News from TBTS International Workshop on Future Linear Colliders, Ganada, Spain, 2011, Alexey Dubrovskiy 27.09.11

Outlines Layout Deceleration Acceleration Improvements PETS & RF components processing TD24 processing Breakdown kick measurements “Flash box” Proposal Alexey Dubrovskiy LCWS2011 27.09.11 2

CTF & TBTS layout Alexey Dubrovskiy LCWS2011 27.09.11 3

Deceleration & RF Recirculation Alexey Dubrovskiy LCWS2011 RF extraction and recirculation model agrees with RF measurements 27.09.11 * Eric Adli (University of Oslo) 4 4

Deceleration & RF Recirculation Alexey Dubrovskiy LCWS2011 Extracted RF power measurements agree with beam energy measurements apart of a calibration factor. 27.09.11 * Eric Adli (University of Oslo) 5 5

PETS RF power extraction Measured RF power extraction MW CLIC requirement Alexey Dubrovskiy LCWS2011 ns The extracted RF from the PETS exceeds the CLIC requirement by about a factor 2 in power. 27.09.11 6

Accelerating structure in 2010 Alexey Dubrovskiy LCWS2011 * Oleksiy Kononenko (CERN) 10 Mhz structure detuning was confirmed during the winter shutdown in Jan 2011. The deformation could appear when clamping the cooling circuit onto the structure. The structure was retuned and it was put back. In spring 2011 RF measurements showed the right tuning frequency. 27.09.11 * Jiaru Shi (CERN) 7

Acceleration 8 Alexey Dubrovskiy LCWS2011 27.09.11 RF in RF out Accelerating structure Beam profile monitor Alexey Dubrovskiy LCWS2011 With RF No RF The acceleration of 145 MeV/m has been achieved. (CLIC acc.g. is 100 MV/m) 27.09.11 8 8

RF measurements Estimated Acceleration from Diodes Drive beam PETS 12GHz PETS output Loop output Alexey Dubrovskiy LCWS2011 ACS output Estimated Acceleration from IQs ACS input Probe beam TD24_vg1.8_disk - RF Diode & IQ measurements All Diode and PETS and Loop output IQ signals are consistent with acceleration. 27.09.11 9

CTF3 night operation Alexey Dubrovskiy LCWS2011 Successful run over nights with the stable beam conditions allowed to measure breakdown rates of RF components. 27.09.11 11 10

BD detection Drive beam PETS 12GHz Probe beam TD24_vg1.8_disk PETS output Loop output ACS output ACS input Probe beam Alexey Dubrovskiy LCWS2011 TD24_vg1.8_disk - RF Diode & IQ measurements of forward and reflected RF Faraday cup Photomultiplier Breakdowns in the recirculation loop are detected only from the reflected power (Pref / Pfwd > ~15%). Breakdowns in attenuator and the waveguide are detected from the missing energy (Utran / (Ufwd * transmission factor) > 15%) Breakdowns in the ACS are detected from the reflected power, the missing energy, the Faraday cup and the photomultiplier. 27.09.11 10 11

Illustration of BDs PETS extracted PETS reflected Attenuated forward Attenuated reflected BD without reflection Alexey Dubrovskiy LCWS2011 ACS reflected ACS forward BD in the waveguide ACS transmitted Drive beam current 27.09.11 No BD 12

PETS: Processing Vacuum level PETS peak power Pulse length at 75% of pp Pulse length at 90% of pp Alexey Dubrovskiy LCWS2011 Number of BD BDR 27.09.11 13

Attenuator: Processing PETS peak power Attenuated peak power Pulse length at 75% of pp Pulse length at 90% of pp Alexey Dubrovskiy LCWS2011 Number of BD BDR 27.09.11 14

Waveguide: Processing Peak power Pulse length at 75% of pp Pulse length at 90% of pp Alexey Dubrovskiy LCWS2011 Number of BD BDR 27.09.11 15

TD24: parameters 42.2 TD24_vg1.8_disk 120o/ cell comments f [GHz] 11.995 S12 0.6542 tf [ns] 64.55 QCu 5732 Gradient averaged over all cells V26 [V]@Pin = 1 W 3340 2 matching +24 regular cells Lacc = 227.7 mm, G26 [V/m]@Pin = 1 W 14661 Pin [MW]@<G26=100MV/m> 46.5 Gradient averaged over regular cells only V24 [V]@Pin = 1 W 3078 24 regular cells only Lacc = 200.0 mm, G24 [V/m]@Pin = 1 W 15390 Pin [MW]@<G24=100MV/m> 42.2 Alexey Dubrovskiy LCWS2011 27.09.11 * A. Grudiev, 25/03/10 16

TD24: Summary of processing Period Pulses Number of BD 2010 1.5 MPulses 40 kBD 2011 beginning 250 kPulses 2.5 kBD 2011 summer 608 kPulses 10 kBD Total 2.4 MPulses 53 kBD This period is considered in the following slides Alexey Dubrovskiy LCWS2011 * At the beginning of 2011 the ACS was taken out and retuned 27.09.11 17

TD24: Processing Forward peak power Vacuum level Pulse length at 75% of pp Pulse length at 90% of pp Alexey Dubrovskiy LCWS2011 Number of BD BDR 27.09.11 18

Explicit BDR measurements bdpppm Alexey Dubrovskiy LCWS2011 MV / m BDR is scaled to a pulse length of 160ns: vertical lines: slim - τ6 and bold - τ3. Horizontal bold lines show the standard deviation of the accelerating gradient variation during the period. 27.09.11 19

TD24: 3 Periods Forward peak power Vacuum level 1 2 3 1 2 3 Periods Pulse length at 75% of pp Pulse length at 90% of pp Alexey Dubrovskiy LCWS2011 Number of BD BDR 27.09.11 20

BDR scaling low for traveling wave structures BDR scaling low for any pulse: BDR ~ (∫ E(t)s1/s2 dt)s2 (E - field and s1,s2 – const.) BDR scaling low for a rectangular pulse (E(t)=Ec) of a pulse length of τ: BDR ~ Ecs1τs2 (Ec and τ – const.) In case if the s2/s1=4, the breakdown rate strongly depends on the pulsed surface heating. This allows to normalize any pulse to a certain gradient or a pulse length: 1) Normalization low to the rectangular pulse of a pulse length of 160ns: Ec = (∫E(t)s1/s2 dt / 160)s2/s1 Alexey Dubrovskiy LCWS2011 2) Normalization low to the rectangular pulse of an accelerating gradient of 100 MV/m: τ = ∫E(t)s1/s2 dt / 100 s1/s2 s1=30, s2=5 s1=12, s2=3 27.09.11 Yellow lines – forward power; red lines – Ec low scaling; blue lines – τ low scaling. 21

TD24: Accelerating gradient vs BDR From data fitting: Period 1: Ec ~ τ1/3.7 Period 2: Ec ~ τ1/3.4 Period 3: Ec ~ τ1/3.9 Alexey Dubrovskiy LCWS2011 BDR scaling low for rectangular pulses: BDR ~ Ecs1τs2 (Ec and τ – const.) Normalization low to the rectangular pulse of a pulse length of 160ns: Ec = (∫E(t)s1/s2 dt / 160)s2/s1 27.09.11 22

TD24: Pulse length vs BDR From data fitting: Period 1: Ec ~ τ1/3.9 Alexey Dubrovskiy LCWS2011 BDR scaling low for rectangular pulses: BDR ~ Ecs1τs2 (Ec and τ – const.) Normalization low to the rectangular pulse of an accelerating gradient of 100 MV/m: τ = ∫E(t)s1/s2 dt / 100s1/s2 27.09.11 23

TD24: Stress vs BDR bdpppm MV / m Alexey Dubrovskiy LCWS2011 MV / m BDR scaling low for rectangular pulses and constant temperature: BDR ~ exp(a Ec2) (Ec– const.) * Flyura Djurabekova (25.05.2011) Normalization low to the rectangular pulse of a pulse length of 160ns: Ec = (∫E(t)4 dt / 160)1/4 27.09.11 24

TD24: Pulsed surface heating Alexey Dubrovskiy LCWS2011 27.09.11 25

TD24: Breakdown distribution Alexey Dubrovskiy LCWS2011 27.09.11 26

TD24: Vacuum level Alexey Dubrovskiy LCWS2011 27.09.11 27

Breakdown kick measurement (0.46, 1.63) (1.43 3.02) Beam kick on OTR screen 1.7 mm kick angle ≈ 0.4 mrad Alexey Dubrovskiy LCWS2011 * Andrea Palaia (Uppsala University) Probe beam ~194 MeV ACS OTR 0.4 mrad 27.09.11 28

FLASH box is installed ACS Flash box Probe beam line “Flash box” is installed in TBTS just before the accelerating structure. It will allow to detect particles emitted during BD and to estimate its energies. All plates in the “Flash box” detect something during a BD in ACS. This study is still going on. There are three consecutive pulses illustrated on each picture. Only the pulse shown with blue lines has a BD in the ACS. ACS ref power ACS fwd power ACS tran power Drive beam current Alexey Dubrovskiy LCWS2011 Some signals from FLASH plates 27.09.11 * Tomoko Muranaka (Uppsala University) 29

Proposal: Mode of Operation TD24 mode of operation: The increase in power provokes a BD. The reduction in power reduces the probability of a BD. Pr(BD | Pi-1<Pi) / Pr(BD) = 1.14 Pr(BD | Pi-1>Pi) / Pr(BD) = 0.86 CLIC mode of operation could be in two phases: Normal two beam operation. (many pulses 103-105) The probe beam is switched off and the PETS peak power is increased (using the ON/OFF mechanism?). This will allow to inhibit several BDs at different places at the same time. Hence the ACS and RF system BDR limitation can be relaxed. (a few pulses <0.1%) Alexey Dubrovskiy LCWS2011 Systematic experiments are needed in order to estimate the effectiveness of such mode of operation. The result of such experiments can help to answer on the important question on “memory” of the structure. 27.09.11 30

Summary The PETS deceleration and power extraction models have been validated with RF and beam measurements. It has been measured that PETS can extracted two times higher power > 260MW than CLIC needs. The TD24 has been retuned. And an acceleration gradient of the probe beam has been measured with beam at 145MeV/m, which is above the CLIC requirement 100MeV/m. This result agrees with the RF measurements. The major limitation to go beyond this values is the RF power splitter, which is already taken out. And the recirculation scheme will be replaced by the PETS ON/OFF mechanism. The TD24 breakdown rate has been measured down to 10-4. The scaling low is estimated as ~E12τ3 in stead of the expected scaling low E30τ3. This is an indication that the pulsed surface heating plays significant role in BDR. There is a “hot” cell or region in TD24, where BDs happen more often. The measured vacuum activity indicates that it can be a change for CLIC. More study is needed. Breakdown kick has a strong impact on the probe beam. The “flash box” is installed and I hope it will show new results soon. There were proposed a generalization BDR scaling low and a new mode of operation of ACSs, which might help to relax the CLIC BDR limitation from 10-7 up to between 10-5 and 10-6. Alexey Dubrovskiy LCWS2011 27.09.11 31

Appendix: TD24 Gradient in 24 regular cells Average unloaded of 100 MV/m Average loaded of 100 MV/m Number of regular cells: Nc 24 Bunch population: N 3.72x109 Number of bunches: Nb 312 Bunch separation: Ncycl 6 rf cycles * A. Grudiev, 25/03/10