Fast-cycling synchrotrons are key instruments for accelerator based nuclear and high-energy physics programs. We explore a possibility to construct fast-cycling synchrotrons by using super-ferric, {approx}2 Tesla B-field dipole magnets powered with a superconducting transmission line. We outline both the low temperature (LTS) and the high temperature (HTS) superconductor design options and consider dynamic power losses for an accelerator with operation cycle of 0.5 Hz. We also briefly outline possible power supply system for such accelerator, and discuss the quench protection system for the magnet string powered by a transmission line conductor

/Fermilab

Hays, S.

Huang, Y.

Piekarz, H.

Shiltsev, V.

UNT Digital Library

  H. Piekarz, S. Hays, Y. Huang and V. Shiltsev, FNAL, Batavia, IL60510, U.S.A.Amagnet stringn injector to the low energy rihigher beam poould provide high intensity proton beam to Main Injector. DESIGN CONSIDERATIONS OF FAST-CYCLING SYNCHROTRONS USING SUPERCONDUCTING TRANSMISSION LINE MAGNETS* bstract Fast-cycling synchrotrons are key instruments for accelerator based nuclear and high-energy physics programs. We explore a possibility to construct fast-cycling synchrotrons by using super-ferric, ~2 Tesla B-field dipole magnets powered with a superconducting transmission line. We outline both the low temperature (LTS) and the high temperature (HTS) superconductor design options and consider dynamic power losses for an accelerator with operation cycle of 0.5 Hz. We also briefly outline possible power supply system for such accelerator, and discuss the quench protection system for the  powered by a transmission line conductor.   MOTIVATION: A POSSIBLE NEW ACCELERATOR COMPLEX AT FNAL Long baseline neutrino oscillation search experiments require high-power proton beams to produce neutrino beams of sufficient intensity. A high-power proton beam can be achieved using both high rate of protons and high energy of protons. The fast-cycling synchrotron can combine both options allowing produce a neutrino beam of intensities comparable to those expected from the Neutrino Factories. At Fermilab, a fast-cycling Dual Super-Ferric Main Ring (DSFMR) accelerator in the Tevatron tunnel is proposed to serve as a high intensity proton source for the long baseline neutrino experiments [1], and in a longer term as ang (LER) of the VLHC [2]. The outline of the proposed new accelerator complex at Fermilab is shown in Fig. 1. The ring circumference of ~ 6300 m would allow acceleration of proton beam up to 480 GeV with 2 Tesla dipole magnets. With total beam intensity of 0.5e14ppp, and the repetition cycle of 0.5 Hz DSFMR can provide up to 4 MW power on two neutrino production targets (total 8 MW). With such a high power, one neutrino beam could be directed to a detector at ~ 7500 km away from Fermilab (e.g. Gran Sasso, Italy), and the other one to a location at ~ 3000 km within the US (e.g. Mt Whitney, CA). Sending neutrino beams into such two detectors is a very attractive option for a firm resolution to the neutrino oscillation physics [3]. The DSFMR will allow the simultaneous operations of NOVA and MINOS experiments but with 10 times wer than presently available at Fermilab.  The DSFMR is also compatible with recently proposed 8-GeV “Project X” SC RF linac which c  Figure 1: Outline of proposed FNAL accelerator complex  d ion onto neutrino targets, or into the VLHC LER     SFM tron  ]         Basic parameters of the DSFMR are listed in Table I, and time sequence for beam stacking, ramping anextract            Table I: Parameters of D R synchro   Radius     [m]    Einj  / Eextr [GeV / GeVGap   [m]  B [T] dB/dt [T/s]    1000     48 / 480    40 2.0    2.0  rings is shown in Fig. 2. The 8 GeV beam batch from Project X is transferred to the Main Injector, accelerated to 48 GeV, and then transferred to one of DSFMR rings where it awaits for a second proton beam batch from the Main Injector to arrive. The DSFMR will accelerate both proton batches up to 480 GeV, and then extract them to two neutrino beam production lines, or to the LER rings of the VLHC.  In simultaneous extraction to the LER rings one proton batch is transferred into the clock-wise VLHC circulation, and the other one into the counter-clock circulation facilitating setting the colliding mode of  operation.        ure 2: Time sequence for beam stacking, ramping andFigextr s.   DSFMR DESIGN CONSIDERATIONS action to neutrino production targets or to LER ring     ___________________________________________  *This work had been authored by Fermi Research Alliance, LLC under DOE Contract DE-AC02-07CH11359     FERMILAB-PUB-08-176-APC     There are two important constraints on the DSFMR accelerator design. The first constraint is the necessity of   In placing dual accelerator rings inside the Tevatron tunnel. This is only possible if the superconducting magnets are used which allows for the minimization of magnetic cores. The second constraint is due to the cryogenic power limitation of 24 kW that is currently available for the Tevatron. This requires very strong optimization of the superconductor design, so both static and dynamic power losses will be contained to this available cryogenic power.     In the superconducting super-ferric magnets the B-field is determined by the iron core, and not by the conductor making easier to secure a high quality of the magnetic field. This is especially true with a window-frame type core. In principle, there are two options for the rrangement of the conductor in a window-frame core.aFig. 3A the conductor is located in an extended space for the beam pipe while in Fig.3B the conductor is located in designated cavities. In the first case the conductor is more exposed to the beam losses while in the second one it is better protected from such losses. Most beam losses occur at the beam injection. The higher the injection energy the smaller is the beam phase-space, and potential for the     Figure 3: Options for conductor placement within a core  scattered beam to hit conductor is reduced. The beam loss effect can be further minimized by placing a protecting carbon scatter block in front of the conductor. For the lower-energy machines hiding the conductor behind the core walls, as shown in Fig.3B, may be well justified as a larger core is more acceptable. As pointed out in [4] option of Fig.3A allows strong minimization of dynamic power losses with HTS tape of single filament strand by orienting its narrow edge to be parallel to the B-filed in the magnet gap. In a larger bore magnet use of the LTS conductor may be appropriate as the B-field lines will more likely cross conductor at various angles.        As discussed in [4] the DSFMR magnet would be powered by four subsets of HTS conductor lines in each current flow direction. The updated design of a one subset is shown in Fig.4. There are 35 344S HTS tapes (0.2 mm x 4.5 mm) from the American Superconductor in a subset allowing for a transport current It = ~20 kA (50% of Ic) at 4.5K with 20K margin. These tapes are separated from each other using the 0.1 mm thick and 2 mm wide kapton rings. These rings are also staggered to create access of liquid helium to ~ 50% of strand surface. The proposed LTS conductor line is also shown in Fig.4. It consists of 23 twisted pairs of the NbTi strands (0.65 mm diameter, SC inner dipole) allowing for a transport currenS t of ~20 kA (80% of Ic) at 4.5K, with temperature margin of 1.5K.    ns of HTS and n rs f DFSMR and Beters of the prop on s e use these parame  e e nsfer from the LH e er-pressure dro r meters of propo ndFigure 4: Conceptual desig LTS co ductofor fast cycling magnets o ooster  nic param     The cryoge osed c toductoratare listed in Table II. Waters stimthe available heat tr e to th  supconductor, and the LHe flow p per conductolength.       Table II: Cryogenic para sed co uctors        CICC geometry HTS LTS Pipe outer diameter [mm] 12.5 12.5 Pipe inner diameter [mm] 1.5 11.5 1Number of strands  35 46 Single strand area [mm2] 0.90 0.43 Total strand area [mm2] 31.5 19.8 Void fraction  0.70 0.81 LHe flow area [mm2]  73 84 Pipe perimeter [mm]  36 64 mTotal strand perimeter [m ] 263 120 ]Cooled perimeter [mm  300 184 Hydraulic diameter [mm] 0.97 1.83        For ideal heat transfer ∆Q from liquid helium coolant to a CICC conductor we use formula (1) from [5]:             Q = 0.0259 (k/Dh) Re0.8 Pr0.4 (Tc/THe)-0716        (1) where k - heat conductivity, Dh -hydraulic diameter, Re = 4 [(dm/dt)/(k x Pcool)], dm/dt helium flow rate, Pcool, cooled perimeter, Pr = (μ x Cp)/k, μ – viscosity, and Tc , THe – are conductor and LHe temperature. The supercritical helium pressure drop ∆P in the CICC conductor of a length L is estimated using formula (2) from [6]:             ∆P/L = 0.5 Ff [Pcool x (dm/dt)2 ]/[ρ x (Aflow)3]   (2) where friction factor Ff  = 0.3164 x Re -0.25 for a turbulent flow in a smooth pipe, ρ – helium density, and Aflow  is the  cross-sectional area of helium flow in CICC conductor. As the CICC conductors are not smooth pipes we arbitrarily assume that a more realistic factor is 3 times higher corresponding to some roughness, ε, over pipe diameter D to be ~ 0.1 (e.g. for NbTi twisted pair: 1.3 mm /12.3 mm). The estimated in the above way heat transfer and pressure drop for the LTS and HTS conductors with parameters listed in Table II is shown in Fig.5. We observe that the pressure drop strongly increases with the flow rate while  the heat transfer saturates at ~5 g/s to that of helium boiling from the metal surface. This suggests that our ICC conductors should be optimized for low LHe flows, Cpossibly just above a laminar flow regime (> 0.5 g/s). Data [5] suggests that the heat transfer efficiency in CICC   Figure 5: Projected heat transfer and pressure drop in LTS and HTS conductor lines.   onductor may be at ~ 25% of the calculated value with a f ~ ng agnet e projected ind of th  magnets is ~ . T ds to mH fo SFMR ring roducing ~50 MW of stored energy.  Supplying this      Th uctance e DSFMR3μH/m his lea  ~18.75 r a single Dpenergy can be handled with a single power supply that can then also be used as the primary quench protection system.  The power supply ramps up and down in one second and therefore can remove the magnet energy at the same one second from any point in the cycle.  In the event of a power system failure the power supply will need to be backed up by a minimum of two dump switches.  These should be Superconducting type to avoid the added voltage drop of a room temperature switch system.      As a result of a large operational temperature margin the quench detection with the HTS conductor will be very different than used in classical LTS magnet systems. To illustrate this we show in Table III crudely estimated heat absorption sharing between liquid helium and copper of 344S HTS strands as the temperature rises. We see that up  to ~ 30 K, where It ≈ Ic, heat is mostly absorbed by helium coolant, and ~ 100 kJ is required to reach 300K.    Table III: Heat absorption sharing in HTS conductor T[K] Q Cu [%] Q LHe [%] Q total  [kJ/m] 5-30      7       93        3 5-300     76       24      100  onsequently, with DSFMR stored eneC rgy of ~ 8 kJ/m we  , so h.  nstalled a e a l e  a e a 0  l of ench ible.  afe  Hays, “Preliminary Considerations   have a time window of ~ 12.5 s to stop the power supply  ofand remove the magnet string energy. The HTSDSFMR magnet remains superconducting up to 25 Kan indicate coming of a quenccthe temperature sensors cformula (1). This still would provide heat absorption o2 edi     The magnet system will still need to have i8 W/m  for ∆T = 0.1K at 0.5 g/s flow, much exceprojected power loss of ~ 0.5 W/m2 for DSFMR m Quench Protection Monitor (QPM) to ensure that thsystem energy is managed safely. The difficulty in using with the HTS conductor [4], but being in a close range to (3-5) W/m2 projected for the LTS conductor [4,7].  Using the transmission line conductor to power the Booster and DSFMR magnets allows consider temperature rise and pressure drop only on the conductor length between the joints of the two magnets; e.g. 6 m length for a 5 m long  magnet. In this case the helium supply and return lines run parallel to the magnet ring.  Assuming initial LHe of 4.4K @ 2.6 bar, and arbitrarily the pressure drop of 0.1 bar with temperature rises of 0.6 K for the LTS and 0.2 K for the HTS in 6m long conductor, a projected cryogenic cooling power for DSFMR is 34 kW for the LTS option and 8 kW classical Quench Detection Unit (QDU) is the signavoltage for thlevels and speed.  The power supply Tevatron is 10,000 volts stepping up in 1 second andl usramp rate 240 amps/second.  Each DSFMR ring wil2000 volt supply and will have the dV/dt of 20,00volts/second.  In addition the ramp current of 68,000sicaamps/sec required for the DSFMR will make clasmbination quench detection rather difficult.  Using a cotemperature pre-quench warning and classical qudetection with a more tolerant trip level may be possDuring development tests we will have to establish a soperating level for the conductors and develop a Quenchin the HTS option. We plan to perform test measurements of both dynamic and static losses in these conductors [7].          POWER SUPPLY AND QUENCH          PROTECTION CONSIDERATIONS  Protection System that will meet the needs of a fast- ramping and fast-cycling accelerator.                               REFERENCES  [1] H. Piekarz and S.         of a Dual, 480 GeV, Fast Cycling Accelerator for        Production of Neutrino Beams at Fermilab”, TM-       2381-AD-TD, 2007 [2] H. Piekarz “Fast-Cycling Superconducting         Synchrotrons and Possible Path to the Future of US        High-Energy Particle Physics, TM-2402-APC, 2008 [3] P. Huber and W. Winter, “Neutrino Factories and the        Magic Baseline”, MPI-PhT/2003-5    [4] H .Piekarz, S. Hays, Y. Huang, V. Kashikhin, G. de        Rijk, L Rossi, “Design Considerations for Fast-       Cycling Superconducting Accelerator Magnets of 2        Tesla Generated by Transmission Line Conductor of        100 kA Current”, IEEE, Transactions of Applied         Superconductivity, p 256, Genoa, 2006 [5] Y. Wachi, M. Ono, T. Hamajima, “Heat Transfer        Characteristics of the Supercritical LHe in CICC        Conductor”, IEEE Trans. Apl. Super., Vol.5, 1995 [6] R. Maekawa, M.R. Smith, S.W. Van Sciver, “Pressure       Drop Measurements of NET-CEA CICC Conductors”,       IEEE Trans. Applied Superconductivity, Vol. 5, 1995  [7] H. Piekarz, “Design Considerations of Fast-Cycling         SC Transmission Line Magnets”, WAMSDO, CERN,        May 19-23, 2008 

Design Considerations of Fast-cycling Synchrotrons Based on Superconducting Transmission Line Magnets

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Design Considerations of Fast-cycling Synchrotrons Based on Superconducting Transmission Line Magnets

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