Transcript Bellittini_Risk

Cold versus Warm, parameters impacting LC
reliability and efficiency
contribution to the discussion on risk factors
Giorgio Bellettini, Seul ITRP meeting, August 11, 2004
Klystrons in Cold and Warm
(s = 500 GeV)
TESLA : 572 klystrons, peak power 10MW.
Acceleration efficiency: 1 klystron feeds 36 cavities providing 850 MeV
accelerating voltage to beam
NLC : 4064 Klystrons, peak power 75MW.
Acceleration efficiency: 8 klystrons feed 24 cavities providing 1000 MeV
accelerating voltage to beam
~8 times more klystrons (modulators, SLEDs) in Warm.
Power on beam : TESLA 226 KW/meter, NLC 42,900 KW/meter after bunch
compression
Power density on beam ~ 200 times larger in Warm
The klystron string of the Warm might turn out not be reliable enough
The power density of the Warm might turn out to fatigue the structures
Power efficiency in Cold and Warm (*)
(s = 500 GeV)
Total AC power for 2 linacs (cryo included) TESLA 95 MW, NLC 150 MW
Total plug to RF to linac beams efficiency: TESLA ~23%, NLC ~9%
Total lab AC power
Total beam to site power efficiency
TESLA 140 MW, NLC 195 MW (**)
TESLA ~16%, NLC ~7%.
The excess power of the Warm is an economical and a social risk.
•(*) ILCTRC Second Report (2003), Chapter 2, tables 3.6 and 3.19 megatables
•(**) Fermilab power ~ 55MW. Difference is ~FNAL.
Delivering luminosity for physics
The general risk factors in delivering useful
luminosity for physics were discussed in the
section on Energy and Luminosity.
A particular attention should be given to energy
scans since they would be essential to study the
properties of new particles.
Energy scanning with Cold and Warm
(s = 500 GeV)
NLC:
Beam bypasses at 50 and 150 GeV in each Linac. In measurements at
intermediate energies beams will have to travel along a varying number of offcavities before getting to the closest bypass. Besides tuning of the external beam
lines, re-tuning of the linac optics will be necessary each time since magnets will
have gone through different cycles.
TESLA:
RF gradients and magnet fields will be reduced to reduce the energy. The same
scaling law of the magnet fields will be valid at all energies.
Taking data at many energies might turn out to be very laborious with
Warm.
Backup slides follow
Parameter table
TESLA
JLC (C)
JLC/NLC
CLIC
RF Frequency in Main Linac (GHz)
1.3
5.7
11.4
30
Loaded Gradient (MV/m)
23.8
31.5
50
150
Q Unloaded
1010
9772
~9024
~3625
Shunt Impedance (MW/m)
107
54.1
81.2
~23.5
Klystron Peak Power (MW)
9.7
50
75
50
1370/1370
2.8/0.55
1.6/0.4
16.7/0.13
Filling Time (ms)
420
0.285
0.120
0.03
Total No. of Modulators
572
4276
508
448
Total No. of Klystrons
572
4276
4064
448
Cavity/Structure Length (m)
1.04
1.8
0.9
0.5
20592
8552
12192
7272
23.3
6.2
8.8
9.3
RF Pulse – before/after compr. (ms)
Total No. of Structures/Cavities
Plug to Beam Efficiency (%)
Parameter table
TESLA
JLC (C)
JLC/NLC
CLIC
RF Frequency in Main Linac (GHz)
1.3
5.7
11.4
30
Design Luminosity (·1034cm-2sec-1)
3.4
1.4
2.5/2
2.1
Linac Repetition Rate (Hz)
5
100
150/120
200
No. of Particles per Bunch (·1010)
2
0.75
0.75
0.4
No. of Bunches per Pulse
2820
192
192
154
Bunch Separation (nsec)
337
1.4
1.4
0.67
Bunch Train Length (msec)
950
0.267
0.267
0.102
Beam Power per Beam (MW)
11.3
5.8
8.7/6.9
4.9
Unloaded Gradient (MV/m)
23.8
41.8
65
172
Loaded Gradient (MV/m)
23.8
31.5
50
150
8/0.02
3/0.02
3/0.02
1.8/0.0
05
Two-Linac-Length (km)
30
17.1
13.8
5
Total Site AC Power (MW)
140
233
243/195
175
Norm Emitt, eNx,eNy, after DR (10-6m-rad)
Efficiency of structures and cavities
Efficiency and site power limitations are driving the beam
power of the LC design. The main difference between the
NC and SC designs lies in their plug-to-beam power
efficiency. The difference in efficiency is related in part to
the amount of losses in the wall. The wall loss can be
calculated from the unloaded gradient and the shunt
impedance. A wall loss factor, wall, can be derived from the
beam power (beam-current x accelerating voltage/m) and
the wall loss.
Wall Loss Factor at 500 GeV cm
PW

Eacc 2

 wall 
zS
W 
 
m
Pbeam
Pbeam  PW f C
TESLA
NLC
CLIC
Loaded, Average Gradient (MV/m)
23.8
50
150
Average Bunch Train Current (mA)
9.5
868
972
Peak RF Power/m at Beam (kW/m)
226
42900
145757
Peak RF Power Loss in Wall (kW/m)**
0.11
30790
270000
Wall Power Loss Factor wall
0.80*
0.58
0.35
*The Carnot “penalty” factor of 500 for the 2K operation is included. ** Shunt Imp. def. for TESLA incl.2.
Total Linac Efficiency
tot  struct  RF aux
Total linac efficiency
Total Efficiency at 500 GeV cm
RF Pulse (total/total-filling) (ms)
TESLA
NLC
1370/950 0.4/0.28
CLIC
0.13/0.1
Structure Efficiency (wout wall-loss&load) (%)
70
70
77
Struct.Eff. (incl. wall-loss and 8% load) struct (%)
57*
38
~25
Modulator Efficiency (%)
85
80
85
Klystron Efficiency (%)
65
55
65
Pulse-Transmission / Compression Eff. (%)
98
75
72
RF System Efficiency RF (%)
54
33
40
Auxiliary Average Static Plug Power (kW/m)
0.3
0.58
~0.4
Beam Duty Factor (freptflat), (%)
0.48
0.0034
0.002
Auxiliary System Efficiency aux (%)
78
72
~90
Total Efficiency tot (%)
24
9
10
*Includes 332 W/m at the plug of dynamic RF loss in couplers and HOM absorbers.
Plug to power efficiency of cold and warm
WARM, ILC-TRC second Report, page 79
note
COLD, ILC-TRC Second Report, pag. 36
LC RF = 167 MW in resp. to
questions, plug-to-beam eff ~ 8%
LC (cryo+RF) = 98 MW in resp.
to questions, eff ~23%.
US study cryo+RF=110.4 MW,
plug-to-beam eff ~ 20%