Precise Temperature Regulation System
for C-band Accelerating Structure
Sunao Takahashi1), Kazuyuki Onoe2), Takahiro Inagaki2), and
Tsumoru Shintake2)
1) SPring-8/JASRI, 2) SPring-8/RIKEN

Ä…0.1ºC temperature regulation of the accelerating structure with/without RF-power is one of the most
challenging parameters in SCSS (SPring-8 Compact SASE Source) project, which is aiming at
constructing X-ray radiation facility based on the SASE-FEL.
Since the heat dissipation in the C-band accelerator is about ten times larger than the conventional S-
band accelerators and it s level varies with different operating modes, an active control system is
necessary.
We designed the precise temperature regulation system for the C-band high-gradient accelerator,
which monitors the structure temperature itself and provides feedback on the water temperature at
inlet using an electric heater and a flow-rate control valve.
The performance of the prototype model of this scheme for the high-gradient test is presented.
Introduction
Eight cooling channels in parallel
Thermometer
(Countercurrent Configuration)
C-band Accelerating Structure
" Consists of 91 cells, made of OFHC, brazed in series.
One-fourth FEM model and the cross-sectional view of a cell.
" Total length : 1.8 m
" Frequency : 5712 MHz

==> twice higher than the conventional technology of S-band accelerator
Flow Rate Flow Rate Velocity
"T1 "T2
RF Power is fed into an accelerating structure.
per channel in total
“!
L/min L/min m/sec
ºC ºC
Heat dissipation is occurred inside cells by high-gradient generation.
2 16 0.48 1.42 1.07
“!
3 24 0.72 0.94 0.79
Dimension of the structure is expanded.
4 32 0.96 0.71 0.60
“!
5 40 1.20 0.57 0.55
Resonant Frequency Shift (Problem!!)
"T1: Temperature increase of the cooling water along
Temperature variation of 1.0ºC corresponds to resonant frequency variation
with passing through the structure of 1.8m.
of 100 kHz
"T2: Temperature difference between the cooling
“!
water and the copper body at the thermometer position.
ÿby FEM ÿ
To Maintain the body temperature of the structure to be
constant by a feedback system. (Target : < Ä…0.1°C )
FEM Analysis (ANSYS)
1. Boundary Conditions
(1) Power Inputting by heat dissipation
Cooling Water (30°C)
In case of an accelerating gradient of 40 MV/m and a pulse-
W/m2
repetition rate of 60 pps with a 0.5-µsec pulse, the heat flux
distribution for the center cell among 91 cells was calculated.
Accordingly, the heat generation for the cell is about 17.3 W,
which corresponds to the total heat generation of 1.6 kW for
the total structure.
(2) Power Removing by cooling water
Convection film coefficient of cooling channels is set to 5350
W/K/m2 based on its hydraulic diameter of 7.8mm and the
water flow rate per channel of 4 L/min.
Heat flux Distribution
All other surfaces are considered to be insulated.
2. Analysis Solutions (1) Steady State Analysis
°C
ÿ"T2=0.6ºC ÿ
1) Body (thermometer position) : 30.6°C
2) Iris Section : 31.9°C
To keep the body temperature being
30.0°C, the cooling water temperature
should be about 29.1°C (30.0- "T2- "T1/2)
at the entrance of the structure on this
condition.
(2) Transient Analysis
Time constants are
1) Thermometer Position : 40 sec
2) Iris Section : 20 sec
Temperature Distribution
Cooling Water Circuit and Feedback System for C-band High Gradient Test
Touch Panel
· ON/OFF operation
· Monitoring the system condition
· Setting the feedback parameters
· Checking alarm histories
Mineral Insulated Platinum Resistance
Thermometer (PT100&!, four-conductor type)
ELECTRIC HEATER
· Thrown into the cooling circuit
directly.
· The maximum power of 8 kW.
· Compensating the heat dissipation of
the structure. Thermistor
FLOW-RATE CONTROL VALVE
· Compensating the temperature Thermometer
fluctuation from the chiller.
Saving the electric consumption
Grease Type Silicon Compound
power on the heater
(High Thermal Conductivity & Hardenability)
Chiller System
To prevent the copper body from corrosion
=> Closed-loop circuit with pressurized N2 gas.
Linearize the stepwise change -> Stabilized below Ä… 0.5°C.
Results of Temperature Regulation without RF Power
< Case 1 > < Case 2 >
Result Result
30.00 Ä…0.1ºC 30.00 Ä…0.06ºC
ZOOM
ZOOM
Control Stop
Control Start
Control Start
Control Stop
Accelerator Body
Accelerator Body
Chiller (Ä…0.2ºC)
Chiller (Ä…0.5ºC)
Heater Power
Heater Power
Valve Opening Valve Opening
Results of Temperature Regulation with RF Power
Time (min)
02468 10 12
29.5

29.4
RF Power OFF
RF Power : 50 MW (=31.4 MV/m)
29.3
Pulse Width : 1.25 µsec
< 2 min
29.2
Pulse-repetition Rate : 50 pps (2.1 kW)
29.1
Cooling Water Flow Rate : 43 L/min (Constant)
29.0

28.9
RF Power ON
Structure Temperature : 29.0°C
28.8
Cooling Water Temperature : 26.5°C
Accelerator Body
28.7
28.6
ACCEPTABLE
28.5
27.0
for practical applications
26.8 Ä…0.2 C
26.6
26.4

Chiller
26.2
26.0 · On both conditions of turning off and turning on of
100
RF power, although it undershot and overshot at one
Heater Power
80
time individually, it could fall in the range of about
60
Ä…0.05°C within less than 2 min using only heater
power.
40
20
Valve Opening
· The chiller temperature was also kept as tight as
0
02468 10 12
Ä…0.2°C even if the large load fluctuation was
Time (min)
occurred
Ä…0.05 C
Temperature ( C)
Temperature ( C)
Output (%)
Relationship between Structure Temperature and RF Phase
Phase Shifter
Klystron
RF Power
Mixer
50 MW, 1.25µsec
1 pps : No heat generation
30pps : 1.2 kW
Thermometer Position
Accelerating Structure
50 pps : 2.1 kW
(Tuned at 29°C)
Water Bulk Temperature : 26.7°C 27.3°C
°C
Target Temp. Phase Shift
°C
(°C)
0° (Reference
1pps 29.0
Value)
30pps 29.0 +10.1°
°C
50pps 29.0 +17.9°
50pps 0°
27.4
Iris Section
· The RF phase property is governed by the temperature at the iris section.
· The ANSYS solution agrees well with the actual operational results.
Summary
1) The precise temperature regulation system of Ä…0.1°C for the C-
band high-gradient accelerator have been developed successfully,
which monitors the structure temperature itself and provides feedback
on the water temperature at inlet using an electric heater and a flow-
rate control valve.
2) We could confirm that the RF phase property is governed by the
temperature at the iris section by linking the experimental results and
the analysis solutions.
3) We are going to proceed system design including an engineering
design check for mass production by basically applying this system to
other components, listed here, which requires the same stability of the
body temperature.