Current CLIC drive beam acceleration CLIC drive beam

Current CLIC drive beam acceleration • CLIC drive beam provide 2. 37 Ge. V beam for both final stage and stage 1. • Means that peak power demand (or number of klystrons) for stage 1 is same as final stage. Then the cost will be high for stage 1. • Using pulse compressors at stage 1 may reduce the number of klystrons, but this kind of compressor does not exit (very long pulse) and will not be used any more in future upgrade. 797 Klystrons, 15 MW, 140 us Final stage: 3 Te. V 70000*8. 4 n. C 2. 37 Ge. V CLIC drive beam accelerator Stage 1: 375 Ge. V 9000*8. 4 n. C

Proposed CLIC drive beam acceleration • Run in CW mode (need super conducting). • The SRF cavities store energy and release them when beam comes. • Less bunch train length → less stored energy demand → less klystron and structure length for stage 1. • Another potential benefits: less klystrons. • Power feeding and beam loading effect are main challenges in the design. Energy 100 Klystrons, 800 KW, CW Final stage: 3 Te. V 70000*8. 4 n. C Final stage CLIC drive beam accelerator 2. 37 Ge. V Stage 1 13 Klystrons, 800 KW, CW Stage 1: 375 Ge. V 9000*8. 4 n. C CLIC drive beam accelerator Release energy 2. 37 Ge. V Store energy Release energy Time

Power feeding issue

Settings •

Power feeding issue • CLIC driven beam total energy: 10 GW*140 μs=1. 4 MJ • Minimum CW RF power: 70 MW • CW mode: no modulator and less peak power, more ohmic loss (more AC power for cryogenics). • Pulse mode: need modulator and more power source, less ohmic loss. Voltage 20 ms CW mode Pulse mode Time Duty time : 140 us

Power feeding issue •

Power feeding (CW mode) • Note: optimum Qe here means the highest power filling factor Voltage CW mode Time

• Power feeding (CW mode) CW mode CDR Klystron power(efficiency) 85. 6 MW CW(66%) 12 GW 0. 7%DF(66%*89%) Klystron amount 107 * 800 KW 797 * 15 MW Cryogenics power 29. 1 MW N/A Total AC power 158 MW 152 MW Filling time = 20 ms (CW mode) Filling time = 1. 5 ms (Pulse mode)

Alternative Power feeding (Pulse mode) • Filling time = 1. 5 ms, Need 13. 3 times higher peak power. • Compressor is not possible (pulse too long : 20 ms). Need to built modulators. ~ ~ Pulse mode CW mode CDR Klystron power (efficiency) 1. 28 GW 5%DF (66%*89%) 85. 6 MW CW (66%) 12 GW 0. 7%DF (66%*89%) Klystron amount 256 * 5 MW 107 * 800 KW 797 * 15 MW Cryogenics power 2. 18 MW 29. 1 MW N/A Total AC power 147 MW 158 MW 152 MW Modulator Klystron Pulse Compressor

Alternative Power feeding (“Travelling wave” CW mode) • …… SRF structure

Alternative Power feeding (“Travelling wave” mode) • TW mode CDR Klystron power (efficiency) 75. 3 MW CW (66%) 85. 6 MW CW (66%) 12 GW 0. 7%DF (66%*89%) Klystron amount 94 * 800 KW 107 * 800 KW 797 * 15 MW Cryogenics power 32. 1 MW 29. 1 MW N/A Total AC power 145 MW 158 MW 152 MW

Summary of Power feeding issue Klystron CW mode Frequency Control Crygenics Advantage: no modulator and easy design Disadvantage: need accuracy frequency control (~20 Hz), need more cryogenics module and power (75 MW) Complexity Klystron Pulse mode Frequency Control Crygenics Advantage: much less cryogenics power need, and tolerant frequency control (~500 KHz). Disadvantage: need modulator and more klystrons Complexity Klystron “Travelling wave” mode Frequency Control Crygenics Complexity Advantage: Less klystron power and tolerant frequency control. Disadvantage: more cryogenics power (80 MW).

Beam loading issue

Basic concept • Each drive beam sub pulse (length : 240 ns) … 2 ns … 1 ns 2 ns

Frequency selection • Problem about 1 GHz: stored energy per length is lower (0. 125 KJ/m scaled from KEK-B cavity) → linac length is too long (also cryogenics power is maybe higher). • Solutions: - Longer bunch train (scaled in time) →larger delay loop and combiner ring (may also need addition CR). - Larger bunch charge and bunch separation →larger beam quality? ? Frequency Bunch charge 1 GHz 8. 4 n. C 500 MHz 16. 8 n. C 333 MHz 25. 2 n. C 250 MHz 33. 6 n. C DB linac length (final stage)

(1) No phase modulation Imag • Real Decelerating Accelerating 2�� Imag Voltage [a. u. ] 2�� Real Voltage [a. u. ]

(1) No phase modulation for CLIC final stage: • Imag Real Decelerating Accelerating Minimum accelerating voltage Maximum accelerating voltage Parameters Value Acc. Length 100 Km External Q 3100 M R/Q per length 255 μΩ/m Klystron power 74. 4 MW CW Klystron amount 93 * 800 KW Cryogenics power 3. 28 GW Total AC power 3. 4 GW

(2) Concept of Linear phase modulation 2�� +�� Voltage [a. u. ] 2�� +��

(2) Beam loading of Linear phase modulation Third bunch Second bunch First bunch Imag Real Imag Real Nth bunch Imag General solution (Radius of a circle) Particular solution (centre point of a circle) Real

Imag Voltage [a. u. ] (2) Beam loading circle of Linear phase modulation Imag Real Voltage [a. u. ] Decelerating Real Accelerating

Imag Voltage [a. u. ] Imag Real Voltage [a. u. ] (2) Beam loading circle of Linear phase modulation Minimum cavity store energy Decelerating Real Accelerating

(2) Linear phase modulation for CLIC final stage Imag Beam loading circle 2�� Real Minimum Accelerating Voltage Maximum Accelerating Voltage Parameters Value Acc. Length 8. 8 Km Frequency shift 321 Hz R/Q per length 0. 091 Ω/m External Q 222 M Klystron power 70. 2 MW CW Klystron amount 89 * 800 KW Cryogenics power 233 MW Total AC power 338 MW

(2) Concept of variable phase modulation

• A proper phase modulation during beam time is able to accelerate all bunches with same voltage. Imag Voltage [a. u. ] (3) Variable phase modulation for constant voltage Real Voltage [a. u. ] Decelerating Accelerating Voltage [a. u. ] Real

(3) Variable phase modulation for constant voltage Imag Real R/Q = 100% of KEK-B

(3) Tuner speed of variable phase modulation Imag Real Decelerating Accelerating R/Q = 100% of KEK-B

(3) Tuner speed limit of variable phase modulation Parameters 1 MHz/ms 100 KHz/ms Acc. Length 2. 16 Km 2. 5 Km Frequency range 12. 7 MHz 3. 2 KHz R/Q per length 29. 76 Ω/m 8. 37 Ω/m External Q 34 M 46 M Klystron power 76. 2 MW CW 72. 8 MW CW Klystron amount 96 * 800 KW 91 * 800 KW Cryogenics power 36. 8 MW 48. 6 MW Total AC power 151 MW 158 MW

(3) Stability of variable phase modulation • For 100 KHz/ms (1 MHz/ms) tuner speed, to order to achieve < 1% energy flatness, require: - Frequency calibration error < 0. 2% (0. 07%) - Cavity resonant frequency vibration < 6000 Hz (500 Hz) - Initial gradient change < 0. 3% (0. 08%) - Initial phase shift < 0. 06° (0. 04°) For 100 KHz/mm tuner speed For 1 MHz/mm tuner speed

(3) Variable phase modulation for stage 1 • Limit ~ 1 MHz/ms. • Klystron power is 12. 5% as final stage. • Length & Cryogenics power is 25% as final stage. • The cavity used for final stage is not optimum for first stage, but still OK. Parameters Stage 1 Final stage Acc. Length 495 m 2. 16 Km Frequency range 5. 3 MHz 12. 7 MHz R/Q per length 29. 76 Ω/m External Q 93 M 34 M Klystron power 8. 81 MW CW 76. 2 MW CW Klystron amount 11 * 800 KW 96 * 800 KW Cryogenics power 12. 2 MW 36. 8 MW Total AC power 25. 4 MW 151 MW

(4) Hybrid-linear phase modulations Fundamental structure Phase shift over all bunch = 140° Beam Imag Beam loading circle 2�� Real Harmonic structure Phase shift over all bunch = 360°

(4) Phase shift limit for Fundamental structure Imag Beam loading circle 2�� Real

(4) Hybrid-linear phase modulations for CLIC final stage • phase shift ↑ , Spare energy ↓, Length and cryogenics power of fundamental structure ↓. • phase shift ↑ , accelerating voltage fluctuation ↑, Length and cryogenics power of harmonic structure ↑. • Optimum solution: R/Q = 4 Ω/m , �� = 70°.

(4) Harmonic modes Fundamental structure Imag Matching circle 1 st harmonic structure Imag Length = 2054 m Frequency shift = 2. 57 KHz Imag Length = 123. 8 m Frequency shift= 7. 153 KHz Length = 23. 8 m Frequency shift = 14. 286 KHz 720° 360° �� 3265 Me. V 2 nd harmonic structure 140° �� 598 Me. V �� 66 Me. V Real Decelerating Accelerating

(4) Hybrid-linear phase modulations for CLIC final stage Parameters Final stage Acc. Length 2. 235 Km • To get 1% voltage flatness (maximum-minimum < 1%*average), 40 th order harmonic compensation is needed. Frequency shift 2. 57 KHz R/Q per length 4. 0 Ω/m • More than 10 th high-order harmonic structures is too short to be built. External Q 30. 3 M Klystron power 82. 6 MW CW • More than 4 th high-order harmonic structures need few input power. Consider solid state power source. Klystron amount 104 * 800 KW Cryogenics power 39. 1 MW Total AC power 164 MW

(4) Stability study • This system works fine with any Qe (support all power feeding scheme)->Normal conducting for Harmonic structures? ? ? • To order to achieve < 1% energy flatness gain, require: - Frequency calibration error < 0. 8% - Cavity resonant frequency vibration < 3000 Hz - Initial gradient change < 1. 3% - Initial phase shift < 0. 2°

(4) Hybrid-linear phase modulations for CLIC first stage • Almost every thing is 12. 5% percent of the final stage. • R/Q of fundamental and harmonic structures are 160 and 400 Ω/m (Huge different from final stage). • Upgrade plan : need to change cavities? Parameters Stage 1 Final stage Acc. Length 0. 3 Km 2. 235 Km Frequency range 20 KHz 2. 57 KHz R/Q per length 200 Ω/m 4. 0 Ω/m External Q 32. 2 M 30. 3 M Klystron power 9. 95 MW CW 82. 6 MW CW Klystron amount 13 * 800 KW 104 * 800 KW Cryogenics power 5. 67 MW 39. 1 MW Total AC power 21. 6 MW 164 MW

(4) Upgrade idea? Parameters Stage 1 Final stage • If energy storage sphere is allowed, the upgradation will be much easier. Acc. Length 0. 3 Km Frequency range 20 KHz 2. 57 KHz R/Q per length 200 Ω/m 28 Ω/m External Q 32. 2 M 30. 3 M • Main cavity geometry is not changing, R/Q from 200 Ω/m → 28 Ω/m Klystron power 9. 95 MW CW 80 MW CW • Length is almost not changed. Klystron amount 13 * 800 KW 100 * 800 KW Cryogenics power 5. 67 MW 39. 5 MW Total AC power 21. 6 MW 160 MW • For energy store per length 700 J/m → 5000 J/m • Works for multiple linear phase modulations. For variable phase modulation, tuner is hard to design. Final stage Stage 1 Upgrade Main cavity Energy storage sphere

Summary of Beam loading issue Stage First stage Final stage Scheme Variable phase modulation Hybridlinear phase modulation Variable phase modulation Hybrid-linear phase modulation Acc. Length 0. 3 Km 495 m 0. 3 Km 2. 16 Km Frequency range/shift 20 KHz 5. 3 MHz 2. 57 KHz 12. 7 MHz R/Q per length 200 Ω/m 29. 76 Ω/m 28 Ω/m 29. 76 Ω/m External Q 32. 2 M 93 M 30. 3 M 34 M Klystron power 9. 95 MW CW 8. 81 MW CW 80 MW CW 76. 2 MW CW Klystron amount 13 * 800 KW 11 * 800 KW 100 * 800 KW 96 * 800 KW Cryogenics power 5. 67 MW 12. 2 MW 39. 5 MW 36. 8 MW Total AC power 21. 6 MW 25. 4 MW 160 MW 151 MW Power feeding Only CW All Idea Energy fluctuation 0 4%

Summary of Beam loading issue Length pgrade complexity Linear phase modulation No phase modulation Klystron power Variable phase modulation ncy control Power feeding complexity Upgrade complexity Instablilty ency control Power feeding complexity Cryogenics Length Advantage: efficiency, less klystron power, small beam voltage fluctuation. Disadvantage: Longer length and more cryogenics power, need high Qe, need very high accuracy control to frequency shifter. Voltage fluctuation Beam dynamics Klystron power complexity Hybrid linear phase modulation Advantage: support low Qe, shorter length and easier upgradation if energy Cryogenics store cavity is possible. Disadvantage: large beam energy fluctuation, more difficulty in beam dynamic design. Need many kind of Voltage fluctuation harmonic structures and more input power.

New idea? 500 MHz deflecting cavity Each drive beam sub pulse (length : 240 ns) 16. 8 n. C each … 4 ns … … 4 ns 2 ns 12 GHz deflecting cavity Each drive beam sub pulse (length : 240 ns) 8. 4 n. C each … 2 ns + 1/24 ns … 2 ns - 1/24 ns 2 ns