A Rare Isotope Beam (RIB) is a dish best served cold Cryogenics system of the ISAC-II superconducting LINAC at TRIUMF Rene Tanaja TRIUMF RIB Operations - Note that this talk will be mainly from the Operator’s point of view. October 17, 2017

Superconducting RF Accelerator Room Temperature Accelerators ISAC Facility SEBT Experiments (≤6.5MeV/u at A/Q=6) Superconducting RF Accelerator HEBT Experiments (≤1.5MeV/u) LEBT Experiments (≤60keV/u) Room Temperature Accelerators The ISAC facility delivers isotopes heavier than hydrogen to experiments. Protons from TRIUMF’s cyclotron are sent to one of two target stations. A mass is selected from the products using two mass separators of increasingresolution. Deliver to low energy experiments. Or accelerate to higher energy experiments. Or accelerate further even higher-energy experiments. This talk will focus on the cryogenic cooling system of the Superconducting RF, or, “SCRF”, accelerator.

ISAC-II Superconducting RF (SCRF) Accelerator This is a picture of the inside of the SCRF accelerator vault. Consists of five medium-beta cryomodules and three high-beta cryomodules, containing a total of 40 accelerating cavities. In the middle of each cryomodule is a focusing solenoid.

ISAC-II Superconducting RF (SCRF) Accelerator Cavities: Bulk niobium,Tc=9.2K LHe-cooled to 4K. Stainless steel vacuum tanks. LN2-cooled copper shielding. Mu-metal shielding under the copper shielding. This is what is inside Cavities, solenoid, and liquid-helium reservoir. Cavities are made of bulk niobium and are cooled to 4K. This is a medium-beta cryomodule during testing. - The outer tank is stainless steel. - LN2-cooled copper thermal shield under the outer shell. - And mu-metal shielding under the thermal shield to prevent trapping any external magnetic field (e.g. Earth’s magnetic field). Note: Mu-metal is a Ni-Fe (soft magnetic) alloy with high permeability. - ~80% Ni, 12-15% Fe, 5% Mo, and the rest others (Si, etc.)

Gaseous He return lines Cooling Down Cavities LHe supply “stinger” Gaseous He return lines Liquid He Reservoir 3-way valve Vacuum chamber Distribution “spider” tubes Solenoid This is a diagram of a cryomodule’s liquid helium distribution. LHe is inserted through a helium supply “stinger” and directed using a three-way valve, through a distribution “spider,” to the solenoid, cavities, and liquid helium reservoir. The reservoir is filled to about 35% full. The rest of the space is to allow for gas He which has been boiled off from use. The gas is extracted through the gas He return lines. Cavities

Quick cooldown to reduce the chance of Q-disease. Cooling Down Cavities Quick cooldown to reduce the chance of Q-disease. Must cool down from ~150K to 50K in less than 1h. Usually within ~30 minutes. Cryomodule solenoid off during cooldown Cooling down of the cryomodules must be done quickly to avoid Q-disease. - Q-disease is when the cavity’s metal forms hydrides with the hydrogen embedded in the metal from the manufacturing, cleaning, and etching of the cavities. - Can severely reduce performance. The solenoid is kept off to avoid trapping fields during cooldown to avoid fields from getting trapped during cooldown. Have a procedure for removing any trapped fields should any somehow gets trapped. Procedure: Degauss the SC solenoid and shut off. Shut off LHe supply to cryomodule and let the temp. rise to >20K, <40K. Cool cavities back down. Once cooled back down (4.2K), turn the solenoid and cavities back on.

Liquid Helium Distribution Test system Compressor The cryogenics systems is divided into two sections: The Phase-1 and Phase-2 systems. Each one has its own coldbox, LHe dewar, and compressor. The Phase-1 system cools the first three cryomodules and the test system. The Phase-II system cools down the rest of the cryomodules. They are isolated from each other, but the cooling lines can be connected if necessary. Each phase is capable of keeping the entire accelerator sufficiently cooled while in use. (The Phase-I system has been tested for this, but the Phase-II system has not, though theoretically it should be just as capable.) Cold box and dewar Phase-1 Phase-2 Compressor Cold box and dewar

Burst Discs A cryomodule is not considered a pressure vessel. If the gas pressure in the tank rises above the rated limit (~2atm), equipment inside can be damaged =>burst discs. If the gas pressure goes above the limit, the burst disc would pop and relieve the pressure and protect the cryomodule from damage.

LHe loss isn’t desirable, however. Burst Discs LHe loss isn’t desirable, however. 3400 litres in the cryogenics system. LHe ~C$18 (~US$15, ~€12) a litre. About C$61,000 (~US$49,500, ~€41,500). Still, far less significant than equipment damage if pressure goes too high! Although equipment damage would be much worse, losing LHe from popping a burst disc still isn’t desirable, as LHe is expensive. The entire ISAC-II LHe inventory would cost about as much as a BMW Z4 (at least in N. America). But equipment damage could

Liquid Nitrogen System Cryomodule thermal shields Supporting the LHe system is an LN2 system. LN2 is mainly used to cool the cryomodule thermal shields, shield the LHe transfer lines, and cool down the first stage of the cold boxes’ heat exchangers. Phase Separator

Operations monitors cryogenics system other times. Operations’ Role Cryogenics staff normally on site only during regular business hours. Operations monitors cryogenics system other times. “First responders” during a situation On-site “hands” for expert help Alarm handler for warnings So what is my role as operator in all this? TRIUMF is not a large enough facility to have cryogenics staff on site 24/7/365. So outside business hours, Operations monitors the system. - We become the “first responders,” should there be a situation. - If needed we become the on-site “hands” with experts on the phone, until the situation is contained or an expert is able to come in. - We have an alarm handler to help us keep watch on the cryogenics.

Some Challenges We have had a few challenges and growing pains over the years. This (first picture) is one of our original LN2 phase separators in ISAC-II. Because the design was probably not suited for the amount of LN2 used and the insulation used was not enough, ice balls like this would often form Adding insulation made it hard to do any repairs. Worn-out valves would get sticky and get stuck open or closed: Percussive treatment (heat gun + rubber mallet/wrench/etc.) to get it unstuck until it can be replaced. Recently replaced with a more reliable phase separator. So far no ice balls or frozen valves anymore! - Frozen valves are in issue for Operations because it takes away from the Control Room. We often have only one operator on shift during the off hours, and taking time to unstuck the valve every ten minutes means that we can’t watch for other issues in the Control Room.

Some Challenges Power outages / bumps Power outages and some power bumps trip off compressors. Recovery compressor to prevent / minimize LHe loss. - Presently manual on only. .

Power outages / bumps Growing pains incident on Nov. 26, 2006. Some Challenges Power outages / bumps Growing pains incident on Nov. 26, 2006. Things learned, subsequent and future upgrades: Independent mini air compressor, on emergency diesel generator, installed. Recovery compressor “auto-on” when cold box trips – work in progress The monitoring of the cryogenics system had just been handed over to Operations. I was on shift alone, and was just reviewing the procedures. - Power outage at 8pm. - I followed the procedures, but the recovery compressor woudn’t start. - It later turned out that one of the valves was on site compressed air, whose compressor tripped off because it lost site power. - A lot of LHe was lost.

Impurities in the He inventory Some Challenges Impurities in the He inventory Can reduce heat exchanger performance, damage cold box turbines. Originally impurity sensors only detected N2. Need < 5ppm N2 impurity to operate. Contamination incident June 29, 2013. After incident: Pressure transducer was moved. Installed check valve. Installed new sensors that also detect H2O, hydrocarbons, oil aerosols. - Impurities in the LHe system can do a lot of damage, so they need to be kept low. In June, 2013, condensation from pipes above dripped onto a Phase-II relief valve pressure transducer, making it think that the He gas pressure was higher than it really was. - The valve opened and sucked in air, contaminating the LHe of the Phase-II system. - (At 0.6 Bara - should open at 1.6 Bara.) (1Bar = 100kpa = 0.987atm, Bara = absolute pressure = atm pressure + gauge pressure). - Eventually the Phase-II inventory had to be purged and replaced.

Reliability Statistics Downtime statistics of the last eight years of operations. - (Previous years’ statistics are very difficult to extract.) This shows that our improvements after our growing pains Have resulted in increased reliability!

Many thanks to… David Kishi, Cryogenics Ruslan Nagimov, Cryogenics Acknowledgements Many thanks to… David Kishi, Cryogenics Ruslan Nagimov, Cryogenics Vladimir Zvyagintzev, RF Bob Laxdal, RF/SRF Department Head Violeta Toma, Operations Manager

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