Chapter 2. Radiation Estimation for Pion Capture Solenoid
File = ParticleDistributionXZ.dat
Neutron distribution (x-z) [COMET Phase I]
Date = 18:07 10-Dec-201plotted by ANGEL 4.35 calculated by PHITS 2.8
1000 500 0 500
400 200 0 200
z [cm]
x [cm]
no. = 2, ie = 1, iy = 1
100 101 102 103 104 105 106 107 108 109 1010 1011 1012
Particle flux [n/cm2/sec]
emin = 0.0000E+00 [MeV]
emax = 8.0000E+03 [MeV]
ymin = -2.0000E+01 [cm]
ymax = 2.0000E+01 [cm]
part. =
pion-File = ParticleDistributionXZ.dat
Neutron distribution (x-z) [COMET Phase I]
Date = 18:07 10-Dec-201plotted by ANGEL 4.35 calculated by PHITS 2.8
1000 500 0 500
400 200 0 200
z [cm]
x [cm]
no. = 3, ie = 1, iy = 1
100 101 102 103 104 105 106 107 108 109 1010 1011 1012
Particle flux [n/cm2/sec]
emin = 0.0000E+00 [MeV]
emax = 8.0000E+03 [MeV]
ymin = -2.0000E+01 [cm]
ymax = 2.0000E+01 [cm]
part. =
muon-negative-pion
negative-muon
11
Figure 2.3: The negative-pion (upper) and negative-muon (lower) transported in the magnetic field in PHITS simulation. The magnetic field applied on target is 5 Tesla, and the magnetic field from TS1a to end of TS2 coils is about 3 Tesla as given in Fig. 2.2.
other particles is set to the order of keV to reduce the computation time. In this simulation, the results are normalized with a proton intensity of 4.4×1013 pps corresponding to the beam power of 56 kW to calculate the neutron flux and dose rate, and the required total protons of 1021 proton on target (pot) until the experiment finished to calculate the neutron fluence and total dose [39], which corresponds to about 280 days.
dominated in the ionization as shown in Fig. 2.5.
10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 10 4 Kinetic energy [MeV]
10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10 10 11
Pa rt ic le fl ux [1 /c m 2 /s ec ]
Neutron Proton Photon
Electron Alpha Deuteron
Figure 2.4: Predicted particle flux hit the innermost layer of CS1 coil. Orange (Green, Blue, Black, Red and Purple) line indicates the flux of neutron (photon, proton, electron, alpha particle and deuteron).
2.2.2 Radiation Level
From a view of magnet design, the peak of radiation in superconducting coil must be suppressed below the degradation limit for each kind of material applied in superconducting magnet as described in Sec. 1.2. With the required total beam time of 1021pot, the peak of radiation in CS and MS coils are listed in Table 2.2. Among the coils in PCS, the neutron fluence and total dose are estimated to be 4×1021n/m2 and 1 MGy. Thus, the mechanical strength of BT-GFRP and critical surface of superconductor will not be affected by the radiation, however, the degradation of RRR may result in the coil temperature rise during the operation. For instance, the RRR of thermal path will degrade down to 10 from 2000 for the irradiation with neutron fluence of 1021 n/m2 if the beam operation is separated to 4 cycles.
To study the thermal characteristics for the superconducting magnet during the beam operation, the three-dimensional distributions of neutron flux and energy deposition are extracted as plotted in Fig. 2.6. As an illustration of CS1 coil, the coil is divided to 4 parts along the azimuth, then, the peaks of neutron flux and energy density are found to be 1.2×1014 n/m2/sec and 0.04 W/kg at the angle of 135◦ to 225◦ since the primary
Chapter 2. Radiation Estimation for Pion Capture Solenoid
recoil ionization photon others
Ratio
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
proton pion- electron alpha deuteron
Ratio
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Figure 2.5: The reaction process contributed to the energy deposition of the superconducting coil (left), and the contributions of each particle contributed to the energy deposition from the ionization (right), where the recoil, ionization, photon and others are the energy deposition from the recoil nuclei (deuteron, tritium,3He, alpha and residual nuclei), the energy loss of charged particles, photon and the remaining excitation energy, respectively. The energy deposition is scored at the innermost layer of CS1 coil.
Table 2.2: The peak of neutron fluence, DPA and energy deposition within the statistical error for CS and MS coils estimated by PHITS simulation.
Coil Neutron fluence Displacement per atom Heat generation Total dose
[n/m2] [DPA] [W/m3] [MGy]
CS0 (3.55±0.02)×1021 (4.0±0.04)×10−4 115±4 0.69±0.03 CS1 (4.18±0.01)×1021 (4.4±0.03)×10−4 163±7 0.97±0.04 MS1 (2.36±0.01)×1021 (2.3±0.02)×10−4 76±1.4 0.45±0.09 MS2 (8.08±0.05)×1020 (7.8±0.07)×10−5 40±1 0.24±0.05 proton beam is injected in the magnet with the tilting angle of 10◦ with respect to the magnet axis.
As a DPA rate and dose rate plotted in Fig. 2.7, apart from the superconducting magnet, the DPA rate for the production target is about 3×10−8 DPA/sec, which indicates that the total DPA is close to 1 DPA for more than 107 sec beam operation, and the radiation damage on the production target must be taken into account for the target design. Furthermore, the power density is predicted to be 2 kW/kg in target corresponding to the total heat load of 163 W, thus the cooling system for production target is necessary for the COMET experiment. Although DPA rate and dose rate in the inner surface of tungsten shielding is one order lower than the production target, the material properties may be degraded by long time irradiation. The influence of irradiation on tungsten shielding must be investigated for further studies.
/sec]2Neutron Flux [n/m
0 0.02 0.04 0.06 0.08 0.1 0.12
1015
= -45.0 - 45.0 [degree] × θ
Z [cm]
−40 −20 0 20 40 60
R [cm]
68 70 72 74 76 78 80 82
= -45.0 - 45.0 [degree]
θ
/sec]2Neutron Flux [n/m
0 0.02 0.04 0.06 0.08 0.1 0.12
1015
= 45.0 - 135.0 [degree] × θ
Z [cm]
−40 −20 0 20 40 60
R [cm]
68 70 72 74 76 78 80 82
= 45.0 - 135.0 [degree]
θ
/sec]2Neutron Flux [n/m
0 0.02 0.04 0.06 0.08 0.1 0.12
1015
= 135.0 - 225.0 [degree] × θ
Z [cm]
−40 −20 0 20 40 60
R [cm]
68 70 72 74 76 78 80 82
= 135.0 - 225.0 [degree]
θ
/sec]2Neutron Flux [n/m
0 0.02 0.04 0.06 0.08 0.1 0.12
1015
= 225.0 - 315.0 [degree] × θ
Z [cm]
−40 −20 0 20 40 60
R [cm]
68 70 72 74 76 78 80 82
= 225.0 - 315.0 [degree]
θ
Energy Deposition [W/kg]
0 5 10 15 20 25 30 35
−3
×10 = -45.0 - 45.0 [degree]
θ
Z [cm]
−40 −20 0 20 40 60
R [cm]
68 70 72 74 76 78 80 82
= -45.0 - 45.0 [degree]
θ
Energy Deposition [W/kg]
0 5 10 15 20 25 30 35
−3
×10 = 45.0 - 135.0 [degree]
θ
Z [cm]
−40 −20 0 20 40 60
R [cm]
68 70 72 74 76 78 80 82
= 45.0 - 135.0 [degree]
θ
Energy Deposition [W/kg]
0 5 10 15 20 25 30 35
−3
×10 = 135.0 - 225.0 [degree]
θ
Z [cm]
−40 −20 0 20 40 60
R [cm]
68 70 72 74 76 78 80 82
= 135.0 - 225.0 [degree]
θ
Energy Deposition [W/kg]
0 5 10 15 20 25 30 35
−3
×10 = 225.0 - 315.0 [degree]
θ
Z [cm]
−40 −20 0 20 40 60
R [cm]
68 70 72 74 76 78 80 82
= 225.0 - 315.0 [degree]
θ
Figure 2.6: The 3D distribution of the predicted neutron flux and energy deposition in CS1 coil. The peak of radiation is located at the angle of 135◦ - 225◦ since the primary proton beam is injected in the magnet with the tilting angle of 10◦ with respect to the magnet axis. The center of target is located at Z = 0 cm, and the center of CS1 coil is at the position of Z = 10 cm.
Chapter 2. Radiation Estimation for Pion Capture Solenoid
File = Det_DepositAll_xz.dat energy deposit distribution Date = 10:12 15-Sep-201
plotted by ANGEL 4.35 calculated by PHITS 2.8
−400 −200 0
−100 0 100
z [cm]
x [cm]
no. = 1, iy = 1
10−3 10−2 10−1 100 101 102 103
Energy Deposition [Gy/sec]
ymin = -3.0000E+00 [cm]
ymax = 3.0000E+00 [cm]
part. = all
File = Det_FluxAll_xz.dat particle flux distribution Date = 10:03 15-Sep-201
plotted by ANGEL 4.35 calculated by PHITS 2.8
400 200 0
100 0 100
z [cm]
x [cm]
no. = 1, ie = 1, iy = 1
107 108 109 1010 1011 1012 1013
Flux [n/cm2/sec]
emin = 1.0000E-03 [MeV]
emax = 8.0000E+03 [MeV]
ymin = -8.0000E+00 [cm]
ymax = 8.0000E+00 [cm]
part. = neutron
File = Det_DpaAll_xz.dat DPA distribution for CS and MS Date = 10:07 15-Sep-201
plotted by ANGEL 4.35 calculated by PHITS 2.8
−400 −200 0
−100 0 100
z [cm]
x [cm]
no. = 1, iy = 1, tot DPA
10−13 10−12 10−11 10−10 10−9 10−8
DPA [DPA/sec]
particle = all ymin = -3.0000E+00 [cm]
ymax = 3.0000E+00 [cm]
File = Det_FluxAll_xz.dat particle flux distribution Date = 10:03 15-Sep-201
plotted by ANGEL 4.35 calculated by PHITS 2.8
400 200 0
100 0 100
z [cm]
x [cm]
no. = 1, ie = 1, iy = 1
107 108 109 1010 1011 1012 1013
Flux [n/cm2/sec]
emin = 1.0000E-03 [MeV]
emax = 8.0000E+03 [MeV]
ymin = -8.0000E+00 [cm]
ymax = 8.0000E+00 [cm]
part. = neutron
File = Det_DpaAll_xz.dat DPA distribution for CS and MS Date = 10:07 15-Sep-201
plotted by ANGEL 4.35 calculated by PHITS 2.8
−400 −200 0
−100 0 100
z [cm]
x [cm]
no. = 1, iy = 1, tot DPA
10−13 10−12 10−11 10−10 10−9 10−8
DPA [DPA/sec]
particle = all ymin = -3.0000E+00 [cm] ymax = 3.0000E+00 [cm]
Figure 2.7: Distribution of energy deposition (left) and DPA rate (right) in PCS from a view of z-x plane.
2.2.3 Heat Loads
In the COMET muon beam line, the superconducting coils in PCS and MTS are cooled by the two-phase forced helium flow with one cryogenic system [31]. To determine the cooling capacity of liquefier in cryogenic system, the heat loads in PCS, comprising the coils, thermal shield and support shell, are estimated as listed in Table 2.3. The total heat load is predicted to be about 240 W, in which the CS and MS coils contribute over 150 W in the PCS, over 50 W of heat load is generated in support shell and thermal shield. For these reasons, a liquefier with the cooling capacity over 600 W at 4.5 K will be adopted in COMET experiment.