Transcript ILC Damping Rings: Configuration Status and R&D Plans Andy Wolski Lawrence Berkeley National Laboratory January 19, 2006

ILC Damping Rings: Configuration Status and R&D Plans
Andy Wolski
Lawrence Berkeley National Laboratory
January 19, 2006
Baseline Configuration
Item
Baseline
Alternatives
Circumference
(e+) 26 km
(e-) 6 km
1. (e+) 6 km
2. (e+) 17 km
Beam energy
5 GeV
Injected emittance & energy spread 0.09 m-rad & 1% FW
0.045 m-rad & 2% FW
Train length (bunch charge)
2700 (2×1010) - 4050 (1.3×1010)
Extracted bunch length
6 mm - 9 mm
Injection/extraction kicker
technology
Fast pulser/stripline kicker
1. RF separators
2. Fourier pulse compressor
Wiggler technology
Superconducting
1. Normal-conducting
2. Hybrid
Main magnets
Electromagnetic
Permanent magnet
RF technology
Superconducting
Normal conducting
RF frequency
500 MHz
(650 MHz)
Vacuum chamber diameter,
arcs/wiggler/straights
50 mm/46 mm/100 mm
2/25
Top Priority: Baseline lattice design by end of March 2006
Circumference
6476.7163 m
Energy
5 GeV
RF frequency
500 MHz
Harmonic number
Transverse damping time e+ (e-)
10802
<25 ms (<50 ms)
Normalized natural emittance
5 µm
Equilibrium bunch length
6 mm
Equilibrium energy spread
<0.13%
Momentum compaction
~ 4×10-4
Damping wiggler peak field
1.67 T
Damping wiggler period
0.4 m
Energy acceptance
||<0.5%
Dynamic aperture
Ax+Ay<0.09 m-rad (up to ||<0.5%)
There are additional specifications on tunes and optics…
3/25
Design studies of dogbone alternative will continue
Circumference
Energy
RF frequency
Harmonic number
Transverse damping time e+ (e-)
17227.9195 m
5 GeV
650 MHz
37353
<25 ms (<50 ms)
Normalized natural emittance
5 µm
Equilibrium bunch length
6 mm
Equilibrium energy spread
<0.13%
Momentum compaction
~ 1.5×10-4
Damping wiggler peak field
1.67 T
Damping wiggler period
0.4 m
Energy acceptance
||<0.5%
Dynamic aperture
Ax+Ay<0.09 m-rad (up to ||<0.5%)
4/25
Baseline lattice specification allows flexibility in fill patterns
Ring circumference [m]
6476.7163
Harmonic number
10802
Ring RF frequency [MHz]
500
Linac RF frequency [GHz]
1.3
Linac pulse length [ms]
0.97
Linac bunch spacing [linac RF wavelengths]
468
390
351
312
234
Linac bunch spacing [ring RF wavelengths]
180
150
135
120
90
360.00
300.00
270.00
240.00
180.00
Linac bunch spacing [ns]
Ring bunch spacing [linac RF wavelengths]
5.2
Ring bunch spacing [ring RF wavelengths]
2
Ring bunch spacing [ns]
4.00
Bunches per train
45
Number of bunch trains
60
72
80
90
120
Gaps per train
45
30
22.5
15
0
Gap length [ns]
184.00
124.00
94.00
64.00
4.00
Total number of bunches
2700
3240
3600
4050
5400
Particles per bunch [×1010]
2.07
1.73
1.56
1.38
1.045/25
Alternative lattice specification also allows flexibility in fill patterns
Ring circumference [m]
17227.9195
Harmonic number
37353
Ring RF frequency [MHz]
650
Linac RF frequency [GHz]
1.3
Linac pulse length [ms]
1.03
Linac bunch spacing [linac RF wavelengths]
540
360
180
Linac bunch spacing [ring RF wavelengths]
270
180
90
415.38
276.92
138.46
Ring bunch spacing [linac RF wavelengths]
18
12
6
Ring bunch spacing [ring RF wavelengths]
9
6
3
13.85
9.23
4.62
6
9
18
Linac bunch spacing [ns]
Ring bunch spacing [ns]
Bunches per train
Number of bunch trains
415
Gaps per train
12
Gap length [ns]
60.00
Total number of bunches
2490
3735
7470
Particles per bunch [×1010]
2.25
1.50
0.75 6/25
ILC Damping Rings R&D Tasks List is in development
1.
Parameter specifications and system interfaces
1.1 Injected beams
1.2 Extracted beams
1.3 Fill patterns and timing issues
2.
Beam dynamics
2.1 Single-particle dynamics
2.2 Multi-particle dynamics
3.
Technical subsystems
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
Injection/extraction kickers
Damping wiggler
Main magnets
Orbit and coupling correction
RF system
Vacuum system
Fast (bunch-by-bunch) feedback system
Instrumentation and diagnostics
7/25
ILC Damping Rings R&D Tasks List: Excerpt
2. Beam dynamics
2.1 Single-particle dynamics
2.1.1 Lattice design
2.1.1.1 Lattice design for 6 km baseline positron damping rings
Produce a lattice design for the 6 km baseline positron damping rings. The lattice should
meet the specifications for damping time, equilibrium emittance, acceptance etc. and
include all major subsystems, including injection/extraction sections, orbit and coupling
correction systems, RF cavities etc. The circumference should be around 6 km, and should
allow for a variety of different fill patterns (different numbers of bunches) without changes
in circumference or RF frequency.
Priority/Need: High priority. Required for Reference Design Report, and to allow
dynamics studies, engineering designs and costing.
Deadline: March 31, 2006
Experimental facilities: None
Investigators: Louis Emery (ANL), Aimin Xiao (ANL), Yi Peng Sun (IHEP)
8/25
Comments on the R&D Tasks List
The intention is to coordinate activities through a working document
that lists R&D objectives, and that can be periodically revised and
updated.
Short-term and long-term (ongoing) goals are included.
Objectives are ideally stated in terms of deliverables with deadlines.
Objectives should be developed in consultation between the
investigators, the DR Area System Leaders. We want to avoid
micromanaging the R&D process.
Resources are widely distributed between different laboratories. This
approach provides a coherent framework for collaboration.
We are still in the very early stages. We hope that this approach
provides sufficient flexibility to respond to changing project needs.
9/25
R&D Tasks List Summary Spreadsheet (Excerpt)
10/25
Links
Final version of Damping Rings Configuration Recommendation Summary Report:
http://www.desy.de/~awolski/ILCDR/DRConfigurationStudy.htm
Final draft of Damping Rings Configuration Studies Report (300 pages):
http://www.desy.de/~awolski/ILCDR/DRConfigurationStudy.htm
Present version of Damping Rings R&D Tasks List:
http://www.desy.de/~awolski/ILCDR/
Present version of Damping Rings Lattice Specifications:
http://www.desy.de/~awolski/ILCDR/
11/25
ILC Damping Rings: Fill Patterns and Timing Issues
Andy Wolski
Lawrence Berkeley National Laboratory
January 19, 2006
General comments
We assume that there will be a benefit in being able to vary the bunch
charge and fill pattern in the damping rings.
Lower charge benefits single-bunch instabilities (e.g. microwave).
Fewer bunches can allow longer gaps in some schemes, with potential benefits
for electron cloud and ion effects: the benefits need to be better understood.
Effects at the IP drive for lower charge (down to 1×1010 particles per bunch).
Optimization during commissioning and operation will probably be of value.
Designing for flexibility in the number of bunches places strong
constraints on the damping rings’ circumference and the lengths of
other systems in ILC.
There are many solutions: here, we consider just two possible
schemes.
We assume that gaps in the bunch train in the linac are to be avoided. If gaps are
acceptable, this opens up further possibilities.
13/25
Scheme A: “Fixed bunch spacing” (increase no. of bunches by reducing the gaps)
Extraction kicker fires regularly at intervals of Tlinac
Bunches numbered “1” are extracted on first turn;
bunches numbered “2” are extracted on second turn, etc.
We always extract over a fixed number of turns, so linac RF pulse length does not change.
RF buckets corresponding to extracted bunches are filled immediately by bunches arriving at
regular intervals of Tlinac
1
2
3 4
1
5
2
3 4
1
5
2
3 4
1
5
2
3 4
5
3 4
5
3 4
5
bunch separation in linac = Tlinac
1
2
3 4
5
1
2
3 4
5
1
2
3 4
5
1
2
3 4
5
1
2
bunch separation in linac = Tlinac
1
2
3 4
5
1
2
3 4
5
1
2
3 4
5
1
2
3 4
5
1
2
3 4
5
1
2
3 4
5
1
2
3 4
5
1
2
bunch separation in linac = Tlinac
14/25
Example A1: A 6476 m damping ring with 500 MHz RF frequency
Numbers in bold face must be integers in a valid solution.
Input values are in red; values in black or blue are calculated from these.
Grey cells indicate an invalid solution.
15/25
Example A2: A 6643 m damping ring with 650 MHz RF frequency
Numbers in bold face must be integers in a valid solution.
Input values are in red; values in black or blue are calculated from these.
16/25
Scheme B: “Fixed gaps” (increase no. of bunches by reducing the bunch spacing)
Extraction kicker fires regularly at intervals of Tlinac
Bunches numbered “1” are extracted on first turn;
bunches numbered “2” are extracted on second turn, etc.
We always extract over a fixed number of turns, so linac RF pulse length does not change.
RF buckets corresponding to extracted bunches are filled immediately by bunches arriving at
regular intervals of Tlinac
1
3
2
5
4
1
6
3
5
bunch separation in linac = Tlinac = 24 ring RF buckets
1
2
3
4
5
6
1
2
3
4
5
6
1
2
3
4
5
6
bunch separation in linac = Tlinac = 12 ring RF buckets
17/25
Example B: A 16.2 km damping ring with 500 MHz RF frequency
Numbers in bold face must be integers in a valid solution.
Input values are in red; values in black or blue are calculated from these.
18/25
Pros and cons…
Scheme A: Fixed bunch spacing
+ Provides greater flexibility than fixed gaps: more possibilities for numbers of
+
-
bunches (e.g. 2700, 3240, 3600, 4050 or 5400 in example A1).
Can be applied in both 6 km and 16 km damping rings…
…but gaps vanish for largest number of bunches in 6 km rings.
“Local current” increases as number of bunches decreased (bunch charge
increases) – may adversely affect ions or electron cloud effects.
Scheme B: Fixed gaps
- Limited flexibility: probably only two options for number of bunches
(e.g. 3010 or 6020 bunches in example B).
- Realistically requires a 16 km ring.
+ Fixed gaps means that ion clearing should be as effective at either number of
bunches.
+ Local current remains constant as number of bunches is changed.
19/25
Lengths of different sections in ILC cannot be chosen arbitrarily
e- damping ring
e+ damping rings
IP
e-
source
e-
linac
e+ source
L1
e-
linac
e+ linac
L2
L3
L4
If L1, L2, L3 and L4 are all integer multiples of the bunch separation in the linacs, then by
“time invariance” we see that bunches are always at the right place at the right time.
To retain flexibility in the fill patterns, we need to look for the least common multiple (LLCM)
of the various linac bunch separations, Llinac.
L1, L2, L3 and L4 should then all be integer multiples of LLCM.
20/25
Lengths of sections are determined by linac bunch separation
e- damping ring
e+ damping rings
IP
e-
source
e-
linac
e+ source
L1
snapshot of bunch positions
e-
linac
e+ linac
L2
L3
L4
If L1, L2, L3 and L4 are all integer multiples of the bunch separation in the linacs, then by
“time invariance” we see that bunches are always at the right place at the right time.
To retain flexibility in the fill patterns, we need to look for the least common multiple (LLCM)
of the various linac bunch separations, Llinac.
L1, L2, L3 and L4 should then all be integer multiples of LLCM.
21/25
We can retain flexibility by choosing lengths carefully
e- damping ring
e+ damping rings
IP
e-
source
e-
linac
e+ source
L1
e-
linac
e+ linac
L2
L3
L4
In example 1, the bunch separations in the linac are Tlinac = (360, 300, 270, 240, 180) ns.
LCM(360, 300, 270, 240, 180) = 10800, or LLCM = 3237.8 m. This is inconveniently large.
LCM(360, 300, 270, 240, 180) = 2160, or LLCM = 647.55 m. This is better.
LCM(360, 300, 270, 240, 180) = 720, or LLCM = 215.85 m. This could be appropriate for the 2nd IP.
22/25
Example, using 6476 m damping ring with 500 MHz RF frequency
L1
L2
L3
L4
L1
L2
L3
6×647.55 = 3885.3 m
10×647.55 = 6475.5 m
L4
16×647.55 = 10360.8 m 33×647.55 = 21369.2 m
Tlinac
L1/(c×Tlinac)
L2/(c×Tlinac)
L3/(c×Tlinac)
L4/(c×Tlinac)
360 ns
36
60
96
198
300 ns
43.2
72
115.2
237.6
270 ns
48
80
128
264
240 ns
54
90
144
297
180 ns
72
120
192
396
Note: If we do not start e+ DR extraction before there are new e+ bunches arriving at the injection
point, then a number of e- bunches at the head of the train have nothing to collide with. We would
lose about 10% of the luminosity this way, compared to the case where all bunches collide.
23/25
Example, with 2nd IP
IP´
L1
L´2
L´3
IP
L4
L1
L´2
L´3
L4
6×647.55 = 3885.3 m
10×647.55 – 215.85
= 6259.65 m
16×647.55 + 215.85
= 10576.65 m
33×647.55 = 21369.2 m
Tlinac
L1/(c×Tlinac)
L´2/(c×Tlinac)
L´3/(c×Tlinac)
L4/(c×Tlinac)
360 ns
36
58
98
198
300 ns
43.2
69.6
117.6
237.6
270 ns
48
77.33
130.66
264
240 ns
54
87
147
297
180 ns
72
116
196
396
24/25
Final Remarks
If the damping ring circumference is chosen carefully, there is significant operational
flexibility (up to a factor of two) in the number of bunches in a full ILC bunch train.
There is little benefit in a 650 MHz RF system in the damping ring, compared to a 500 MHz
RF system, in terms of the flexibility in fill patterns.
In a ~ 6 km damping ring, operating with ~ 5400 bunches means eliminating any gaps. This
could cause problems with ions or electron cloud. The rings can still operate with ~ 4000
bunches, with gaps of 64 ns.
A damping ring circumference of ~ 17 km would allow retention of the gaps with a large
number of bunches.
Before a change to the baseline DR configuration is proposed (e.g. from 6 km to 17 km rings)
- the impact on the damping rings (ion effects, acceptance etc.) needs to be quantified;
- the benefits of lower bunch charge at the IP need to be quantified.
Lengths of other sections in the ILC (linacs, e+ transport lines, distance between IPs) must be
chosen carefully if operational flexibility in the numbers of bunches is desired.
There are many solutions. Some example have been shown; there may be better solutions. It
is not clear how to approach optimization of the parameters.
25/25