DFBs Current Leads Amalia Ballarino Training LHC Powering

DFBs, Current Leads Amalia Ballarino Training LHC Powering Amalia Ballarino

Summary • Introduction: DFB and Current Leads • Naming, quantity and location • Current Leads: types and functionalities HTS Current Leads Resistive current Leads • Operation of current leads in the DFBs • Current Leads ancillary equipment • Conclusion Training LHC Powering Amalia Ballarino 2

DFB and Current Leads Current lead: cryogenic and electrical device transporting the current from/to room temperature to/from the liquid helium environment (4. 5 K saturated bath). DFB: cryostat containing the current leads and the bus-bar that transport the current from/to the magnets, and providing the cryogenic environment required for their operation. Training LHC Powering Amalia Ballarino 3

DFB: naming and location Electrical feed-boxes: DFB. They are 52 in total. DFBA: at the end of the arcs. They are 16 in total, and they contain the leads that power the magnets in the arcs. DFBM: in the LSS. They are 23 in total, and they contain the leads powering the standalone magnets or magnet groups in the LSS. DFBL: in the RRs caverns. They are 5 in total, and they contain the leads powering via the superconducting links the stand-alone magnets or magnet groups in the LSS. DFBX: in the LSS, next to Q 3. There are 8 in total and they contain the leads powering the Inner Triplets in IP 1, IP 2, IP 5 and IP 8. The DFBX, with the incorporated leads, were provided by the US collaboration. Training LHC Powering Amalia Ballarino 4

Current Leads: naming, current rating and location Current leads: DFL. They are 3286 in total. They transport in total about 3 MA of current from/to room temperature to/from the liquid helium environment via ~ 1800 electrical circuits. They are rated for currents ranging from 60 A a to 13000 A. They are incorporated in the DFB cryostats or directly integrated in the LHC SSS. Lead Max current Location Number Type DFLA 13000 A DFBA 64 HTS DFLB 600 A DFBA-DFBM-DFBL 708 HTS DFLC 6000 A DFBA-DFBM-DFBL 258 HTS DFLD 60 A SSS 1504 Resistive DFLE 120 A SSS 324 Resistive DFLF 120 A DFBA-DFBM-DFBL 196 Resistive DFLX 7500 A DFBX 40 HTS DFLY 600 A DFBX 112 Resistive DFLZ 120 A DFBX 80 Resistive Training LHC Powering Amalia Ballarino 5

LHC HTS Current Leads A B C Room temperature HTS LHe temperature Q QA = 47 W/k. A QB = 1. 04 W/k. A QC = ? Training LHC Powering Amalia Ballarino 6

Current Leads: naming, current rating and location The LHC current are of two types : High Temperature Superconducting (HTS) leads and resistive. The HTS leads are all the leads rated at 13000 A, 6000 A and 600 A, with the exception of the 600 A leads in the DFBX which are resistive. The resistive leads are all the leads rated at 60 A and 120 A, plus the 600 A leads in the DFBX cryostats. There are two types of resistive leads: self-cooled in the DFBX (600 A and 120 A), and conduction cooled in other DFBs (120 A) and in the SSS (120 A and 60 A). All current leads are active components. Training LHC Powering Amalia Ballarino 7

Resistive Current Leads B A A′ Room temperature m. He LHe temperature Q QA = 47 W/k. A QB = 1. 04 W/k. A Training LHC Powering Amalia Ballarino 8

Why HTS Current Leads? Reduction by a factor 10 of heat load into the helium bath. Reduction by a factor 3 of the total exergetic power. Training LHC Powering Amalia Ballarino 9

Temperature profile of resistive top part T 1(x) : (IL/A) > (IL/A)OPT, m. He > m. He OPT T 2(x) : (IL/A) = (IL/A)OPT, m. He = m. He OPT T 3(x) : (IL/A) < (IL/A)OPT, m. He > m. He OPT Training LHC Powering Amalia Ballarino 10

LHC Current Leads RT RT RT 50 -75 K 20 K He gas 50 K 4. 5 -20 K LHe HTS leads From 600 A to 13000 A DFBA/M/L LHe Resistive leads 600 A in DFBX 120 A in DFBX Training LHC Powering Amalia Ballarino LHe Resistive leads 120 A in DFBA/M/L 60 A and 120 A in SSS 11

LHC HTS Current Leads THe=20 K THTS=50 K LHe Training LHC Powering Amalia Ballarino 12

LHC HTS Current Leads BSCCO 2223 multi-filamentary tape 31 km in the LHC current leads: first large scale application of HTS material. Training LHC Powering Amalia Ballarino 13

LHC HTS Current Leads Training LHC Powering Amalia Ballarino 14

HTS Leads in the DFB cryostats Training LHC Powering Amalia Ballarino 15

HTS Leads in the DFB cryostats Training LHC Powering Amalia Ballarino 16

Resistive leads RT 50 -75 K 4. 5 -20 K LHe 60 A and 120 A leads in the SSS: heat sinks are provided by the LHC beam screen and thermal screen lines. No cooling and gas recovery. 120 A leads in the DFBs: heat sinks are cooled by helium gas vaporized at the bottom end of the leads. Training LHC Powering Amalia Ballarino 17

Operation of Current Leads Instrumentation is integrated in all current leads for their operation and protection: • Temperature sensors for the control of the 20 K helium gas cooling the resistive part of the leads. The flow is controlled by a warm valve, one per lead, that maintain the top part of the HTS element at 70 K in stand-by operation and at 50 K during powering; • Temperature sensors for the control and monitoring of the temperature at the top part of the leads; • Voltage taps for the protection of the resistive part against overheating (100 m. V threshold) and of the HTS part in case of quench (3 m. V threshold). In addition, instrumentation is integrated in the DFBs for the monitoring of the liquid helium level and of the helium flow rates. Training LHC Powering Amalia Ballarino 18

Operation of Current Leads Training LHC Powering Amalia Ballarino 19

Operation of Current Leads Some requirements (Ref. EDMS N. 350602): • Over-cooling should be avoided. Flow in the resistive part of the leads should always be below the maximum specified values. Risk: irreversible damage of components (O-rings, insulators, …) and loss of electrical insulation. Alarms and interlocks have been foreseen by the cryogenic operators. • Liquid helium should always cover the bottom part of the leads and the low temperature superconductor. Risk: irreversible transition of the low temperature superconductor soldered to the bottom end of the HTS conductor. • For the HTS leads, the liquid helium should never be above the maximum specified value. Risk: “bubbling effect” following the penetration of the liquid through the porosity of the superconductor and irreversible degradation of the HTS element. Training LHC Powering Amalia Ballarino 20

Current Leads Ancillary Equipment Cartridge heaters are integrated on the top of the current leads. They are powered by 220 V/24 V insulation transformed installed on the DFB frames and controlled by heater control units installed in the LHC caverns. They maintain at room temperature at the top of the leads and the exit gas when the current is below the nominal one and in stand-by operation. But they do not compensate for over-cooling or too cold cryostat environment ! Ice and/or humidity formation must be avoided since they compromise the electrical insulation of the circuit and the integrity of the components. Training LHC Powering Amalia Ballarino 21

Current Leads Ancillary Equipment Electrical equipment for the leads Leads in the DFB in the LHC tunnel Training LHC Powering Amalia Ballarino 22

Hazardous Never touch the top of the leads ! This is the only accessible part of the LHC machine at the same potential of the electrical circuit. Training LHC Powering Amalia Ballarino 23

Conclusion The DFB with the incorporated leads are complex cryogenic and electrical devices. The current leads were all tested up to maximum current in ad-hoc designed cryostats reproducing the LHC cryogenic environment. The system DFB with incorporated leads was never tested. The five DFBs with the leads in the sector 7 -8 underwent a complete thermal cycle, and they are now being prepared for the first powering tests. We will learn as much as possible for the future operation from the powering of the first LHC sector. Training LHC Powering Amalia Ballarino 24

Glossary Current Lead DFB HTS LTS BSCCO 2223 High Temperature Superconductor HTS Current Lead Resistive Current Lead Bus-bar Conduction Cooled Current Lead Heat Sink Self-cooled Current Lead Training LHC Powering Amalia Ballarino 25