Post on 01-Feb-2022
Towards More Flexibility in Operation of the XFEL Linac
J. Sekutowicz October 25th, 2013
DESY
Outline
1. Introduction and motivation a. XFELs and their technologies b. Continuous wave (cw) and long pulse (lp) operation modes c. Limitations of DF for the XFEL linac
2. Cw and lp operation; 3 experiments a. Dynamic heat load vs. DF b. Dynamic heat load vs. Eacc c. Dynamic heat load for Large Grain Cryomodule
3. Final remarks a. Possible upgrade scenario b. Subsystems for cw/lp operation c. Summary
2 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
XFELs are based on LC technologies and therefore they have low Duty Factors (DF) and limited flexibility in time structure of the electron and photon beam
Facility LC-project & technology
f [GHz]
Energy [GeV]
RF-pulses Max DF
[%] Length [µs] Rep. Rate [Hz]
LCLS SLC nc 2.8 14.7 3 120 <0.04
SACLA JLC nc 5.7 8 3 60 <0.02
Swiss-FEL JLC nc 5.7 5.8 3 100 <0.03
XFEL TESLA sc 1.3 17.5 1300 10 1.30
3
1. Introduction and Motivation: a. XFELs and their technologies
The XFEL facility, because it is driven by sc linac, has potential for substantially larger DFs and more flexibility.
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
1. Introduction and Motivation: a. XFELs and their technologies
Layout of the XFEL sc linac
E = 120 MeV, Slice energy spread: 50 keV Slice emittance: εx,y~1µrad σx,y < 0.8 mm
E= 17.5 GeV Slice energy spread: 1 MeV
Slice emittance: εx,y~1.4 µrad σx,y < 30 µm
101 cryomodules in total: 17 in the injector section (IS) and 84 in the main linac Each cryomodule houses eight 1.3 GHz 9-cell sc TESLA cavities.
4
σs= 2 mm
Ipeak= 50 A
σs= 0.02 mm
Ipeak= 5 kA
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
Inje
ctor
lina
c
4 cr
yom
odul
es
3rd
harm
onic
RF
sect
ion
Boos
ter L
inac
12 c
ryom
odul
es
Undulators
BC2
E=2 GeV
e- g
un
E=5MeV
BC1
Time structure of the XFEL nominal electron beam (sp, short pulse operation)
Nominal Energy GeV 17.5
Beam pulse length ms 0.65
Repetition rate Hz 10
Max. # of bunches per pulse 2700
Min. bunch spacing ns 240
Bunch charge nC ≤ 1
5
1. Introduction and Motivation: a. XFELs and their technologies
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
600 µs
100 ms 240 ns
~100 fs
XFEL will generate high average brilliance photon beam at very short λ:
1.6·1025 photons/0.1%bw/s/mm2/mrad2 @ 1 Å
Two additional features could make the XFEL photon beam even more attractive
An increased, to several µ-seconds, intra pulse distance between bunches, which will allow for less technically demanding detectors
A few kHz photon burst repetition rate, which will allow to use less expensive optical lasers (few kHz rep.-rate) for pump-and-probe experiments
For the nominal beam, these features will lead to substantially reduced number of bunches/s and significantly lower average brilliance.
6
1. Introduction and Motivation: a. XFELs and their technologies
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
1. Introduction and Motivation: b. Continuous wave (cw) and long pulse (lp) operation modes
We proposed (several years ago) additional operation modes;
Continuous wave (cw) operation for Eacc ≤ 7 MV/m Long pulse (lp) operation at Eacc > 7 MV/m with DF ≤ (7/Eacc)2 The bunch quality should be as high as for the nominal sp operation
7
Example of lp operation at Eacc = 14 MV/m with DF up to 25%
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
≥ 750 ms frep = 1Hz
~100 fs
1s
≤ 250 ms
4 µs, up to 0.5 nc
≥ 100 ms
~100 fs
≤ 33 ms
4 µs, up to 0.5 nc
The main XFEL linac will be split in 7 cryogenic-strings (CS = 12 cryomodules)
2.2 K forward 5 K forward 40 K forward
2-phase tube: 240 W (~20W/cryomodule) is the estimated limit for one CS
2 K, Gas Return Tube
80 K, Return 8 K, Return
1st limit: Heat load at 2K for each cryomodule should not exceed ca. 20 W
1. Introduction and Motivation: c. Limitations of DF for the XFEL linac
What are the technical and “practical” limits for DF ?
8 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
TESLA cavity was designed for ca. 1% DF (1992)
End groups (FPC and HOM couplers) are cooled by means of heat conduction
HOM coupler HOM coupler
FPC
9
1. Introduction and Motivation: c. Limitations of DF for the XFEL linac
2nd limit: Heating of the HOM couplers must not cause quenching of the end-groups
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
HOM antenna is exposed to the residual magnetic field of the FM
To reduce antennae heating all XFEL cavities will be equipped with high thermal conduction feedthroughs connected with copper braids directly to the 2-phase tube.
10
1. Introduction and Motivation: c. Limitations of DF for the XFEL linac 2nd limit: cont.,
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
Ti
Cu
Nb (RRR 400)
Sapphire
Mo
11
1. Introduction and Motivation: c. Limitations of DF for the XFEL linac 2nd limit: cont.,
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
High thermal conduction HOM feedthroughs with sapphire windows
HOM feedthrough with cable, thermal connection and load
Ti
Cu
Nb (RRR 400)
Sapphire
Mo
Other, “practical” limits
12
1. Introduction and Motivation: c. Limitations of DF for the XFEL linac
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
Existing Cryo-Plant High Duty Factor Operation
Capacity 2450 [W] (T=2K) 4980 [W] (T=1.8K)
3th limit: An upgrade of the cryogenic plant should be “doable”
Upgraded cryo-plant will have capacity of one unit at JLab
4th limit: New RF-sources will be added to klystrons used for the sp operation They should fit in the XFEL tunnel. We plan to have one RF-source/CM
IOT seems to be the best choice (at present): It is very compact, what makes it superior to solid-state amplifiers
It takes energy from the mains only when it generates RF-power. This makes IOT more efficient for the lp operation than a cw klystron
Other, “practical” limits, cont.
13
1. Introduction and Motivation: c. Limitations of DF for the XFEL linac
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
The second prototype will be delivered in fall 2013.
Parameter Unit Spec Measured (1stprototype)
Output P [kW] 120 85
Gain [dB] >21 22.3
Efficiency [%] >60 54
The first prototype of the IOT was built by CPI and delivered to DESY in 2009.
Goal: Measurement of dynamic heat load (DHL) vs. DF Technical conditions:
1. < Qload > = 1.5E7, 3 dB resonance width 87 Hz 2. Eacc= 5.6 MV/m 3. Only 3 cavities had new feedthroughs and new thermal connections 4. The measurements were done for DF = 38, 60, 75 and 100% (cw) 5. 7 cavities in operation (cavity #7 had detuned HOM coupler)
2. cw and lp operation; 3 experiments a. Dynamic heat load vs. DF
We equipped in 2011 Cryo-Module Test Bed at DESY with the IOT prototype Since May 2011 we tested 5 pre-series cryomodules in cw and lp modes
14
I. Example of the lp/cw run at 2K (cryomodule PXFEL3_1, June 2012)
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
Experiments with pre-series CMs at 1.8 and 2K (3 examples)
Measured dynamic heat load
15 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
0
5
10
15
20
25
12 AM 4 AM 9 AM 2 PM 7 PM 12 AM 4 AM
DHL [W]
Time [h]
DF=
75
%
DH
L=12
.4 W
Eacc
=0 M
V/m
DH
L=4W
DF=
60
%
DH
L=9.
7 W
DF=
38
%
DH
L=5.
2 W
cw
DH
L=16
.5 W
Eacc
=0 M
V/m
DH
L=5W
2. cw and lp operation; 3 experiments a. Dynamic heat load vs. DF
DF [%] 38 60 75 100
Estimated DHL [W] 4.2 6.5 8.3 10.7
Additional Heat / End group [W] 0.07 0.23 0.29 0.41
Conclusion: Following operations of the XFEL linac should be possible for 20W limit: cw operation at Eacc ≤ 6.1 MV/m ………. lp with DFs of ca. 38% at Eacc = 11.5 MV/m
16 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
11.5
8.1 7.1
6.1
0
4
8
12
0
8
16
24
20 40 60 80 100
Eacc [MV/m]
THL [W]
DF [%]
THL= DHL at 1.8K + static 4.5WMax Eacc for 20W THL budget
Eacc vs. DF at 1.8 K (scaled from test I) 2. cw and lp operation; 3 experiments a. Dynamic heat load vs. DF
Goal: Measurement of DHL vs. Eacc at 2K Technical conditions:
1. < Qload > = 1.5E7, 3 dB resonance width 87 Hz
2. Only 2 cavities had new feedthroughs and new thermal connections
3. The measurements were done for DF = 20%
4. Eacc = 7.4, 9.0, 9.8, 10.5 and 10.7 MV/m
17
II. Example of the lp run (cryomodule PXFEL2_3, May 2013)
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
Measured dynamic heat load
2. cw and lp operation; 3 experiments b. Dynamic heat load vs. Eacc
18 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
2. cw and lp operation; 3 experiments b. Dynamic heat load vs. Eacc
0
4
8
12
16
20
10 AM 12 PM 2 PM 5 PM 7 PM 10 PM 12 AM 2 AM
DHL [W]
Time [h]
E=7.4 MV/m DHL = 4.6 W
Eacc=0 MV/m DHL= 0.5W
E=9.0 MV/m DHL = 8.5 W
E=10.5 MV/m DHL=14.5 W
E=9.8 MV/m DHL= 11 W
E=10.7 MV/m DHL=16 W
Eacc [MV/m] 7.4 9 9.8 10.5 10.7
Estimated . DHL [W] 4.5 6.8 7.8 9.3 9.7
Additional Heat / End group [W] 0.01 0.1 0.2 0.32 0.39
19 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
2. cw and lp operation; 3 experiments b. Dynamic heat load vs. Eacc
20
40
60
80
100
16
18
20
22
24
6 7 8 9 10 11 12
DF [%]
THL [W]
Eacc [MV/m]
THL at 1.8KDF at 1.8K
DF vs. Eacc at 1.8 K (scaled from test II)
Conclusion: Following operations of the XFEL linac should be possible for 20W limit: cw operation for Eacc ≤ 7.8 MV/m ………. lp with DFs of ca. 24 % at Eacc = 11 MV/m.
Goal: Measurement of the DHL at 2K and 1.8K vs. Eacc and DF
Technical conditions:
1. < Qload > = 1.5E7, 3 dB resonance width 87 Hz
2. All cavities had new HOM feedthroughs and new thermal connections
3. 7 cavities had cells (not end-groups) made of LG-niobium, 1 of FG-niobium
4. DF range {13% - 100%}
5. Eacc range {5.7 MV/m - 14.7 MV/m}
20
III. Example of the cw/lp run with LG cryomodule (XM-3, Sept. 2013)
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
2. cw and lp operation; 3 experiments c. Dynamic heat load for Large Grain Cryomodule
1.E+10
2.E+10
3.E+10
4.E+10
0 4 8 12 16
Qo
Eacc [MV/m]
AC114 AC156 AC146 AC154AC157 AC158 AC151 AC152
21 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
XM-3 cavities: vertical tests at 2K (7 Large Grain +1 Fine Grain cavity)
2. cw and lp operation; 3 experiments c. Dynamic heat load for Large Grain Cryomodule
Measured dynamic heat load
22 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
2. cw and lp operation; 3 experiments c. Dynamic heat load for Large Grain Cryomodule
0
4
8
12
16
20
11.09.13 12.09.13 13.09.13 14.09.13 15.09.13 16.09.13
DHL [W]
Date
Operation at 1.8 K Operation at 2 K
We performed 23 tests with that cryomodule varying DF, T and Eacc
0
4
8
12
16
20
0:00 2:30 5:00 7:30 10:00 12:30 15:00 17:30
DHL [W]
Time [h]
Eacc = 7.04 MV/m DHL = 8.9 W
Eacc = 9.5 MV/m DHL = 16.1 W
23 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
2. cw and lp operation; 3 experiments c. Dynamic heat load for Large Grain Cryomodule
Test examples: cw operation at 1.8K and 2K for Eacc 7 MV/m and 9.5 MV/m
Eacc= 0 MV/m DHL=0W
Eacc = 7.04 MV/m DHL = 13.5 W
Operation at 2 K Operation at 1.8 K
0
4
8
12
16
9:00 12:00 15:00 18:00 21:00
DHL [W]
Time [h]
24 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
2. cw and lp operation; 3 experiments c. Dynamic heat load for Large Grain Cryomodule
Test examples, cont.: lp operation at 1.8K and Eacc = 14.7 MV/m
Eacc= 0 MV/m DHL=0.2 W
Eacc = 14.7 MV/m DF = 25%
DHL = 10.7 W
25 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
2. cw and lp operation; 3 experiments c. Dynamic heat load for Large Grain Cryomodule
Conclusion from run III : DF vs. Eacc for T = 1.8 K
37.4%
0
20
40
60
80
100
0 3 6 9 12 15
DF [%]
Eacc [MV/m]
DF for 20 W THL
DF demonstrated
26 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
2. cw and lp operation; 3 experiments c. Dynamic heat load for Large Grain Cryomodule
Comparison of cryomodules: cw operation at Eacc = 5.7 MV/m
PXFEL3_1 PXFEL2_3 XM-3 XM-3
Type of Nb FG FG LG LG # of cavities in operation 7 8 8 8 # of cavities with new HOM output 3 2 8 8 T [K] 2 2 2 1.8 Measured DHL [W] 19.5* 18.7 11.5 5.1 Ratio: M-DHL / (M-DHL of XM-3 at 2 K) 1.69 1.63 1 0.44 *scaled to 8 cavities
One must note here that we have not tested yet standard XFEL-type CM housing 8 FG cavities, all equipped with new HOM output lines.
To ensure bunch quality for cw/lp operations gradients in the injector section (IS) have to be as for the nominal sp operation
27
Gradients in the IS are > 7 MV/m, so we will need 136 low current 9-cell TESLA-like cavities operating cw at gradients up to 16 MV/m.
3. Final remarks a. Possible upgrade scenario
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
Inje
ctor
lina
c:
4 CM
E ac
c = 1
1 M
V/m
Boos
ter L
inac
: 12
CM
E ac
c = 1
5 M
V/m
E= 2 GeV
Inje
ctor
CM
E ac
c = 1
6 M
V/m
IS
BC2
e- g
un
BC1
Averaging results from the presented tests with FG pre-series cryomodules and assuming that
the injector section will be equipped with 136 new cw-cavities 12 out of 17 standard CMs from IS will be relocated to the end of ML
one can estimate end beam energies and DFs.
28
Operation mode Energy [GeV]
Eacc ML [MV/m]
Max DF [%]
sp 17.5 1.3 cw 7.6 7 100 lp 10 10 -> 35 lp 14 15 -> 15
Beam Energies and DFs for the scenario with new IS and 768 cavities in ML
J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
3. Final remarks a. Possible upgrade scenario
We may expect these numbers to be higher for the standard XFEL cryomodules, because they will have better cooling of end-groups.
R&D program at DESY for cw-operating TESLA like cavity.
29 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
3. Final remarks b. Subsystems for cw/lp operation
For the modified HOM coupler, H is lower by 50%, antenna is shorter, F-part has better shape for cooling.
Modeling of HOM-coupler with hidden antenna
Cour
tesy
D.
Kost
in, D
ESY
H= 0.022 A/m Peak H field on the antenna for the same stored energy
Antenna is “hidden” in the output tube
H= 0.045 A/m
R&D program at DESY for cw-operating TESLA like cavity, cont.
30 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
Copper model of 9-cell cw-cavity is almost ready to test HOM damping
Nb-prototype is scheduled for next year
Should we use LG niobium?
3. Final remarks b. Subsystems for cw/lp operation
R&D program at DESY for cw-operating TESLA like cavity, cont.
31 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
1.E+10
2.E+10
3.E+10
4.E+10
0 4 8 12 16
Qo
Eacc [MV/m]
AC112 AC113 AC115 AC117 AC122 Z93Z100 Z104 AC155 AC153 AC154 AC158
LG vs. FG comparison of vertical tests at 2.0 K for cavities chemically treated at DESY
<Qo> = 1.7·1010
<Qo> = 2.2·1010
3. Final remarks b. Subsystems for cw/lp operation
32 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
LG Vertical test at 1.8 K
2.E+10
4.E+10
6.E+10
8.E+10
0 4 8 12 16
Qo
Eacc [MV/m]
AC154 AC155 AC153 AC158
<Qo> = 4.1·1010
3. Final remarks b. Subsystems for cw/lp operation
R&D program at DESY for cw-operating TESLA like cavity, cont.
What is the benefit to use high Q cavities? Assumptions:
Linac has 140 cavities operating at 15 MV/m
7000 h operation per year
0.20 € for 1 kWh
10 years of operation
33 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
3. Final remarks b. Subsystems for cw/lp operation
R&D program at DESY for cw-operating TESLA like cavity, cont.
What is the benefit to use high Q cavities? Assumptions:
Linac has 140 cavities operating at 15 MV/m
7000 h operation per year
0.20 € for 1 kWh
10 years of operation
34 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
1.5E10; 24.7M€
1.7E10; 21.8M€
2.2E10; 16.8M€
2.8E10; 13.2M€
4.1E10; 9.0M€
0
10
20
30
1.E+10 2.E+10 3.E+10 4.E+10 5.E+10
Elect. Bill for Cryo of IS
[M€]
Qo
3. Final remarks b. Subsystems for cw/lp operation
R&D program at DESY for cw-operating TESLA like cavity, cont.
9 XF
EL L
G c
aviti
es
at 2
K, P
rep.
DES
Y
9 XFEL LG cavities at 1.8 K, Prep. DESY
24 XFEL FG cavities at 1.8 K, Prep. Indust.
Scaled !
24 X
FEL
FG
cav
ities
at
2 K
, Pre
p. In
dust
.
6 XF
EL F
G c
aviti
es
at 2
K, P
rep.
DES
Y
Seems that LG is much more attractive and can save operation costs, but…. Very recent results at Cornell and HZB showed that with a proper cool-down procedure one can enhance Qo of FG cavities by factor of 2. How should we proceed:
At first, we need to test the Cornell/HZB cool-down recipe to XM-3 cryomodule, to check if for LG material there is still some Qo improvement
Then, we should test FG cavities (AMTF) and 2-3 cryomodules, housing FG
cavities to verify the new cool-down procedure for the XFEL structures.
Having results of these experiments we will be able to make the decision on type of niobium.
35 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
3. Final remarks b. Subsystems for cw/lp operation
R&D program at DESY for cw-operating TESLA like cavity, cont.
36 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
3. Final remarks b. Subsystems for cw/lp operation
Other R&D programs towards cw/lp operation 1. All superconducting electron gun (with sc cathode) needs more attention.
Open questions: How to recover at 2K QE of the sc cathode demonstrated at 300K? How to integrate better cathode plug in the clean sc cavity?
2. 3-rd harmonic cavities operating cw will be developed in collaboration with FERMI.
1.E+09
1.E+10
1.E+11
0 20 40 60
Qo
Ecath [MV/m]
Baseline Test with Nb-plugTest with Pb-coated plug
Courtesy P. Kneisel, JLab
1. The experiments showed feasibility of more flexible operations for the XFEL
2. We have demonstrated:
Gradients for beam energy of 7.6 GeV in cw mode and 14 GeV in lp mode
Benefit of operation at 1.8 K Benefit to use LG material for the standard cool-down procedure
3. We need to test several SERIAL XFEL CRYOMODULES to determine more precisely relation: DF vs. Eacc for the main linac.
4. Following R&D programs are in “slow” progress: For new SRF electron source For cw-operating low current cavities For new RF-sources For LLRF stabilizing accelerating gradient for cw and lp operation
37 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
3. Final remarks c. Summary
Acknowledgements
I want to express my gratitude to all Colleagues contributing to the experiments and R&D programs:
DESY: V. Ayvazyan, J. Branlard, M. Ebert, J. Eschke, T. Feldmann, A. Gössel, D. Klinke, D. Kostin, M. Kudla, F. Mittag, W. Merz, W.-D. Möller, C. Müller, R. Onken, D. Reschke, I. Sandvoss, X. Singer, W. Singer, A. Sulimov
TUL: W. Cichalewski, A. Piotrowski, K. Przygoda
EICS GmbH: W. Jalmuzna
WUT: K. Czuba
NCBJ: M. Barlach, J. Lorkiewicz, R. Nietubyc, J. Szewinski,
JLab: G. Ciovati, P. Kneisel,
BNL: T. Rao, J. Smedley
38 J. Sekutowicz, Towards More Flexibility in Operation of the XFEL Linac, DESY, October 25th, 2013
Thank you for your attention