REDUCTION OF OUTGASSING FROM THE FERRITE CORES IN THE KICKER MAGNET OF J-PARC RCS

Kicker magnets are used to kick out the accelerated beam to the transport lines in the RCS of the J-PARC. A high voltage is applied to kickers for a short period, so they must be installed in a vacuum to prevent discharge. Therefore, it is important to reduce the outgassing of water vapour from the ferrite cores. This time, we have decided to construct the reserve magnets with very low outgassing at high-voltage discharge. First of all, the thermal desorption behaviour of the ferrite was investigated. Water vapour has two peaks: at 150C and 300C. Carbon dioxide is rather largely emitted with the peak around 275C and then decreases with the temperature. From these results, the ferrite cores were vacuum-fired at 450C for 48 h. Then the good properties for the magnetic cores were confirmed. And now the assembling of the kicker magnet is undertaken. INTRODUCTION Kicker magnets have been used to extract a 3 GeV proton beam and inject it into a downstream beam transport line [1]. They are fast pulse magnets whose current rise time and flat top length is about 80 ns and 1 s, respectively. The whole magnet is placed in a vacuum because its excitation voltage is quite large. Being completely in a vacuum, it is important for kickers to prevent electrical breakdown. In addition, suppression of the outgassing is needed since outgas interacts with the beam and causes beam loss. Figure 1 shows the outline structure of a kicker magnet. Figure 1: Outline structure of a kicker magnet. Table 1: Main Components and Their Outgassing Rate for the Working Kicker Magnet Material Outgassing Rate (Pam/s) Ferrite ~ 10 (200C 300h bake) Al alloy (A5052) < 10 (Pit-free electrical polishing +150C 25h bake) SUS304 < 10 (450C 48h bake) The main materials of the magnet, which are listed in Table 1, are ferrite, aluminium alloy (A5052) and stainless steel SUS304. The ferrite has the nominal composition of AFe2O4 (A=Ni and Zn) and good highfrequency properties, so it is used as the magnetic core. Aluminium alloy is used for all the electrodes and conductors for exciting current. The stainless steel is used for the mechanical support. PREVIOUS TREATMENTS TO REDUCE THE OUTGASSING FROM THE COMPONENTS Aluminium Alloy According to the reference [2], the surface of Al alloy, which is treated by the pit-free electrical polishing method and successively baked out at 150C for 25 h, has a good vacuum property. The outgassing rate is reported to be less than 10 Pam/s after bake-out. So, all the Al alloy surfaces in the working kickers were treated by the above treatment. The same treatment is also employed for the Al alloy in the reserve magnets. Stainless Steel SUS304 As well known, the surface treatment and the heat treatment for the stainless steel SUS304 have been widely investigated. We adopted the combination of electrical polishing and the vacuum-firing at 450C for 30 h. The low outgassing rate less than 10 Pam/s was reported [3]. Ferrite Core The ferrite PE14 produced by TDK was used in the working kicker magnets. The outgassing rate of the ferrite has been found to be ~ 10 Pam/s[4]. As the rate was too large to enable us to use in a vacuum of RCS, the ferrite cores were baked out in a vacuum at 200C for 300 h. Finally the rate of ~ 10 Pam/s was obtained [5]. ----------------------------------------------ogiwara.norio@jaea.go.jp Proceedings of IPAC2012, New Orleans, Louisiana, USA MOPPD053 04 Hadron Accelerators T12 Beam Injection/Extraction and Transport ISBN 978-3-95450-115-1 487 C op yr ig ht c ○ 20 12 by IE E E – cc C re at iv e C om m on sA tt ri bu tio n 3. 0 (C C B Y 3. 0) — cc C re at iv e C om m on sA tt ri bu tio n 3. 0 (C C B Y 3. 0) NEW TREATMENT FOR REDUCTION OF OUTGASSING FROM THE FERRITE CORES Thermal Desorption Measurements As shown in Table 1, the outgassing rate from the ferrite is 100 times larger than the other main materials. The vacuum properties might be greatly improved when the ferrite were well de-gassed. Thus, we investigated the ferrite through the thermal desorption spectroscopy (TDS) method for the construction of the reserve kicker magnets. The block of ferrite PE14 was cut into test pieces. The size of the piece is 10mmx10mmx1mm. We made three kinds of sample from these pieces. First of all, all the pieces were ultrasonically rinsed in C2H5OH for 15 min and then dried quickly. Some of the pieces were used as the samples “as-received”. Then the others were vacuum-fired at 450C for 48 h. Some of these vacuumfired samples are used as the samples “450C-48h”. The rest pieces were additionally rinsed in distilled water for 15 min (as “450C-48h+water” ones). Main gas species from the sample “as-received” are H2O and CO2. The water vapor has the peaks at 150C and 300C as shown in Fig. 2. The two peaks have rather sharp distributions. The water molecules from the peak at 150C have the binding energy about 0.44 eV. This low binding energy implies that this peak is ascribed to the absorbed water molecules. On the other hand, the peak at 300C is supposed to be originated from the hydrate, because the binding energy is rather high (~1.7 eV). The carbon dioxide has the broad peak at 275C.