortening is occurred in the higher gradient cavity group only in the case of output power of DRFS klystron is kept same as kW.
If b is around 2, peak power increases 12.5% and fraction of above violet part is
less than 20%. The cryomodules having sorting bin A are installed to the
fixed area of HLRF station with different specification above.
Dec
10 Hz Cost Review Webex

10. Summary
In new DRFS scenario is consistent from low-energy 10 Hz option to revision to SB2009, and from SB2009 to upgrade to full power scheme.
Comparing with the previous SB2009 DRFS scheme proposed before, there are much advantages concerning about the power consumption loss and the cost effect.
If fraction of 12.5% is operated in the longer pulse width, power consumption and cost is roughly 0.54　( *0.5*0.33） of the RDR for the SB2009. ( Old scenario : 0.67)
For the low energy 10 Hz option, same configurations are introduced, and these system are kept using in SB2009 and in full energy option ( cost up of 2% ).
Cost effect for the tap-off system for MA modulator and iris loaded structure is under study and this will be reported in BAW2 in SLAC .
In 10 Hz option, this new scenario result in reducing to 9.3 Hz. Comparing with the case of all longer-pulse system, there is a much advantage.
More detailed presentation will be done inBAW-2 in January 2011.
Dec
10 Hz Cost Review Webex